Search Results (109)

The buckling and post-buckling responses of carbon fibre-reinforced polymer (CFRP) structures are strongly affected by geometric imperfections, boundary conditions, and material nonlinearities, making their reliable numerical prediction challenging. This work presents an integrated experimental–numerical investigation of a stiffened CFRP panel subjected to compressive loading, with the aim of improving model validation in instability regimes. The experimental campaign combines full-field measurements obtained through digital image correlation with local strain data from strain gauges, adopting a back-to-back configuration to capture the strain reversal associated with global buckling. The experimental results are compared with nonlinear finite element simulations incorporating intralaminar damage based on Hashin’s failure criteria. A good agreement between the numerical and experimental results is observed in the pre-buckling and early post-buckling regimes. However, increasing discrepancies arise at higher load levels, mainly due to manufacturing imperfections and uncertainties in boundary conditions, which influence the onset and evolution of localized deformation. Statistical indicators are employed to quantitatively assess the correlation between the experimental and numerical responses. The analysis focuses on the key response parameters, including the load–displacement behaviour, out-of-plane displacements, strain evolution, and damage initiation, enabling a comprehensive comparison of experimental and numerical results. The results demonstrate the effectiveness of combining full-field and point-wise measurements for validating numerical models of composite structures. Furthermore, the study highlights the limitations of idealized modelling assumptions and provides insights into the sensitivity of CFRP structures to imperfections in post-buckling and failure regimes. Full article

The nonlinear dynamic response of aerospace thin-walled structures in a post-buckling state under thermo-acoustic loads is critical for their design. This study investigates this phenomenon through integrated experimental and numerical approaches. Acoustic tests on thermally stressed flat plates yielded results in close agreement with finite element and reduced-order modal (FEM/ROM) simulations, with first-order frequency deviations within ±2 Hz and strain values of the same order of magnitude (10.7 µε vs. 9.5 µε at 50 °C). A key observation is the non-monotonic variation in the thermal modal frequency, which initially decreases then increases with the buckling coefficient, while dynamic strain data further validate the computational model. Comparative analysis of three Haynes 188 alloy geometries—flat plates, cylindrical shells, and spherical shells—reveals distinct behaviors rooted in their critical buckling temperatures (68.46 °C, 151.20 °C, and 698.28 °C, respectively): flat plates exhibit softening–hardening transitions with a frequency range of 491–624 Hz; cylindrical shells show irregular responses with a dramatic frequency drop from 1120 Hz to 360 Hz; and spherical shells maintain the highest stability and frequency range (1913–2109 Hz), governed by the buckling coefficient’s linear effect. Time-domain and probability density function (PDF) analyses elucidate the snap-through phenomena and the modulating roles of the buckling coefficient and sound pressure level (SPL). These findings underscore that geometric configuration and inherent stiffness are critical to post-buckling performance, providing a theoretical basis for designing aerospace components in extreme environments. Full article

Numerical predictions of the wrinkling behavior of biaxially fiber-reinforced elastomer sheets are carried out under consideration of finite deformations. The Holzapfel–Gasser–Ogden material model is used to account for the anisotropic hyperelastic material behavior of the sheets, where material parameters are identified based on experimental data of tensile tests from literature. A Finite Element Method-based simulation strategy is presented to extract critical loading conditions and to access the postbuckling response using geometrical imperfections. Depending on the layup and aspect ratio of the sheets, wrinkling onset was predicted for global stretches between 10% and 25%. For sheets with fiber orientations [±45°] wrinkling is predicted at larger global stretches than for sheets with fiber orientations of $[+{30}^{\circ }/-{60}^{\circ }]$ for the same aspect ratio. Furthermore, it is shown that short sheets have a tendency towards symmetric wrinkling patterns whereas for long sheets asymmetric wrinkles are more likely to occur. Comparison of the numerical predictions with experiments from the literature shows that the geometrical characteristics of the wrinkles, such as wavelengths and amplitudes, can be well predicted. Far into the postbuckling regime, the deviations of the predicted wrinkling amplitudes and their experimental counterparts are around 30% or less. Full article

