Applied Mechanics doi: 10.3390/applmech7040084

Authors: Chi Zhang Shaoying Li Yongli Zhang Guangzhi Nan Bin Sun Yingchao Ma Lipeng Jiu

Equivalent continuum models provide an efficient alternative to explicitly resolving the internal architecture of lattice structures, but their accuracy in finite components depends strongly on structural scale, boundary effects, constitutive behavior, and numerical discretization. This study quantitatively evaluates the finite-size accuracy and engineering applicability of a first-order equivalent continuum model for body-centered cubic (BCC) lattice structures. A periodic representative unit cell is first used to determine the effective elastic stiffness of a BCC lattice with a unit-cell size of 5 mm, a strut radius of 0.3 mm, and a relative density of 6.99%. The resulting stiffness matrix exhibits the expected cubic symmetry and pronounced directional anisotropy, while the maximum component-wise difference between the 0.050 and 0.025 mm RVE meshes is only 0.0584%. Explicit lattice structures and corresponding homogeneous continua containing N = 1–5 cells along each direction are then compared under lateral loading and quasi-static compression. The lateral displacement deviation decreases overall from 18.69% at N = 1 to 10.84% at N = 5. Under consistent linear-elastic compression, the reaction-force deviation decreases monotonically from 74.52% to 22.62%, confirming that substantial finite-size and boundary-related effects remain even after constitutive inconsistency is removed. Comparison with elastoplastic simulations further shows that plastic softening can partially mask the underlying lattice–continuum discrepancy. The explicit solid-element modeling strategy is independently verified against a published 7 × 7 × 7 BCC compression experiment, predicting an effective modulus of 0.565 GPa compared with the reported 0.54 GPa, a difference of approximately 4.6%. A dedicated macro-mesh study further demonstrates that the homogeneous model can be substantially coarsened while retaining accurate global response. These results provide practical guidance for selecting between explicit and equivalent-continuum representations according to structural scale, response quantity, constitutive regime, and required engineering accuracy.

Applied Mechanics doi: 10.3390/applmech7040083

Authors: Tewodros Y. Yosef

Lateral impact of a soil-embedded pile mobilizes pressure-dependent yielding, large deformation, and post-peak degradation of the surrounding granular soil. In a rate-independent softening formulation, the governing equations lose hyperbolicity once the tangent stiffness becomes negative, and deformation may concentrate in a mesh-controlled zone. This paper examines whether the Duvaut–Lions-type rate update of a pressure-dependent damage formulation changes this behavior in full-scale pile–soil impact. Three-dimensional explicit models were analyzed in pairs that differed only in the rate parameters: a rate-independent elastoplastic-damage variant (Model EP) and its rate-dependent extension (Model EVP). Two tests were analyzed: a lower-energy (51 kJ), rotation-dominated impact used to back-analyze the soil parameters, and a higher-energy (252 kJ) impact with combined pile rotation and structural bending used to assess parameter transfer. Model EP developed deformation trapping after the initial transient, producing a localized pile bend that was not observed in the lower-energy test and excessive sustained resistance in the higher-energy test. In the lower-energy case, this occurred even though the cumulative work approached the measured value. With the rate update active, cumulative force–displacement work at the last common displacement was within about 5% of the measurements in both cases, the rotation-dominated mechanism was reproduced, and the plastic-hinge location in the higher-energy case was within 5 mm of the measured position. Cumulative work alone did not identify the deformation mechanism; force history, integrated resistance, and permanent deformation must be assessed together. Within the investigated formulation, discretizations, and configurations, the improvement reflects the combined action of physical rate dependence and the numerical effect of the rate-dependent stress update.

Applied Mechanics doi: 10.3390/applmech7040082

Authors: Andrii Velychkovych Ivan Shatskyi

Vibration isolators based on a slit cylindrical shell with an elastic filler are proposed for the needs of the mining, oil and gas, and construction industries; in these devices, energy dissipation is provided by the effects of distributed positional dry friction between the contacting elements. Such vibration isolators are intended to operate under considerable loads and severe dimensional constraints, which requires a combination of high load-bearing capacity, sufficient compliance, and efficient energy dissipation. The aim of this work is an analytical study of hysteretic energy dissipation in the nonconservative contact system “slit cylindrical shell–deformable filler” with dry friction at the contact interface, and the determination of the conditions of maximum energy dissipation. A quasi-static model is developed in which the bending compliance of the slit shell is reproduced by an energetically equivalent orthotropic shell, while the filler is assumed to be elastic and incompressible. An analytical description of the hysteresis loop and an explicit expression for the energy dissipated per cycle are obtained. A nonmonotonic influence of the friction coefficient on energy dissipation is established: as friction increases, the dissipation first grows, reaches a maximum, and then decreases. The extremum is caused by the competition between the growth of the work of the friction forces and the reduction of the region of relative slip. An optimal level of compliance of the contact system is also established. As the depth of the loading cycle decreases, this optimum shifts toward larger values, while the maximum attainable dissipation is reduced. Joint variation of friction and compliance does not produce an isolated interior maximum, but forms an extended region of enhanced energy dissipation. Within a prescribed domain of admissible parameters, the global maximum is attained on its outer boundary. The relationships obtained provide a physically justified analytical basis for the rational design of shell-type vibration isolators, for the construction of numerical models, and for the planning of experimental tests.

Applied Mechanics doi: 10.3390/applmech7040081

Authors: Keonhak Lee Innyoung Kim

Computational fluid dynamics (CFD) workflows remain strongly dependent on expert decisions in geometry preparation, meshing, model and solver configuration, convergence assessment, post-processing, and design iteration. This review examines agentic artificial intelligence (AI) for CFD automation and engineering design, with emphasis on reinforcement learning (RL) agents and large language model (LLM) agents. RL agents provide rapid, task-specific, and physics-aware execution within predefined observation and action spaces, whereas LLM agents offer flexible goal interpretation, knowledge access, planning, and tool orchestration. To organize these potentially complementary capabilities, a unified taxonomy is introduced based on decision paradigm, CFD role, and degree of autonomy, while multi-agent organization is treated as a separate architectural property. The reviewed evidence indicates that neither RL nor LLM agents alone are sufficient for trustworthy autonomous CFD. A hierarchical autonomous-CFD-engineer architecture is therefore proposed, combining an LLM orchestrator, domain-specialized agents, conventional CFD tools, independent numerical and physical verification, shared provenance, and human governance. Extending this architecture toward hypothesis formulation, numerical-experiment design, and model discovery suggests a pathway to an AI CFD scientist; however, current systems support bounded automation and supervised scientific collaboration rather than independent scientific judgment.

Applied Mechanics doi: 10.3390/applmech7040080

Authors: Jingru Cui Jiaxin Zhao Jiarong Mao Fengshuo Zhang Yuhang Su Zihan Liu Jianglong Gu Shanshan Wang

Triply periodic minimal surface (TPMS) structures offer smooth, interconnected flow channels and are promising as additively manufactured flow-equalizing inserts for local inert-gas delivery systems. This study used pore-resolved simulations to analyze argon transport through Diamond (D), Gyroid (G), and Primitive (P) TPMS architectures. Equivalent flow resistance was assessed via pressure drop-based permeability metrics, and outlet-flow uniformity was measured with a velocity uniformity index. The impacts of porosity, unit-cell size, wall thickness, and topology were examined, recognizing their coupled nature. Higher porosity enhances gas throughput but slightly improves outlet uniformity. Larger unit cells significantly lower hydraulic resistance and boost permeability but tend to create preferred flow paths, reducing uniformity. Thicker walls decrease effective flow area and increase viscous resistance. Among the configurations studied, G-type topology offers the best balance between gas throughput and outlet-flow uniformity. Based on permeability and uniformity rankings, G-type structures with high porosity and medium-to-large unit cells are promising for future device evaluations. This work is an idealized, single-component numerical study, without considering external Ar-air mixing, oxygen levels, thermal effects, manufacturing variations, or experimental validation. Therefore, the identified parameter space should be viewed as a hydrodynamic screening outcome rather than a definitive engineering design for shielding performance.

Applied Mechanics doi: 10.3390/applmech7040079

Authors: Kirill Doronin Alexander Ilyinsky Aleksandr Umanskii Artem Kondratev

In this work, the load-dependent indentation response of as-built Inconel 718 produced by direct laser deposition was studied, followed by local mapping around a single surface-intersecting pore. A working load of 100 mN was selected because the indentation modulus approached a depth-independent plateau and the penetration depth was substantially larger than the measured surface roughness. At this load, the reference matrix response was HIT = 2.69 ± 0.26 GPa and EIT = 160 ± 11 GPa. An equivalent contact radius ac was calculated from the projected contact area, and pore-edge distance was normalized as ξ = s/ac. For the reference response, ac ≈ 3.44 µm and the first numerically defined position at s = 20 µm corresponded to ξ ≈ 5.8. Robust regression of 56 individual measurements showed no statistically resolved dependence of EIT on ξ, whereas a small negative HIT slope was observed and interpreted cautiously because of directional variability. The analysis is restricted to this single pore and to ξ ≥ 5.8; the immediate pore-edge regime was not experimentally resolved. The contact-scale normalization provides a reproducible framework for interpreting local indentation data near a geometrical defect without treating the two-dimensional pore-area fraction as bulk porosity.

Applied Mechanics doi: 10.3390/applmech7040078

Authors: Md Bahar Uddin Tyler Patterson Sriram Praneeth Isanaka Mohammad Masud Parvez Frank Liou

Miniaturized tests can offer significant material and time savings while still providing representative results comparable to macro-scale tests for relevant applications. Moreover, in challenging fields like hazardous materials research in nuclear, chemical, and similar industries, miniaturized testing presents an even more compelling and practical solution to counter safety, specimen preparation, and material disposal constraints. With an emphasis on optimization to guarantee maximum stress concentration, a uniform stress distribution, and the fact that failure always occurs within the gage, this study investigates the bending fatigue behavior of meso-scale Krouse specimens. Initially, theoretical and finite element analyses were performed for geometry optimization. Subsequently, the optimized geometry was experimentally validated through constant amplitude, load-controlled bending fatigue tests with prescribed stress ratio, R=0. Both theoretical framework and experimental validation confirmed the effective optimization of the specimen design for stress behavior. Furthermore, the S-N curve generated from the experiments demonstrated consistent patterns when compared with analytical and literature data, proving the validity of the optimized specimen design. The scientifically validated specimen design serves as a novel and innovative approach that could be applied in applications where small size, and bending loads are critical.

Applied Mechanics doi: 10.3390/applmech7030077

Authors: Zayneb Hmila Mohieddine Ben Salah Mabrouk Mosbahi Ayoub Msaddak Anoire Ben Jdidia Mohamed Haddar Antonio Pantano Donatella Cerniglia Mohamed H. Mohamed Tullio Tucciarelli Ali Fellah

Flow behavior can be changed by parameters such as fluid properties, geometry, and operating conditions. This paper presents a 2D numerical analysis of incompressible fluid flow in a channel with either a circular or square cylinder using the multiple relaxation time Lattice Boltzmann method (LBM-MRT). All simulations are performed at a fixed Reynolds number of Re = 100. A parabolic velocity profile is imposed at the inlet, while no-slip boundary conditions are adopted at the channel walls and obstacle surfaces. The numerical model is validated by comparing the mean drag coefficient with findings in the literature. Subsequently, the effects of obstacle shape, size, and position on the flow behavior and hydrodynamic forces are investigated. The effects of three obstacle sizes and three distinct positions are investigated for circular and square geometries under identical flow conditions. The results show that increasing the obstacle size modifies the flow and wake structure, and affects the drag and lift coefficients. Compared with the circular obstacle, the square obstacle creates stronger flow disturbances because of its sharp corners. The results also highlight the important effects of obstacle shape, size, and position on the flow characteristics and hydrodynamic coefficients.

Applied Mechanics doi: 10.3390/applmech7030076

Authors: Vasudevan Muthukumaran Dachepalli Sanyasi Setty Bethavolu Venkata Arun Kiran

Resistance end-closure welding of Zircaloy-4 nuclear fuel elements is a critical operation in Pressurized Heavy Water Reactor fuel fabrication. Weld quality and dimensional integrity depend on upset formation, reflecting combined effects of heat generation and forging during welding. Control of pre-heat upset is essential for establishing intimate contact at the faying surfaces, whereas total upset must be maintained within specified limits to satisfy dimensional requirements for fuel bundle assembly. In the present study, Random Forest (RF) regression models were developed to predict pre-heat and total upset. A comprehensive dataset was generated using a validated Finite Element (FE) model by varying pre-heat current, post-heat current, pre-heat duration, post-heat duration, and squeeze force over the practical operating range. The RF hyperparameters were optimized using a coarse-to-fine grid search strategy with five-fold cross-validation and Root Mean Square Error (RMSE) as the optimization metric. The optimized models were evaluated using an independent blind-test dataset and achieved RMSE values of 0.06 mm for pre-heat upset and 0.08 mm for total upset. The validated models rapidly screened 4725 full-factorial weld schedules and identified candidate schedules whose predicted responses satisfied the required upset criteria. Experimental verification demonstrated good agreement with the model predictions. The proposed FE–RF approach provides an efficient tool for weld-schedule development in nuclear fuel manufacturing while reducing the need for extensive simulations and experiments.

Applied Mechanics doi: 10.3390/applmech7030075

Authors: Akar Hama Khdhir Ghafur H. Ahmed

While predefined cambering is widely implemented in prestressed concrete (PSC) girder bridges to counterbalance dead load deflections, the literature addressing its direct influence on structural behavior remains limited. Existing research focuses primarily on providing the required camber during fabrication and accidental deflections, with sparse attention dedicated to the interactive effects of diverse predefined initial profiles on structural performance. In this paper, an experimental investigation on the effect of predefined camber and accidental deflection on the structural behavior of both reinforced and prestressed rectangular concrete girders under four-point bending loading is presented. Fourteen large-scale beam specimens were tested, including eleven prestressed and three conventional reinforced concrete (RC) girders having concrete compressive strengths of 30, 40, and 80 MPa with predefined initial profiles ranging from −30 mm to +30 mm on key structural parameters, including cracking propagation, stiffness degradation, structural efficiency, displacement ductility, and total energy absorption. Test results have shown that all girders failed in a ductile manner via progressive cracking. It has been observed that positive predefined cambers could positively affect the performance of prestressed girders to a large extent, as the +30 mm predefined camber improved the ultimate load capacity by 19.3%.

Applied Mechanics doi: 10.3390/applmech7030074

Authors: Rehan Farid Mustafa Zahid Ahmad Siddiqi Muhammad Ali Khan Ali Ajwad Muhammad Nouman Amjad Raja

Cold-formed steel (CFS) lipped channels are widely used in lightweight construction, yet their open, thin-walled geometry makes them highly vulnerable to torsion-driven instability and premature buckling under bending. To address this limitation, this study introduces an innovative riveted Delta-Channel concept that partially “closes” the section, shortens free edges where buckling initiates, and increases torsional rigidity. Full-scale four-point bending tests were performed on nine specimens (three Delta sections and six lipped channels), supported by nonlinear finite element (FE) models developed in ABAQUS. Across comparable geometries, Delta sections delivered a 66–140% increase in peak load capacity and markedly improved deflection control. The developed FE models showed good agreement with the experimental results and successfully reproduced the observed flexural behaviour of the investigated sections. Despite a modest increase in material usage, the proposed Delta sections achieved substantially higher flexural capacities than comparable conventional lipped channel sections.

Applied Mechanics doi: 10.3390/applmech7030073

Authors: Yongxiang Gao Anjie Huang Shujie Zhao Pu Xu Hainan Zhong Ullah Zahid Ben He Na Lv

Grouted connection segments are key load-transfer components in offshore wind jacket structures, and their axial compressive performance is essential for the safety and reliability of the foundation system. This paper develops a finite element model of a grouted connection segment incorporating steel-fiber-reinforced high-strength grout to investigate its mechanical behavior and parametric effects under axial compression. A 1:7-scale model test is conducted to verify the numerical model through comparisons of the load–displacement response and strain responses at key locations. The steel tubes are simulated using a trilinear hardening elastoplastic model, while the steel-fiber-reinforced high-strength grout is represented using the concrete damaged plasticity model with corresponding tensile and compressive constitutive relationships and damage parameters to characterize its nonlinear response. Based on the validated model, a full-scale numerical model is established to analyze the effects of steel tube thickness, shear key spacing, shear key height, and shear key width using the control variable method. The results indicate that steel tube thickness has the most significant influence on the ultimate bearing capacity and can improve the load-bearing capacity and ductility of the structure. Shear key spacing mainly affects axial stiffness and deformation compatibility, while shear key height and width have limited effects on the ultimate bearing capacity but contribute to local deformation control and stiffness enhancement. The findings provide a validated numerical basis for evaluating the axial compressive behavior of steel-fiber-reinforced grouted connections and offer a useful reference for the design and parameter optimization of grouted connection segments in deep-water offshore wind jacket structures.

