Search Results (2,665)

The widespread application of planetary gear trains is accompanied by inevitable crack failures, especially for the internal ring gear, which may lead to catastrophic accidents. There is relatively little research on internal ring gear cracks and mostly only make assumptions about the crack damage morphology at a certain stage. Moreover, there is no answer on what will happen in the next stage after the crack occurs, or how to avoid serious failure. In view of this, this study considers rim and support configurations, tooth geometries, and crack parameters, and analyzes crack evolution mechanisms. The results indicate that compared to the internal ring gear outer surface constraint condition, the use of pin support for the internal ring gear increases the risk of severe rim-fracture failure. A thicker rim can avoid rim failure, especially when the initial crack is close to the tooth root. In addition, a larger root fillet helps to reduce the occurrence of rim failure over tooth failure. Increasing pin support diameter and stiffness results in a tendency for the crack trajectory to move away from the rim. This study gives support for the cracked ring gear failure analysis and safety design. Full article

This study investigates the mechanical behaviour of continuous carbon-fibre-reinforced additively manufactured composite structures aimed at applications in aeronautical structures, through a combination of experimental testing and numerical simulation. Tensile, compressive, and shear tests established stiffness and failure characteristics, while finite element analyses were used for a preliminary calibration-based reproduction of the measured coupon response, with an emphasis on the initial elastic part of the impact event. The integration of measured data with structural modelling provides a clearer understanding of load transfer and damage initiation in continuous-fibre AM, supporting more accurate simulation-based design of additively manufactured composite components. Experimental results show pronounced anisotropy, and a stable, rate-dependent impact response. The preliminary numerical model based on CT-derived homogenized properties accurately reproduces the initial part of the measured quasi-static and dynamic responses. Full article

As is well known, vibration, especially ultra-low-frequency vibration, is harmful to machinery’s accuracy and service life and even human health. This paper experimentally validates vibration isolation technology for low-frequency applications based on quasi-zero stiffness (QZS) properties. Firstly, a platform for isolating low-frequency vibration, referred to as LFVIP, is introduced, featuring a quasi-zero stiffness characteristic. Then, the dynamic stiffness of this platform is analyzed and established. Based on this analytical model, a solution for designing the platform to obtain the desired stiffness in the equilibrium state is suggested. Secondly, an experimental setup is established to verify the isolation performance of the platform under base displacement excitation. In addition, the isolation effectiveness of the LFVIP is compared with that of its linear counterpart (LC). The experimental results indicate that the LFVIP provides the starting isolation for effective isolation at approximately 2 Hz, while that of LC is around 6 Hz. Moreover, the vibration attenuation of the LFVIP is greater than that of the LC. Vibration isolation technology based on quasi-zero stiffness is superior to the LC, particularly in the low-frequency region. This work offers useful insights for the design of vibration isolators, suspension systems, and related applications, particularly by demonstrating how the superior vibration attenuation of the LFVIP can be leveraged to improve the performance of these systems. Full article

Wood–polymer composites (WPCs) produced through monomer impregnation have attracted increasing interest as a strategy to improve the durability and performance of wood materials. However, the limited permeability of certain wood species often restricts the effectiveness of impregnation treatments. This study investigates the use of microwave (MW) pretreatment as a drying and microstructural modification step to enhance methyl methacrylate (MMA) impregnation and in situ polymerization in maritime pine (Pinus pinaster) heartwood specimens. Wood specimens were subjected to MW treatment of 700 W and 5 min cycles prior to vacuum-pressure impregnation with MMA and subsequent thermal polymerization. Scanning electron microscopy and treatability parameters confirmed that MW pretreatment increased wood impregnability by generating microcracks and improving monomer penetration, thereby resulting in higher polymer retention and a higher weight percentage gain. As a result, the combined MW+MMA treatment produced a more homogeneous distribution of polymethyl methacrylate within the wood structure. The modified specimens showed a substantial reduction in water absorption and the highest water repellence efficiency among the studied groups, while dimensional stability improved to a lesser extent. In addition, the combined treatment significantly increased bending strength and stiffness, indicating an effective reinforcement of the wood structure through polymer loading. These results demonstrate that MW pretreatment is an efficient strategy to improve the treatability of maritime pine heartwood and to enhance the performance of MMA-based WPCs. Full article

