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[Display omitted] Cells respond to the stiffness of their surrounding environment, but quantifying the stiffness of a fibrous matrix at the scale of a cell is complicated, due to the effects of nonlinearity and complex force transmission pathways resulting from randomness in fiber density and connections. While it is known that forces produced by individual contractile cells can stiffen the matrix, it remains unclear how simultaneous contraction of multiple cells in a fibrous matrix alters the stiffness at the scale of a cell. Here, we used computational modeling and experiments to quantify the stiffness of a random fibrous matrix embedded with multiple contracting inclusions, which mimicked the contractile forces of a cell. The results showed that when the matrix was free to contract as a result of the forces produced by the inclusions, the matrix softened rather than stiffened, which was surprising given that the contracting inclusions applied tensile forces to the matrix. Using the computational model, we identified that the underlying cause of the softening was that the majority of the fibers were under a local state of axial compression, causing buckling. We verified that this buckling-induced matrix softening was sufficient for cells to sense and respond by altering their morphology and force generation. Our findings reveal that the localized forces induced by cells do not always stiffen the matrix; rather, softening can occur in instances wherein the matrix can contract in response to the cell-generated forces. This study opens up new possibilities to investigate whether cell-induced softening contributes to maintenance of homeostatic conditions or progression of disease. Mechanical interactions between cells and the surrounding matrix strongly influence cellular functions. Cell-induced forces can alter matrix properties, and much prior literature in this area focused on the influence of individual contracting cells. Cells in tissues are rarely solitary; rather, they are interspersed with neighboring cells throughout the matrix. As a result, the mechanics are complicated, leaving it unclear how the multiple contracting cells affect matrix stiffness. Here, we show that multiple contracting inclusions within a fibrous matrix can cause softening that in turn affects cell sensing and response. Our findings provide new directions to determine impacts of cell-induced softening on maintenance of tissue or progression of disease. [ABSTRACT FROM AUTHOR]

• Time-varying buckling and post-buckling of tapered columns in fire. • Temperature-dependent material properties. • The convective–radiative condition. • Geometric nonlinearity and yield strength. • Effects of transient localised fire on the tapered column. This paper presents time-varying flexural buckling and post-buckling responses of tapered columns under a transient fire of which the temperature is non-uniform along the length. First, the transient temperature field within the column is determined by solving a dimensionally reduced transient heat transfer problem considering the convection-radiation boundary conditions and temperature-dependent (TD) material properties. Subsequently, the von Kármán geometric nonlinear theory is applied to obtain the nonlinear equilibrium equation. The nonlinear heat transfer and equilibrium equations are solved by the differential quadrature (DQ) method. According to a yield criterion, the ultimate load at which the material failure occurs is predicted. The influences of a transient localised fire on the temperatures, buckling and post-buckling responses of tapered steel tubular columns are discussed. [ABSTRACT FROM AUTHOR]

• Accurate buckling model is proposed for hygro-thermo-magneto-electro-elastic shells. • Non-uniform pre-buckling effect is introduced to enhance the accuracy of critical buckling loads. • Both axisymmetric and non-axisymmetric buckling solutions are obtained simultaneously. • Critical buckling stresses and analytical buckling modes are obtained simultaneously. • Parametrical effects on buckling behaviors under multi-physical fields are revealed. An accurate buckling model for the magneto-electro-elastic (MEE) composite cylindrical shell under hygro-thermo-magneto-electro-elastic (HTMEE) loads is proposed by considering non-uniform pre-buckling effects. Nonlinear governing equations involving HTMEE multi-physical coupling effects are derived based on the higher-order shear deformation theory (HSDT) and von Karman geometrical nonlinearity. Critical buckling stresses and analytical buckling mode for both the axisymmetric and non-axisymmetric buckling are obtained by the Galerkin method. In numerical examples, comparisons between theoretical predictions and existing results are presented, and excellent agreements are observed. Special attention is paid to evaluation of pre-buckling effects on buckling behaviors of HTMEE shells subjected to multi-physical fields. A comprehensive parametric study is performed to reveal effects of key influencing factors on critical buckling stresses and buckling modes. It is believed that present results will be useful for assessing other numerical methodologies and contributing the rapid design of sensors and actuators with HTMEE cylindrical shells. [ABSTRACT FROM AUTHOR]

Welded omega-stiffened panels made of thermoplastic carbon composite with initial damage in the conduction welded joint are analysed and tested to investigate the damage tolerance in post-buckling. Finite element analyses are performed, using the virtual crack closure technique to investigate skin-stringer separation for both the pristine welded joint and joints with initial damage. A sensitivity study is executed for the initial damage size and location with different geometrical imperfections. Four omega-stiffened panels are tested, of which three have initial damage consisting of a foil at the welded skin-stringer interface. During the test, digital image correlation is used to measure the panels' deformation to determine the evolution of the buckling shape and the interaction with the initial damage. A high-speed camera is placed on the stringer side of the panel to capture the final failure. The panels fail in post-buckling when skin-stringer separation occurs, starting from the initial damage. The finite element analysis is able to predict the overall structural behaviour well, with conservative failure load predictions for panels with initial damage in the middle stringer. Although the initial buckling shape is predicted well, the buckling shape evolution at higher loads is difficult to predict. [ABSTRACT FROM AUTHOR]

The structural efficiency of composite stiffened panels can be substantially improved by utilizing curved stiffening components due to their exceptional mechanical performance and design flexibility. This paper aims to explore the impressive potential offered by the curved stiffening concept in the design of T-shaped stiffened composite panels featuring curved sub-stiffening components. An optimization design framework is proposed to optimize the laminates sequence of skin, ply orientation angles and distribution of the curved sub-stiffeners as well as the curvature of the sub-stiffeners of the proposed curved grid sub-stiffened composite panels to yield higher buckling performance without additional weight. Results demonstrate that introducing composite curved grid sub-stiffeners to the T-shaped stiffened composite panel leads to substantial improvements (+254.42%) in buckling performance, while maintaining equivalent weight designs. Furthermore, the introduction of composite curved grid sub-stiffeners reveals alterations to the post-buckling deformation paths of grid sub-stiffened composite panels, leading to varied collapse loads and degrees of deformation in the composite panels. This highlights the importance of utilizing the composite curved grid sub-stiffeners to improve stability and reduce the risk of failure in thin-walled structures, all while meeting lightweight design criteria. • A novel grid sub-stiffening concept (composite curved grid sub-stiffeners) was introduced and optimized to improve the initial buckling performance of an existing T-stiffened composite panel design with no additional weight. • Substantial improvements in buckling performance were achieved when compared to the T-shaped stiffened and sub-stiffened composite panel with equivalent weight designs. • The curvature of the sub-stiffeners has a considerable influence on the buckling performance and alters the buckling mode shapes. • The introduction of composite curved grid sub-stiffeners alters the post-buckling deformation paths and further affects the initiation and propagation of various failure modes. [ABSTRACT FROM AUTHOR]

• An accurate nonlinear buckling model is proposed for the flexoelectric cylindrical nanoshell. • The pre-buckling nonlinear deformation is employed to improve the accuracy of critical buckling stresses and buckling mode shapes. • The effects of key influencing parameters on buckling characteristics of the flexoelectric cylindrical nanoshell is investigated and reveal. In this paper, a buckling analysis for flexoelectric cylindrical nanoshells under axial compression is performed by considering the higher-order shear deformation theory and non-uniform pre-buckling deformation. Size-dependent critical buckling stresses and buckling mode shapes are obtained by the Galerkin's method with newly proposed displacement functions. Numerical results are compared with existing solutions and excellent agreements are observed. Furthermore, a comprehensive parametric study of boundary conditions, geometrical parameters and applied electric voltage is carried out to reveal the influence of flexoelectric effect on the size-dependent buckling characteristics of flexoelectric cylindrical nanoshells. [ABSTRACT FROM AUTHOR]