This study presents a mechanics-based comparison of the buckling and ultimate strength behavior of stiffened plates reinforced with bulb-type and built-in angle stiffeners, with particular emphasis on the trade-off between structural performance and weight efficiency. Although these stiffener types are commonly treated as equivalent when designed to provide the same sectional moment of inertia, their nonlinear collapse behavior under realistic loading conditions has not been sufficiently quantified. To address this gap, a two-stage finite element framework is employed, consisting of linear eigenvalue buckling analysis to identify imperfection-sensitive modes, followed by geometrically and materially nonlinear imperfection analysis (GMNIA) to capture post-buckling behavior and ultimate strength. High-fidelity three-dimensional solid models incorporating classification-society-based material properties are used to simulate axially compressed stiffened plates representative of jack-up rig Living Quarter structures. The results demonstrate that, while both stiffener types exhibit comparable elastic buckling resistance, their nonlinear responses differ in terms of stiffness degradation, stress redistribution, and collapse localization. Importantly, the angle stiffener achieves an ultimate strength comparable to that of the elastically equivalent bulb stiffener while requiring less material, thereby exhibiting superior weight efficiency. These findings indicate that elastic equivalence alone is insufficient for optimal stiffener selection and highlight the necessity of nonlinear, imperfection-sensitive assessment in the design of lightweight and high-performance marine structures. Full article

This study investigates the bending response of a thin-walled asymmetric cold-formed steel angle using a combined experimental and numerical approach. Full-scale four-point bending tests were carried out on an L180 × 130 × 3 cold-formed steel angle and compared with numerical simulations using shell finite element models developed in ANSYS 2025 R2 and simplified beam-based models implemented in ARSAP. The experimental results showed that the load-carrying capacity, reaching approximately 25–27 kN, is governed by the interaction of global bending and local buckling of the compressed walls, leading to a pronounced post-peak softening response. The ANSYS shell finite element models accurately reproduced both the initial stiffness and nonlinear deformation mechanisms. The best agreement with the experimental force–displacement response was obtained for an effective load eccentricity in the range of 15 to 18.5 mm, which reflects realistic load transfer and contact conditions and results in errors below 10% in terms of stiffness and peak load. In contrast, the beam-based models captured the elastic behaviour but showed limited capability in reproducing local instability effects and post-peak response. The study is intentionally limited to a single geometry and loading configuration and should be interpreted as an experimentally calibrated case study. The obtained results allow the applicability limits of simplified beam models to be identified and confirm the necessity of shell finite element modelling for the analysis of thin-walled asymmetric steel angle members subjected to bending. Full article

This study investigates the compressive behavior of glued-laminated timber (Glulam) columns reinforced with different configurations of fiber-reinforced polymer (FRP) materials, including glass (GFRP) and carbon (CFRP) fibers in the form of rods, strip/panel, and fabrics. Axial compression tests were performed under controlled laboratory conditions to examine the influence of reinforcement type and configuration on mechanical performance. Descriptive statistics, one-way ANOVA, and Tukey’s post hoc tests were used to determine the significance of differences between the tested groups. Finite element analysis (FEA) using ANSYS software2023 R1 was also conducted to validate the experimental results and to provide insight into stress distribution within the strengthened columns. The results revealed that FRP reinforcement clearly enhanced both the ultimate load and compressive stress compared to unreinforced samples. The highest performance was achieved with double CFRP rods and 5 cm carbon strips, which reached stress levels of about 43 MPa, representing an improvement of nearly 60% over raw wood. Statistical analysis confirmed that these increases were significant (p < 0.05), while FEA predictions showed strong agreement with the experimental findings. Observed failure modes shifted from crushing and buckling in unreinforced specimens to shear-splitting and delamination in reinforced ones, indicating improved confinement and delayed failure. Full article

Thermal gradients induced by friction frequently trigger buckling deformation of the friction elements, especially in heavy-duty helicopters. Nevertheless, the subsequent influence of such post-buckling deformation on transient thermal characteristics during helicopter successive shifting remains insufficiently addressed in existing research. In the present work, a gap model for friction pairs with conical separate discs is first proposed. Subsequently, a comprehensive thermal-fluid-dynamic model incorporating spline friction, split springs, and time-varying thermal parameters is developed to investigate the transient thermal characteristics of wet clutches with conical separate discs in successive shifting. A corresponding qualitative analysis is performed to explore the transient thermal response and influence mechanisms of operating parameters, including shifting interval, rotation speed and control oil pressure. The results indicate that a rise in the control oil pressure from 1.5 MPa to 1.9 MPa facilitates a 42.65% increase in the maximum radial temperature gradient and augments the maximum axial temperature gradient by 24.35%. Meanwhile, an increase in rotation speed accelerates heat dissipation but compromises the uniformity of the temperature field. Additionally, extended shifting intervals under inadequate heat dissipation exacerbates thermal buildup, driving a persistent and significant escalation in the temperature of friction elements. The conclusions can provide a theoretical basis for the optimal design, condition monitoring, and fault diagnosis of aviation clutches. Full article