Vibration energy harvesting has emerged as a sustainable solution for powering low-energy devices such as wireless sensors and wearable electronics. However, conventional vibration energy harvesters often suffer from narrow operational bandwidth and limited output performance under ultra-low excitation conditions. To overcome these limitations, this study proposes an asymmetric tristable vibration energy harvester integrated with an elastic magnifier (EM), hereafter referred to as the asymmetric TVEH with EM, to enhance energy conversion efficiency under weak excitation. A nonlinear two-degree-of-freedom electromechanical model is developed to describe the coupled dynamics between the cantilever beam and the EM, incorporating nonlinear restoring forces and electromechanical coupling effects. The system performance is investigated using the harmonic balance method (HBM) and time-domain numerical simulations. In addition, parametric studies are conducted to examine the influence of the EM mass and stiffness ratios on the dynamic response and energy harvesting performance. The numerical results demonstrate that the inclusion of the EM significantly amplifies the system response under ultra-low excitation $(f=0.055)$, enabling improved inter-well motion and enhancing energy conversion efficiency by up to 45%. To validate the analytical and numerical findings, an experimental prototype is fabricated and tested. The experimental results confirm the effectiveness of the proposed design, achieving a root mean square voltage of $V_{\mathrm{rms}}=5\mathrm{V}$ across a load resistance of $R_L=100\mathrm{k}\Omega$ under a base acceleration of $1.4{\mathrm{m}/\mathrm{s}}^2$ at 14 Hz, measured over a 30 s window with a low-pass filter cut-off frequency of 100 Hz. The proposed asymmetric TVEH with EM consistently outperforms both the symmetric TVEH with EM and the asymmetric configuration without EM. Overall, the results highlight the pivotal role of the elastic magnifier in enhancing the dynamic response and harvesting performance under weak excitations, demonstrating strong potential for powering low-power electronic devices in practical applications. Furthermore, this work supports the United Nations Sustainable Development Goal SDG 7 (Affordable and Clean Energy) by promoting decentralized and renewable vibration-based energy harvesting technologies. Full article

This paper presents the application of a structural finite element model (FEM) of a light patrol aircraft for numerical flutter analysis. The thin-walled structure was developed using 2D shells and additional 1D beam elements. The virtual structure was supplemented with additional point elements imitating lumped masses of non-structural on-board components. The model was subjected to validation for qualities such as the mass distribution, its CG location, the structural stiffness of its airframe units, and the similarity of natural modes. The comparative analyses showed satisfactory consistency of the mass and stiffness properties of the FEM with the actual aircraft. Numerical flutter analysis was then performed with the MD Nastran for an integrated aeroelastic model consisting of the FEM and the simplified aerodynamic model. The critical velocities of basic flutter modes were determined. Using simplified kinematic models of flight control systems built into the FEM, an analysis of the sensitivity of control surface flutter due to the pilot’s influence was carried out. The stick grip and the support of control pedals with the pilot’s legs cause specific conditions related to the imposition of additional stiffness and mass on the control manipulators. These conditions directly affect the natural frequencies of control surface modes, which translates into a change in the critical flutter speed of the tail. For the established range of changes in stiffness and mass added to the stick and pedals, a series of analyses of natural vibrations and flutter were carried out. The influence of the change in the support conditions of control manipulators was illustrated in graphs. Full article