• A criterion for simulation of delamination is proposed. • An imperfection induced pre-buckling must be incorporated into failure analysis of open-hole laminate under in-plane compression. • Rules for selection of a scale factor for the pre-buckling analysis are set forth. • Various failures of notched laminate under compression are predicted with no parameter adjustment and no iteration. Failure prediction of open-hole laminates under compression still remains a great challenge. A number of unique mechanics theories for composites developed by the author are successfully applied to analyze in plane compression induced various failures of the notched laminates in this paper. A buckling mode must be incorporated into the analysis of the compression induced delamination, and the rules for selecting a scale factor for the buckling analysis through ABAQUS are established. To simulate delamination, the interlaminar matrix stress modification method is applied. A more pertinent criterion for delamination is proposed. When and where is delamination initiated, how can the initiated delamination be propagated and how much is the delaminated area to be attained can be easily reproduced. Intralaminar failures are estimated based on Bridging Model and the matrix true stress theory. The ultimate strength of a notched laminate is assumed when any primary layer element outside neighborhoods of the stress singularity and weak singularity points firstly attains an ultimate failure. A limited, if not the minimum, number of inputs are required all measurable independently and following existing standards with no data calibration. Except for the pre-buckling analysis, no iteration is needed for prediction of all the other failures. The predicted failure modes and ultimate compressive loads of several laminates with single or double holes agree well with our measured counterparts. [ABSTRACT FROM AUTHOR]

• The paper investigates rib-based reinforcement strategies for improving structural integrity of form-found shell structures. • The study introduces diverse stiffening patterns for shell structures, designed with geometric, biomimetic, and optimization-derived methodologies. • The paper demonstrates through mechanical testing and numerical simulations that these patterns significantly improve stiffness and buckling resistance of form-found shells. • The study validates that integrating form-finding with targeted rib-based reinforcements can lead to sustainable and structurally resilient solutions. This paper investigates innovative approaches for enhancing the structural integrity of form-found shell structures with a focus on rib-based reinforcements. It discusses the significance of ribs in enhancing stability and addressing the sensitivity of form-found structures to various loads. Traditional methods such as increasing shell thickness or introducing supports often compromise efficiency and aesthetics. A more intelligent approach involves reinforcing the shell with ribs and advanced materials. Diverse rib patterns are presented, including geometric, biomimetic, and topological optimization-inspired designs, each adhering to a 50 % volume constraint, when compared to the original shell. Physical testing and numerical simulations demonstrate that these rib patterns significantly increase stiffness and buckling resistance. The findings presented in the paper suggest that combining form-finding methodologies with well-designed rib patterns can create sustainable and resilient structures, contributing to a reduction in both the consumption of materials and the environmental impact of these structures. [ABSTRACT FROM AUTHOR]

Thin-walled cylindrical shells under axial compression load are prone to buckling. The influencing factors leading to a reduction of the buckling load are a major design challenge. The sensitivity to imperfection increases with rising slenderness. In literature, cylinders with the same parameters and different slenderness are rarely tested in a larger number of samples. In this contribution, seven cylindrical shells, six of them nominally identical, are tested on two different test rigs and compared with twelve specimens with a smaller radius and same wall thickness from a previous series of tests. It is shown how the imperfection sensitivity is dependent on the R/t-ratio. Additionally, it is demonstrated how the quality of the test set ups corresponds with the achieved buckling load. Finally, the suitability of selected design approaches is determined based on the test results. Based on that, recommendations for the choice of a suitable approach are given. [ABSTRACT FROM AUTHOR]

This paper presents a three-dimensional analysis of the buckling behavior of functionally graded (FG) skew plates using a novel meshfree elastoplasticity-based formulation. To solve the nonlinear buckling problem, a Tchebychev-radial point interpolation approach, which combines radial basis functions (RBFs) with Tchebychev polynomials, is developed. The governing equations are obtained using the principle of virtual work. The Prandtl-Reuss flow rule is utilized to model incremental plastic deformation, along with the von Mises criterion and isotropic hardening. To determine the effective elastoplastic properties of the functionally graded material (FGM), the Tamura-Tomota-Ozawa (TTO) model is employed. The results demonstrate an excellent agreement with those available in the literature. Furthermore, this study explores the impact of several parameters, including inhomogeneity parameter, skew angle, thickness ratio, aspect ratio, boundary conditions (BCs), and loading ratio, on the elastoplastic buckling behavior of the FG skew plates. • Presenting the 3D elastoplastic buckling response of functionally graded skew plates. • Developing a Tchebychev-radial point interpolation approach for solving the problem. • Confirming TRPIM results through comparison with existing authentic solutions. • Investigating effects of material slopes, geometric parameters, loading ratio, and BCs. [ABSTRACT FROM AUTHOR]

Buckling and sound radiation characteristics of curved sandwich panels subjected to combined thermo-mechanical loads are presented in the paper. The panel comprises a 3-D functionally graded graphene porous core sandwiched between FG-V Λ CNT reinforced composite face sheets (3DGrF-CF). The governing differential equations of 3DGrF-CF sandwich panels are derived using the parabolic shear deformation theory (PSDT), and the vibration responses are predicted using Navier's approach. The vibration response thus obtained is fed into the Rayleigh integral to capture the acoustic pressure. The buckling and sound radiation characteristics were found to vary significantly with the core's porosity coefficient and porosity grading pattern. However, the impact of this influence also depends on the magnitude of thermal & mechanical loading. This implies that selecting a core for acoustic comfort depends on the dominance of loading conditions and is illustrated using octave band analysis. • Buckling & vibro-acoustic analysis of 3DGrF-CF panels under thermo-mechanical loads. • Analytical prediction using Navier's & Rayleigh's approach considering PSDT. • Optimum porosity coefficient & grading pattern for different loading conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

• A competitive-failure analysis framework of composite cylinder was proposed. • The material degradation model was adapted to judge the failure mode of composites. • The effectiveness and precision of the proposed framework were validated. • The effects of several design parameters on the competitive-failure were examined. When thin-walled composite cylindrical shells are subjected to combined loads, not only will they buckle, but they could fail under overstressing. Buckling-failure and stress-failure are two types of failure that compete mutually, and if one of them occurs, the structure loses its ability to carry the load. However, there is a lack of study, and very little attention was paid to the competitive-failure of the composite cylindrical shells under combined loads. To bridge this research gap, a competitive failure analysis framework of degraded composite cylindrical shells exposed to combined axial compression and external pressure loads was developed, considering the nonlinear buckling-failure interacting curve approach for buckling-failure analysis and the Tsai-Wu failure criterion for stress-failure analysis. The material degradation model was adopted to modify the properties of the failed ply based on two degrading philosophies. The proposed framework agrees well with the published results. Extensive parametric studies are accomplished and presented to detect the failure mode of composites. For material parametric study, the variation of material properties does not significantly affect the shape of the normalized buckling-failure interacting curve, while it appreciably affects the behavior of the stress-failure interacting curve. Moreover, it is found that as the proportions of the longitudinal compressive strength to longitudinal modulus and transverse tensile strength to transverse modulus of composite materials increase, the tendency for buckling-failure increases; otherwise, stress-failure happens. For a geometric parametric study, decreasing the radius-to-thickness ratio leads to an increase in the shape of the buckling-failure interacting curve and the possibility of stress-failure. [ABSTRACT FROM AUTHOR]