Applied Mechanics doi: 10.3390/applmech7030072

Authors: Mazahir Hussain Shah Shaheer Ul Hassan Luděk Pešek

This paper presents a systematic experimental and computational investigation of the free-vibration characteristics of a Laser Powder Bed Fusion (LPBF) AlSi10Mg thick-walled cylinder, a geometry relevant to electric-machine housings, hydraulic sleeves, and pressure-carrying components exposed to resonance-critical service loads. The specimen has an outer diameter of 94 mm, an inner diameter of 64 mm, a wall thickness of 15 mm, and a height of 90 mm, placing it firmly in the thick-walled regime (d/D=0.68). A three-dimensional finite element model comprising 23,864 total elements (23,236 SOLID186 solid elements and 628 surface/contact elements) and 106,015 nodes was constructed in Ansys Mechanical using the AlSi10Mg material database entry (E = 75 GPa, ρ = 2670 kg/m3, ν = 0.33) and solved with the Block Lanczos eigensolver under free–free boundary conditions. Experimental modal analysis (EMA) was conducted using Brüel & Kjær software with an impact hammer with a 260-node measurement grid covering the outer surface and both end rings; frequency response functions were acquired over 0–22,500 Hz. Fourteen flexible modes were identified in simulation; nine corresponding experimental modes were resolved with frequency deviations ranging from 0.13% to 1.10%. In addition to frequency correlation, this paper introduces a non-conservative damping characterization framework comprising: (i) Rayleigh (proportional) damping coefficient extraction from EMA data and assessment of its frequency-domain validity; (ii) a viscoelastic complex-modulus model relating the real storage modulus E′ and imaginary loss modulus E″ to the modal loss factor η and damping ratio ζ; and (iii) a practical design workflow for resonance mitigation of future AM structures including electric machine frames. Experimental damping ratios (ζ=0.013–0.311%) are converted to per-mode E″ values and loss factors, revealing that energy dissipation in LPBF AlSi10Mg is strongly mode-shape-dependent and cannot be accurately represented by a single Rayleigh model.

Applied Mechanics doi: 10.3390/applmech7030071

Authors: Rustam Abirov Javlonbek Turdibekov

This paper addresses the elastoplastic torsion and tension of a prismatic bar with a multiply connected circular cross-section containing one central and four symmetrically arranged lateral holes. The relevance of this problem stems from the fact that internal contours alter the shear-stress flow, amplify local gradients, and cause non-uniform development of plastic zones. The study considers a two-parameter loading scenario. It is demonstrated that for the same final combination of axial force and torque under different strain trajectories, the equivalent-stress fields and effective torsional stiffness significantly depend on the loading sequence. The obtained results confirm the necessity of simultaneously considering hole geometry, plastic flow, and loading history when analyzing multiply connected bars.

Applied Mechanics doi: 10.3390/applmech7030070

Authors: Matheus de Carvalho Dias Rafael Beltrame Flávia Costa de Mattos Kelvin Techera Barbosa Rafaella dos Passos Nörnberg Alessandra Buss Tessaro Jorge Luiz Saes Bandeira Rafael de Avila Delucis

The growing demand for more sustainable construction materials has driven the development of composites incorporating industrial and agricultural residues, contributing to the reduction in virgin raw material consumption and the valorisation of by-products. In this context, the present study investigated the influence of incorporating rice husk subjected to different chemical treatments and the partial replacement of commercial gypsum with recycled gypsum on the flexural strength, compressive strength and microstructural characteristics of gypsum-based composites. Initially, formulations containing 5 wt.% and 10 wt.% rice husk in three different conditions, untreated, treated with calcium hydroxide, and treated with acetic acid, were produced and evaluated in terms of compressive strength and flexural strength. The formulation containing 5 wt.% rice husk treated with acetic acid exhibited the best overall performance and was therefore selected for the subsequent stage of the study. In the second phase, mixtures incorporating 20 wt.%, 30 wt.% and 40 wt.% recycled gypsum, with and without the addition of 5 wt.% treated rice husk, were investigated. Furthermore, particle size distribution, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) analyses were performed. The results demonstrated that the acetic acid treatment resulted in higher flexural and compressive strength compared with the other treatment conditions evaluated. Partial replacement with recycled gypsum also yielded promising results, with the formulation containing 70 wt.% commercial gypsum and 30 wt.% recycled gypsum exhibiting the highest mechanical strength among the composites without lignocellulosic reinforcement. Microstructural characterisation revealed the preservation of the principal mineralogical phases following the recycling process, and SEM micrographs showed the incorporation of rice husk within the gypsum matrix. Overall, the combination of 30 wt.% recycled gypsum and 5 wt.% rice husk treated with acetic acid represents a technically viable alternative for the development of gypsum composites intended for non-structural applications in the construction industry, while promoting the beneficial utilisation of waste materials.

Applied Mechanics doi: 10.3390/applmech7030069

Authors: Arseniy D. Berezner Victor A. Fedorov Nikolai S. Perov Gregory V. Grigoriev

In this study, novel exact solutions of the Duffing equation with their phase portraits are proposed and reasoned. It is shown that phase trajectories are initially elliptical and become distorted in the unstable area with the growth of the variable parameter in the damped case. The instability criteria of the identified solutions have been determined together with the Fourier series transformation up to the first and high harmonics in the sense of the physical interpretation. An explicit form for the Ax=dx/dt=(x+M)2⋅N non-linear differential operator corresponding to the considered functions has been derived, and its main functional spectrum has been evaluated. Non-isothermal creep tests of different materials were completely described using the Duffing equation via noted solutions up to the fracture as processes with a personal deformation response. We successfully examined the relationship between the thermal and magnetic properties of the ferromagnetic amorphous alloy under its non-linear deformation, using the critical exponents equal to α1 = 2 and α2 = 1. With high linear correlation coefficients (0.9 and above) between our model and experiments (within ±0.01 mm of residual error), the behavior of organic and metallic systems is well predicted under the same thermomechanical testing conditions on the mesoscale.

Applied Mechanics doi: 10.3390/applmech7030068

Authors: Hussein Sayed Tamer A. El-Sayed

This paper presents a novel control strategy for hybrid rotor–bearing systems integrating hydrodynamic journal bearings with active magnetic bearings (AMBs) to address the persistent challenge of nonlinear vibrations in high-speed rotating machinery. The study introduces the application of a state-dependent parameter proportional-integral-plus (SDP-PIP) controller designed within a non-minimal state-space framework, offering a significant advancement over conventional control approaches. A four-degree-of-freedom model incorporating short-bearing approximation for hydrodynamic forces and nonlinear electromagnetic force characterization is developed to capture the complex system dynamics. The controller performance is evaluated through numerical simulations over a range of rotational speeds from 130 to 500 rad/s, together with sensitivity analyses under parameter variations and comparisons with a conventional PID controller. The results show that the proposed controller effectively suppresses nonlinear vibrations and stabilizes oil-whirl and oil-whip instabilities over the investigated operating conditions. In comparison with the PID controller, the SDP-PIP controller provides improved vibration attenuation and maintains stable journal motion with lower oscillation amplitudes, particularly near unstable operating regimes. These findings demonstrate the potential of the SDP-PIP control strategy for enhancing the dynamic performance and operational stability of hybrid journal bearing systems.

Applied Mechanics doi: 10.3390/applmech7030067

Authors: Alagulakshmi Rajendran Ramalakshmi Ramar Arumugaprabu Veerasimman Sundarakannan Rajendran Arnas Majumder Flavio Stochino

The process of predicting mechanical properties in composite materials is an important challenge owing to their nonlinear and composition-dependent nature. In this research, a hybrid deep learning architecture fusing Artificial Neural Network (ANN) with Long Short-Term Memory (LSTM) networks is employed for the prediction of tensile strength, flexural strength, impact strength, and hardness for different weight composition composites. The composite was prepared with fiber contents of 0%, 5%, 10%, and 15% and was tested mechanically with respect to four different tests—tensile test, flexural test, impact test, and hardness test—to study the influence of fiber content variation on the physical characteristics of the material. The experimental dataset was used for both training and validation, while the intermediate compositions were suitably estimated using the devised hybrid architecture. It is observed that the ANN LSTM model exhibits superior predictability with R2 greater than 0.996 in all cases, which validates its capability to model complex material-property relations. This hybridization is a very computationally efficient and reliable approach for material optimization by minimizing the need for large-scale experimental trials. The results substantiate the value of ANN LSTM hybridization as a very strong predictive tool for composite material engineering.

Applied Mechanics doi: 10.3390/applmech7030066

Authors: George Tzoumakis George Lampeas

With the aim of reducing and eventually eliminating CO2 emissions, the aviation industry is investigating alternative fuels, with liquid hydrogen (LH2) being one of the most promising. Several research projects that deal with the subsystem design of liquid hydrogen aircraft have commenced, with specific attention given to the development of lightweight cryogenic tanks. Composite materials are potential candidates for cryogenic aviation applications, yet they experience issues with thermal stresses that result to various types of damage that should be thoroughly investigated, to enable reliable composite cryogenic structures. In this direction, the present work investigates the alternative finite element techniques for the thermo-mechanical analysis of the characteristic geometrical structural configuration. Thermo-mechanical stress analysis results derived from the investigated analysis methodologies are verified by their comparison to published results. The assessment of the alternative modeling techniques contributes to the adaptation of the FE modeling development strategy to the desired analysis type and the expected results and is directly applicable to the thermo-mechanical design of cryogenic components. The outcome of the investigation is demonstrated in the case of thermo-mechanical analysis of an outer tank of an LH2 storage system, performed with the optimal combination of shell and solid elements.

Applied Mechanics doi: 10.3390/applmech7030065

Authors: Mahesh Kumar Gupta Ratnakar Das

This research work investigates the machinability of WP7V die steel of very high toughness and wear resistance in turning with a TiAlN-coated carbide tool, with the chip reduction coefficient (CRC) serving as a guide for machining performance and energy requirements. The machining parameters, like cutting speed, feed rate, depth of cut, and machining environment, were assessed to find parameter combinations that encourage established cutting and enhanced chip control. The results illustrate that the CRC is strongly influenced by cutting speed, and at a higher cutting speed (210 m/min), the lowest CRC values are obtained. In dry machining, a medium feed rate (0.1 mm/rev) favors chip breaking, and wet machining results in medium-spiral chips. Long, continuous chips with laminar and sheared surfaces are produced at a low cutting speed (70 m/min). The findings suggest that low CRC values are correlated with stable machining behavior and decreased energy utilization. High cutting speed and the suitable selection of feed rates are needed for the efficient machining of WP7V steel.

Applied Mechanics doi: 10.3390/applmech7030064

Authors: Hareram Lohar Anirban Mitra Sarmila Sahoo

The analysis of beams resting on elastic foundations has attracted significant attention in structural and mechanical engineering due to its extensive applications in different domains. Beams on elastic foundations interact continuously with deformable media. To represent this interaction mathematically, researchers have developed a variety of single-parameter, two-parameter and three-parameter models as well as continuous models. Among the structural elements employed to investigate these models, functionally graded material (FGM) beams have emerged as an attractive platform due to their continuously varying material properties and extensive use in modern engineering applications. Over the past two decades, extensive research has been conducted on the behavior of graded beams resting on elastic foundations using various beam theories, foundation models and analytical as well as numerical solution techniques. The present paper puts forward a detailed review of the existing literature concerning static bending, buckling, free and forced vibration analyses of FG beams supported by elastic foundations. Various material gradation schemes, including power law, exponential, sigmoid, porous and carbon nanotube-reinforced FGMs, are discussed. The review further examines the application of different classical foundation models, such as the Winkler, Pasternak, Kerr and Vlasov models. These classical models may be linear or nonlinear depending on the nature of the foundation medium. A comparative evaluation of the available studies is provided to identify current trends and limitations. Finally, potential future research directions involving multi-physics coupling, advanced foundation modelling, machine-learning-assisted prediction and micro/nanoscale applications are highlighted. The review aims to serve as a valuable reference for researchers and engineers working in the field of FG beams interacting with elastic foundations.

Applied Mechanics doi: 10.3390/applmech7030063

Authors: Shunqi Mei Undrakh Mishigdorzhiyn Valeriy Svinin Andrey Irincheev Aleksey Pyatykh Alexander Makaruk Nikolay Ulakhanov

In low-rigidity technological systems, face milling can cause undesirable vibrations, including forced and self-excited vibrations. These vibrations can be suppressed by selecting a mill with a variable tooth pitch. This paper analyzes existing face mill designs that implement this approach and describes the design of a developed mill with an adjustable tooth pitch. Experimental substantiation of the mill’s performance demonstrated that proper selection of the difference between adjacent tooth pitches reduces the fundamental harmonics of self-excited vibrations by a factor of 28.

Applied Mechanics doi: 10.3390/applmech7030062

Authors: Hyung Suk Mun Chan Woo Park

Rack railway systems operating on steep-gradient routes rely on rack-and-pinion propulsion mechanisms that generate substantial vibrational excitation through cyclic gear mesh contact, adversely affecting passenger comfort and long-term mechanical reliability. Conventional integrated steel gears transmit propulsive forces without inherent vibration attenuation, and a systematic design methodology for optimising the internal rubber spring configuration of elastic gears for such applications has not been established. This study develops a kinematic spring-mass model for both conventional steel and elastic rubber gear configurations in a Korean rack railway propulsion system and validates it through controlled experimental testing. A high-speed rail–wheel contact simulator was employed to measure vertical vibrational accelerations under rigid–rigid (steel–steel) and rigid–resilient (steel–rubber elastic gear) contact conditions, with a load simulating steep-gradient operational forces applied to the gear assembly. The elastic gear achieved a 25.1-fold reduction in vertical vibrational acceleration relative to the steel gear baseline (6.4 m/s2 vs. 160.7 m/s2). Time-domain statistics (mean, RMS, standard deviation and peak envelope) are reported for both configurations from repeated runs. Analysis of the normalised effective stiffness as a function of the number of rubber springs predicts that four springs represent a practical optimum, beyond which the incremental stiffness change falls below 0.5%; experimental validation of intermediate spring counts is identified as future work. A spring-number optimisation framework is proposed that returns both a spring count and a rubber compound specification, balancing vibration attenuation against load distribution, torque-transmission capacity and component fatigue life.

Applied Mechanics doi: 10.3390/applmech7030061

Authors: Maria de la Luz Suarez-Hernandez Guillermo Urriolagoitia-Sosa Beatriz Romero-Ángeles Francisco Javier Gallegos-Funes Francisco Carrasco-Hernández Edder Jair Rodríguez-Granados Gabriela Ramirez-Sanchez Jonathan Rodolfo Guereca-Ibarra Jorge Alberto Gomez-Niebla Jonatan Mireles-Hernández

The soft Bankart lesion is characterized by the abnormal translation of the humeral head during dislocation, which places excessive stress on the labrum and causes it to stretch along with other structures that provide joint stability. This lesion is described as a purely soft tissue injury and occurs due to the detachment of the anteroinferior labroligamentous complex. This research aimed to evaluate the computational biomechanics of a biomodel of the shoulder joint with a soft Bankart lesion during pure abduction using the Finite Element Method (FEM). It evaluates the tissue mechanics of the structures with the lesion, such as ligaments, the articular capsule, and the labrum, which guide and limit the bones of the joint during movement. A healthy shoulder joint biomodel is developed for comparison. The results of stress and strain in the healthy shoulder and the soft Bankart biomodel are analyzed. The results for the soft Bankart biomodel show an increase in stress on the MGHL, with the pIGHL assuming a primary stabilizing role. The CHL and articular capsule limit the excessive displacement of the humeral head.

Applied Mechanics doi: 10.3390/applmech7030060

Authors: Hang Zhou Shichao Zhang Guoxu Jin Tianbao Lan Xiaomei He Rong Xu

Design deviations introduced during the fabrication and installation of nuclear-grade piping systems can alter structural response and substantially increase reanalysis effort. This study develops a mechanics-based framework to identify critical parameters controlling the code-stress ratio of a representative nuclear piping system. Finite-element analysis, Monte Carlo sampling, and Sobol global sensitivity analysis were combined to evaluate the effects of gravity, thermal-pressure loading, and seismic excitation. The results show that parameter sensitivity is strongly load-dependent. Under Level-A conditions, the response is governed mainly by constrained thermal deformation, and the dominant parameters are support locations that control deformation compatibility and the redistribution of secondary stress. By contrast, structural and weight-related parameters have only limited influence in this regime. Under Level-D conditions, however, the governing mechanism shifts to inertia-driven amplification. The dominant variables then become those associated with dynamic constraint, concentrated mass, and eccentric loading, including key support positions, valve eccentricity, and valve weight. Multi-parameter analyses further reveal clear interaction effects, showing that simultaneous deviations in critical supports, concentrated masses, or eccentricities can significantly amplify the stress response and, in some cases, drive the stress ratio beyond the allowable limit. These results show that the mechanical importance of design parameters depends on both the loading regime and system-level parameter interactions, and they provide a quantitative basis for condition-specific tolerance allocation in nuclear piping design.