The increasing use of biodegradable polymers, especially poly (lactic acid) (PLA), has raised concern about their entry into conventional post-consumer recycling streams. This review examines the technical and systemic consequences of PLA contamination in the high-density polyethylene (HDPE) circular economy through the “drop-in delusion,” defined here as the mistaken assumption that a sustainability-marketed polymer can enter an established recycling stream without compromising system compatibility. Focusing on contamination-sensitive conditions in which segregation, sorting, or stream purity are insufficient to prevent cross-contamination, the review discusses the immiscibility of HDPE/PLA blends and the resulting changes in stiffness, ductility, toughness, and aging behavior. It also analyzes mitigation routes such as improved sorting, compatibilization, and policy measures, while emphasizing that the practical severity of contamination depends on local infrastructure and contamination levels. In addition, it considers the risk that contaminated materials diverted into lower-value applications may become more vulnerable to interfacial damage, weathering, and secondary fragmentation. Overall, the review argues that circular-plastics strategies must distinguish biodegradability from recycling-system compatibility to protect the quality and value of HDPE recyclates. Full article

The water-resistant properties of a chitosan/OCL wax composite were evaluated on cotton fabrics using a dip-coating method. The plant-based wax was extracted from discarded outer cabbage leaves. The influence of the chitosan-to-OCL wax weight ratio on textile properties—including wettability, air permeability, mechanical performance, and stiffness—was systematically investigated. In addition, laundering tests were conducted to assess the durability of the coating. The results demonstrated that the cotton fabric coated with a chitosan/OCL wax composite at a 70/30 weight ratio exhibited the highest hydrophobicity, achieving a water contact angle of 157.87°. The coated cotton fabrics also showed good washing stability. Measurements of bending length and flexural rigidity revealed that cotton fabrics coated with the chitosan/OCL wax composite exhibited greater stiffness than the untreated samples. The combined use of chitosan and OCL wax provided a synergistic enhancement in water-resistant performance. These findings highlight the potential of the chitosan/OCL wax composite as a non-toxic and environmentally friendly finishing agent for cotton fabrics. Full article

Three-dimensional braided carbon-fiber-reinforced polymer (CFRP) composites are promising for lightweight aircraft propeller blades. Aircraft composite structures may approach temperatures of 80–90 °C under the combined effects of solar radiation, infrared heating, and ground reflection. Yet the thermo-mechanical failure mechanisms of low-braiding-angle architecture remain insufficiently understood. This study comparatively investigates the tensile behavior and damage evolution of low-angle four-directional (3D4A-20°) and five-directional (3D5A-20°) braided CFRP composites under axial tension at both room temperature and 90 °C. A multi-scale approach integrating in situ X-ray computed tomography, digital image correlation, digital volume correlation, and scanning electron microscopy was used to characterize strain localization, internal cracking, and fracture morphology. At room temperature, 3D5A-20° shows higher stiffness and strength than 3D4A-20° because additional axial yarns improve load-transfer and three-dimensional constraint. At 90 °C, matrix softening and interfacial degradation accelerate crack initiation, strain localization, and damage propagation in both architectures. Nevertheless, 3D5A-20° maintains more stable and progressive damage evolution, whereas 3D4A-20° exhibits earlier crack coalescence and greater mechanical degradation. Overall, elevated temperature accelerates damage evolution through matrix softening and interfacial degradation, whereas braided architecture determines load transfer and crack connectivity. These findings provide guidance for the design of low-angle braided composites for thermally exposed aircraft propeller blades. Full article

An integrated rebar box connection is proposed for the horizontal joints of fully prefabricated composite walls to simplify joint detailing and reduce on-site wet construction. Experimental tests and numerical analyses were conducted to evaluate the behavior of this connection. The results show that both specimens exhibited shear-dominated failure. The box connection and horizontal joint did not experience obvious fracture or pull-out failure, although local cover spalling, mortar crushing, and connector deformation were observed, suggesting effective force transfer between the upper and lower wall panels under the tested conditions. Compared with the cyclically loaded specimen, the monotonically loaded specimen exhibited higher peak load and larger deformation capacity under monotonic loading, whereas the initial stiffness was similar. The numerical results agree reasonably well with the experimental responses. The parametric finite element analyses indicate that increasing the integrated rebar diameter, the longitudinal reinforcement ratio in the rib columns, the concrete grid strength, and the axial compression ratio improves the load-carrying capacity of the wall, although a higher axial compression ratio reduces ductility. The proposed connection shows promising potential for use in the horizontal joints of fully prefabricated composite walls, and further studies with additional specimens and comparative connection details are warranted. Full article