The paper investigates the validity and reliability of the blind-bolt repair method for repairing delaminated composite aircraft panels. The delaminated specimens are prepared by inserting Teflon films during the manufacturing process to simulate interlayer damage. Subsequently, these specimens are repaired using the blind-bolt method. Modal and uniaxial compression tests are conducted to quantitatively evaluate the natural frequency, mode shape and load-bearing strength of both delaminated and bolt-repaired specimens. Digital image correlation and ultrasonic phased array techniques are employed to characterize buckling instability and damage evolution of specimens. The results reveal that the natural frequency and compressive buckling strength of delaminated specimens significantly decrease. The mode shape also changes nonlinearly with the stiffness reduction. This variation is proportional to the size and the quantity of delaminations. The blind-bolt repair method effectively restores the vibration and mechanical properties of the delaminated composite structure by reconnecting separated sub-laminates. A repair tolerance of 20 mm–60 mm is recommended for a single blind-bolt. When the delamination length is 35 mm, the repair efficiency for the critical buckling load and the ultimate load is the highest, at 58.3% and 64.4%, respectively. [Display omitted] [ABSTRACT FROM AUTHOR]

• Buckling behavior of spherical shells with patterned surface under indentation is investigated. • Shells with discontinuous protrusions exhibit unique multiple snap-through due to local buckling. • Mechanical response and buckling morphology can be controlled by tuning surface patterns. A well understanding of instability mechanics of soft shell structures is key issue due to its important implications in functional shape morphing, flexible electronics, soft robotics, nanotechnology, biological engineering, etc. Despite abundant studies, buckling analysis of flexible shells with patterned surface under indentation is rare, primarily because of the complexities of high nonlinearities in geometry, material, and surface contact. In this paper, buckling behavior of spherical shells with patterned surface under indentation is comprehensively investigated by using experimental, numerical and theoretical analyses. It is found shells with stripes show similar variation in the force-displacement curves and post-buckling morphologies like perfect shells. Unlike perfect ones, shells with discontinuous protrusions exhibit multiple snap-through due to local buckling under indentation. What is more, mechanical response and buckling morphology can be well controlled by tuning shell thickness as well as positions and sizes of protrusions. These results can not only deepen understanding of mechanism of spherical shell buckling under local loads, but also provide a designing guidance for flexible electronics, soft robotics, and other future devices. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, both the buckling and material failure for ring-stiffened composite shells under hydrostatic pressure are studied by theoretical and finite element (FE) methods. Theoretical formulas to predict the critical buckling pressure and material failure load for ring-stiffened composite shells are proposed. To validate the proposed analytical solutions, FE models are built and the buckling and material failure analyses are performed. Moreover, two experimental tests on unstiffened and ring-stiffened composite shells were carried out. Analytical solutions, FE results and experimental tests were compared and it shows great accuracy of the proposed theoretical solution. Parametric studies are performed, the effects of rib height, width, and number on the stability as well as the effects of winding angle and thickness on the material failure are discussed. The buckling mode of a ring-stiffened composite shell will transform from overall to local buckling as the rib height, width, and number increase. The material failure pressures are mainly affected by winding angle and thickness. The composite shell with winding angles of [90/±40/90] or [±50/±50] have larger material failure pressure than other winding angles. [ABSTRACT FROM AUTHOR]

• Semi-analytical method to study agglomerated CNT composite cylindrical panel considering non-local elasticity is presented. • Buckling and free vibration behaviours of agglomerated CNT nano composite panel under non-uniform edge load are presented. • Effects of non-local parameter, nature of agglomeration and non-uniform edge loadings are analysed. • The results obtained using the present approach are in good agreement with the results available in literature. A semi analytical nonlocal elasticity model to analyze the effect of non-uniform edge loads on static stability and free vibration characteristics of agglomerated carbon nanotubes (CNTs) reinforced nano cylindrical panels are presented. Effective material properties of the agglomerated CNT reinforced composite are obtained using a two-parameter micro-mechanics model while Eringen's non-local theory is used to account the size effect. Sinusoidal shear deformation theory is adopted to analyze the buckling and vibration parameters using Galerkin's approach. The accuracy of the proposed model is presented first by comparing the results in the literature. Then a comprehensive study is carried out to analyze the influence of various degrees of agglomeration (complete, partial), nature of edge load, and non-local effects on the buckling and free vibration response of CNT reinforced nano cylindrical panel. The results revealed that non-local size effect leads to a reduction in stiffness and thus reduces buckling and dynamic characteristics. Moreover, it is observed that critical buckling load varies with type of in plane load and reduction in natural frequency is different for different in plane loading conditions. [ABSTRACT FROM AUTHOR]

In the analytic modeling of shell buckling, much attention has been paid to closed cylindrical shells or cylindrical panels with at least two opposite edges simply supported whose solutions are known to be Lévy-type solutions. However, there have been very few reports on analytic solutions of commonly used non-Lévy-type cylindrical panels, which is mainly attributed to the widely acknowledged difficulty in solving the governing higher-order partial differential equations under prescribed boundary conditions. To address this gap, the present study provides some new analytic buckling solutions of non-Lévy-type cylindrical panels within the Hamiltonian-system-based symplectic framework. The buckling of a cylindrical panel is first formulated in the Hamiltonian system to realize a new matrix-form governing equation. An original problem with non-Lévy-type boundary conditions is then treated as the superposition of two elaborated subproblems that are solved by the rigorous symplectic approach. The final solution is obtained according to the equivalence between the superposition of the subproblems and the original problem. For benchmark use, comprehensive buckling loads and buckling modes are presented for typical non-Lévy-type panels with different ratios of in-plane dimensions, different ratios of in-plane dimension to radius of curvature, and different ratios of thickness to in-plane dimension. The present study is the first successful extension of the symplectic superposition method to the buckling analysis of cylindrical panels, which may enable access to more new analytic solutions for similar issues. [ABSTRACT FROM AUTHOR]

• Comparison of experimental and numerical buckling variability of a set of additively manufactured lattice structures. • Reduction of computational time for prediction, sensitivity and optimization steps of an uncertain propagation problem. • Efficient coupling between a Reduced Order Model and a surrogate model. • Improvement of the calculation precision with projection basis composed of high order perturbed modes. This paper presents a new method to efficiently approximate both linear buckling loads and associated mode shapes of finite element structures subject to perturbations. To achieve this, a coupling between a Reduced Order Model (ROM) based on the Homotopy Perturbation Method (HPM) and a Kriging model is presented here. The ROM maintains the link between eigenvalues, related eigenvectors and the dependencies between each eigenvector components, leading to a high precision level. The computational time is greatly reduced by the surrogate model which avoids the computation of modified finite element matrices for each prediction. Next, the capabilities of the method allow to efficiently handle the prediction, sensitivity and optimization steps of an uncertain propagation problem using fuzzy formalism. Additive Manufacturing is a powerful and impressive process but many factors can be responsible for relatively large discrepancies in the mechanical and geometrical characteristics of the manufactured structure. Lastly, a study shows how the proposed fuzzy strategy allows the prediction of the buckling variability of a set of lattice structures. [ABSTRACT FROM AUTHOR]

