Applied Mechanics

Additive Manufacturing, or 3D Printing, is based on manufacturing physical objects by sequential deposition of layers of material. Although the usage of AM is growing, no straightforward methodology exists to produce parts with specific, or optimized, mechanical properties. In this work, an approach for optimizing the mechanical properties of AM specimens under bending stress is presented, using DOE. For the experimental procedure, Fused Deposition Modeling (FDM) technology was used along with Polylactic acid (PLA) as the in-process material. Nozzle temperature, printing speed, infill pattern and printing orientation were selected as manufacturing factors to be optimized to achieve so maximum load and deflection to be acquired. Both optimized sets of values were increased by 53% and 28%, respectively, and were experimentally checked to validate the accuracy of the approach. Full article

Liquid-storage tanks are critical components in industrial plants, especially during seismic events. Tank failures can cause significant economic losses, operational disruptions, and environmental damage. Therefore, accurate design and performance evaluation are essential to minimize these risks. However, past earthquakes have highlighted the need for a better understanding of tanks’ seismic behavior. This requires selecting the appropriate seismic input and ground motion records to properly simulate tank responses. This study examines the seismic behavior of various tank types using different earthquake record sets, including both far-field and near-field events. The tanks were modelled with varying geometries, such as diameter–height ratios, wall thickness, liquid height, and radius. Time-history analyses were conducted to generate fragility curves and evaluate the seismic performance of the tanks based on specific limit states. The findings show that the choice between far- and near-field records significantly influences seismic response, particularly in terms of fragility curve variation. The fragility curves derived from this analysis can serve as valuable tools for risk assessments by governments and stakeholders, helping to improve the safety and resilience of industrial plants. Full article

A testing method is developed to evaluate the acceleration- and strain-based fatigue life of a thermal interface layer in the high-cycle fatigue regime. The methodology adopts vibration-based fatigue testing, where adhesively bonded beams are excited at their resonant frequency under variable amplitude loading using an electrodynamic shaker. Fatigue failure is monitored through shifts in modal frequency and modal damping. Key findings include the identification of a 4% frequency shift as the failure criterion, corresponding to macro-delamination. The thickness of the thermal interface material influences acceleration-based fatigue life, decreasing by a factor of 0.2 when reduced from 0.3 mm to 0.15 mm and increasing by 5.5 when increased to 0.5 mm. Surface quality has a significant impact on both acceleration-based and strain-based fatigue curves. Beams from chemically etched aluminum–magnesium alloy specimens exhibit a sevenfold increase in fatigue life compared to beams from untreated printed circuit boards. Strain-based fatigue life increases with temperature, with a 0.2 reduction at $-40$ °C and an eightfold increase at $100$ °C relative to $23$ °C. The first principal strain ${\epsilon }_{1,\mathrm{rms}}$ is validated as a reliable local damage parameter, effectively characterizing fatigue behavior across varying TIM thicknesses. Full article

In the seismic design of steel moment-resisting frames (MRFs), the panel zone region can significantly affect overall ductility and energy-dissipation capacity. This study investigates the influence of panel zone flexibility on the seismic response of steel MRFs by comparing two modeling approaches: one with a detailed panel zone representation and the other considering fixed beam-column connections. A total of 30 2D steel MRFs (15 frames incorporating panel zone modeling and 15 frames without panel zone modeling) are subjected to nonlinear time–history analyses using four suites of ground motions compatible with Eurocode 8 (EC8) soil types (A, B, C, and D). Structural performance is evaluated at three distinct performance levels, namely, damage limitation (DL), life safety (LS), and collapse prevention (CP), to capture a wide range of potential damage scenarios. Based on these analyses, the study provides information about the seismic response of these frames. Also, lower-bound, upper-bound, and mean values of behavior factor (q) for each soil type and performance level are displayed, offering insight into how panel zone flexibility can alter a frame’s inelastic response under seismic loading. The results indicate that neglecting panel zone action leads to an artificial increase in frame stiffness, resulting in higher base shear estimates and an overestimation of the seismic behavior factor. This unrealistically increased behavior factor can compromise the accuracy of the seismic design, even though it appears conservative. In contrast, including panel zone flexibility provides a more realistic depiction of how forces and deformations develop across the structure. Consequently, proper modeling of the panel zone supports both safety and cost-effectiveness under strong earthquake events. Full article