Applied Mechanics doi: 10.3390/applmech7030059

Authors: Kieu-Tuan Trinh The-Thanh Luyen Duc-Toan Nguyen

Roll-bonded stainless steel/aluminum laminates are increasingly used in lightweight structural applications; however, their deep-drawing behavior and thickness evolution remain insufficiently understood due to the mechanical mismatch between constituent layers. This study investigates the deep drawing of a SUS304/AA1050/SUS430 laminated sheet through a combined experimental and finite-element approach. The laminate was manufactured by roll bonding and exhibited sound interfacial integrity without observable delamination. To account for load transfer and deformation compatibility among the bonded layers, the material was modeled as an equivalent homogeneous laminate whose constitutive response was identified directly from tensile tests performed on the three-layer sheet. Full-field strain measurements were obtained using digital image correlation (DIC), and anisotropic plasticity was described using the Hill48 yield criterion combined with Swift and Voce hardening laws. Numerical predictions were validated against experimentally measured thickness distributions in cylindrical cup deep drawing. Among the investigated constitutive models, the Voce-RD0 calibration provided the closest agreement with experimental results. The validated model was subsequently employed to evaluate the effects of blank holder force, punch–die clearance, and die radius on thickness evolution. Based on the systematic parametric investigation, the combination of a blank holder force of 14 tons, a punch–die clearance of 3.2 mm, and a die radius of 10 mm yielded the most uniform thickness distribution among the conditions investigated. Under these conditions, localized thinning was reduced and the thickness distribution became more uniform. The finite element predictions agreed well with the experimental measurements, with deviations below 3%. The proposed experimental–numerical approach offers a practical framework for constitutive characterization and process parameter selection in the deep drawing of roll-bonded multilayer sheet materials.

Applied Mechanics doi: 10.3390/applmech7030058

Authors: Nicolás Sau-Soto Ana Cecilia Borbón-Almada Gema Karina Ibarra-Torúa Leny García-Moraga Juan Pedro Ayala-Moreno

A new micropolar peridynamic framework incorporating stress- and stretch-based failure criteria was developed for simulating concrete structures. A nonlocal micropolar peridynamic stress tensor was employed to solve plane stress problems; this approach inherently manages cracks and damage. A direct correspondence was established between the classical constitutive stress–strain tensor and the associated micropolar peridynamic stress tensor for linearly elastic materials. Moreover, in contrast to standard peridynamic models that treat the material horizon as a purely abstract parameter, this research defines the horizon based on Poisson’s ratio, material strength, and fracture toughness. In addition, a numerical matrix-based scheme was implemented to model concrete problems using a nonlinear explicit dynamic relaxation solver. To assess the model’s performance, concrete structures under plane stress were examined. The model’s results align closely with the crack paths and experimental data from physical testing and demonstrate mesh independence. The implementation of the model with stress and stretch failure criteria mitigates spurious boundary effects, ensuring spatial convergence.

Applied Mechanics doi: 10.3390/applmech7030057

Authors: Armine Ulukhanyan

The first approximation (N=1) of a three-dimensional micropolar elastic prismatic body in moments of displacement and rotation, obtained via Legendre polynomial expansion, is applied to two related problems: field reconstruction and damage identification. In the first problem, two- and three-dimensional field distributions are reconstructed for a simply supported square prismatic body under three loading configurations, with first-order moment loading as the primary case. Two distinct resonances are identified within the N=1 framework. At the material cutoff ωc=4α/J, micro-rotation amplitudes are amplified while translational amplitudes are suppressed (displacement locking). At the geometric cutoff ωgeo∝h−1, the bending mode is resonantly excited while micro-rotation remains near its quasi-static level. In the second problem, a scalar damage model αeff=α(1−D) is introduced. The material cutoff follows ωc(D)=ωoc1−D, confirmed numerically for all four decoupled subsystems and different prismatic body thicknesses. Geometric branches remain insensitive to damage, producing a spectral separation that may serve as a damage indicator. A critical thickness h* is identified where ωgeo=ωoc, leading to role reversal between material and geometric branches. Numerical results are presented for the polyurethane foam of Lakes.

Applied Mechanics doi: 10.3390/applmech7030056

Authors: Tarik Zarrouk Mohammed Jeyar Jamal-Eddine Salhi Mohammed Barboucha

This study examines the low-speed impact response of Nomex honeycomb-core sandwich structures using an approach combining experimental tests and three-dimensional numerical modeling. A finite element model was developed using Abaqus/Explicit to predict contact force, displacement, damage evolution, and absorbed energy under different impact configurations. The influence of core density, skin thickness, and impactor geometry was analyzed to identify the parameters governing impact resistance and energy dissipation mechanisms. The numerical results show good agreement with experimental measurements, with maximum relative differences between 7.3% and 8.3% for the maximum force and between 1.8% and 4.3% for the absorbed energy. Core density appears to be a determining factor: the D144 configuration reaches a maximum force of approximately 4400 N, compared to 2600 N for the D80 configuration, representing an increase of approximately 69%. However, sensitivity analysis indicates that skin thickness exerts the most dominant overall influence on load-bearing capacity; increasing this thickness from 0.2 mm to 1.2 mm leads to a fivefold increase in maximum force (from 1800 N to over 10,000 N) and a significant rise in absorbed energy (from 20 J to 105 J). The geometry of the impactor strongly controls the damage modes and stress distribution. A 60° conical impactor promotes localized deformation and rapid perforation, while a 70° angle offers a better compromise between local resistance and progressive energy absorption. At 80°, the stresses are distributed over a larger surface area, which delays perforation. The geometry of the impactor strongly controls the spatial distribution of damage modes. A sharper 60° conical impactor induces highly localized core crushing and rapid skin perforation, while a 70° angle offers a better compromise between local resistance and progressive energy absorption. At 80°, the stresses are distributed over a wider area, promoting diffuse damage and delaying perforation. These results show that the combined optimization of core density, skin thickness, and the impactor–structure interaction is an effective way to improve the impact tolerance of lightweight sandwich structures intended for aerospace, automotive, and marine applications.

Applied Mechanics doi: 10.3390/applmech7030055

Authors: Manfred Euler

The spin of an electron is an intrinsic quantum property that cannot be explained using classical mechanics. Nevertheless, it is possible to conceive semiclassical systems with internal degrees of freedom that exhibit spin-like properties. Building on the analysis of phase modulation by elliptical gears and kinematically equivalent antiparallelogram linkages, we present a novel semiclassical model of Zitterbewegung, a rapid oscillatory motion closely connected with spin. The kinematical analog is based on including the internal rotation of the linkage represented in spacetime. The system’s dynamics is related to two-center electron models, which describe the constant momentum of the center of mass and the lightlike oscillation of the center of charge at twice the Compton frequency for a particle at rest. A two-dimensional extension provides an intuitive illustration of topological spin properties and can be used to calculate the spin and magnetic moment of an electron.

Applied Mechanics doi: 10.3390/applmech7030054

Authors: Yide Bu Ting Long

Impact dynamics problems are ubiquitous in various engineering applications, often involving nonlinear phenomena such as material fracture, damage, and fragmentation. It poses significant challenges to numerical simulation methods. To deal with these challenges, this paper develops an adaptive axisymmetric coupling method that combines the edge-based smoothed finite element method (ES-FEM) with smoothed particle hydrodynamics (SPH), referred to as the ES-FEM-SPH method. Initially, the entire computation employs ES-FEM, which effectively alleviates the excessive stiffness inherent in conventional FEM while maintaining high accuracy, particularly when using linear triangular elements. During the simulation, if any element undergoes severe distortion, the algorithm converts it into an SPH particle and continues the computation with SPH automatically. Thus, it can effectively address issues such as large deformation. To validate the efficacy and reliability of the proposed method, this study performs numerical simulations on several representative cases, including Taylor bar impact, projectile penetration into aluminum plates, and flat-nosed projectile impact on metal target plates. The results demonstrate that the adaptive axisymmetric ES-FEM-SPH coupling method exhibits good performance in both computational accuracy and efficiency, making it well suited for numerical simulations of impact-related problems and holding substantial promise for engineering applications.

Applied Mechanics doi: 10.3390/applmech7020053

Authors: Kohei Tateyama Kentaro Ishioka Hiroyuki Fujiki

The mechanical response of cellular structures is governed not only by relative density and average cell geometry but also by the spatial arrangement of cells. However, the manner in which arrangement-dependent effects evolve with increasing cell number has not been systematically clarified. In this study, the compressive behavior of closed-cell structures with varying cell numbers was investigated using finite element analysis under dynamically equilibrated compression conditions while maintaining constant relative density and identical material parameters. Cellular models were generated using hierarchical Poisson disk sampling combined with Voronoi tessellation. The number of cells was increased through three distinct approaches: mirror replication of a reference structure, enlargement of the overall specimen size, and refinement of cell size under fixed external dimensions. To characterize arrangement-dependent effects, two distinct features of the compressive response were introduced: averaging, defined as a reduction in variability across responses from different initial cell arrangements, and smoothing, defined as the suppression of abrupt stress fluctuations within an individual response. Quantitative metrics were employed to evaluate both effects. Averaging was observed in plate-type models compressed in the z-direction and in fixed-size models, whereas mirror-connected models retained strong arrangement dependence despite large cell numbers. Smoothing occurred predominantly in plate-type models compressed in the z-direction and was strongly correlated with the number of cell layers aligned along the compression direction rather than with total cell number alone. The simulations were conducted in a dynamically equilibrated regime in which internal stress equilibrium was achieved during deformation. These results demonstrate that compressive behavior is governed not only by cell number but also by structural arrangement and directional cell-layer alignment, providing mechanistic insight into the transition from arrangement-dependent variability to stable macroscopic response under dynamic compression.

Applied Mechanics doi: 10.3390/applmech7020052

Authors: Baojun Yuan Mirjam Kloos Hamid Sadegh-Azar

Housner’s classical rocking model assumes a rigid base, which often leads to inaccurate seismic assessments under real–world soil conditions. This study quantitatively establishes the applicability limits of the rigid–base assumption and defines a reference range for its validity. To address these limitations, a novel soil–structure interaction (SSI) rocking model was developed using Lagrange’s formulation, incorporating an event–driven spring–dashpot mechanism to characterize contact forces. Validation against LS–DYNA simulations and existing compliant base models confirms high predictive accuracy across diverse geometries and ground motions. Crucially, an empirical formulation for the interface stiffness of rocking structures was derived to ensure the alignment of the proposed analytical model with numerical observations, thereby enhancing its practical utility in industrial design. Our findings reveal that rocking behavior depends not only on soil stiffness but also on the inherent stiffness of the structure. Specifically, soft soils significantly alter rocking initiation thresholds and amplify peak angles. The proposed SSI–rocking model provides a computationally efficient and FE–compatible tool for optimizing the seismic stability of unanchored structures on flexible foundations.

Applied Mechanics doi: 10.3390/applmech7020051

Authors: Bruna Corina Emanuely Schibicheski Kurelo Gelson Biscaia de Souza Francisco Carlos Serbena Gabriel Ossovisck

This study aimed to optimize the nitriding parameters for Plasma Immersion Ion Implantation (PIII) of stainless steels. UNS S32750 super duplex stainless steel, widely employed in the petrochemical industry, was subjected to PIII under varying nitriding atmospheres (mixtures of H2 and N2) and treatment pressures. The fixed PIII nitriding parameters included a temperature of 300 °C, a duration of 3 h, a bias voltage of approximately −10 kV, a frequency of 500 Hz, and a pulse width of 30 μs. Following the treatments, the phases were characterized by X-ray diffraction (XRD), while the hardness and elastic modulus of the modified surfaces were evaluated via nanoindentation. Regarding the nitriding atmosphere, gas mixtures approaching a 60% N2/40% H2 (vol.) ratio yielded a higher volume fraction of nitrogen-rich expanded phases in solid solution. Furthermore, higher treatment pressures promoted the formation of these expanded phases, consequently enhancing the surface hardness up to 2.7 times the hardness value of the untreated sample. These findings stand in contrast to those found for low-energy plasma nitriding (PN) processes.

Applied Mechanics doi: 10.3390/applmech7020050

Authors: Sami Soufi Amina Mseddi Riadh Chaari Mohamed Haddar Imed Bouzida

End milling productivity is reduced by regenerative chatter. In this paper, a hybrid Fractional-Order PID with Active Disturbance Rejection Control (ADRC-FOPID) is proposed to suppress chatter in half-immersion milling. A Timoshenko cantilever flexible workpiece is modeled together with a delay-dependent regenerative cutting-force model. The lumped disturbance is canceled on-line by an Extended State Observer, and the five FOPID gains are tuned off-line using Particle Swarm Optimization with a ±27 N actuator-saturation constraint. The RMS tip displacement is reduced by 68.5% by the ADRC-FOPID controller. Moreover, it increases the minimum and maximum stable depth of cut from 1.00 mm to 2.67 mm and from 23.17 mm to 37.67 mm, respectively. A robustness analysis over plant uncertainties and the operating window, with 38 points, results in a low mean RMS of 4.2 µm. Compared with classical controllers and robust controllers such as PID, LQR, H∞, and μ-synthesis, ADRC-FOPID achieves the highest critical limiting depth (7.58 mm) and peak stable depth (49.52 mm) on the same benchmark. Thus, the proposed strategy is an effective, robust candidate strategy for chatter suppression in milling.

Applied Mechanics doi: 10.3390/applmech7020049

Authors: Ahmed Yaseen Al-Tuhami Ahmed Ghallab Soliman Ali El-din

Achieving adequate load capacity and ensuring ductile behavior are crucial for reinforced-concrete knee joints to prevent a complete structural collapse if an adjacent member fails. The reinforcement detailing plays a critical role in achieving these factors. In this study, the performance of a knee joint under closing moments was analyzed using innovative truss-shaped reinforcement and simplified mechanical joints, in comparison to traditional reinforcement detailing, through four large-scale specimens. The findings showed that incorporating a truss-shaped reinforcement system with the suggested detailing effectively redistributed stresses in the knee-joint area and decreased stress concentration at the bent-bar zone, thus helping to prevent premature joint failure when compared to conventional specimens. Overall, the proposed system shifted the failure mode towards a highly ductile response. Furthermore, the suggested specimen experienced significant increases in both the yield load and the ultimate load, with the yield-load boost ranging from around 29.5% to 70.5%, and the ultimate-load increase ranging from 20% to 81%. Additionally, the proposed reinforcement system exhibited notably higher displacement capacity, with increases ranging from 88% to 347%. The proposed specimen also showed a considerable enhancement in displacement ductility, with an increase of roughly 160% to 382% relative to traditional specimens. The results matched well with the created analytical models confirming the effectiveness of the proposed load-transfer system.

Applied Mechanics doi: 10.3390/applmech7020048

Authors: Jian Chen Wei Wang Kun He Xiufang Gong Xiaoying Cao Yuhui Peng Chunmei Tang Juanqiang Ding Xin Cao Zhenbing Cai

This study presents the fabrication of a Cr3C2-25NiCr/NiCr coating on Co3W3 steel utilizing high-velocity oxygen fuel (HVOF) spraying. The effects of the vacuum heat treatment process on the microstructures, mechanical properties, and wear mechanisms of the coating were systematically analyzed. The results indicated that the microstructure became denser following heat treatment. During the spraying procedure, decarburization resulted in transformation of the metastable phase structure into a stable one. In comparison to the sprayed coating, there was a 93.8% reduction in porosity. The precipitation of nano-secondary carbides shifted the mechanism of solid-solution strengthening to precipitation strengthening, resulting in a 29.1% increase in microhardness. Meanwhile, the thermal softening effect led to a 114.3% increase in fracture toughness. Wear experiments demonstrated that the friction-induced amorphous structure effectively mitigated stress concentration and inhibited crack initiation. The polycrystalline interface transition region between the nano-secondary carbides and the matrix facilitated the shedding of nano-secondary carbides, forming abrasive particles that generated a rolling effect, which significantly reduced the coefficient of friction. The semi-coherent interface between secondary carbides and NiCr decreased the interfacial energy and enhanced the bonding strength, effectively preventing the shedding of carbides during the wear process. Consequently, a dense microstructure, the type of interface, and high hardness and toughness were critical factors in enhancing its wear resistance.

Applied Mechanics doi: 10.3390/applmech7020047

Authors: Abtin Baghdadi Harald Kloft

This study presents a discrete–continuous flux-guided shape-refinement framework for freeform shell geometries under self-weight. The method evaluates the directional relation between a prescribed support-directed transmission field and the shell surface normal, identifies locally underperforming regions, applies top-down geometric updates, and reconstructs a continuous surface at each step. It is intended as a transparent intermediate stage between intuitive freeform design and high-fidelity structural verification. The framework is demonstrated on nine shell cases with different geometries, support conditions, height ranges, and surface irregularities. Across all the cases, the results show reduced normal-component misalignment and increased tangential alignment relative to the prescribed transmission field. A representative finite-element comparison provides case-specific supporting evidence that under a linear-elastic gravity-load model the refined geometry can reduce deformation and stress levels over large surface regions; however, it does not prove general structural optimality or fully membrane-dominated behavior. Geometric roughness remains a key limitation requiring explicit regularization in future work. The approach is positioned as a lightweight geometric pre-optimization tool for conceptual shell design, rather than as a substitute for equilibrium-based form-finding or detailed structural optimization.