• Symplectic-superposition framework for buckling of thick plates is formulated. • New analytic buckling solutions of thick rectangular plates are obtained. • The present method has the advantages of strictness and high accuracy. This paper presents a first attempt to explore the symplectic superposition method for analytic buckling solutions of non-Lévy-type moderately thick rectangular plates, which were hard to tackle by classical semi-inverse methods. In contrast with the conventional Lagrangian-system-based expression that is solved in the Euclidean space, this study describes the issue in the Hamiltonian system for treatment in the symplectic space. The follow-up solution procedure involves the conversion of an original problem into subproblems with symplectic solutions and superposition for final analytic buckling solutions, where the constitution of symplectic eigenvalue problem and symplectic eigen expansion are crucial. Comprehensive buckling load and mode shape results for representative plates are tabulated or plotted, which are all well validated by satisfactory agreement with other solution methods. With the present solutions, parametric analysis has been investigated. Due to the advantages on strictness and accuracy, the developed method provides a solid approach for exploring new analytic solutions of similar problems. [ABSTRACT FROM AUTHOR]

The occurrence of buckling during cooling of an injection-molded fiber-reinforced plastic (FRP) object is a complex phenomenon which can result in unacceptably large deformations. The present work focuses on the thermal buckling of injection-molded thin disks, as they are representative for the local behavior in parts of a more complex object. An analytical approach based on the Föppl-von Kármán theory for thin elastic plates is presented and used to analyze its buckling stability and initial post-buckling behavior. The system of equations is formulated in a coordinate-free approach for a thin anisotropic linear thermo-elastic body with residual thermal stresses. Large out-of-plane displacements are assumed. The particular case of a free disk with cylindrical orthotropy and uniform thermo-elastic properties through its thickness is considered. A general technique to study the bifurcation in the solutions (i.e., buckling) based on a perturbation approach and the Fourier-Galerkin method to determine post-buckling deflections is proposed. Experimental and numerical results available in the literature are used as validation cases. The results of the present model show qualitative agreement with the experimental data. It is found that the periodicity of the first buckling mode for orthotropic disks is fully determined by the ratio between the elastic moduli in the tangential and radial directions. The predictions are also in excellent quantitative agreement with the numerical results of FEM models for the same cases. The effect of the disk thickness on the buckling temperature and warpage magnitude is correctly captured. [ABSTRACT FROM AUTHOR]

• Static, stability and free vibration analysis of FG plate are carried out. • Free vibration of plates with inner point, line and area supports is studied. • The finite strip method with longitudinal RKPM functions based on FSDT is used. • A decent way is used to impose boundary conditions considering meshfree functions. • Elimination of shear-locking, as an undesirable phenomenon, is elaborated. This paper is focused on the application of a novel reproducing kernel particle finite strip method (RKP-FSM) for the static, mechanical and thermal buckling, and free vibration analyses of rectangular functionally graded (FG) plates with different boundary conditions and internal supports. Conventional reproducing kernel particle method (RKPM) is incorporated into the finite strip method (FSM), and the governing equations are derived based on the first-order shear deformation theory (FSDT). As a convenient approach, boundary conditions are imposed using a simple method based on the RKPM correction function and the essence of the FSDT displacement field. Several examples are studied using this method, and the results are compared to those obtained from other numerical methods. The proposed method is also extended to consider different support geometries and complex inner conditions, and the results are validated using COMSOL finite element software. The shear-locking error, which occurs when considering C0 plate theories, is noticeably reduced by considering the RKPM parameters in the finite strip formulation. [ABSTRACT FROM AUTHOR]

In this paper, the Dual Mesh Control Domain Method (DMCDM) is used to carry out the free vibration and buckling analysis of two-constituent Functionally Graded Beams (FGBs) with through-thickness material variation. The material composition (modulus and density) is varied continuously through the beam thickness according to a power-law. The Euler-Bernoulli beam model consisting of the displacements and bending moment as the primary nodal degrees of freedom (i.e., mixed model) and the Timoshenko beam model with the displacement degrees of freedom (i.e., displacement model) are formulated as eigenvalue problems using the DMCDM. The numerical examples presented consider typical beam boundary conditions and various power-law exponents and slenderness ratios. The accuracy of this method is demonstrated by comparing the numerical results with those available in the literature. [ABSTRACT FROM AUTHOR]

• Altering the distribution patterns of graphene reinforcement across the flanges and web, while keeping the geometrical parameters constant, can enhance the critical buckling end-shortening and load-bearing capacity by approximately 80% and 25%, respectively. • The study revealed that the suggested approach (LW-TSDT) accelerates the running time by about 31% compared to the FEM. • In cases where web buckling is predominant, variation in graphene distribution across the flanges has negligible influence on the web's stability response. • Disregarding the specific graphene distribution patterns, the point of highest membrane stress occurs at the junction of the flange and web. The role of local buckling on the behavior of slender members under compression has received considerable attention in structural engineering. For thin-walled sections, in particular, there is a noticeable decrease in the axial compressive stiffness, resulting in a substantial reduction in their load-bearing capacity due to the occurrence of local buckling. The principal purpose of this article is to explore the potential improvements in the postbuckling characteristics of polymeric composite channel section struts subjected to a progressive end-shortening by employing multi-layer graphene sheets reinforcements. The solution methodology incorporates the von Karman geometrical nonlinearity and is based on the layerwise third-order shear deformation theory (LW-TSDT). To verify the accuracy of the results obtained based on LW-TSDT and to evaluate its computational efficiency, a three-dimensional (3D) finite element model is also developed using ABAQUS for the comparative analysis. A thorough examination of nonlinear instability is conducted on composite laminated channel section struts, featuring distinctive graphene distribution patterns through the thickness directions of the flanges and webs to identify the most effective material distribution with the objective of a significant increase in critical end-shortening and axial compressive stiffness. The influence of the geometrical parameters on the critical end-shortening, postbuckling equilibrium paths, and load-bearing capacity of functionally graded graphene reinforced composite (FG-GRC) laminated channel section struts are elicited. The conducted parametric analyses emphasize that altering the distribution patterns of graphene reinforcement across the flanges and web can enhance the critical end-shortening and load-bearing capacity by 80% and 25%, respectively. [ABSTRACT FROM AUTHOR]

• Investigation of the interaction between buckling and lateral buckling of thin-walled beams with arbitrary open cross-section using nonlinear modeling in large rotation and with warping. • The dimensionless equilibrium equations are established. • Introduction of various dimensionless parameters that control the interaction between buckling and lateral buckling. • The proposed analytical solutions are validated and compared to numerical solutions obtained from B3Dw beam elements based on Asymptotic Numerical Method. This paper investigates the interaction between buckling and lateral buckling of thin-walled beams with arbitrary open cross-section using nonlinear modeling in large rotation and with warping. First, the equilibrium equations have been transformed into dimensionless ones, and within a nonlinear stability model, various dimensionless parameters are introduced to control the interaction between buckling and lateral buckling. In comparison to a reference of literature, this work focuses on the case of arbitrary sections and includes a greater number of higher-order terms in our analysis. These additions have an impact on the coefficients of the stability formula by expanding its applicability to non- symmetric sections. Then, the effect of the different dimensionless parameters, thus introduced on the stability curve, has been studied. The proposed solutions are validated and compared to numerical solutions obtained by a general finite element package including the warping developed by the authors using Asymptotic Numerical Method (ANM) to solve the initial nonlinear equations. [ABSTRACT FROM AUTHOR]