Masked Stereolithography (mSLA) is an additive manufacturing technique that has been recently explored. Currently, studies in the literature addressing the investigation of stress concentrators in photosensitive resin parts printed on mSLA devices using the Whitney–Nuismer analytical method combined with Finite Element Analysis (FEA) and Digital Image Correlation (DIC) are rare. This work utilizes the combination of these techniques to analyze stress concentrators in specimens subjected to axial and eccentric loads, considering the effects imposed by the clamp restraint and a complementary study considering the free loading condition. For axial loading, the results are consistent, with variations in the stress concentration factor ranging from 0.42% to 5.25%. For the eccentric loading studies, the results indicate that the most suitable method for the test was the analysis considering the restraint imposed by the clamp, as the deformation results show a maximum error of 6.9% compared to 24.7% when the restraints were disregarded. The consistency of the results reinforces the quality of the employed technique, demonstrating that this study not only achieved its objectives but also provided a foundation for future investigations in the field. Full article

Burst pressure is one of the critical strength parameters used in the design and operation of pressure vessels because it represents the maximum pressure that a vessel can withstand before failing. Historically, the Barlow formula was used as a design base for estimating burst pressure. However, it does not consider the plastic flow response for ductile steels and is applicable only to thin-walled cylinders (i.e., the diameter to thickness ratio D/t ≥ 20). A new multiaxial plastic yield theory was developed to consider the plastic flow response, and the associated theoretical (i.e., Zhu–Leis) solution of burst pressure was obtained and has gained extensive applications in the pipeline industry because it was validated by different full-scale burst test datasets for large-diameter, thin-walled pipelines in a variety of steel grades from Grade B to X120. The Zhu–Leis flow theory of plasticity was recently extended to thick-walled pressure vessels, and the associated exact flow solution of burst pressure was obtained and is applicable to both thin and thick-walled cylindrical shells. Many full-scale burst tests are available for thin-walled line pipes in the pipeline industry, but limited pressure burst tests exist for thick-walled vessels. To validate the newly developed exact solutions of burst pressure for thick-walled cylinders, this paper conducts a series of burst pressure tests on small-diameter, thick-walled pipes. In particular, six burst tests are carried out for three thick-walled pipes in Grade B carbon steel. These pipes have a nominal diameter of 2.375 inches (60.33 mm) and three nominal wall thicknesses of 0.154, 0.218, and 0.344 inches (3.91, 5.54, and 8.74 mm), leading to D/t = 15.4, 10.9, and 6.9, respectively. With the burst test data, comparisons show that the Zhu–Leis flow solution of burst pressure matches well the burst test data for thick-walled pipes. Thus, these burst tests validate the accuracy of the Zhu–Leis flow solution of burst pressure for thick-walled cylindrical vessels. Full article

This study investigates the effect of a polyurethane (PUR) foam layer on impact force, impact duration, and deformation with regard to radiosondes during drop tests. Numerical (Finite Element Method) and experimental approaches were used to model collisions with and without protective PUR layers. The numerical results demonstrated that adding a soft PUR foam layer reduced peak impact force by 10% while it increased impact duration up to 71%. Experimental drop tests confirmed the numerical outcomes as peak impact force difference was 7% between simulations and experiments, while impact duration differed only by 11%. Besides force and duration, impact deformation was also investigated by an FEM model and high-speed camera footage on radiosondes with a PUR foam layer. The FEM model was able to approximate well the deformation magnitude since the numerical deformation was only 2% lower compared to the experimental data. In summary, a reliable and validated FEM model was created. On the one hand, this model allows the analysis of different protective layers around a radiosonde. On the other hand, it can adequately predict the impact behavior of radiosondes by incorporating multiple important factors. In addition, it has been confirmed that incorporating a soft PUR foam layer significantly improves safety by reducing impact force and extending impact duration. Full article