The mechanical recycling of mono-material biaxially oriented polypropylene (BOPP) packaging films produces recycled polypropylene (rPP) with degraded properties, limiting its use in higher-performance applications. This study investigates rPP reinforcement with 6–12 µm microcellulose fibres (MCFs, 2–10 pbw) and microcellulose-derived biochar (BC, 5–20 pbw), characterized by DSC, TGA/DTG, MVR/MFR, temperature-dependent rheology, mechanical testing and water contact angle (WCA) measurements. Both fillers acted as heterogeneous nucleating agents, shifting crystallization by up to 4 °C and increasing crystallinity by 2–4%. MCF introduced an additional low-temperature degradation step, whereas BC increased onset and peak degradation temperatures by up to 20 °C and increased char yield. Low MCF loadings increased MVR/MFR by 20–25% and reduced melt viscosity, while BC decreased flow indices by up to 50% and stiffened the melt. Tensile and flexural moduli increased by 15–25% with MCF and 40–50% with BC, with a stiffness–toughness trade-off at the highest BC contents. MCF reduced the water contact angle to 63.0° at 10 pbw, while BC increased it to 108.1° at 20 pbw, indicating opposite effects on surface wettability. Converting a single cellulosic feedstock into fibrous or carbonised fillers enables bio-based upgrading of rPP, in line with circular economy principles. Full article

Indisputably, the evolution of innovative manufacturing methods such as additive manufacturing (AM) or 3D printing in the last decade has started gradually to influence the construction field, offering significant benefit potential, particularly in the field of metallic materials. In the case of aluminium alloys, the implementation of the wire arc additive manufacturing (WAAM) method, an AM sub-type, has recently emerged as a promising alternative to conventional rolling and extrusion, enabling unprecedented geometric flexibility, lower energy demand, and reduced tooling costs. However, the selection of an appropriate feedstock alloy poses a major challenge, as inherent trade-offs between strength, ductility, and printing-induced anisotropy arise. In this context, this study presents a thorough multi-scale numerical investigation, spanning from the cross-sectional to the global structural scale. The structural performance of several two-story moment-resisting frames was evaluated, comparing frames featuring WAAM-fabricated columns against conventional extruded and rolled benchmarks. The assessment included three 3D-printed alloys (Al-Mg, Al-Cu, Al-Mg-Si), differing in ductility levels, featuring topology-optimized and internal lattice-reinforced cross-sectional geometries. Linear elastic analyses reveal that global lateral stiffness heavily governs the response of slender frames, where WAAM was able to efficiently decrease the corresponding inter-story drifts by maximizing cross-sectional inertia without necessitating the utilization of larger external member dimensions. Furthermore, nonlinear static (pushover) analyses provided valuable insight into critical design considerations, exposing a profound strength-ductility trade-off in printed aluminium alloy load-bearing members. Full article