Despite the substantial steps made in understanding the mechanics of reinforced concrete structures, effectively addressing, and mitigating inelastic buckling remains a complex and enduring challenge. Consequently, this paper provides a comprehensive review of all the previous studies on modelling the inelastic buckling of reinforcing bars, and the capability of current state-of-the-art numerical models to simulate the nonlinear stress-strain response of reinforcing bars with the effect of buckling under monotonic and cyclic loading. This review paper consists of four different clusters including: (i) inelastic buckling of reinforcing bars under monotonic loading with and without corrosion, (ii) inelastic buckling of reinforcing bars under cyclic loading with and without corrosion, (iii) influence of inelastic buckling on low-cycle fatigue life of reinforcing bars with and without corrosion, and (iv) influence of tie reinforcement on global stability of longitudinal bars and buckling length calculation. For each group, a summary and critical review of all the previous research is provided. A quantitative comparison between the most widely used uniaxial material models have been made and their performance have been assessed against experimental data. Finally, the current limitations in existing literature are examined, unresolved issues for future research are identified, and some recommendations for future research are suggested. ● Modelling inelastic buckling of reinforcing bars under monotonic and cyclic loading. ● Influence of corrosion on inelastic buckling of reinforcing bars. ● Influence of corrosion and buckling on low-cycle fatigue of reinforcing bars. ● Tie reinforcement, global stability of bars, and buckling length calculation. [ABSTRACT FROM AUTHOR]

The paper "Buckling of stretched strips" [1] , published in the year 2000, seemed to deal with a rather specific problem of buckling of thin structures. Nevertheless, it aroused quite broad interest and prompted a considerable series of further treatments. Deeper theoretical considerations and advanced applications have been published. Various specific aspects of this type of problem have been addressed in these papers. However, a general and systematic consideration of how and to what extent the Poisson's ratio affects the critical stretch of strips of different length to width ratios, L / B , was lacking. Accomplishing this task is the focus of this paper. Given the increasing use of auxetics, strips made from such materials are also being investigated. In addition, the occurrence of previously undiscovered mode transitions is shown. All results are presented in dimensionless form, which allows for fairly general usage. • Influence of Poisson ratio on buckling of stretched strips quantified and discussed. • So far unknown mode transition detected and explained. • Buckling of stretched strips made of auxetic materials – diagrams for buckling factor in dependence of Poisson ratio. [ABSTRACT FROM AUTHOR]

The buckling of a slender monofilament is a standard clinical method used to assess touch sensory perception, with specific applications to somatosensory impairment in patients after a stroke, detecting carpal tunnel syndrome, and as a prognosis tool for diabetic peripheral neuropathy. The basis of this approach is the Semmes-Weinstein monofilament, which comprises a calibrated set of thin, polycarbonate rods with different diameters. Application of a monofilament onto the surface of the skin with increasing pressure causes the rod to buckle. That is, at a specific force of pushing down on the far end, the monofilament suddenly bows out sidewards - the buckling load. The ability of a patient to detect increasingly finer monofilament buckling (pressure threshold) is then used to assess sensory deterioration. This paper addresses the underlying mechanics of the buckling process. Despite the accuracy and repeatability problems that have been reported in the literature, and the necessarily subjective aspects of sensory physiology, the mathematical modeling of the monofilament buckling is unambiguous and provides some fundamental insight into the parameters that underlie this approach. • Mathematical Analysis of Semmes-Weinstein monofilaments. • Experimental verification of the theory using scaled-up monofilaments. • Parameter sensitivity analysis. • Suggestions for effective usage. [ABSTRACT FROM AUTHOR]

Compliant constant-force mechanisms are compliant mechanisms that provide a nearly constant force over a prescribed deflection range. Topology optimization is an effective method for compliant constant-force mechanism design. However, instabilities caused by buckling often cause the optimization algorithm to fail to converge. This study analyzes the causes of buckling-induced instability and proposes methods to avoid this instability. A mechanism with three torsional springs is proposed, and its three force–displacement curves are analyzed. These bifurcated force–displacement curves cause the optimization algorithm to be unstable. Several topology optimization models with buckling constraints are proposed for designing compliant constant-force mechanisms. Their effects are tested and analyzed in numerical examples with different target constant forces and constant-force strokes. Almost all optimization results have three hinges, corresponding to a proposed mechanism with three torsion springs. A slight change in their initial design causes a large change in the force–displacement curve, which eventually leads to buckling-induced instability. This instability can be avoided by constraining the buckling load calculated at the configuration near the start of the constant-force stroke. • The causes of buckling-induced instability are analyzed. • A three-point approach is proposed to avoid buckling-induced instability. • The similarity between optimized results and a mechanism is observed. [ABSTRACT FROM AUTHOR]

• Size-dependent responses of 2D FG porous microbeams are studied using the modified strain gradient theory. • Two different porosity distribution models for 2D FG microbeams are considered. • Material length scale parameter (MLSP) is varied in both the axial and thickness directions as well as porosity. • The effects of small size, MLSP, porosity, gradient indexes and boundary conditions are investigated. • The effect of variable MLSP is significant and should be considered for analysis of 2D FG porous microbeams. Finite elemen model for the structural behaviours of bi-directional (2D) FG porous microbeams based on a quasi-3D theory and the modified strain gradient theory (MSGT) is presented. As the main novelty of this study, in order to capture accurately the size effects, the MSGT is employed with three material length scale parameters (MLSPs) rather than the modifed couple stress theory (MCST) with only one MLSP. The material properties including three MLSPs are varied in both the axial and thickness directions as well as porosity. By using a quasi-3D theory, which inludes normal and shear deformations, the governing equations for static, vibration and buckling analysis are derived and solved by Hermite-cubic beam element for various boundary conditions. Through numerical examples, effects of variable MLSP and porosity as well as gradient index in two directions on the deflections, natural frequencies and buckling loads of 2D FG porous microbeams are examined. [ABSTRACT FROM AUTHOR]

This paper presents a study of the elastic buckling behavior of Triangular Rollable And Collapsible (TRAC) booms under pure bending. An autoclave manufacturing process for ultra-thin composite booms is presented and the behavior of three test samples is investigated experimentally. Two regimes are observed, a pre-buckling regime and a stable post-buckling regime that ends when buckling collapse is reached. The buckling collapse moment, marking the end of the stable post-buckling regime, is typically four times higher than the initial buckling moment. A numerical simulation of the boom behavior with the Abaqus finite element package is presented and all of the features observed experimentally are captured accurately by the simulation, except buckling collapse. The numerical model is also used to study the effect of varying the boom length from 0.3 m to 5.0 m. It is shown that the pre-buckling deformation of the flanges under compression leads to a constant wavelength lateral-torsional buckling mode for which the critical moment is mostly constant across the range of lengths. [ABSTRACT FROM AUTHOR]

A predictor–corrector reduced-order modeling method based on Koiter theory is proposed for nonlinear buckling analysis of thin-walled structures with initial geometric imperfections. The imperfections are implemented into the von Kármán kinematics and are considered using an a priori and a posteriori manners, respectively, in buckling analysis. Since the nonlinear predictor obtained from the reduced order model with imperfections provides a fairly large step size in path-tracing, the a priori account of imperfections still shows advantages in computational efficiency. The advantages are more significant when considering a posteriori the effects of imperfections in the reduced order model of the structure without imperfections, which means building once and for all, by simply adding some independent imperfection terms in the reduced system. The a posteriori accounts of imperfections with the first/second-order accuracies, are developed, respectively, to deal with the linear/nonlinear prebuckling behaviors and small/large imperfection amplitudes. The good performance of the proposed method in terms of reliability, accuracy and computational effort is demonstrated with several examples using the linear buckling modes or measured geometric shapes as whole-field geometric imperfections. • The initial geometric imperfection is applied into reduced-order modeling method. • A priori account of imperfections is also very computationally efficient. • A posteriori account of imperfections with first/second-order accuracy is developed. • The proposed method can be used for small/large imperfection amplitudes. [ABSTRACT FROM AUTHOR]