One of the challenging aspects of designing body-in-white stiffness test rigs is measuring test accuracy. This paper proposes a method of integrating the body-in-white stiffness test rig and the body-in-white into an overall model for the optimization design. It establishes an optimization mathematical model based on the overall structure of the stiffness test rig, taking into account the factors affecting the accuracy of the test results of the body-in-white stiffness test rig. The stiffness test rig’s testing accuracy can be significantly increased by designating the degrees of freedom at each connection position as discrete variables. The Hybrid and Adaptive Metamodeling Method (HAM) is used to optimize the mathematical model. This approach uses and integrates three distinct metamodels with various attributes. The body-in-white torsional stiffness test result error is only 1.1%, and the body-in-white bending stiffness test result error is only 3.4%, owing to the optimization result that was used to design and manufacture a set of body-in-white stiffness test rigs and use them for a body-in-white stiffness test verification. Full article

This study investigates the influence of various printing parameters on the tensile, compressive, and bending stiffness of fused deposition modeling (FDM)-printed polylactic acid (PLA) parts through a comprehensive full factorial design of experiment. Key factors, including infill percentage, infill pattern, number of outer shells, and part orientation, were systematically varied to quantify their impact on mechanical performance. A total of 36 parameter combinations, selected based on a literature review and experimental feasibility, were tested using standardized specimens: beams for bending, cylinders for compression, and dogbones for tensile testing. Mechanical tests were performed according to ISO 5893:2019, employing a 1 kN load cell to determine stiffness and elastic modulus. The results indicate that the number of outer shells and infill density are the most influential parameters, whereas infill pattern and part orientation have a minor effect, depending on the loading condition. This study provides a novel and robust evaluation of the interactions between key printing parameters, offering new insights into optimizing the mechanical properties of FDM-printed parts. These findings establish a foundation for further optimization and material selection in future additive manufacturing research. Full article

The aim of this work is to perform a detailed dilatometric analysis of the decomposition of austenite during the cooling process using experimentally derived continuous cooling transformation (CCT) diagrams for two specific tool steels, X153CrMoV12 Bohdan Bolzano, Bratislava, Slovakia and 100MnCrW4. The dilatometric curves were compared with metallographic evaluations using scanning electron microscopy (SEM). In addition, hardness measurements were performed to obtain additional information about the mechanical properties of the materials. All experimental work was performed using a DIL 805A. The accuracy of the resulting CCT diagrams was verified by comparing them with those calculated with the JMatPro software v12.4. The cooling rates ranged from 20 °C/s to 0.01 °C/s, depending on the specific type of steel tested. The novelty of this research is the combination of experimental and simulation methods to analyze the influence of alloying elements on the kinetics of phase transformations in tool steels. It was found that one of the most significant factors affecting the CCT diagrams is the weight percentage of alloying elements in the steels. These results clearly show that increasing the weight percentage of the content of alloying elements has a significant impact on the accuracy of the simulation results derived from the JMatPro software. Full article

Chatter is a complex dynamic instability in machining processes and presents nonlinear and nonstationary behavior. Detection of this phenomenon before a catastrophic failure occurs has great importance in the industry today. This behavior demands online monitoring signal-processing techniques suitable for facing these kinds of dynamics such as approximate entropy (AE) and wavelet transform. Moreover, AE is useful for dealing with noisy signals and requires a relatively small amount of observations. In this study, we propose an improved AE methodology, the multiscale maximum approximate entropy (MMAE), to detect chatter in milling processes. The maximum AE is achieved by the calculation of the parameter r proposed by Sheng and Chon. In the past, the calculation of this parameter was a drawback of the AE technique. The results show the effectiveness of this proposed technique in detecting clearly different gradual and drastic changes in chatter conditions. Moreover, a more known technique is presented: the time–frequency maps provided by continuous wavelet transform (CWT). The results also show the efficacy of this technique in detecting different levels of chatter. The results are corroborated by the machining piece observation of the chatter phenomenon. MMAE is also compared with sample entropy (SE) and the Hurst exponent obtained by the R/S analysis. At the end, a comparison analysis of the mentioned techniques is carried out, showing that they all have advantages and disadvantages. However, the disadvantages of MMAE and CWT can be solved, as mentioned in the comparison section. Thus, the conclusion is that MMAE and CWT techniques are optimal for the online monitoring of chatter in machining processes. Full article