The study presented an analysis of the behaviour of cellular structures under bending, produced using the PolyJet Matrix (PJM) additive manufacturing method with photopolymer resin. Structures with regular cell geometry were designed to achieve a balance between stiffness, weight reduction, and energy absorption capacity. The aim of this study was to investigate the influence of unit-cell topology (quasi-similar, spiral, hexagonal honeycomb, and their core–skin hybrid combinations) on the flexural properties and deformation mechanisms of PolyJet-printed photopolymer beams under three-point bending. Additionally, all cellular configurations were fully infiltrated with a low-modulus platinum-cure silicone to evaluate the effect of complete polymer–elastomer interpenetration on load-bearing capacity, stiffness, ductility, and energy absorption. All tests were performed according to bending standard on specimens fabricated using a Stratasys Objet Connex350 printer with RGD720 photopolymer at 16 µm layer thickness. The results showed that the dominant failure mechanism was local buckling and gradual collapse of the cell walls. Among the silicone-filled cellular beams, the QS-Silicone configuration exhibited the best overall flexural performance, achieving a mean peak load of 37.7 ± 4.2 N, mid-span deflection at peak load of 11.4 ± 1.1 mm, and absorbed energy to peak load of 0.43 ± 0.06 J. This hybrid core–skin design (quasi-similar core + spiral skin) provided the optimum compromise between load-bearing capacity and deformation capacity within the infiltrated series. In contrast, the fully dense solid reference reached a significantly higher peak load of 136.6 ± 10.2 N, but failed in a brittle manner at only ~3 mm deflection, characteristic of UV-cured rigid photopolymers. All open-cell silicone-filled lattices displayed pseudo-ductile behaviour with extended post-peak softening, enabled by large-scale elastic buckling and silicone deformation and progressive buckling of the thin photopolymer struts. The results provided a foundation for optimising the geometry and material composition of photopolymer–silicone hybrid structures for lightweight applications with controlled stiffness-to-weight ratios. Full article

Fiber-Reinforced Polymer (FRP)-laminated composite materials are increasingly recognized as a transformative solution for future structural applications, due to their exceptional properties, such as lightweight, superior fatigue life, corrosion resistance, and ease of manufacturing. These advantages make them highly suitable for innovative applications in various sectors, including aerospace, automotive, marine, energy and defense. As one of the load-carrying members, the composite laminated plate structures are widely used in aircraft structures, such as the fuselage, wing and tail. These thin-walled structures will buckle under compressive or shear loading, which is a major consideration in the structural design process. Due to their high specific strength, laminated FRP composite structures are gaining increasing attention and are widely used in advanced lightweight structures. However, to fully exploit the large post-buckling reserves of FRP structures, their damage behavior and failure modes must be well understood. In this study, a progressive failure analysis based on ANSYS finite element (FE) simulations has been carried out to predict the nonlinear response and failure characteristics of a laminated composite plate under compressive loading. The FE-based progressive failure analysis utilized shell elements based on the Classical Laminate Plate Theory (CLPT) to calculate the in-plane stresses. The failure model employed the 3D failure criterion LaRC04 for damage detection and the stiffness degradation model for damage propagation in an FRP-laminated composite plate structure. The analysis results are found in close agreement with the published simulation and experimental results. This study has proposed an efficient methodology to accurately predict the post-buckling response, i.e., failure modes and collapse loads of laminated FRP composite constructions under compressive loading. Full article

Wind turbine tower structures composed of slender steel cylindrical shells mainly serve as primary load-bearing components and can be particularly susceptible to buckling due to their thin walls. Ensuring the structural safety of wind turbines therefore requires a clear understanding of the behavior of slender cylindrical shells, which is influenced by material properties, boundary conditions, and loading scenarios. This study experimentally investigates the structural responses of scaled cylindrical structures representing wind turbine towers beyond the proportional limit including the ultimate and post-ultimate strength depending on boundary conditions (fully and frictionally supported). Lateral loads were applied at the top of the specimens to simulate concentrated loads transferred from wind forces on the blades. Furthermore, a numerical model was developed to analyze the structural behavior of the tower validated against the experimental test results. The results provide valuable insights into optimizing the structural design of both onshore and offshore wind turbine towers, contributing to enhanced safety and performance under varying load conditions. Full article

The static stability of an elastic, incompressible nanorod subjected to an extensional force is analyzed. The force is applied to a rigid rod that is welded to the free end of the nanorod. The material behavior of the nanorod is described using a two-phase local/nonlocal stress-driven model. Mathematically, the problem is formulated as a system of nonlinear differential equations suitable for nonlinear analysis. For the analysis, the Liapunov–Schmidt method is employed. Depending on a geometric parameter (the length of the rigid rod) and nonlocal parameters (the small length-scale parameter and the phase parameter), the buckling load and post-buckling behavior of the nanorod are determined. The results show that the nonlocal effect increases the buckling load, indicating a stiffening effect. An increase in the length of the rigid rod decreases the buckling load. Regarding the post-buckling behavior, it is shown that both supercritical and subcritical bifurcations can occur, depending on the values of the geometric and nonlocal parameters. The occurrence of a subcritical bifurcation, which is highly undesirable in real-world constructions, is a novel effect not observed in the classical Bernoulli–Euler theory. Full article