A semi-analytical method is developed for the analysis of composite stiffened panels, where stiffness variability is achieved through a combination of fiber steering and curvilinear stringers. The approach relies upon a 2D plate model for the skin and a 1D beam description for the stiffeners, according to first-order shear deformation theory. The approach is developed in the framework of a displacement-based formulation, where Legendre polynomials are used for approximating the displacement field, and the Ritz method is used for the solution strategy. The resulting tool is characterized by its excellent computational efficiency, and allows problems in free-vibrations, buckling and thermal buckling to be solved with reduced effort. The quality of the results is assessed by an extensive set of comparison against results from the literature, demonstrating the potential of the tool as a means for performing preliminary parametric studies for these variable-stiffness, variable-geometry structures. [ABSTRACT FROM AUTHOR]

The buckling of a stiff thin film on a compliant substrate has been widely studied over the past decade due to its wide applications such as stretchable electronics, micro- and nano-metrology, and surface engineering. Instead of a single-layer compliant substrate, a bi-layer compliant substrate is usually encountered in practical applications. In this paper, the buckling of a stiff thin film on a bi-layer compliant substrate of finite thickness is studied theoretically, numerically and experimentally. The theoretical models based on the small-deformation theory and the simple finite-deformation theory accounting for the geometry change by using the energy method are both developed and presented. The good agreement among theoretical predictions, finite element analysis and experimental measurements of the buckling behavior validates the theoretical model. The influences of finite thickness of the bi-layer substrate and substrate modulus ratio on the buckling wavelength and critical buckling strain are systematically investigated. The buckling configurations at various applied strains are also measured to further validate the theoretical model. These results shed light on the influence of finite substrate thickness on buckling of the bi-layer substrate-supported thin films and are helpful to provide design guidelines in practical applications. [ABSTRACT FROM AUTHOR]

The exact-constraint design principle is commonly applied to flexure mechanisms to ensure deterministic behavior, but at the cost of reduced robustness, support stiffness, load capacity and usually an increased complexity of design. To explore the potential benefit of overconstrained design in flexure mechanisms, this paper investigates an elementary two-flexure cross-hinge with a single overconstraint as a case study. The stiffness effects of inadvertent stress due to misalignment are investigated experimentally, numerically and analytically. A measurement set-up with controllable misalignment has been designed. Measurements show that the first natural frequency of the cross-hinge decreases strongly with misalignment, suggesting that the actuation stiffness decreases due to the misalignment stress, and ultimately vanishes due to bifurcation buckling at a critical misalignment of the order of 0.1 mm for the mechanism at hand. Simulations with a detailed numerical model support the measurements and expose some additional factors, such as warping and shuttle compliance, which influence the system behavior. Importantly, they also show that the compliance in the support directions of the mechanism increases strongly at the critical misalignment, demonstrating that the mechanism no longer functions at the critical misalignment. An extensive analytical buckling analysis shows how the stress due to misalignment poses a functional operation limit on the overconstrained mechanism in terms of bifurcation buckling. The analysis serves to corroborate the numerical predictions. An expression is derived for the critical misalignment force and displacement as a function of the geometry and material of general cross-hinge mechanism designs. • A practical misalignment bound below which overconstrained flexure mechanisms are feasible. • An analytical buckling analysis that provides a theoretical explanation. • An overconstrained demonstrator set-up with controllable misalignment. • Measurements that corroborate the practical misalignment formula. • Numerical simulations that support the measurements and the analytical model. [ABSTRACT FROM AUTHOR]

• Develop Hencky bar-net model for circular and annular single layer graphene sheets. • Calibrate Eringen's small length scale coefficients for nonlocal circular and annular plates. • Calculate real buckling loads of circular and annular graphene sheets with clamped and simply supported restraints. This paper is focused on the modeling of circular and annular graphene sheets via Hencky bar-net model (HBM 1 1 HBM: Hencky bar-chain model.) and calibrating the Eringen's small length scale coefficient e 0 in Eringen's nonlocal theory. The buckling solutions of circular and annular graphene sheets based on Eringen's nonlocal continuum plate theory are first obtained. On the other hand, HBM is developed to model the same structure from the discrete view. HBM is a grid system comprising rigid bars and arcs connected by frictionless hinges with elastic rotational and torsional springs. By regarding the length of straight segments in HBM equal to the characteristic length of Eringen's nonlocal model (ENM 2 2 ENM: Eringen's nonlocal model.) and matching their solutions, the Eringen's small length scale coefficient e 0 is calibrated. It is found that for circular graphene sheet, e 0 = 0.258 for clamped edge and e 0 = 0.300 for simply supported edge. For annular graphene sheet, e 0 is dependent on the inner to outer radius ratio χ and boundary conditions. The scale coefficient e 0 takes 0.307–0.367 for clamped edges while 0.219–0.290 for simply supported edges with χ varying from 0.2 to 0.8. Another finding is that the graphene sheet will buckle with a very small load when its dimension is large, regardless of models adopted. However for small dimensions, ENM and HBM predict lower buckling loads than the classical local model because the scale effect is more obvious. [ABSTRACT FROM AUTHOR]

• Distinct buckling modes of BLGSs on a foundation are studied. • New morphology evolutions of the post-buckling deformation are reported. • Novel finite element for analyzing atomic van der Waals interactions is developed. The buckling and the post-buckling of bilayer graphene sheets (BLGSs) on an elastic foundation subjected to an axial compressive load in plane-strain condition are studied. The solutions for the buckling strain and the characteristic wavelength at the onset of the buckling are obtained by using proposed continuum models describing deformations of BLGSs. The buckling analysis reveals that the buckling of BLGSs on an elastic foundation could be categorized into four. When the foundation is very soft, the Euler beam kinematics prevails in the entire BLGSs. On the stiffer foundation, the shear deformation on the cross-section of BLGSs occurs, and the characteristic wavelength changes sensitively as the stiffness of the foundation varies. With the foundation whose stiffness is almost the same as the shear modulus of the graphene interlayer, the buckling strain and the characteristic wavelength are nearly linear versus the elastic modulus of the foundation in logarithmic scale. When the foundation is much stiffer than the rigidities of the graphene interlayer, detachment between graphene layers could occur. Finally, we conduct the post-buckling analysis by using the proposed finite element model and obtain various morphology evolutions which contain detachment between graphene layers, period doubling, localization, period switching, and folding. Also, we present a diagram includes distinct deformation patterns according to the stiffness of the foundation and the magnitude of the applied compressive strain. [ABSTRACT FROM AUTHOR]

• The effect of pits on the collapse pressure of cylinder under axial compression was experimental and numerical studied. • A novel shell model with pitting defects was proposed. • Realistic pits can be simulated based on the user defined Python program. • The distribution of pit affects the bucking mode hence govern the collapse pressure. • Volume loss is a good parameter to relate the collapse pressure and corrosion damage. This paper is aimed at assessing the effects of uniformly and randomly distributed pitting defects on the collapse pressure (F CO) of thick-wall cylinder under axial compression, which is exposed to the marine splash zone. The buckling performance of locally corroded cylinder was experimental and numerical studied. The experimental program involved seamless stainless steel tubes (316L) with different size of pitting defects, which were simulated by cylindrical hole. The pitting defects were introduced into the outside surface of cylinder by milling and drilling, and then the buckling strength of such structure was obtained experimentally. The profile of cylinder was examined in details using RA7320 Portable Arm Coordinate Measuring Machine (PACMM), and the measured data was analyzed carefully. A novel shell model was also established by a user defined Python program, where both uniformly and randomly distributed pits can be considered and the computational efficiency was highly improved. After calibrated with the experiment results, the model was used to carry out a systematic parametric study. It indicated that the radial imperfection and out-of-straightness as well as pitting defects (pitting size, perforated or un-perforated and distribution pattern) are key parameters governing the collapse pressure of such cylinder, and the maximum cross sectional area loss or volume loss are good parameter to correlate the collapse pressure and pitting damage. For engineering practice, the uniformly distributed pits model is better due to the convenience and conservative point of view, and the computational cost is also lower. However, the randomly distributed pitting model is more realistic, and some special collapse mode can only be observed when the random nature was taken into account. [ABSTRACT FROM AUTHOR]