Viscous fluid dampers are widely used for mechanical vibration reduction to ensure the stability and safety of structures and systems. However, when a small amount of air (less than 10%) is mixed into the fluid, the compressibility of the fluid increases, leading to a decrease in the physical series stiffness of the damper. Consequently, under dynamic excitation, the proportion of elastic force in the total output force rises, resulting in an increase in the equivalent parallel additional stiffness—a concept often conflated with the series stiffness in the literature. This paper aims to demonstrate these two aspects of stiffness change by investigating the dynamic characteristics of air-mixed viscous fluid dampers through nonlinear modeling, finite element simulation, and experimental validation. Starting from a nonlinear series model comprising nonlinear damping and a nonlinear fluid spring (series stiffness), the energy dissipation and physical series stiffness under different air mixtures are simulated using a finite element model. To further explore the influence of air, an equivalent linear parallel model is established based on the equal energy principle, yielding an equivalent parallel additional stiffness. The results reveal that the energy dissipation effectiveness and the dynamic stiffness of viscous fluid dampers decrease as the air mixture increases. Nevertheless, the additional stiffness is increased with the air content. When the amount of air mixing is the same, the energy dissipation characteristics of the viscous fluid damper under different excitation frequencies vary. Both the damper efficiency and the additional stiffness are increased with the increase of the excitation frequency. The proposed equivalent linear model effectively captures the coupled effects of air mixture and excitation conditions on damper performance. Full article

Giant cantilevered tree-shaped steel structures are highly susceptible to cumulative deformation and geometric deviation during staged construction due to their complex spatial configuration, long cantilever characteristics, and nonlinear load transfer mechanisms. To address these challenges, this study investigates deformation monitoring and control of such structures based on 3D laser scanning, taking the “Tree of Life” project as a representative case. A high-precision full-field monitoring system is established to acquire multi-stage point cloud data throughout the construction process. The collected data are registered with the BIM model to quantify spatial deviations and track the deformation evolution of key structural components. Meanwhile, a staged preloading–unloading strategy is implemented to simulate operational loads, reconstruct load transfer paths, and regulate structural deformation during construction. Based on continuous field measurements, the deformation characteristics of different structural regions, including ring beams, rotating platforms, and trunk–branch systems, are systematically analyzed. The results indicate that the structure exhibits a pronounced global torsional deformation pattern. The displacement of ring beams ranges from 40.35 mm to 80.15 mm, while the maximum local displacement reaches 131.37 mm in geometrically complex regions, primarily attributed to the coupling effects of complex geometry, long cantilever action, stiffness discontinuity, and load concentration. Furthermore, deformation exhibits a progressive and stage-dependent accumulation pattern under sequential loading–unloading processes. The proposed monitoring and control approach achieves millimeter-level accuracy and enables effective feedback for construction adjustment and deviation mitigation. The integration of 3D laser scanning with staged load regulation provides a reliable technical framework for deformation monitoring and control of complex cantilevered steel structures. While the findings are based on a single complex project, further validation on additional cases is required to fully establish the general applicability of the proposed framework, although its integration of 3D monitoring, BIM registration, and staged load regulation suggests potential transferability to other large-scale cantilevered steel structures with similar geometric complexity. Full article

Bone plates are widely used in orthopaedic surgery to stabilise fractured bones and support healing following traumatic injuries or osteotomies. However, conventional metallic bone plates suffer from stress shielding and stiffness mismatch with bone, which can hinder optimal healing. Additive manufacturing enables the incorporation of novel metamaterial architectures into polymer-based implants to enhance mechanical properties. The fatigue behaviour of these implants during the healing period is critical to ensuring their structural integrity and long-term performance. In this study, the compressive fatigue performance of fused deposition modelling (FDM)-printed carbon fibre-reinforced polylactic acid (CF-PLA) bone plates were investigated. Four metamaterial structures—tetrachiral, re-entrant, rotating square, and hexagonal—were evaluated under strain-controlled cyclic loading at 20%, 40%, 60%, and 80% of their respective yield strains. The results showed a strong dependence of fatigue behaviour on lattice geometry. Among the tested configurations, the re-entrant structured bone plate exhibited the best overall fatigue performance, sustaining up to 100,000 cycles at moderate strain levels and showing delayed stiffness degradation under high strain conditions. In contrast, rotating square and hexagonal structures showed early stiffness loss and failure at higher strain levels. These findings highlight the importance of lattice design in fatigue performance, although FDM-induced printing defects significantly influence overall fatigue behaviour. Full article