Applied Mechanics doi: 10.3390/applmech7020046

Authors: Ziheng Zhou Liujie Li Xinfeng Zhang Jie Bai Bing Rao Jiawen Dai Bangji Zhang Zheshuo Zhang

This paper investigates the flight-control problem of a vector–rotor UAV (VR-UAV) for orchard crop-inspection tasks, where wind acts as the dominant external disturbance source. In such tasks, the UAV is required to maintain position while adjusting its attitude for flexible sensor pointing. For a conventional quadrotor UAV (QUAV), however, position and attitude are strongly coupled because the thrust directions are fixed relative to the fuselage, which limits its ability to perform stable hovering and directional sensing simultaneously. Although gimbal-based solutions can provide sensing-direction adjustment, they may become less suitable for wind-affected low-altitude inspection tasks involving large, elongated, or multi-sensor payloads, due to the added mass, inertia, structural compliance, and vibration sensitivity introduced by the additional mechanism. To address these limitations, this paper proposes a compact VR-UAV platform together with an adaptive robust constraint-following control (ARCFC) method. By incorporating tilting motors for thrust-vector adjustment, the proposed VR-UAV enables decoupled regulation of position and attitude, thereby improving fixed-point hovering capability and flexible sensor pointing. From the control perspective, the thrust-vectoring mechanism introduces strongly nonlinear coupled dynamics, while wind-induced disturbances and modeling uncertainties further complicate the control problem. To address these challenges, a constraint-following control framework is developed to handle the nonlinear dynamics, and an adaptive robust compensation mechanism is introduced to estimate the uncertainty bound online and compensate for unknown but bounded disturbances. The closed-loop stability and robustness of the proposed method are rigorously established by theoretical analysis. Comparative simulation results demonstrate that, relative to a conventional QUAV, the proposed VR-UAV with ARCFC achieves superior flight stability, stronger wind-disturbance rejection, and better trajectory-tracking performance in wind-affected orchard inspection scenarios.

Applied Mechanics doi: 10.3390/applmech7020045

Authors: Milan Perkušić Stipe Pleština Vjekoslav Tvrdić Karlo Dvornik

This paper presents a numerical assessment of bending-fatigue durability in the tooth root region of cylindrical involute gears. Multiple gear pairs were modelled with different numbers of teeth and varying gear rim thicknesses. The generated geometry was implemented in the ANSYS 2025 R2 software suite, where the maximum normal stresses at critical locations in the tooth root region were determined through numerical simulation. A deformation-based method derived from Socie’s models was applied to estimate the duration of the phase leading up to fatigue crack formation in terms of load cycle accumulation. The gear geometry, together with the generated finite element mesh, was transferred to the FRANC2D/L version 4 software suite, where fatigue crack propagation was numerically simulated. Numerical analysis provided effective stress intensity factors, which then enabled an estimation of the number of load cycles required for an initiated crack to grow to the critical length associated with tooth failure. The total fatigue life in the tooth root region was evaluated as the sum of load cycles in the crack initiation phase and the crack propagation phase up to the critical crack length. The results show that all analysed factors exhibit very high resistance to fatigue fractures in the tooth root region. Furthermore, for gears with a rim thickness ratio greater than 0.7, the fatigue crack propagates through the tooth and reaches the fracture toughness limit of the material (KIc), whereas for lower rim thickness ratios, crack propagation occurs through the gear rim itself.

Applied Mechanics doi: 10.3390/applmech7020044

Authors: Chih-Ping Wu Hao-Ting Hsu

Within the framework of consistent couple-stress theory (CCST), we develop a semi-analytical finite layer method (FLM) to investigate the three-dimensional (3D) coupled electro-mechanical behavior of an exponentially graded (EG) piezoelectric circular hollow microscale cylinder under simply supported boundary conditions. The microscale cylinder is subjected to mechanical loads and electric voltages and is placed under closed-circuit surface conditions on its outer and inner surfaces. Using the principle of stationary potential energy, we first derive a 3D Galerkin weak formulation for this study. We divide the microscale cylinder into nl layers and select each layer’s elastic displacements and electric potential as the primary variables. We then incorporate a layer-wise generalized displacement model into the weak formulation to develop the semi-analytical FLM. The novelty of our method lies in its ability to accurately determine the electric and elastic field variables induced in the microscale cylinder. This feature has not been explored in previous research. We rigorously validate our method’s accuracy by comparing its solutions for EG piezoelectric circular hollow macroscale cylinders with the corresponding 3D solutions reported in the literature, with the material length-scale parameter set to zero. We also examine the impact of several key factors on the coupled electro-mechanical behavior of the microscale cylinder, including the radius-to-thickness ratio, inhomogeneity index, piezoelectricity, and material length-scale parameter, which appear to be significant.

Applied Mechanics doi: 10.3390/applmech7020043

Authors: Mihail Kolev Tatiana Simeonova

Understanding the complex relationships between processing conditions and mechanical properties in aluminum alloys remains a critical challenge in materials science. This study presents a data-driven framework using explainable artificial intelligence to quantify and interpret how different processing routes influence the strength–ductility trade-off in aluminum alloys. Using a comprehensive dataset of 1154 aluminum alloy samples with 10 distinct processing conditions, optimized XGBoost models were developed via Bayesian hyperparameter tuning to predict yield strength (R2 = 0.9392), tensile strength (R2 = 0.9491), and elongation (R2 = 0.6767). The strength models showed high predictive accuracy, whereas elongation showed lower and less uniform reliability, with the largest relative errors in the 0–5% elongation regime. SHAP (SHapley Additive exPlanations) analysis revealed that processing condition is the most influential feature for yield strength prediction, while Cu dominates tensile strength prediction. True SHAP interaction analysis identified Processing_encoded interactions with Cu as the strongest processing-coupled contribution, followed by Mg and Al, with Zn, Si, and Li showing smaller but non-negligible interaction contributions. The decision-tree surrogate is presented as an exploratory rule-extraction tool rather than as a standalone processing-selection classifier. These findings demonstrate that explainable Machine Learning (ML) can support interpretation of processing–property relationships in aluminum alloys when predictive limitations, class imbalance, and the associative nature of SHAP explanations are explicitly considered.

Applied Mechanics doi: 10.3390/applmech7020042

Authors: Konstantin Manuel Prabitz Alexander Walzl Martin Stockinger

This study examines the deformation behaviour of laser powder bed fusion-produced A20X aluminium alloy and its accurate representation using flow curve models that account for die–specimen friction. Tests across multiple strain rates at room temperature were conducted on a Gleeble 3800; force–displacement data were friction-corrected to derive constitutive flow curves. A mathematical model was developed to capture barrelling and its impact on the stress–strain response, yielding corrected stresses significantly lower than measured values and validating the correction. An equation linking key post-deformation geometric parameters to their mathematical representation correlated well with a calibrated 2D finite element model, which reliably predicted plastic strain and deformation. The model’s friction factors agreed with experimental data, enabling efficient determination of the friction coefficient. Microstructural analysis and micrographs supported the predicted plastic strain distributions. Together, the corrected experiments and validated simulations provide a robust description of A20X’s response and inform performance and application potential.

Applied Mechanics doi: 10.3390/applmech7020041

Authors: Sherif Fakher

Oil and gas well cement is routinely exposed to aggressive chemical and mechanical environments that can compromise long-term zonal isolation. Conventional Portland cement systems, which rely on hydration products such as calcium silicate hydrate (C–S–H), are particularly vulnerable to acid attack, carbonation, high salinity, and thermal stress. This study investigates a polymer–mineral composite cement in which Class F fly ash is incorporated into an epoxy resin matrix at 0, 25, and 50 weight percent (wt%) loading. The composite samples were exposed for ten days to harsh downhole-representative environments, including hydrochloric acid (HCl, 15–28 wt%), sodium hydroxide (NaOH, 15–28 wt%), sodium chloride (NaCl) brines (20 wt%), crude oil, elevated temperatures up to 100 °C, and high-pressure carbon dioxide (CO2). Compressive strength was evaluated using a universal testing machine, capturing both deformation strength and ultimate failure strength to assess elastic and structural performance. Across most conditions, the composite maintained strengths exceeding 5000 psi, demonstrating strong chemical resistance. Acidic and CO2 exposures primarily reduced elastic deformation rather than ultimate strength, suggesting localized interaction with the polymer matrix. Elevated temperature reduced strength to ~2800 psi and diminished elasticity, marking the material’s upper thermal limit. Acetone exposure progressively degraded the polymer network, highlighting potential controlled removability. These findings indicate that embedding industrial fly ash in a polymer matrix produces a mechanically resilient and chemically robust cement alternative with up to 50 wt% industrial waste incorporation. This hybrid system offers a promising approach for wells exposed to acidic, CO2-rich, or high-salinity environments, where conventional Portland cement may fail.

Applied Mechanics doi: 10.3390/applmech7020040

Authors: Yuxuan Wang Chenlin Zhang Hao Liu Zhaohui Hu

To address high-dimensional coupling and extrapolation errors in vehicle lightweighting, this paper proposes a “Macroscopic Topology—Microscopic Data-Driven Size Synergy” methodology. Macroscopically, strain-energy-driven topology optimization on a simplified skeleton reduces mass by 9.4% (2835.8 kg to 2566.9 kg). Microscopically, a global ANOVA mechanism compresses 169 thickness variables to 39 core dimensions, mitigating the curse of dimensionality. Crucially, an active learning-based sequential approximate optimization (SAO) framework rectifies severe static model extrapolation errors (up to 475%) by injecting high-entropy boundary samples, boosting the R2 accuracy to near 0.90. Consequently, this approach secures the true Pareto solution, reducing full vehicle mass by 2.59% (to 6229.4 kg) while strictly adhering to EN12663 and EN15227 standards. This paradigm effectively resolves epistemic uncertainties, unlocking extreme lightweighting potential in complex systems.

Applied Mechanics doi: 10.3390/applmech7020039

Authors: Muhammad Umer Sohail Anees Waqar Muhammad Hammad Ajmal

This study presents a computational investigation of an ingenious Twain co-flow jet (CFJ) airfoil system featuring independently controlled micro-compressors for active flow control. Unlike conventional single-point or synchronously controlled CFJ configurations, the proposed system enables independent tuning of jet momentum coefficients at multiple locations along the airfoil surface. Reynolds-averaged Navier–Stokes (RANS) simulations are employed to analyze the impact of this independent control strategy on boundary layer behavior, lift enhancement, stall delay, and aerodynamic efficiency. The objective of this work is to establish a quantitative relationship between jet momentum distribution and aerodynamic performance, while also evaluating the associated energy consumption characteristics of the system. This technology works incredibly well at low speeds, significantly increasing stall angles and lift coefficients; at higher speeds, it uses less energy and improves the lift-to-drag ratio. Twain configuration offers more accurate control over pressure gradients, enabling adaptive performance during all flight phases. In this work, a Twain-compressor-integrated CFJ system is presented, in which jet momentum coefficients (Cμ = 0.05 and 0.1) are dynamically controlled by two independently controlled micro-compressors across various flight conditions (11.34 m/s, 138 m/s, 208 m/s). By optimizing injection at the leading edge and mid-chord—paired with synchronized suction at strategic withdrawal points—the system achieves precise boundary layer control with near-zero net mass flux. Modulating Cμ improves aerodynamic efficiency while limiting the total propulsion energy expenditure, allowing a smooth transition from high-lift takeoff to low-drag cruise, according to computational fluid dynamics (CFD) analysis. Due to these developments, Twain-compressor CFJ systems are now a scalable option for aircraft that need to be extremely aerodynamically versatile without sacrificing efficiency.

Applied Mechanics doi: 10.3390/applmech7020038

Authors: Masoud Ziaei

Despite their excellent torsional and bending strength, the economical production of hypotrochoidal profiles (H-profiles) remains an obstacle to their use. Due to the tool clearance angle, the commercially available twin-spindle turning process has limited ability to manufacture many of the profiles standardized according to DIN 3689 (Deutsches Institut für Normung). On the other hand, the manufacturing of cycloidal as a non-involute special geometry using generating processes (hobbing or continuous generating grinding) depends critically on the accuracy of the tool geometry—whether a hobbing cutter or a grinding worm. Conventional tool design methods—based on approximations, involute-derived profiles, or iterative trial-and-error corrections—face fundamental limitations: unpredictable cutting force variations, elevated surface roughness, and limited process capability. However, if the exact tool geometry has been determined analytically, the same machine achieves significantly better performance. In this work, the exact tool geometry conjugated to the H-profile for profile manufacturing is determined based on the gearing law. This provides modular H-profile manufacturing without deviations. Consequently, a design concept that enables the implementation of all existing rolling processes—including gear hobbing, gear shaping, gear planning, and other variants such as gear grinding—is presented. For profile shaping of hollow contours, the transfer ratio is considered and a curve conjugated to the profile contour is determined for the tool. A CAD-based simulation shows very good consistency with the analytically determined tool geometry.

Applied Mechanics doi: 10.3390/applmech7020037

Authors: Bassel Bakleh George Wardeh Hala Hasan Izabela Drygała Ali Jahami

Many existing reinforced concrete (RC) structures have undergone increases in service loads due to changes in use, functional upgrades, and evolving design codes. This highlights the need for reliable requalification methods that account for long-term degradation mechanisms, particularly those related to sustained loading and creep. This study investigates the residual flexural behavior of RC beams after long-term loading and evaluates its effects on stiffness and ultimate strength. Three RC beams were loaded to 43% of their short-term yielding moment and kept under sustained load for 210 days, while three identical specimens were maintained as unloaded references. Afterward, all beams were subjected to repeated four-point loading–unloading cycles to detect changes in stiffness, strength, and cyclic response. The results indicate that long-term loading did not significantly affect the beams’ ultimate load-carrying capacity compared with the reference specimens. However, the long-term-loaded beams exhibited a clear reduction in initial stiffness. This difference was most evident during the first loading cycle and gradually decreased in subsequent cycles. To interpret these findings, a layered fiber model was developed to simulate cyclic behavior while incorporating time-dependent concrete effects. The model successfully reproduced the main experimental trends, reinforcing the reliability of both the testing program and the analytical approach. The study enhances understanding of stiffness degradation in RC elements subjected to increased service loads.

Applied Mechanics doi: 10.3390/applmech7020036

Authors: Nikolaos M. Papadakis Georgios E. Stavroulakis

The present study investigates the influence of geometric parameters on the vibro-acoustic performance of piezoelectric speakers, with the objective of establishing quantitative design guidelines for resonance tuning and sound pressure level (SPL) enhancement. Understanding the dimension-dependent behavior of such devices is essential for the development of compact and efficient acoustic transducers. To this end, a fully coupled electromechanical–acoustic finite element model is developed in the frequency domain, incorporating linear piezoelectric constitutive relations, structural dynamics, and an external acoustic air domain. The model systematically examines the effects of variations in piezoelectric disc thickness, brass diaphragm thickness, and diaphragm radius. The results demonstrate that increasing the piezoelectric disc thickness leads to a noticeable increase in resonance frequency and a measurable enhancement in SPL due to strengthened electromechanical coupling. In contrast, reducing the brass membrane thickness primarily shifts the resonance frequency to lower values, while producing negligible changes in SPL amplitude. Furthermore, enlarging the diaphragm radius significantly decreases the fundamental resonance frequency, confirming its dominant influence on stiffness-controlled vibration behavior. These findings quantitatively establish the relationship between geometric design parameters and acoustic response, providing a predictive framework for performance optimization. The proposed modeling approach offers an effective and reliable tool for the design and refinement of high-performance piezoelectric speaker systems.

Applied Mechanics doi: 10.3390/applmech7020035

Authors: Foteini Konstandakopoulou George Hatzigeorgiou

This study investigates the nonlinear seismic response of elevated rectangular metallic silos subjected to sequential earthquake events, incorporating soil–structure interaction (SSI) and the influence of granular material fullness levels. Using three-dimensional (3D) finite element modeling and real seismic sequences recorded within short time windows, the study evaluates the effects of repeated earthquakes on maximum displacement, residual deformation and base shear. The analysis explicitly incorporates flexible elastic foundation systems to account for SSI effects, which significantly influence dynamic behavior. While considerable research exists on cylindrical silos, the seismic performance of rectangular configurations under multiple consecutive earthquakes remains poorly understood. The research systematically compares structural behavior and deformation patterns under single earthquake events versus multiple consecutive seismic sequences. The results demonstrate that consecutive seismic events produce significantly more severe structural responses than individual earthquake occurrences, with sequential earthquakes leading to amplified residual deformations (30–45% higher), increased stress concentrations in critical regions, and progressive degradation of structural capacity. These findings indicate that conventional single-event seismic design approaches may underestimate the vulnerability of rectangular silos in seismically active areas by approximately 30–40%, highlighting the critical importance of considering multiple-event scenarios in performance-based assessment and design procedures.