The present study focuses on buckling and collapse behaviors of cracked steel panel by accounting for the crack opening/closure. A rectangular panel with a transverse through crack to the loading direction is selected to better understand the typical mechanical characteristics of a panel subjected to a sequence of tensile to compressive loading. When a tensile load is applied to the cracked panel, a through crack gradually opened and yielding occurs around the crack tip. When a compressive load is applied after the tensile load, the crack gradually closed and elastic/elasto-plastic buckling occur. A shell-solid mixed finite element (FE) model is adopted to effectively analyze the crack opening/closure. Shell FEs are employed in the rectangular panel (shell model), while solid FEs are partially adopted around the crack (solid model). Double nodes and contact condition are imposed on the crack face. The shell and solid models are joined together with a rigid body element (RBE). The buckling and collapse behaviors of the panel models under a sequence of tensile to compressive loading is critically examined, as well as its local behavior, i.e. , crack opening displacement (COD) varying displacement amplitude, panel aspect ratio and panel thickness. The results show that the crack opening/closure strongly affect the buckling and collapse behaviors of the cracked panel. • Buckling and collapse behavior are examined in a rectangular cracked panel. • Shell-solid FE modeling is adopted to analyze the cracked panel simulation. • The ultimate strength is analyzed under tensile and compressive load. • Crack opening distance is investigated by changing aspect ratio and plate thickness. [ABSTRACT FROM AUTHOR]

• Hellinger-Reissner variational formulation leads to a modified theory of pretwisted bars. • The modified theory satisfies stress free boundary conditions on the side surface of pretwisted bars. • In the modified theory pre-twisted bars have bending stiffness that decreases with increasing magnitude of pretwist. • The modified theory leads to substantially lower buckling loads. • According to the modified theory, buckling load monotonically decreases with pretwist increasing past a threshold value that depends on the bar's cross section and on the boundary conditions. Some seventy years ago the so-called "helical fiber model" was proposed to address existing discrepancies between experimental observations and theoretical predictions for pretwisted bars. The discrepancies concerned effects the pretwist had on bending and torsional behavior of such bars, but the same model was later used to show that the previously used theory is also likely to provide unconservative (thus unsafe) estimates of their buckling loads. In spite of the theoretical and practical significance of that finding the "helical fiber model" was deemed too approximate, intuitive and, ultimately, it seems to have been abandoned. As far as buckling is concerned, all publications of the last several decades appear to be based on the original theory that was earlier shown to possibly significantly overestimate the buckling load for pretwisted bars. Thus, in this work the problem of pretwisted bars' buckling is revisited. As most formulations of the problem, the proposed approach is approximate but, as much as possible, it is justified using established principles of mechanics. In particular, two-field Hellinger-Reissner mixed method is used to define axial and bending stiffness of pretwisted bars, with special attention paid to the definition of the stress field. Although the developments presented in this work follow a different path, the main features of the final model are similar to those of the "helical fiber model" introduced much earlier. However, the proposed formulation affords some additional flexibility in the way it may be used. Numerical examples are presented to illustrate effects of the discussed developments. [ABSTRACT FROM AUTHOR]

Thermoplastic composite three-stringer panels with omega stiffeners and conduction welded joints are designed, analysed and tested until final failure to investigate the performance of the welded joint in post-buckling. The three-stringer panels are designed to be structurally representative of the fuselage demonstrator of the Clean Sky 2 project STUNNING. A simplified model of the fuselage keel section is analysed by finite element analysis, using the virtual crack closure technique to model skin-stringer separation of the welded joint. The post-buckling and skin-stringer separation behaviour of the fuselage section is then adopted as the reference for the design of the three-stringer panels. Two panels are then tested. The test setup utilises digital image correlation to measure the deformation of the panels, and a high-speed camera to capture the final failure mode. The panels failed in post-buckling due to the separation of the middle stringer, with unstable separation growth followed by separation of the outer stringers and then stringer fracture. The numerical analysis of the panels, with geometrical imperfections included, is able to predict the structural behaviour accurately, with only minor differences in buckling shape and separation behaviour. [ABSTRACT FROM AUTHOR]

In contrast to continuous-fiber-reinforced polymer (cFRP), the random distribution of fibers in short-fiber-reinforced polymer (sFRP), which depends on the manufacturing process, has a significant impact on the mechanical properties of sFRP components. In this study, an automatic joint injection-buckling analysis framework was developed that can simulate the injection process and predict the mechanical performance in sequence. This automatic analysis framework can be directly utilized to optimize the manufacturing process to improve mechanical properties. Based on this method, it is demonstrated that an sFRP plate (consisting of carbon fiber-reinforced polyphenylene sulfide) has better buckling resistance than an aluminum alloy plate with the same design weight. The buckling resistance can be further improved by manipulating the gate location in the injection molds. The optimization scheme was verified using the conventional analysis framework. Moreover, the optimization method was improved by utilizing a tensor-similarity-based algorithm, which can substantially decrease the time required to locate the optimal solution. [ABSTRACT FROM AUTHOR]

This article reports on the manufacturing, experimental testing, and finite element analysis of very thick and long carbon-fiber-reinforced polymers (CFRP) tubes under uniaxial compression (radius-to-thickness ratio ∼ 10 and length-to-radius ratio ∼ 21). Herein, long and hollow axisymmetric composite cylinders were produced through bladder molding. The CFRP tubes have two oppositely located cutouts in the middle of the structures. Three test specimens with different cutout diameters (5, 10, and 15 mm) were experimentally tested until failure. The experimental testing campaign was supported by digital image correlation, acoustic emission, and infrared thermographic measurements to investigate the damage propagation and failure analysis. The CFRP tubes failed at the cutout location due to fiber fracture. Linear static and geometrically non-linear analyses were performed using ABAQUS to analyze the CFPR tubes under axial compression. In general, numerical and experimental results are in good agreement if the maximum stress or Hashin criteria are applied. [ABSTRACT FROM AUTHOR]

• The buckling of carbon fiber composite cylindrical shells with annular ribs under external pressure is investigated numerically and experimentally. • The effects of rib cross-sections, rib geometry and distribution on buckling load and buckling mode are explored. • The overall stability of the ribbed CF-CCS is sensitive to the rib section parameters, distance and thickness-radius ratio. • The numerical results obtained by nonlinear buckling analysis agree well with the experimental results. The buckling of carbon fiber composite cylindrical shells (CF-CCSs) with annular ribs under external pressure was investigated numerically and experimentally. The effects of rib cross-sections, rib geometry and distribution on buckling load and buckling mode were analyzed numerically. In addition, the ribbed polymer composite cylindrical shell was fabricated and tested. The geometry, thickness, buckling load and final collapse mode of the ribbed polymer composite cylindrical shell were measured. Finally, a nonlinear buckling analysis with geometrical imperfections was carried out based on the measured data; the numerical results were in agreement with the experimental results. The results show that different rib cross-sections have limited influence on the load carrying capacity of CF-CCSs, but the distribution of the ribs and the geometry of the ribs have a greater influence on CF-CCSs. [ABSTRACT FROM AUTHOR]