In model calibration, the identification of the unknown parameter values themselves, but also the uncertainty of these model parameters, due to uncertain measurements or model outputs might be required. The analysis of parameter uncertainty helps us understand the calibration problem better. Investigations on the parameter sensitivity and the uniqueness of the identified parameters could be addressed within uncertainty quantification. In this paper, we investigate different probabilistic approaches for this purpose, which identify the unknown parameters as multivariate distribution functions. However, these approaches require accurate knowledge of the model output covariance, which is often not available. In addition, we investigate interval optimization methods for the identification of parameter bounds. The correlation or interaction of the input parameters can be modeled with a convex feasible domain that belongs to a feasible solution of the model output within given bounds. We introduce a novel radial line-search procedure that can identify the boundary of such a parameter domain for arbitrary nonlinear dependencies between model input and output. Full article

Transfer-path analysis (TPA) is a reliable and effective diagnostic tool for determining the dominant vibration transfer paths from the actively vibrating components to the connected passive substructures in complex assemblies. Conventional and component-based TPA approaches achieve this by estimating a set of forces that replicate the operational responses on the passive side of the assembly, requiring separate measurements of the transfer-path admittance and the operational responses, followed by an indirect estimation of the interface forces. This demands significant measurement effort, especially when only the dominant transfer paths are desired. Operational transfer-path analysis (OTPA) overcomes this by identifying transfer-path contributions solely from operational response measurements. However, OTPA is susceptible to measurement errors as minor inaccuracies can result in discrepancies regarding transfer-path characterization. This is especially evident when poor placement of the sensors results in similar response measurements from multiple channels, introducing redundancy and amplifying measurement noise. This is typically resolved using regularization techniques (e.g., singular-value truncation and Tikhonov regularization) that promote vibration transfer related to dominant singular vectors. As an alternative, this paper explores the benefits of using established reduction-based approaches from dynamic substructuring within OTPA. Measured responses are projected onto different dynamic sub-spaces that include the dominant dynamic behavior of the interface between the active and passive sides (i.e., dominant interface modes). In this way, only the vibration transfer related to the interface modes included in the reduction step is evaluated, leaving stiff modes obscured by noise unobserved. This paper proposes using interface-deformation modes and physical modes, demonstrating their feasibility via various experimental setups and comparing them to standard OTPA. Full article

In this work, an analytical solution for the natural frequencies of elastically supported stepped beams with rigid segments is presented. The elastic end boundary conditions are modeled with a translational stiffness element, a rotational stiffness element, and an end-concentrated mass. This model is of great significance in machine construction studies. Under the assumption of Euler–Bernoulli beam theory, the non-dimensional equations of the motion and main equations that can give all of the boundary conditions were obtained by using Hamilton’s principle. After deriving the transverse displacement functions by means of using the separation-of-variables technique, the frequency equation was found by setting the determinant of the coefficient matrix to zero. The natural frequencies of the transverse vibrations were found according to physical and geometric parameters. The method was validated by using FEM results and findings from the literature. This study indicates that the physical and geometric parameters of the elastic supports and rigid segments affect the natural frequencies of the beam. The revealed analytical method can be used to calculate the natural frequencies and mode shapes of all beam types, such as elastically supported uniform beams and single-step beams with or without concentrated mass and/or rigid segments. Full article

In this paper, the dynamic response of the Timoshenko cracked beam subjected to a mass is investigated. In turn, it is assumed that the beam has its ends restrained with both transverse and rotational elastic springs. Based on an alternative beam theory, truncated Timoshenko theory (TTT), the governing equations of motion of the cracked beam are derived and the influence of a mass on the behavior of free vibrations is investigated. The novelty of the proposed approach lies in the fact that the variational method used in the truncated theory simplifies the derivation of the equation of motion via the classical theory, and the perfect analogy between the two theories is shown. The objective of the present formulation lies in finding the equations of the truncated Timoshenko model with their corresponding boundary conditions and establishing their mathematical similarity with the geometric approach. It is shown that the differential equations with their corresponding boundary conditions, used to solve the dynamic problem of Timoshenko truncated beams through variational formulations, have the same form as those obtained through the direct method. Finally, some numerical examples are carried out to evaluate the influence of a mass and its position on the vibration performances of the cracked Timoshenko model. Additionally, the effects of the crack positions, the shear deformation and rotational inertia, and the yielding constraints on the natural frequencies are also discussed in some numerical examples. Full article