Applied Mechanics doi: 10.3390/applmech7020034

Authors: Maksat Temirkhan Ilyas Yessengabylov Assem Kyrykbayeva Azamat Kaliyev Sharaina Zholdassova Chingis Kharmyssov

This study presents a comparative investigation of MgCu intermetallic compounds, CuCoMnSn Heusler alloys, and carbon steel for spur gear applications using a novel tooth contact analysis (TCA) method. The TCA employs a nonlinear two-variable equation, providing a fast and accurate computational tool for evaluating gear contact behavior. By integrating material-specific elastic properties from density functional theory (DFT) studies, the analysis predicts contact paths, stress distributions, and responses to angular misalignments. Material selection strongly influences gear performance: MgCu is promising for lightweight applications, while CuCoMnSn is better suited where mechanical performance is prioritized. The CuCoMnSn alloy also exhibits half-metallic ferromagnetic behavior, offering potential functional advantages beyond mechanical performance. These results highlight the promise of intermetallics and Heusler alloys for high-performance, misalignment-tolerant gears and demonstrate the effectiveness of combining DFT-informed material modeling with the novel TCA method for optimized spur gear design.

Applied Mechanics doi: 10.3390/applmech7020033

Authors: Malati Mazumder Mahtab U. Ahmmed Md. Mamun Molla Md Farhad Hasan Sheikh Hassan

Hybrid nanofluids possess exceptional thermal conductivity, but one of the major concerns with nanoparticles is agglomeration. While the usage of surfactants or dispersants can be used to mitigate this issue, numerical investigation and sensitivity analyses can be more affordable when attempting to optimize and design a thermal device. The consideration of thermal radiation with conductive and convective heat transfer and appropriate nanoparticles may provide a greater solution without compromising the efficacy of hybrid nanofluids. In the present work, the concept of magnetohydrodynamics (MHD) is used to examine the impact of thermal radiation on a stable, two-dimensional, incompressible hybrid fluid consisting of nanoparticles (MWNCT)-Fe3O4 and water flowing over a vertical surface. The flow is governed by established equations of fluid dynamics, which use the Rosseland diffusion model to incorporate radiation effects. The implicit finite difference (IFD) was used to solve the mathematical equations. Sensitivity analyses were conducted as functions of volume fraction, radiation and magnetic variables. This study also examines the streamlines and isotherm lines with respect to the volume fraction, radiation parameter and magnetic parameter of the heat source. The results indicate that for a fixed radiation parameter, increasing the nanoparticle volume fraction by up to 20% leads to a reduction of approximately 37% in the skin friction coefficient, while the corresponding Nusselt number increases by nearly 50%. Furthermore, the introduction of a magnetic field parameter significantly suppresses wall shear stress and modifies the thermal boundary layer thickness, demonstrating the competing interaction between Lorentz-force-induced momentum damping and radiation-enhanced thermal diffusion. These quantified trends highlight the sensitivity of coupled momentum and heat transport to combined magnetic and radiative effects in hybrid nanofluid systems.

Applied Mechanics doi: 10.3390/applmech7020032

Authors: Thathsarani D. H. Herath Mudiyanselage Manjriker Gunaratne Andrés E. Tejada-Martínez

Most computational studies of vehicle hydroplaning have emphasized structural realism through fluid–structure interaction, tire deformation, tread geometry, and pavement surface characterization. By contrast, the hydrodynamics governing the flow in the tire vicinity, particularly the role of turbulence, have received comparatively limited attention. In a significant number of studies, the flow has been treated as laminar despite turbulent flow conditions, while in a few other studies turbulence modeling has been adopted without an explicit assessment of its impact on hydroplaning predictions. In this study, we present a simplified three-dimensional computational fluid dynamics (CFD) model designed to isolate the flow regimes governing hydroplaning and to quantify the mean effect of the turbulence modeling on the predicted hydroplaning speed. Using a finite-volume formulation with a volume-of-fluid representation of the air–water interface, the flow around and beneath a smooth 0.7 m-diameter tire sliding in locked-wheel mode over a flooded, nominally smooth pavement is simulated. The tire is represented as a rigid body with an idealized rectangular bottom patch whose area is determined from the tire load and inflation pressure, avoiding the need to prescribe a measured or assumed deformed footprint. Steady-state hydroplaning is modeled for a uniform upstream water film thickness of 7.62 mm with a 0.5 mm gap between the tire and the pavement, over tire inflation pressures ranging from approximately 100 to 300 kPa, and predictions are verified against the empirical NASA hydroplaning equation. For these conditions, simulations without turbulence closure exhibit a consistent, systematic underprediction of the hydroplaning speed of approximately 13.5% relative to the NASA relation. Incorporating turbulence effects through Reynolds-averaged closures substantially reduces this bias, with average deviations of about 6% for the realizable k–ε model and 2.4% for the shear stress transport (SST) k–ω model. An analysis of the results indicates that hydrodynamic lift is dominated by pressure buildup associated with stagnation at the lower leading edge of the tire, with a significant contribution from shear-dominated flow in the thin under-tire gap, and that turbulence acts to moderate the integrated lift from these pressure fields. These results demonstrate that explicitly accounting for turbulence in the tire vicinity is essential for reproducing empirical hydroplaning trends and for avoiding systematic bias in CFD-based hydroplaning predictions.

Applied Mechanics doi: 10.3390/applmech7020031

Authors: Biljana Mladenović Stepa Paunović Andrija Zorić Žarko Petrović Bojan Milošević

In structural engineering practice, the problem of thick plate bending occurs in designing shelters, foundations of high-rise buildings, counter-slabs, etc. In such cases, neglecting shear deformation can lead to significant errors in predicted behavior, especially when a plate is subjected to a concentrated force. In practice, neither a fully clamped nor an ideal simple support can be achieved during construction, so the plates are partially clamped, and this also applies to thick plates. Bending of thick rectangular plates with partially clamped edges has not been studied in the literature, so this paper addresses this issue. A comprehensive numerical analysis using a developed simple analytical model in the form of a Lévy-type solution based on Reissner theory has been carried out. The presented model is able to account for different degrees of rotational restraint in plates with two opposite edges simply supported and the other two partially clamped by introducing the fixity factor. The obtained results are compared with those available in the literature, as well as with a numerical FEM model, whereby good agreement is observed. The significant difference when using the proposed model to analyze a thick plate, as opposed to the models based on Kirchhoff theory, is underlined.

Applied Mechanics doi: 10.3390/applmech7020030

Authors: Qamar Maqbool Rashid Naseer Imran Akhtar

This study investigates the mechanisms of nonlinear modal interactions in a circularly curved cantilever beam, utilizing the geometrically exact Timoshenko beam formulation. The governing equations take into account shear deformation, rotary inertia, and the geometric nonlinearities associated with significant deflections. A Chebyshev pseudospectral scheme is employed to achieve highly accurate linear eigenvalues, which are subsequently used in a nonlinear modal projection to develop a reduced-order model. Explicit expressions for the quadratic and cubic modal coupling coefficients are derived. The Harmonic Balance Method is then applied to explore internal resonance phenomena, frequency modulation behavior, and the transfer of energy between non-commensurate lateral and normal vibration modes.

Applied Mechanics doi: 10.3390/applmech7020029

Authors: Fernando Jorge Mendes de Sousa José Renato Mendes de Sousa

In recent years, the discovery of new ultra-deepwater reservoirs has significantly increased both the importance and the complexity of offshore oil production. One of the main challenges in qualifying structures to operate under such severe conditions is the fatigue limit state, particularly fatigue induced by ocean waves. Wave-induced fatigue remains, both at the design stage and during the operation of flexible risers, one of the most demanding issues for engineers responsible for ensuring their structural integrity. This study presents a state-of-the-art review of wave-induced fatigue analysis in flexible risers. It includes a brief historical overview of the problem, a summary of the fatigue assessment methodologies traditionally adopted in offshore engineering, a discussion of pioneering contributions to stress calculation, and an overview of the main research trends currently being pursued. These trends reflect emerging challenges related to fatigue life prediction, including the high computational cost of time-domain analyses, the presence of elevated contaminant levels in transported fluids, the development of new materials to reduce loads or enhance resistance to aggressive environments, and the assessment of remaining service life in the presence of damaged or corroded tensile wires. The potential use of monitored data to reduce uncertainties in numerical modelling is also addressed. Despite the challenges discussed, the main conclusion of this work is that ongoing technological developments are expected to ensure that flexible risers remain key components of offshore oil and gas production systems.

Applied Mechanics doi: 10.3390/applmech7020028

Authors: North Yates Fernando Ponta Joshua Reese Alayna Farrell

Since the inception of utility-scale wind turbines, there has been a continual increase in the size of the devices used. One drawback of turbine size increase is that the weight of the rotor blades has grown dramatically. Technological advancements have allowed for the creation of light blades to overcome this issue. These lighter rotors are also less stiff than their predecessors and prone to experiencing aeroelastic vibrations that can lead to fatigue damage. Aerodynamic damping occurring during blade vibration has the potential to mitigate those oscillations; thus, understanding its underlying physics provides an extremely useful tool for future blade design. In a series of previous publications, the authors presented a novel reduced-order characterization technique for the oscillatory response of wind turbines, which allows for the analysis of rotor vibrations when excited by wind gust pulses. In this paper, the authors will apply the same gust pulse technique to analyze the physics of blade’s aerodynamic damping, identifying two physical mechanisms. The first acts either as a damper, or as an energy feeder, depending on operational conditions. The second operates in a purely dissipative manner. Results of numerical experiments on several operational scenarios illustrating these behavioral responses will be presented and discussed.

Applied Mechanics doi: 10.3390/applmech7020027

Authors: Jing Zhang Miao Yu Chuang Shi Qiying Li Ruipeng Li Hongwei Guo Rongqiang Liu

Space-deployable antennas have development requirements of an ultra-large aperture, high stiffness, and multi-frequency multiplexing. To address the challenge of stiffness characterization in the multi-closed-loop complex systems of deployable mechanisms, this paper proposes a parametric stiffness modeling method and a static stiffness model is established, ranging from components and limbs to the overall mechanism. The motion/force mapping model of the deployable mechanism is obtained using screw theory, and the stiffness mapping from joint space to workspace is achieved via the Jacobian matrix. A comprehensive stiffness model of the deployable mechanism incorporating joint effects is established based on the principle of virtual work and the superposition principle of deformations, and its validity is verified through finite element simulation. Building on this, stiffness characteristics based on structural configuration are investigated, and structural forms with excellent stiffness performance are selected through comprehensive evaluation. Six configurations of the deployable mechanism are derived topologically from this structure, and the optimal configuration is selected based on stiffness performance. The parametric stiffness modeling method proposed in this study can effectively characterize the contribution of each component to the overall system stiffness. It lays a theoretical foundation for establishing a quantitative relationship between stiffness performance and configuration, enabling performance-based configuration optimization and dimensional optimization.

Applied Mechanics doi: 10.3390/applmech7020026

Authors: Vladimir Kodnyanko

This paper presents the results of a study of the dynamic performance of an aerostatic thrust bearing with a microgroove and simple diaphragms. The objective of this study was to determine the influence of the lubrication gap thickness and the volume of the microgroove and pockets on the structural dynamics. Unlike most studies that typically use the second-order harmonic oscillator equation as the characteristic equation, the root criteria are determined with high accuracy when the characteristic equation is of an order no lower than the fourth order. The presented formulas allow one to find the optimal calculated dimensional gap, microgroove and pocket volume in terms of the best dynamic performance. For a well-damped thrust bearing, the required response speed and sufficient stability margin can only be achieved within a narrow range of 1–2 times the bearing gap volume. Calculations have shown that to ensure satisfactory thrust bearing dynamics, the calculated gap should not exceed 10–15 µm.

Applied Mechanics doi: 10.3390/applmech7010025

Authors: Sheldon Wang Clayton Brasher Jimmy Tran Pavle Kalaba Ty Criss

A sucker rod pump is an artificial lift system widely used in oil wells to extract crude oil from deep underground. Due to the clearance between the barrel and the pump plunger, a phenomenon termed slippage occurs in which the annulus column of oil returns to the pump chamber due to the plunger motion and the pressure difference at the two ends of the plunger. Although it is important to maintain the clearance for lubrication between the plunger and the pump barrel in order to prevent excessive wear and tear along with galling, excessive clearance can also be a primary factor in the reduction of oil well production and must be managed. In this research, after briefly reviewing the Couette and Poiseuille flows within the annulus region, the relaxation time for the transients, and the eccentricity effects, we focus on the derivation of important system parameters such the effective mass, stiffness, and damping ratio based on the measurements of the sucker rod displacement and the pressures or loads. Analysis of experimental measurement data can provide better understanding of the sucker rod pump system parameters, helping to quantify and manage the so-called slippage issues.

Applied Mechanics doi: 10.3390/applmech7010024

Authors: Eduardo Alcantara-Rojas Boris Miguel López-Rebollar Jesús Ramiro Félix-Félix Martha Fernanda Mohedano-Castillo Carlos Roberto Fonseca Ortiz Gerardo Cano-Perea

Wind energy has become an essential resource for the development and diversification of the energy sector in México and worldwide. In this context, the mechanical design of turbine blades has emerged as a priority research topic, given its impact on performance and viability. The present research evaluates the aero-structural response of multiple lay-up configurations of a 6 m blade by coupling computational fluid dynamics (CFD) and finite element analysis (FEA). The fluid–structure interaction (FSI) was simulated in ANSYS, a commercial software chosen for its capacity for multivariable analysis. The nominal operating conditions included a wind speed of 10.5 m/s and a rotational speed of 100 rpm, leading to a theoretical power output of 6591 W. For the proposed lay-up configurations, the Tsai-Wu and Puck (Global IRF) criteria were estimated and remained below the critical threshold of 1.0, indicating no risk of structural failure. However, some carbon fiber/epoxy layers, including unidirectional layers in the spar caps and bidirectional layers in the structural shear web, may present failure risks under extreme loading conditions. This applies to configurations with the lowest number of layers in the mid-span spar caps; this fact is reinforced by the main effects analysis. The results emphasize the relevance of conducting comprehensive composite failure evaluations to optimize material selection and structural design, even for small-scale blades.

Applied Mechanics doi: 10.3390/applmech7010023

Authors: S. M. Anas Rayeh Nasr Al-Dala’ien Mohammed Benzerara Mohammed Jalal Al-Ezzi

In many densely populated towns and semi-urban areas, masonry buildings often stand close to busy roads, exposing them to blasts from improvised explosives or other localized sources. Such structures are rarely designed to resist sudden explosive forces, making severe damage or even progressive collapse likely. Even moderate-intensity blasts can weaken walls, endanger occupants, and cause significant property loss. Unlike reinforced concrete, masonry is highly susceptible to explosive impact. Therefore, understanding how these buildings behave under blast loads and developing affordable protection methods is crucial. Low-rise unreinforced masonry (URM) structures, usually up to about 13 m in height (roughly 2–4 stories), common in villages, semi-urban regions, and conflict-prone zones, are particularly at risk. In many areas, these poorly constructed buildings lack proper engineering design and are therefore highly vulnerable to blast damage. Non-load-bearing internal dividers and perimeter enclosures are especially prone to lateral displacement, which can initiate instability and, in severe cases, lead to overall structural failure. This research focuses on reducing catastrophic damage in URM walls when exposed to close-proximity blast forces using concrete-based protective coatings, both with and without embedded steel-welded wire mesh. The study references a previously tested laterally supported clay brick wall built with cement–sand mortar as the baseline model, with its behavior validated against experimental findings from existing literature. Two blast cases were considered corresponding to scaled stand-off distances of 2.19 m/kg1/3 and 1.83 m/kg1/3, representing moderate flexural-shear cracking and full structural failure, respectively. To replicate the observed behavior, a comprehensive 3D numerical simulation was developed using the ABAQUS/Explicit 2020 solver. The model’s predictions were benchmarked and verified through comparison with reported test data. While both blast intensities were used to confirm computational accuracy, the effectiveness of UHPC and UHPFRC protective coatings with and without embedded wire mesh was specifically evaluated under the more severe collapse scenario (Z = 1.83 m/kg1/3). Results indicated that at a scaled distance of 1.83 m/kg1/3, the uncoated URM wall could not withstand the blast because of poor tensile and bending capacity. In contrast, the UHPC- and UHPFRC-coatings provided improved confinement and better stress distribution. When welded wire mesh was embedded, crack control improved further, the interface bond strengthened, and a larger portion of blast energy was absorbed and dissipated.

Applied Mechanics doi: 10.3390/applmech7010022

Authors: Bhagyashri Bachhav Dawei Zhang Hanghang Gao Hauke Schmidt Chen Gang Songyun Ma Franz Bamer Bernd Markert

Fatigue failure constitutes an issue that cannot be ignored when designing welded steel structures due to the initiation of cracks at weld toes and defects under cyclic loading conditions. Traditional methods, such as the notch stress approach, estimate fatigue life by modeling local stress distributions using idealized weld geometries. While these methods are widely accepted in design codes, they can be limited by complexity and reduced accuracy in real-world applications. This study explores the use of artificial neural networks (ANNs) to enhance fatigue life prediction through data-driven modeling. The proposed method involves training an ANN using synthetic data generated through finite element simulations of S355 steel weldments under various loading histories, rates, and frequencies. The objective is to capture the influence of local geometric and stress features without relying solely on assumptions used in conventional approaches. The FEM-based training data incorporate both classical experimental findings and validated modeling practices. While performance evaluation of the ANN model is reserved for future work, this study lays the groundwork for replacing or supplementing the notch stress approach with a more adaptable and efficient predictive tool. The integration of machine learning into fatigue assessment has the potential to improve reliability, reduce computational burden, and support more informed maintenance and design decisions.