This paper presents a validated computational workflow for simulating the fire-induced collapse of steel moment-resisting frames, comparing static general and dynamic explicit analysis procedures. Whereas most existing studies employ dynamic explicit analysis for collapse validation, this work evaluates the capability of the static general approach as a viable alternative. Finite element models developed with beam and shell elements capture both global instability and local failure modes. The results show that the static general procedure effectively reproduces quasi-static post-buckling behaviour and predicts the critical failure temperature within 2–3% of experimental results, similar to the dynamic explicit method. For the dynamic explicit procedure, sensitivity analyses are conducted to optimise time scaling, mesh refining, and ensure realistic physical response while maintaining computational efficiency. The study demonstrates that, along with dynamic explicit analysis, static general procedure also offers a practical and reliable alternative for simulating fire-induced structural collapse, reducing computational time by up to eighteen times for beam models and around six times for shell models, while maintaining reliable accuracy. Full article

Composite materials have gained prominence in aerospace engineering due to their high strength-to-weight and stiffness-to-weight ratios. However, their susceptibility to interlaminar damage, particularly delamination, remains a significant concern, especially under compressive loads. This study presents a detailed numerical investigation into the buckling behavior and delamination propagation in flat and curved composite panels with centrally located circular delaminations. Four configurations were analyzed, differing by geometry (flat vs. curved) and delamination interface. The critical buckling load was first estimated through linear eigenvalue analysis, while post-buckling behavior and damage progression were studied using a nonlinear static analysis enhanced by the Smart-time XB (SMXB) tool. Numerical results, including out-of-plane displacements and delamination length evolution, were validated against experimental data from the literature. The findings confirm the accuracy of the adopted FEM approach and highlight the beneficial role of curvature in increasing buckling resistance and improving damage tolerance, offering valuable insights for the design of aerospace composite structures. Full article

This work aims to investigate the buckling and post-buckling behaviour of wood-based sandwich structures with and without a manufacturing defect, under compressive loading. The specimens were made by gluing birch veneers to a balsa wood core. The defect consisted of a central zone where glue was lacking between the skin and the core. A compression load was applied to the plate using the VERTEX test rig, with the plate placed on the upper surface of a rectangular box and bolted at its borders. The upper surface of the plate was monitored using optical and infrared cameras. The stereo digital image correlation method was used to capture the in-plane and out-of-plane deformations of the specimen, and to calculate the strains and stresses. The infrared camera enabled the failure scenario to be identified. The buckling behaviour of pristine specimens showed small local debonding in the post-buckling range, which was not detrimental to overall performance. In the presence of a manufacturing defect, the decrease in buckling load was only about 15%, but final failure occurred at lower compressive loads. Full article

This review investigates interlayer hybrid fiber composites for wind turbine blades (WTBs), focusing on their potential to enhance blade damage tolerance and maintain structural integrity. The objectives of this review are: (I) to assess the effect of different hybrid lay-up configurations on the damage tolerance and failure analysis of interlayer hybrid fiber composites and (II) to identify potential fiber combinations for WTBs to supplement or replace existing glass fibers. Our method involves comprehensive qualitative and quantitative analyses of the existing literature. Qualitatively, we assess the damage tolerance—with an emphasis on impact load—and failure analysis under blades operational load of six distinct hybrid lay-up configurations. Quantitatively, we compare tensile and flexural properties—essential for WTBs structural integrity—of hybrid and glass composites. The qualitative review reveals that placing high elongation (HE)-low stiffness (LS) fibers, e.g., glass, on the impacted side reduces damage size and improves residual properties of hybrid composites. Placing low elongation (LE)-high stiffness (HS) fibers, e.g., carbon, in middle layers, protects them during impact load and equips hybrid composites with mechanisms that delay failure under various load conditions. A sandwich lay-up with HE-LS fibers on the outermost and LE-HS fibers in the innermost layers provides the best balance between structural integrity and post-impact residual properties. This lay-up benefits from synergistic effects, including fiber bridging, enhanced buckling resistance, and the mitigation of LE-HS fiber breakage. Quantitatively, hybrid synthetic/natural composites demonstrate nearly a twofold improvement in mechanical properties compared to natural fiber composites. Negligible enhancement (typically 10%) is observed for hybrid synthetic/synthetic composites relative to synthetic fiber composites. Additionally, glass/carbon, glass/flax, and carbon/flax composites are potential alternatives to present glass laminates in WTBs. This review is novel as it is the first attempt to identify suitable interlayer hybrid fiber composites for WTBs. Full article