Researchers are currently conducting several studies in the field of navigation systems and sensors. Even in the past, there was a lot of research regarding the field of velocity sensors for unmanned underwater vehicles (UUVs). UUVs have various services and significance in the military, scientific research, and many commercial applications due to their autonomy mechanism. So, it’s very crucial for the proper maintenance of the navigation system. Reliable navigation of unmanned underwater vehicles depends on the quality of their state determination. There are so many navigation systems available, like position determination, depth information, etc. Among them, velocity determination is now one of the most important navigational criteria for UUVs. The key source of navigational aids for different deep-sea research projects is water currents. These days, many different sensors are available to monitor the UUV’s velocity. In recent times, there have been five primary types of sensors utilized for UUV velocity forecasts. These include Doppler Velocity Logger sensors, paddlewheel sensors, optical sensors, electromagnetic sensors, and ultrasonic sensors. The most popular sensing sensor for estimating velocity at the moment is the Doppler Velocity Logger (DVL) sensor. DVL sensor is the most fully developed sensor for UUVs in recent years. In this work, we offer an overview of the field of navigation systems and sensors (especially velocity) developed for UUVs with respect to their use with tidal current sensing in the UUV setting, including their history, evolution, current research initiatives, and anticipated future. Full article

The increasing demand for sustainable construction practices has prompted the exploration of innovative materials, such as waste plastics, to enhance both the environmental and mechanical performance of concrete, particularly for rigid pavements. This review investigates the mechanical properties of concrete incorporating four types of waste plastics—high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyvinyl chloride (PVC), and polypropylene (PP). The primary focus is on how these materials affect key mechanical properties, including compressive strength, tensile strength, and flexural strength. The analysis reveals that HDPE and PP, at optimal levels (5–10%), can enhance flexural and crack resistance, making them suitable for non-structural applications. Conversely, LDPE and PVC tend to reduce both compressive and tensile strengths at higher substitution levels due to poor bonding with cementitious materials. Despite these challenges, incorporating waste plastics into concrete presents significant environmental and economic benefits, including plastic waste reduction and lower reliance on natural aggregates. The review also highlights the need for further research on improving plastic–cement bonding through surface treatments and hybrid mix designs. This study contributes to the growing body of knowledge aimed at promoting the use of waste plastics in concrete, offering insights for the development of sustainable, high-performance construction materials. Full article

Experimentable Digital Twins are capable of combining different simulation domains on a system level. This has been shown for a multitude of simulation domains, e.g., rigid body dynamics, control, sensors, kinematics, etc., and application scenarios, e.g., automotive, space, and industrial engineering. In our work, we investigate how to include structural loads into an Experimentable Digital Twin while maintaining computational efficiency and interoperability on a system level. We combine rigid body dynamics with the transfer matrix method to simulate forces and stresses. We show our approach for statically determinate beam structures in a simulation on a system level and validate it experimentally and numerically with static and dynamic example problems. The results show a strong agreement in these comparisons, confirming the accuracy and reliability of our method. For practical applications, we see force and stress simulation using the transfer matrix method as an additional tool to facilitate simulation-based engineering in the early stages of structural design processes, e.g., when dealing with uncertain loading conditions and operational complexity on a system level. Full article

An extensive application of stiffened panels is considered standard for aerospace wing construction both for reducing the structural weight and fulfilling the regulatory requirements. The connection based on the adhesive layer between the skin and stringer introduces the possibility of debonding during operative conditions. The design procedure is strongly influenced by this anomaly, requiring the definition of a criterion for identifying the limit in debonding extension for safe operation. A procedure based on the investigation of the stress state in the adhesive layer is proposed in order to identify the typical behaviour of compressed plate, including damage situation, and a specific indication for design procedure is derived based on the debonding dimension. Critical and post-critical configuration were investigated both globally and locally to fix sensitive parameters. A conclusive guideline is discussed and presented. The analysis is applied to an isotropic plate in order to point out the main characteristics of the related design procedure. No conceptual changes are expected with the introduction of composite material that can influence the distribution of stress according to the chosen lay-up but not the basic design concept in the plate behaviour. Full article