Applied Mechanics doi: 10.3390/applmech7010021

Authors: Raed Hossain Tanvir Ahmad Mohammed Aksir Talukder Md Mazedur Rahman Gyula Varga Saiaf Bin Rayhan

This study proposes two novel stiffened panel configurations, designated X and X-30, manufactured from the conventional aerospace alloy Al 2024-T3 to enhance the critical buckling resistance under in-plane compression. Their performance was evaluated against traditional T-, I-, L-, and Omega-type stiffeners, as well as a newly introduced Y-panel found in the literature. Initial results show that both proposed designs achieve 80–200% higher buckling capacity than conventional panels, with only a 4.54% difference between the X and X-30 configurations. A weight-constrained optimization was then conducted using a Box–Behnken design of experiments combined with a multi-objective genetic algorithm in Ansys DesignXplorer. After correcting inconsistencies in the initial optimization ranges, the prediction error in the optimized buckling values was reduced to 4%. The optimized X panel attained the highest critical buckling load of 2920 kN, followed by the X-30 panel with 2744.3 kN, corresponding to a 114–258% improvement over traditional stiffener geometries. A Pearson correlation matrix further suggested that, for all the stiffened panels except Omega, the base plate showed a strong correlation with the critical buckling load, typically ranging from 0.83 to 0.99. In contrast, for the X-30 panel, the lower base part also showed a strong correlation of 0.93.

Applied Mechanics doi: 10.3390/applmech7010020

Authors: C. Bhargavi K. S. Sreekeshava Manish S. Dharek B. K. Raghu Prasad J. V. Raghavendra

This study evaluates bamboo–coir hybrid composite panels developed for formwork applications using an 80:20 fiber–matrix ratio and a 50:50 bamboo-to-coir distribution. The novelty of this study lies in the combined assessment of formwork-relevant mechanical performance, Mode I and Mode II fracture behavior, finite element validation and post-fracture microstructural correlation for a high fiber volume fraction natural fiber hybrid panel. Mechanical, durability, fracture, numerical and microstructural investigations were performed and benchmarked against 10 mm thick construction-grade plywood. The hybrid panels exhibited a density of 805 ± 10.84 kg/m3, which is within 0.7% of plywood, a tensile strength of 50.20 ± 2.85 MPa, representing an increase of 41.8% over plywood, and a flexural strength of 38.60 ± 2.10 MPa, corresponding to an increase of 12.9% as compared to plywood. The impact energy absorption of hybrid panels was 7.85 ± 0.62 J, which is 26.6% greater than plywood. Mode I fracture testing yielded a fracture toughness of 456.65 ± 15.42 J/m2, corresponding to an increase of 9.3% over plywood, while Mode II fracture toughness yielded a value of 792.42 ± 30.18 J/m2, representing an increase of 13.7% over plywood. Finite element predictions deviated from experimental load–displacement responses by 5–13%. SEM observations identified fiber bridging, fiber pullout and interfacial sliding in the hybrid panels, consistent with the measured fracture energy values. The results indicate that bamboo–coir hybrid panels satisfy the mechanical and fracture performance requirements for reusable formwork systems.

Applied Mechanics doi: 10.3390/applmech7010019

Authors: Monica Ciminello Vittorio Memmolo Assunta Sorrentino Fulvio Romano

This paper presents the structural health monitoring (SHM) system applied to a 9 m composite outer wing box (OWB) specifically designed for a brand-new regional aircraft to detect barely visible impact damage (BVID) based on structural response data. The approach relies on different technologies to offer multilevel diagnosis, including impact detection as well as disbonding identification, localization, and sizing. The use of different sensing techniques based on piezoelectric transducers and distributed fiber optic sensors deployed all over wing structures is explored. Different features are simultaneously extracted from the propagating waves and from light scattering, able to detect low-energy BVID impact. In addition, the combined use of static and dynamic interrogation allows the estimation of the delamination surface after impact with good accuracy. The final test results on the OWB provided effectiveness in detecting, localizing, and tracking impact damage in the composite structure, ensuring long-term reliability and safety, as well as characterizing barely visible damage by a fully integrated onboard SHM system.

Applied Mechanics doi: 10.3390/applmech7010018

Authors: Abdelkader Hassein-Bey Nadir Belgroune Assia Bessi Omar Kebour Mohamed Mohammedi Ahmed Rafik Touil Amel Boudjemaa

This work reports the elaboration and testing of polydimethylsiloxane/titanium dioxide (PDMS/TiO2) polymer nanocomposites, focusing on producing and combining TiO2 nanoparticles with a polymer matrix through an ex situ route. By mixing the inherent flexibility of PDMS with the unique properties of nanoparticles, the nanocomposites aim to enhance mechanical stability, optical response, and photocatalytic activity. X-ray diffraction (XRD) confirmed the successful incorporation of TiO2 into the PDMS matrix. UV–visible spectroscopy monitored photocatalytic performance using metronidazole as a model pollutant under 365 nm irradiation. Kinetic analysis revealed degradation and showed that the reaction rate constant (k) increased with TiO2 loading, reaching a maximum of 0.0019 min−1 for the 6 wt.% composite. These findings indicate that while the reaction kinetics are slower than those of free powders, the PDMS/TiO2 nanocomposites provide a viable, recoverable, and flexible solution for environmental remediation applications. Future efforts will target improved durability, broadened visible light absorption, and process optimization for scalable fabrication.

Applied Mechanics doi: 10.3390/applmech7010017

Authors: Milad Kazemian Aleksandr Cherniaev

Non-crimp fabric (NCF) composites are increasingly adopted for structural components due to their high mechanical performance and processability. Like other fibre-reinforced plastics, NCFs remain vulnerable to in-service damage from tool drops or unintended collisions, which can substantially reduce load-bearing capacity. This study aimed to develop a validated numerical model capable of simulating damage initiation and post-impact behaviour through an integrated experimental–numerical approach. The mechanical properties of a representative unidirectional NCF composite were first experimentally established. Then, tubular NCF subcomponents were fabricated and tested under a two-phase loading protocol. In the first phase, damage was introduced using quasi-static indentation or controlled low-velocity impact. In the second phase, the residual load-bearing capacity of the damaged subcomponents was assessed under four-point bending. To support the research objective, a finite element model was developed in LS-DYNA to simulate both phases, using the MAT_ENHANCED_COMPOSITE_DAMAGE (MAT54) material formulation. Non-measurable input parameters, including stress limit factors and erosion strain thresholds, were calibrated via parameter estimation, sensitivity analysis, and iterative refinement. The final model showed close agreement with experiments in predicted damage location, deformation mode, and residual strength. X-ray computed tomography was used to validate delamination predictions. The findings support the development of reliable and cost-effective numerical tools for damage assessment in advanced composite structures.

Applied Mechanics doi: 10.3390/applmech7010016

Authors: Omar Kebour Rabah Magraoui Nadir Belgroune

The dynamic behavior of the DS306 detacher, a critical component in industrial fiber processing lines, plays a decisive role in maintenance performance and overall operational reliability. This study introduces a strengthened preventive maintenance strategy that leverages vibration analysis and dynamic modeling with a strong emphasis on early fault anticipation. A detailed numerical finite element model of the detacher was developed to determine its natural frequencies, critical modes, and dynamic response under real operating conditions. Experimental vibration measurements were conducted to validate the numerical model and identify characteristic frequencies associated with imbalance and wear. The results show that the proposed predictive framework not only reproduces the machine’s dynamic behavior with high accuracy but also anticipates mechanical degradation trends well before the occurrence of critical failures. This early-warning capability allows maintenance teams to plan interventions proactively, significantly reducing unexpected downtime, avoiding cascading damage, and improving long-term equipment availability. Overall, the study provides a robust and practical methodology for dynamic diagnosis, fault prediction, and optimized preventive maintenance in industrial rotating machinery.

Applied Mechanics doi: 10.3390/applmech7010015

Authors: Piotr Klejment

The Discrete Element Method is widely used in applied mechanics, particularly in situations where material continuity breaks down (fracturing, crushing, friction, granular flow) and classical rheological models fail (phase transition between solid and granular). In this study, the Discrete Element Method was employed to simulate stick–slip cycles, i.e., numerical earthquakes. At 2000 selected, regularly spaced time checkpoints, parameters describing the average state of all particles forming the numerical fault were recorded. These parameters were related to the average velocity of the particles and were treated as the numerical equivalent of (pseudo) Acoustic Emission. The collected datasets were used to train the Random Forest and Deep Learning models that successfully predicted the time to failure. SHapley Additive exPlanations (SHAP) was used to quantify the contribution of individual physical parameters of the particles to the prediction results. The main novelty of this study was the prediction of time to failure for entire event sequences. Using only instantaneous particle velocity statistics and without using information about the history of previous events, coefficients of determination in the range R2 = 0.81–0.96 were obtained.

Applied Mechanics doi: 10.3390/applmech7010014

Authors: Homa Haghighi Girum Urgessa

Traditional expansion joints in bridge structures are prone to durability problems, such as leakage, corrosion, and high maintenance demands, which can significantly reduce service life. To overcome these limitations, ultra-high-performance concrete (UHPC) link slabs have emerged as an effective jointless solution; however, their mechanical performance and sensitivity to key design and modeling parameters are not yet fully understood. This study presents a nonlinear finite element investigation of UHPC link slabs using the Concrete Damaged Plasticity (CDP) model in ABAQUS. A baseline model, validated against the experimental results, was established with a link slab length of 1100 mm and representative material and detailing properties. A systematic sensitivity analysis was then performed by varying five geometrical parameters (link slab length and thickness, debonding length, reinforcement diameter, and reinforcement spacing) and five numerical/material parameters (non-debonding and debonding interface friction coefficient, UHPC and normal concrete compressive strength, and steel yield strength). For each case, the load–displacement response was examined through initial stiffness (K0), yield and peak load–deformation values (Py, Δy and Pu, Δu), and ductility ratio (μ). The results highlight the dominant role of reinforcement detailing; larger bar diameters and closer spacing substantially increased stiffness and strength while maintaining ductility. Debonding length emerged as a critical tuning parameter, with longer debonding improving ductility but slightly reducing strength. Slab thickness primarily influenced stiffness, whereas overall length showed minor effects on peak capacity. On the numerical side, steel yield strength proved to be the most influential input, affecting all response measures, while the non-debonding interface friction coefficient strongly governed yield capacity. Variations in the debonding friction coefficient, UHPC compressive strength, and normal concrete strength exhibited secondary influence within the tested ranges. Overall, the findings provide practical guidance for both the designing and detailing of UHPC link slabs and the calibration of FEM (finite element modeling) models. By clarifying which parameters most strongly govern stiffness, strength, and ductility, this study supports more reliable structural design and efficient numerical modeling of UHPC link slabs in accelerated bridge construction applications.

Applied Mechanics doi: 10.3390/applmech7010013

Authors: Spyridoula G. Farmaki Dimitrios A. Exarchos Vasileios Dracopoulos Anastasios Gkotzamanis Konstantinos G. Dassios Theodore E. Matikas

Recent advances in nanotechnology have highlighted the transformative potential of carbon-based nanomaterials, such as carbon nanofibers, carbon nanotubes, and graphene, in cementitious systems. These materials have shown a remarkable ability to enhance the mechanical strength, fracture toughness, and overall functional performance of cementitious composites. Their nanoscale dimensions and exceptional intrinsic properties allow for effective stress bridging, crack arrest, and matrix densification. Despite these promising features, the current understanding remains limited, particularly regarding their application to concrete. Furthermore, literature lacks systematic, parallel evaluations of their respective effectiveness in improving both mechanical performance and long-term durability, as well as their potential to impart true multifunctionality to concrete structures. It is worth noting that significant and statistically significant improvements in fracture behavior were observed at specific nanofiller concentrations, suggesting strong potential for the material system in next-generation innovative infrastructure applications. Experimental results demonstrated that both CNTs and GNPs significantly enhanced the mechanical performance of concrete, with flexural strength increases of approximately 49% and 38%, and compressive strength improvements of 22% and 47%, respectively, at optimum contents of 0.6 wt.% CNTs and 0.8 wt.% GNPs. SEM analyses confirmed improved matrix densification and interfacial bonding at these concentrations, while higher dosages led to agglomeration and reduced performance. This gap highlights the need for targeted experimental studies to elucidate the structure-property relationships governing these advanced materials.

Applied Mechanics doi: 10.3390/applmech7010012

Authors: Habib Shorekandi Nima Refahati Meysam Nouri Niyaraki

In this study, the influence of nanochitosan and kenaf fibers on the tensile strength, elastic modulus, and impact strength of polylactic acid (PLA)/natural rubber (Standard Malaysian Rubber, grade 20—SMR20) biocomposites was investigated experimentally using Response Surface Methodology (RSM). The independent variables included the weight percentage of nanochitosan (2, 4, and 6 wt%), kenaf fibers (5, 10, and 15 wt%), and SMR20 natural rubber (10, 20, and 30 wt%). Composite samples were prepared by melt mixing in an internal mixer and subsequently fabricated into test samples using hot compression molding in accordance with relevant standards. Tensile tests were conducted to evaluate tensile strength and elastic modulus, while Charpy impact tests were performed to assess impact strength. The results revealed that increasing nanochitosan content up to 4 wt% enhanced tensile strength, elastic modulus, and impact strength by 39%, 22%, and 27%, respectively; however, further addition (6 wt%) led to a decline in these properties due to nanoparticle agglomeration. Increasing kenaf fiber content to 15 wt% improved tensile strength, elastic modulus, and impact strength by 44%, 26%, and 37%, respectively, demonstrating their effective reinforcing role. The incorporation of SMR20 natural rubber significantly increased impact strength by 59% (at 30 wt%), while causing a reduction of 17% in tensile strength and 20% in elastic modulus, consistent with its elastomeric nature. Furthermore, field emission scanning electron microscopy (FESEM) was employed to examine the dispersion of nanochitosan and kenaf fibers within the PLA/SMR20 matrix, providing insights into the interfacial adhesion and failure mechanisms. The findings highlight the potential of optimizing natural filler and rubber content to tailor the mechanical performance of sustainable PLA-based biocomposites.

Applied Mechanics doi: 10.3390/applmech7010011

Authors: Carlos D. Constantino-Robles Francisco Alberto Castillo Leonardo Jessica Hernández Galván Yoisdel Castillo Alvarez Luis Angel Iturralde Carrera Juvenal Rodríguez-Reséndiz

This paper presents a systematic review conducted under the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) framework, analyzing 286 scientific articles focused on vibration-based predictive maintenance strategies for wind turbines within the context of advanced Prognostics and Health Management (PHM). The review combines international standards (ISO 10816, ISO 13373, and IEC 61400) with recent developments in sensing technologies, including piezoelectric accelerometers, microelectromechanical systems (MEMS), and fiber Bragg grating (FBG) sensors. Classical signal processing techniques, such as the Fast Fourier Transform (FFT) and wavelet-based methods, are identified as key preprocessing tools for feature extraction prior to the application of machine-learning-based diagnostic algorithms. Special emphasis is placed on machine learning and deep learning techniques, including Support Vector Machines (SVM), Random Forest (RF), Convolutional Neural Networks (CNN), Long Short-Term Memory networks (LSTM), and autoencoders, as well as on hybrid digital twin architectures that enable accurate Remaining Useful Life (RUL) estimation and support autonomous decision-making processes. The bibliometric and case study analysis covering the period 2020–2025 reveals a strong shift toward multisource data fusion—integrating vibration, acoustic, temperature, and Supervisory Control and Data Acquisition (SCADA) data—and the adoption of cloud-based platforms for real-time monitoring, particularly in offshore wind farms where physical accessibility is constrained. The results indicate that vibration-based predictive maintenance strategies can reduce operation and maintenance costs by more than 20%, extend component service life by up to threefold, and achieve turbine availability levels between 95% and 98%. These outcomes confirm that vibration-driven PHM frameworks represent a fundamental pillar for the development of smart, sustainable, and resilient next-generation wind energy systems.