This article focuses on the buckling response of columns formed by pre-twisting a flat, narrow and straight material strip of a rectangular cross section. The experimental analysis accomplished for birch plywood strips covers twisting up to 90 degrees. The corresponding computational analysis covers the twisting process (geometrically nonlinear analysis) and the subsequent compression (linear buckling analysis, including the residual stresses from the twisting process) and includes comparisons for 3D solid and 2D shell finite elements within orthotropic linear elasticity. A further finite element analysis provides findings up to twisting angles of 400 degrees and includes nonlinear post-buckling analyses for the compression subsequent to twisting, in addition to the linear buckling analyses. These sets of analyses reveal some new findings regarding this classical problem. Most importantly, there are four characteristic twisting angles which are associated to mode jumps in buckling, to a plateau in the curve relating the critical load and the twisting angle and, finally, to a loss of stability during the twisting process. The influence of the twisting-induced stresses on the buckling response is investigated as well. • Compression response of twisted (by up to 90 degrees) plywood strips is studied experimentally. • 3D solid and shell FE models confirmed significant increase in critical buckling load. • FE analyses (for twisting up to 400 degrees) revealed four characteristic angles associated to: • (1) Mode jumps in buckling, (2) A plateau in the curve relating critical load and twisting angle, (3) A loss of stability during the twisting process. [ABSTRACT FROM AUTHOR]

This paper presents a cross-sectional optimization procedure to increase the load carrying capacity of a perforated rack column under a compression load. The optimization method is based on a Genetic Algorithm (GA) combined with the Generalized Beam Theory (GBT), which allows to take perforations as well as sectional deformations into account. The results indicate that the optimal cross-section geometry depends on the dominant buckling mode. Therefore, a combined optimization criterion to consider distortional and global buckling is defined. Finally, nonlinear shell finite elements analyses are done in order to assess the structural behaviour of optimized cross-sections. • Cross-sectional optimization of rack columns under compression load. • Influence of perforations and sectional deformations. • Combination of Genetic algorithm and Generalized Beam Theory. • Influence of dominant buckling mode. [ABSTRACT FROM AUTHOR]

Carbon fibre composites are widely used in low specific stiffness and high strength structures such as airframes. Compressive loading of these assemblies can lead to buckling and localised deformation around defects and imperfections that can hinder performance and lead to overengineering via excessive safety factors. Synchrotron X-Ray Diffraction (SXRD) has recently been shown to be capable of performing lattice strain mapping within carbon fibre composites at the microscale, a previously unprecedented resolution. In this study SXRD and radiography was performed on carbon fibre composite columns produced via two different methods (standard lamination and half square) at a range of different load states: unbuckled, one-third of the buckling load and post buckling. The results provide quantitative insights into the impact of these different production methods on lattice strain and fibre orientation, as well as the influence these factors have on reducing buckling load (by up to 22%). As well as being the first use of SXRD on industrially representative full-size carbon fibre samples, these insights provide invaluable detail into the factors which limit performance and the origins of column failure; crucial factors required to optimise structural design, production and loading capability. [Display omitted] [ABSTRACT FROM AUTHOR]

The present study explores the buckling and failure behavior of the silicon carbide (SiC) ceramic cylindrical shell under hydrostatic pressure using experimental and nonlinear numerical methods. An innovative experiment setup is designed and built. The hydrostatic test of the SiC ceramic cylindrical shell is carried out. The buckling deformation of the shell is captured by a high-speed camera and the strain response is recorded by strain gauges. In order to compare with the experimental results, the failure behavior of the SiC ceramic cylindrical shell subjected to hydrostatic pressure is simulated using a nonlinear numerical approach. Both the ultimate tensile strength and ultimate compression strength of the material are taken into consideration. The maximum equivalent stress is used as the failure criterion. The buckling mode simulated by the numerical method is in good agreement with the deformation shape observed in the test. As for the buckling pressure, the deviation from the experimental result is only 3.62%. Both the experimental and numerical results show that the failure of the SiC ceramic cylindrical shell under hydrostatic pressure is a typical coupling failure of strength damage and structural instability. • In this study, the buckling and failure behavior of the SiC ceramic cylindrical shell under hydrostatic pressure is investigated. To accomplish this, an innovative experiment setup is established, which combines a hydrostatic chamber, strain instruments, and a high-speed camera. A hydrostatic test is performed on the SiC ceramic cylindrical shell with one end fixed and the other end simply supported. Additionally, a nonlinear numerical simulation is conducted to predict the progress of the structure failure behavior under hydrostatic pressure. The following conclusions are drawn from the study: • The buckling of the SiC cylindrical shell subjected to hydrostatic pressure is a critical behavior. Prior to the critical buckling pressure, the strain response of the SiC cylindrical shell shows significant nonlinearity. • The maximum equivalent stress criterion is found to be an accurate way to evaluate the strength damage of the SiC ceramic cylindrical shell under hydrostatic pressure. The ultimate buckling strength of the SiC ceramic cylindrical shell is mainly determined by the ultimate compressive strength of the material. • Once the material damage occurs in the SiC ceramic cylindrical shell under hydrostatic pressure, even a slight increase in the external load can lead to structural collapse. • It is revealed that failure of the SiC ceramic cylindrical shell under hydrostatic pressure is a typical coupling failure involving both strength degradation and structural instability. [ABSTRACT FROM AUTHOR]

Composite materials have been widely used in the field of pressure shells for underwater vehicles due to their great potential. This paper presents an experimental study of composite cylindrical shells with and without the circular hole subjected to external hydrostatic pressure. The mechanical response of the composite cylindrical shells under external hydrostatic pressure is recorded by the strain acquisition system, and the buckling deformation process of the shells is also captured by the high-speed camera system. According to the experimental results, the entire compression process of the shell can be divided into three stages based on variations in strain. Based on the findings that buckling starts very early and accounts for about 35 % of the entire process, the concept of initial buckling pressure is proposed to distinguish the critical point of the shell transition from a stable state to an unstable state. It is found that the damage positions of the three shells all correspond to the troughs in the buckling waveform, and the final fiber breakage of the perforated shells with the reinforcements both occur near the reinforcement component. Finally, a comparative analysis of the strain response of the shell with the hole and the complete shell is carried out to explore their similarities and differences. The experimental results in this paper provide valuable information for the design of perforated composite pressure shells for underwater vehicles. [ABSTRACT FROM AUTHOR]

In this work, a laminated sandwich plate model with external piezoelectric layers is extended for buckling and dynamic stability analysis. In-plane harmonic uniformly distributed loads are considered in the dynamic stability problem, and the Mathieu-type equilibrium equations are solved using Bolotin's method to obtain the regions of dynamic instability. The model is validated to begin with, using available results in the literature for static and dynamic buckling of laminated soft core sandwich panels. Ultimately, the model is used to simulate the behaviour of laminated composite and sandwich plates with piezoelectric patches, controlled using a closed loop law with proportional and derivative gains, for buckling and dynamic stability analysis. This control system is used to postpone buckling, increase fundamental frequencies and reshape the regions of dynamic instability. • Dynamic buckling of soft core sandwich plates with piezoelectric patches. • Finite element model developed for active soft core sandwich plates. • Proportional and derivative control used to reshape the dynamic instability regions. [ABSTRACT FROM AUTHOR]