Applied Mechanics doi: 10.3390/applmech7010010

Authors: Adil Yucel Alaeddin Arpaci Asli Bal Cemre Ciftci

This study investigates the dynamic behaviors of re-entrant unit-cell-shaped steel frames through numerical and experimental modal analyses. Inspired by re-entrant honeycomb structures, individual frame units were modeled to explore how natural frequencies vary with beam cross-sectional dimensions and frame angles. Twenty distinct frame models—incorporating four cross-sectional sizes (4 × 4 mm, 8 × 8 mm, 12 × 12 mm, and 16 × 16 mm) and five main frame angles (120°, 150°, 180°, 210°, and 240°)—were developed using 3D modeling and finite element analysis (FEA) tools, and the first eight natural frequencies and corresponding mode shapes were extracted for each model. The results reveal that lower modes exhibit global bending and torsional behaviors, whereas higher modes demonstrate increasingly localized deformations. It is found that the natural frequencies decrease in the straight frame configuration and increase in the hexagonal configurations, highlighting the critical influence of the frame geometry. Increasing the cross-sectional size consistently enhances the dynamic stiffness, particularly in hexagonal frames. A quadratic polynomial surface regression analysis was performed to model the relationship of the natural frequency with the cross-sectional dimension and frame angle, achieving high predictive accuracy (R2 > 0.98). The experimental validation results were in good agreement with the numerical results, with discrepancies generally remaining below 7%. The developed regression model provides an efficient design tool for predicting vibrational behaviors and optimizing frame configurations without extensive simulations; furthermore, experimental modal analyses validated the numerical results, confirming the effectiveness of the model. Overall, this study provides a comprehensive understanding of the dynamic characteristics of re-entrant frame structures and proposes practical design strategies for improving vibrational performance, which is particularly relevant in applications such as machine foundations, vibration isolation systems, and aerospace structures.

Applied Mechanics doi: 10.3390/applmech7010009

Authors: Emmanouil Bacharidis Panagiotis Seventekidis Alexandros Arailopoulos

This work investigates a data-driven approach for detecting structural damage in the wing of a Cessna 172 aircraft using reduced-order finite element (FE) models. This study focuses on the ability of machine learning methods to generalize across different structural conditions, aiming to support reliable Structural Health Monitoring (SHM) in aeronautical applications. The wing was first modeled in detail using the FiniteElement Method, followed by the development of a simplified FE model to reduce computational cost while maintaining accuracy. The similarity between the two models was evaluated through modal analysis and the Modal Assurance Criterion (MAC). Dynamic excitation representing turbulence effects was applied to simulate healthy and damaged conditions, producing acceleration data used to train one-dimensional and two-dimensional neural network classifiers. The 1D models processed raw vibration signals, while the 2D models used image representations of the same data. Both architectures were tested against results from the detailed FE model to assess their generalization capability. The 2D networks achieved higher classification accuracy, demonstrating improved robustness in identifying both minor and severe damage. The findings highlight the potential of combining reduced FE models with data-driven methods for efficient and accurate aircraft wing damage detection.

Applied Mechanics doi: 10.3390/applmech7010008

Authors: Maria Luísa Braga Farinha Nuno Monteiro Azevedo Sérgio Oliveira

An explicit coupled two-dimensional (2D) hydromechanical model (HMM) that can simulate discontinuous features in the foundation, as well as the effects of grout curtains and drainage systems, is employed to evaluate the influence of key parameters such as dam height, foundation behaviour, joint patterns, joint stiffness and strength, hydraulic apertures, and grout curtain permeability. A parametric sensitive study using four gravity dams, and a real case study of an operating dam are presented. The results presented show that dam height influences the relationship between water level in the reservoir and drain discharges, with higher dams showing more pronounced curved nonlinearity. The strength properties of the concrete–rock interface are also shown to have a meaningful influence on the HM response, especially for an elastic foundation and for higher dams, showing the need to properly characterize this interface through in situ testing. The joint aperture at nominal zero stress is shown to be the parameter with the most significant effect on the HM response. The results also show that a progressive degradation scenario of the concrete–rock interface or of the grout curtain permeability is easier to identify through the hydraulic measurements than in the mechanical displacement field.

Applied Mechanics doi: 10.3390/applmech7010007

Authors: Xolani Prince Hadebe Bernard Xavier Tchomeni Kouejou Alfayo Anyika Alugongo Desejo Filipeson Sozinando

Large-diameter butterfly valves are essential control components in high-flow hydraulic systems, where blade geometry directly impacts operational reliability, energy efficiency, and lifecycle cost. This study presents an integrated structural–hydraulic optimization of a DN3000 Boving butterfly valve blade rated for a maximum operating pressure of 10 bar with comparative analysis of a conventional flat blade and an optimized curved blade. The work applies a CFD–FEM framework specifically to DN3000 Southern African valves, which is rare in the literature. Numerical simulations evaluated stress distribution, deformation, pressure losses, and flow stability under design and hydrostatic test conditions. The curved blade achieved a 58.6% reduction in peak von Mises stress, a 50% reduction in weight, a 22% reduction in load loss, and a 33% reduction in actuation torque requirements, while maintaining seal integrity. Cost analysis revealed a 50% reduction in material costs and simplification of manufacturing. The results confirm that the introduction of curvature significantly improves structural strength and hydraulic efficiency, thus providing a reproducible framework for the design of lighter and more economical valves in hydropower, municipal and industrial applications.

Applied Mechanics doi: 10.3390/applmech7010006

Authors: Tong Wang Xin Du Shufa Chen Qixin Sun Yue Jiang Hengjie Dong

This study conducts systematic experimental and numerical investigations to address the parameter calibration issue in the discrete element model of seashells, aiming to establish a high-fidelity numerical model that accurately characterizes their macroscopic mechanical behavior, thereby providing a basis for optimizing parameters of seashell crushing equipment. Firstly, intrinsic parameters of seashells were determined through physical experiments: density of 2.2 kg/m3, Poisson’s ratio of 0.26, shear modulus of 1.57 × 108 Pa, and elastic modulus of 6.5 × 1010 Pa. Subsequently, contact parameters between seashells and between seashells and 304 stainless steel, including static friction coefficient, rolling friction coefficient, and coefficient of restitution, were obtained via the inclined plane method and impact tests. The reliability of these contact parameters was validated by the angle of repose test, with a relative error of 5.1% between simulation and measured results. Based on this, using ultimate load as the response indicator, the PlackettBurman experimental design was employed to identify normal stiffness per unit area and tangential stiffness per unit area as the primary influencing parameters. The Bonding model parameters were then precisely calibrated through the steepest ascent test and design, resulting in an optimal parameter set. The error between simulation results and physical experiments was only 3.8%, demonstrating the high reliability and accuracy of the established model and parameter calibration methodology.

Applied Mechanics doi: 10.3390/applmech7010005

Authors: Liguang Kang Sandeep Suresh Babu Muhammet Muaz Yalçın Abdel-Hamid Ismail Mourad Mostafa S. A. ElSayed

This paper presents a unified aerodynamic design and optimization framework for morphing Blended-Wing-Body (BWB) Unmanned Aerial Vehicles (UAVs) operating in subsonic and near-transonic regimes. The proposed framework integrates parametric CAD modeling, Computational Fluid Dynamics (CFD), and surrogate-based optimization using Response Surface Methodology (RSM) to establish a generalized approach for geometry-driven aerodynamic design under multi-Mach conditions. The study integrates classical aerodynamic principles with modern surrogate-based optimization to show that adaptive morphing geometries can maintain efficiency across varied flight conditions, establishing a scalable and physically grounded framework that advances real-time, high-performance aerodynamic adaptation for next-generation BWB UAVs. The methodology formulates the optimization problem as drag minimization under constant lift and wetted-area constraints, enabling systematic sensitivity analysis of key geometric parameters, including sweep, taper, and twist across varying flow regimes. Theoretical trends are established, showing that geometric twist and taper dominate lift variations at low Mach numbers, whereas sweep angle becomes increasingly significant as compressibility effects intensify. To validate the framework, a representative BWB UAV was optimized at Mach 0.2, 0.4, and 0.8 using a parametric ANSYS Workbench environment. Results demonstrated up to a 56% improvement in lift-to-drag ratio relative to an equivalent conventional UAV and confirmed the theoretical predictions regarding the Mach-dependent aerodynamic sensitivities. The framework provides a reusable foundation for conceptual design and optimization of morphing aircraft, offering practical guidelines for multi-regime performance enhancement and early-stage design integration.

Applied Mechanics doi: 10.3390/applmech7010004

Authors: Mohamed-Fouad Maouche Mabrouk Hecini

This work presents an analytical homogenization model developed to predict the tensile and bending behavior of double-wall corrugated cardboard. The proposed approach replaces the complex three-dimensional geometry, composed of five paper layers, with an equivalent two-dimensional homogenized plate. Based on lamination theory and enhanced by sandwich structure theory, the model accurately captures the orthotropic behavior of the material. To achieve this objective, three configurations of double-wall corrugated cardboard were investigated: KRAFT LINER (KL), DUOSAICA (DS), and AUSTRO LINER (AL). A comprehensive experimental characterization campaign was conducted, including physical analyses (density measurement, SEM imaging, and XRD analysis) and mechanical testing (tensile tests), to determine the input parameters required for the homogenization process. The proposed model significantly reduces geometric complexity and computational cost while maintaining excellent predictive accuracy. Validation was performed by comparing the results of a 3D finite element model (ANSYS-19.2) with those obtained from the homogenized H-2D model. The differences between both approaches remained systematically below 2%, confirming the ability of the H-2D model to accurately reproduce the axial and flexural stiffnesses of double-wall corrugated cardboard. The methodology provides a reliable and efficient framework specifically dedicated to the mechanical analysis and optimization of corrugated cardboard structures used in packaging applications.

Applied Mechanics doi: 10.3390/applmech7010003

Authors: Ali Makke Julien Gardan Naman Recho Marouene Zouaoui

This methodology investigates the determination of the fracture toughness of 3D-printed specimens under monotonic loading conditions. The application is based on the use of a Single Edge Notch Bending (SENB) specimen made by a 3D-printing process (17-4PH stainless steel). The load–displacement curves exhibited linear behavior until crack initiation, indicating that the Linear Elastic Fracture Mechanics (LEFM) can be used under a small-scale yielding assumption. This study extends a previous methodology, originally applied to a polymer, to a metal additively manufactured material. The methodology established in the paper represents a major outcome: the ability to characterize the fracture toughness of the material. This study extends our previous Digital Image Correlation-based methodology from thermoplastic polymers to 17-4PH stainless steel produced by metal additive manufacturing (ADAM). Its novelty lies in combining DIC with a finite element sub-model to evaluate fracture parameters, enabling accurate crack initiation detection in challenging metal AM specimens, and providing a methodology that can be generalized to other metals and AM processes. The aim of this study is to establish a robust DIC-based methodology for the identification of crack initiation and the determination of fracture toughness parameters (K_IC and J) in 3D-printed 17-4PH stainless steel produced by the ADAM process.

Applied Mechanics doi: 10.3390/applmech7010002

Authors: Anastasia Bogdanova Anna Kamenskikh Andrey Muhametshin Yuriy Nosov

The present article relates to the description of phenomenological relations of amorphous material behavior within the framework of viscoelasticity and elastic-viscoplasticity theory, as well as to the creation of its digital analog. Ultra-high-molecular-weight polyethylene (UHMWPE) is considered in the study. The model is based on the results of a series of experimental studies. Free compression of cylindrical specimens in a wide range of temperatures [−40; +80] °C and strain rates [0.1; 4] mm/min was performed. Cylindrical specimens were also used to determine the thermal expansion coefficient of the material. Dynamic mechanical analysis (DMA) was performed on rectangular specimens using a three-point bending configuration. Maxwell and Anand models were used to describe the material behavior. In the framework of the study, the temperature dependence of a number of parameters was established. This influenced the mathematical formulation of the Anand model, which was adapted by introducing the temperature dependence of the activation energy, the initial deformation resistance, and the strain rate sensitivity coefficient. Testing of the material models was carried out in the process of analyzing the deformation of a spherical bridge bearing with a multi-cycle periodic load. The load corresponded to the movement of a train on a bridge structure, without taking into account vibrations. It is shown that the viscoelastic model does not describe the behavior of the material accurately enough for a quantitative analysis of the stress–strain state of the structure. It is necessary to move on to more complex models of material behavior to minimize the discrepancy between the digital analog and the real structure; it has been established that taking into account plastic deformation while describing UHMWPE would allow this to be performed.

Applied Mechanics doi: 10.3390/applmech7010001

Authors: Harouna Illou Abdoulaye Rabii El Maani

This paper presents a numerical study of fluid–structure interaction (FSI) applied to wind turbines, combining computational fluid dynamics (CFD) and finite element analysis (FEA). The study focuses on a 3D wind turbine blade inspired by the GE 1.5XLE model. The blade features a twisted geometry with S818, S825, and S826 aerodynamic profiles, and is made of an orthotropic composite material with variable thickness and an internal spar. The fluid domain is defined by two circular sections upstream and downstream, aligned along the Z-axis. Simulations are performed under a wind speed of 12 m/s and a rotational speed of −2.22 rad/s (Tip Speed Ratio (TSR) = 8), with air modeled as an incompressible fluid at ambient temperature. On the CFD side, a periodic and symmetric modeling approach is applied, reducing the fluid domain to one-third of the full configuration by simulating flow around a single blade and extrapolating results to the remaining ones. This method achieves a 47% reduction in computation time while maintaining high accuracy in aerodynamic results. On the FEA side, spar condensation is performed by creating a superelement using the substructuring method. This strategy reduces structural computation time by 45% while preserving reliable predictions of displacements, stresses, and natural frequencies. These results confirm the effectiveness of the proposed techniques for accurate and computationally efficient aeroelastic simulations.

Applied Mechanics doi: 10.3390/applmech6040091

Authors: Rafael Shaikhutdinov

Creep in metals as a phenomenon has been comprehensively studied in solid mechanics as well as in materials science. This interest stems from two key motivations: assessing the strength characteristics of components subjected to prolonged exposure at high temperatures and enhancing our understanding of plastic deformation mechanisms. As it is known, the mechanics of deformable solids employ constitutive equations when describing creep behavior, whereas strength physics utilize models aimed at quantifying a particular creep deformation mechanism or mechanisms in novel materials and to predict the performance of the parts manufactured from them. However, such models are rarely encountered within traditional mechanics problem-solving frameworks. To bridge this gap, this study demonstrates how some classic boundary value problems can incorporate the kinetic equation of a metal creep model with a real structural parameter derived from the theory of irreversible deformations. The main derivation steps and numerical solutions are provided for steady and transient creep conditions, along with visualizations illustrating the distribution of actual structural parameters. This research outlines promising pathways for incorporating diverse structural creep models—typically associated with materials science—into solid mechanics. These findings lay the groundwork for more accurate predictions of evolving material properties in applications where creep deformations play a critical role.

Applied Mechanics doi: 10.3390/applmech6040090

Authors: Hana Driss Abderrahim El Mahi Mourad Bentahar Moez Beyaoui Mohamed Haddar

This paper presents the mechanical characterisation of sandwich composites. Different specimen configurations have been tested with a three-point bending load and their mechanical behavior has been discussed. In addition, the acoustic emission technique was used to detect the onset of damage mechanisms and to monitor their evolution. The proposed analysis is based on processing recorded acoustic emission bursts. An unsupervised classification approach, combining the k-means algorithm with Principal Component Analysis (PCA), is used to group the detected acoustic events. The cluster analysis of the acquired data allows for correlation with the damage mechanisms occurring in sandwich composites. In addition to the advantages of multivariate data analysis, the results highlight the influence of sensor placement on the analysis of damage mechanisms is investigated. A suitable sensor configuration is proposed to improve the detection of acoustic emission activity. The originality of this work lies in the combined mechanical–AE interpretation that provides new insight into the damage behaviour of both a synthetic and a bio-based sandwich material. The comparative analysis of these two types of materials, coupled with a dedicated evaluation of sensor placement effects on defect detection, offers a contribution not previously reported in the literature.

Applied Mechanics doi: 10.3390/applmech6040089

Authors: Bekzodjon Fayziev Otabek Sagdullaev Shukhrat Djalilov Odil Khaydarov Jabbor Mustofoqulov Erkin Akhmedov Asror Mustafakulov Akbar Toyirov

Degradable solute transport in porous media significantly influences various ecological, geological, and industrial processes. In this paper, a mathematical model for solute transport in porous media with varying hydrodynamic dispersion is examined, integrating balance and kinetic equations alongside initial and boundary conditions. The model is enhanced by include variable hydrodynamic dispersion. Numerical approaches are utilized to address the problem, and a solution algorithm founded on the finite difference method is introduced. Computer simulations are conducted to examine the impact of different model parameters on solute transport, and the findings are evaluated. Numerical tests were performed for constant dispersion and three representative spatially variable forms—exponential, linear, and parabolic—for same other model parameters. Simulations show that neglecting diffusion/dispersion significantly delays the transport of material and underestimates both aqueous concentrations and adsorbed reserves. The results demonstrate that accounting for variable hydrodynamic dispersion significantly enhances the accuracy of solute transport predictions. The exponential form of dispersion produces stronger spreading effects, while the linear and parabolic forms show moderate variations. These findings underline the importance of incorporating scale-dependent dispersion in modeling contaminant migration in porous media.

Applied Mechanics doi: 10.3390/applmech6040088

Authors: Hagen Bankwitz Jörg Matthes Jörg Hübler

Additive Manufacturing (AM) using Fused Layer Modelling (FLM) often results in polymer components with limited and highly anisotropic mechanical properties, exhibiting structural weaknesses in the layer direction (Z-direction) due to low interlaminar adhesion. The main objective of this work was to investigate and quantify these mechanical limitations and to develop strategies for their mitigation. Specifically, this study aimed to (1) characterize the anisotropic behavior of unreinforced Polycarbonate (PC) components, (2) evaluate the effect of continuous, unidirectional (UD) carbon fiber tape reinforcement on mechanical performance, and (3) validate experimental findings through Finite Element Method (FEM) simulations to support predictive modeling of reinforced FLM structures. Methods involved experimental tensile and 3-point bending tests on specimens printed in all three spatial directions (X, Y, Z), validated against FEM simulations in ANSYS Composite PrepPost (ACP) using an orthotropic material model and the Hashin failure criterion. Results showed unreinforced samples had a pronounced anisotropy, with tensile strength reduced by over 70% in the Z direction. UD tape integration nearly eliminated this orthotropic behavior and led to strength gains of over 400% in tensile and flexural strength in the Z-direction. The FEM simulations showed very good agreement regarding initial stiffness and failure load. Targeted UD tape reinforcement effectively compensates for the weaknesses of FLM structures, although the quality of the tape–matrix bond and process reproducibility remain decisive factors for the reliability of the composite system, underscoring the necessity for targeted process optimization.

Applied Mechanics doi: 10.3390/applmech6040087

Authors: Maria Anna De Rosa Maria Lippiello

This paper investigates the effects of shear deformation on the flutter and divergence instabilities of a cantilever beam subjected to a concentrated mass and applied dynamic couple. The beam is modeled using classical and truncated Timoshenko beam theory, accounting for both shear deformation and rotary inertia. The inclusion of rotary inertia is shown to significantly influence the dynamic response, particularly for beams with greater thickness. According to Hamilton’s principle, the equations of motion for the cantilevered beam are derived, applying both classical and truncated Timoshenko beam theories. Auxiliary functions are utilized to solve the resulting system analytically. Various numerical examples are presented, illustrating typical results to demonstrate the effectiveness of the proposed approach. The numerical findings show significant convergence and computational effectiveness. The effect of the location of a concentrated mass and the dynamic couple applied at the free end is analyzed for various beam slenderness ratios and curvature positions, emphasizing their impact on modifying the critical instability limits. To highlight the significance of shear effects, a comparison is made between the outcomes of the Timoshenko model and those of the Euler-Bernoulli beam model, showing notable variations in the anticipated divergence and flutter stability characteristics. All the examples were executed using both classical theory and the truncated Timoshenko theory, and the findings indicated a remarkable level of convergence. Finally, a numerical comparisons with literature papers was performed. The results achieved showed strong alignment.

Applied Mechanics doi: 10.3390/applmech6040086

Authors: Vladimir Kobelev

This manuscript examines the rotational dynamics of rigid bodies in five-dimensional Euclidean space. This results in ten coupled nonlinear differential equations for angular velocities. Restricting rotations along certain axes reduces the 5D equations to sets of 4D Euler equations, which collapse to the classical 3D Euler equations. This demonstrates consistency with established mechanics. For bodies with equal principal moments of inertia (e.g., hyperspheres and Platonic solids), the rotation velocities remain constant over time. In cases with six equal and four distinct inertia moments, the solutions exhibit harmonic oscillations with frequencies determined by the initial conditions. Rotations are stable when the body spins around an axis with the largest or smallest principal moment of inertia, thus extending classical stability criteria into higher dimensions. This study defines a 5D angular momentum operator and derives commutation relations, thereby generalizing the familiar 3D and 4D cases. Additionally, it discusses the role of Pauli matrices in 5D and the implications for spin as an intrinsic property. While mathematically consistent, the hypothesis of a fifth spatial dimension is ultimately rejected since it contradicts experimental evidence. This work is valuable mainly as a theoretical framework for understanding spin and symmetry. This paper extends Euler’s equations to five dimensions (5D), demonstrates their reduction to four dimensions (4D) and three dimensions (3D), provides closed-form and oscillatory solutions under specific inertia conditions, analyzes stability, and explores quantum mechanical implications. Ultimately, it concludes that 5D space is not physically viable.

Applied Mechanics doi: 10.3390/applmech6040085

Authors: Jianfeng Fang Gentian Hong Xin Wen Runmin Wang Qiang Shentu Tao Chen Weichao Li

A method based on a statically indeterminate planar frame model was developed for the analysis and evaluation of box-type subgrade structures in high-speed railways. The objective of this study is to establish a concise and mechanically rigorous framework capable of quantifying the effects of key geometric parameters on bending moments, shear forces, and slab deflection, thereby providing guidance for structural refinement. Symbolic derivation and structural mechanics theory are combined to formulate the analytical model, and finite element simulations in Abaqus are used to verify the theoretical predictions under the design loads of the Quzhou–Lishui railway section located between Quzhou City and Lishui City in Zhejiang Province, China. Key findings show the maximum bending moments at the slab center and web-slab junction, reaching 14,818 kN·m, and the maximum shear forces of 16,934 kN at the web-slab junction. The top slab center showed the maximum deflection, approximately 7.5 × 10−2 mm. Simulation errors were below 5%. The optimization results recommend a web spacing of 4.5–5 m and a web height of 5–8 m. In an engineering case, reducing the web spacing from 6 m to 5 m and adjusting the web height from 7 m to 6.5 m dropped the top-slab mid-span bending moment from 10,628 kN·m to 5603 kN·m (an 89.7% reduction). Concrete use fell by 2.61% (from 24,900 to 24,250 m3/km), and overall costs dropped by about 5%. These findings demonstrate that the proposed analytical method provides an effective basis for rational parameter selection and preliminary structural design of box-type railway subgrades.

Applied Mechanics doi: 10.3390/applmech6040084

Authors: Felix Deckert Lukas Lippold Thomas Most Carsten Könke

Within the present paper, Physics-Informed Neural Networks (PINN) are investigated for the analysis of frame structures in two dimensions. The individual structural elements are represented by Euler–Bernoulli beams with additional axial stiffness. The transverse and axial displacements are approximated by individual neural networks and the differential equations are considered by minimizing a joined global loss function within the simultaneous training process. The boundary conditions at the supports of the structure and the coupling conditions at the element connections are considered in the global loss function and specific weighting factors are defined and tuned within the training. The combination of several structural elements within one analysis by training a set of neural networks simultaneously by a joined loss function is the main novelty of the current study. The formulation of coupling conditions for different scenarios is illustrated. Additionally, a nondimensionalization approach is introduced in order to achieve an automatic scaling of the individual loss function terms. Several examples have been investigated as follows: a simple beam structure first with quadratic load and second with varying cross-section properties is analyzed with respect to the convergency of the networks accuracy compared to the analytical solutions. Two more sophisticated examples with several elements connected at rigid corners were investigated, where the fulfillment of the consistency of the displacements and the equilibrium conditions of the internal forces is a crucial condition within the loss function of the network training. The results of the PINN framework are verified successfully with traditional finite element solutions for the presented examples. Nevertheless, the weighting of the individual loss function terms is the crucial point in the presented approach, which will be discussed in the paper.

Applied Mechanics doi: 10.3390/applmech6040083

Authors: Anna Kim Adil Kadyrov Kirill Sinelnikov Karibek Sherov Vassiliy Yurchenko

Cutting fluids are widely used in mechanical engineering to reduce friction and heat generation during metal machining. However, during operation, these fluids become contaminated with metal particles, dust, and microorganisms, leading to degradation of their functional properties and environmental concerns. This study investigates the ultrasonic cleaning and regeneration of contaminated cutting fluids. A rheological model of the elastic–viscous medium was analyzed, and a physical model describing the ultrasonic cleaning mechanism was proposed. Experimental investigations were conducted to validate the theoretical assumptions. The results confirmed that ultrasonic treatment promotes dispersion and phase separation of the fluid, removes putrefactive odor, and partially destroys microorganisms. The regenerated fluid exhibited enhanced clarity and stability compared with the contaminated samples. The findings contribute to a deeper understanding of the physicochemical processes occurring during ultrasonic treatment and demonstrate the potential of this method for sustainable reuse of cutting fluids in industrial applications.

Applied Mechanics doi: 10.3390/applmech6040082

Authors: Mihaela Constantin Cătălina Dobre Anca Chelmuș Nicolae Băran Daniel Taban Beatrice Ibrean Daniel Dima Mugurel Oprea

Cyclone separators are widely used for gas–solid separation due to their robustness and low operating cost. This study focuses on the experimental validation of a single cyclone configuration and the development of a MATLAB-based numerical framework. The model employs a Euler–Lagrange approach to capture centrifugal, drag, and gravitational forces acting on spherical polyethylene particles (D = 5 mm). Laboratory-scale measurements of airflow, pressure drop, and separation efficiency showed strong agreement with the numerical model (deviation < 6%), confirming its reliability for the single cyclone case. Beyond this validated framework, exploratory simulations were carried out for series and parallel cyclone configurations to provide predictive insights into possible design trade-offs. Unlike high-fidelity CFD–DEM models, which are computationally intensive and allow detailed turbulence and particle–particle interactions, the present MATLAB model is simplified but transparent and fast to implement. Its originality lies in demonstrating a low-cost, experimentally calibrated tool that can support preliminary design decisions. The multi-cyclone results should be interpreted as predictive trends, as no direct experimental validation was possible within the present setup. These findings offer preliminary guidance for balancing efficiency, energy demand, and throughput in applied mechanics of multiphase flow systems.

Applied Mechanics doi: 10.3390/applmech6040081

Authors: Šárka Němcová Jan Heřmánek Pavel Crha Karolina Macúchová Václav Němec Radek Pobořil Tomáš Tichý Ondřej Uher Martin Smrž Tomáš Mocek

This article demonstrates that 3D-printed parts can replace metal parts in optomechanics in the correct circumstances. Three examples are shown: a clamping fork for pedestal holders where stability is important, an adjustable mirror holder where the rigidity is the main criterion, and a stray light shield where the transmissivity is critical. By combining carbon-fiber-reinforced polymers (CFRPs) with 3D printing, it is possible to produce components that fill the gap between standard 3D-printed plastics and metal parts in terms of strength and stability. These parts are designed to be lighter, more compact, and easier to modify, while keeping good mechanical properties such as resistance to vibration, shape accuracy, and controlled thermal expansion. The article focuses on the application of composite 3D printing on optomechanical components. It compares different methods of composite 3D printing, including fused filament fabrication (FFF) with either chopped fibers or with continuous fiber reinforcement. Three examples from the HiLASE Centre demonstrate how these parts are used in practice, confirming that it is indeed possible to 3D print components that are lighter and cheaper yet still highly functional compared to their off-the-shelf counterparts—for example, lightweight and stiff mounts, shielding against stray laser light, or flexible elements allowing fine mechanical adjustments. Simulations of the deformations are included to compare the printed and metal versions. The article ends with a summary of the benefits and limitations of using 3D-printed composites in optomechanics.

Applied Mechanics doi: 10.3390/applmech6040080

Authors: Jifan Zhang Hua Su Yiting Su Kun Zhou

This study proposes a combined finger seal configuration composed of different structural laminates. An equivalent dynamic model of the finger seal system, accounting for thermal effects, is established. The effects of configuration type and operating conditions, including pressure differential, rotor displacement excitation, and temperature, on the dynamic leakage and rubbing force of the combined finger seal are investigated. The finger seal composed of two structural forms (X-type and Y-type) of finger laminates in this paper has a comprehensive advantage in leakage rate and rubbing force compared with the finger seal composed of a single structural seal slice. Compared with the leakage performance of the combined type of finger seals with different finger beam lengths, the maximum leakage rate of the 3Y+2X type finger seal proposed in this paper can be reduced by 29%. For the 3Y+2X finger seal structure and the calculation conditions (including pressure difference, displacement excitation and temperature) of this work, as the pressure difference increases, the seal leakage rate increases, and the peak value and impulse of the rubbing force also increase. The increase in rotor displacement excitation leads to an increase in both the leakage rate and the rubbing force. The increase in environmental temperature leads to an increase in leakage rate of the finger seal, but both the peak value of the rubbing force and the impact force reduce. Under different pressure differences and displacement excitation, the sealing leakage in a 300 °C high-temperature environment is slightly greater than that at normal temperature, but the friction force is less than that at normal temperature.

Applied Mechanics doi: 10.3390/applmech6040079

Authors: Ralph Kenneth Castillo Neamul Khandoker Sumaiya Islam Abdul Md Mazid

Resistance spot welding is a process used to join overlapping metals using pressure and electric current, commonly applied in the automotive industry for joining car bodies. This study aimed to understand the mechanical performance of spot welds under dynamic impact conditions. Various welding schedules were tested to observe the effects of different welding currents and times on the impact energy absorbed by spot welds. The results showed that the impact energy absorbed ranged from 26 J to 98 J, with higher welding currents and times generally increasing the impact energy due to more heat input. However, excessive welding parameters led to decreased impact energy. Statistical analysis and modeling revealed that optimal impact energy is achieved with a welding current of 5 kA and welding time of 6.728 cycles.

Applied Mechanics doi: 10.3390/applmech6040078

Authors: Guilherme Garcia Madsen Mariana Alvarenga Alves Luiz Alberto Oliveira Rocha Elizaldo Domingues dos Santos William Ramires Almeida Liércio André Isoldi

Thin steel plates with stiffeners are widely employed in several branches of engineering, combining mechanical strength with low weight and serving as both structural and cladding components. However, the influence of the side-wall inclination angle of hat-stiffeners on the stiffness distribution and deflection patterns of steel plates remains insufficiently explored. This study conducts computational modeling to evaluate the deflection of thin steel plates reinforced with hat-stiffeners. The plates were considered simply supported and subjected to a uniformly distributed load. The Constructal Design method and the exhaustive search technique were employed, allowing for geometric evaluation and optimization. A fraction corresponding to 30% of the plate volume was removed and redistributed to generate longitudinal hat-stiffener geometries by varying its side-wall angle and thickness. The smaller base of the hat-stiffeners was imposed as a geometric constraint and therefore kept fixed. The results indicate a nonlinear trend between the side-wall angle, the moment of inertia, and the resulting deflection, leading to a new geometrical pattern that connects the angular inclination to the overall stiffness behavior of the plate. Angles between 105° and 130° provided the best performance, reducing the maximum deflection by 93.72% compared with the reference plate and improving it by around 7.5% relative to previous studies. These findings illustrate how geometric configuration can enhance performance in line with Constructal Design principles.

Applied Mechanics doi: 10.3390/applmech6040077

Authors: Riyam Basim Al-Tameemi Hashem Mazaheri Jumaa Salman Chiad Mahdi Shaban

Bone-anchored implants have transformed prosthetic technology by providing a promising alternative to traditional socket-based prostheses through enhanced stability, comfort, and natural limb functionality. These advancements result from developments in osseointegration techniques, improved surgical methods, and innovative implant materials. To address current limitations, continued research remains essential to enhance safety and effectiveness, thereby promoting wider adoption of these advanced prosthetic solutions. This study focuses on modeling bone-anchored implants for limb prostheses in amputees. The research evaluates structural behavior and performance of osseointegrated implants under various conditions while optimizing implant design. The investigation examines different materials including aluminum, Ti-6Al-4V, and Ti-6Al-4V coated with 10 µm platinum. Additionally, implants of different lengths (207 mm, 217 mm, and 197 mm) were analyzed. The results indicate that Ti-6Al-4V and Ti-6Al-4V coated with ten µm platinum reduce stress by 46% and 65%, respectively. Ti-6Al-4V coated with platinum demonstrates the lowest equivalent stress, highlighting the coating’s effectiveness. Furthermore, the coated implant exhibits the lowest deformation—22.92% less than aluminum and 5.13% less than uncoated Ti-6Al-4V. Shorter implant lengths reduce deformation through increased stiffness, whereas longer implants, such as the 217 mm length display greater deformation due to enhanced flexibility.

Applied Mechanics doi: 10.3390/applmech6040076

Authors: Spyridoula G. Farmaki Dimitrios A. Exarchos Panagiota T. Dalla Elias A. Ananiadis Vasileios Kechagias Alexandros E. Karantzalis Theodore E. Matikas

The increasing reliance on conventional coatings such as WC-Co raises serious environmental and health concerns due to the toxicity of cobalt and the ecological footprint of these materials. To address this challenge, the present study explores the development of eco-friendly multifunctional coatings via the Plasma Spray (PS) process, using titanium (Ti), silicon carbide (SiC), and tungsten carbide-cobalt (WC-Co) mixtures as alternative feedstocks. Steel substrates were coated under different deposition strategies (powder mixing, layer-by-layer) and current settings (800-900 A). The coatings were characterized by scanning electron microscopy (SEM/EDX), 3D profilometry, sliding wear testing, and potentiodynamic corrosion measurements. Results showed that Ti-WC (mix, 900 A) and Ti-SiC (layer, 900 A) coatings achieved the most favorable performance, combining excellent adhesion, uniform coverage, reduced porosity, and improved resistance to wear and corrosion compared to conventional Cr2O3 coatings. Notably, Ti-WC coatings provided surface roughness values comparable to Cr2O3, while significantly lowering the environmental impact. These findings demonstrate that PS-based Ti-WC and Ti-SiC systems can serve as sustainable and high-performance alternatives for protective applications in harsh environments, particularly in marine industries, supporting the transition toward coatings with reduced ecological footprint.