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The collapsible tubular mast (CTM) can be compactly folded for transport and deployed in orbit to serve as a key structural element. Once deployed, the CTM is vulnerable to buckling under axial load and bending moments, compromising its load-bearing capacity. The intricate relationship between the CTM's cross-section and its buckling behavior poses a significant challenge for designers. This is due to the ultra-thin nature of the CTM, which gives rise to highly localized buckling modes rather than global ones. To overcome this challenge, we developed surrogate models using a neural network (NN) trained with data from finite element analysis (FEA). These NN-based surrogate models provide high computational accuracy in predicting nonlinear buckling loads under axial force and bending moments around the two principal axes of the CTM's cross-section, achieving R 2 values of 0.9906 , 0.9987 , and 0.9628 , respectively. These models also significantly improve computational efficiency, reducing prediction time to a fraction of a second compared to several minutes with FEA. Furthermore, the NN-based surrogate models enable the usage of the non-dominated sorting genetic algorithm (NSGA-II) for multi-objective optimization (MOO) of the CTMs. These models can be integrated in the NSGA-II algorithm to evaluate the objective function of existing and new individuals until a set of 1000 non-dominated solutions, i.e., cross-sectional configurations optimizing buckling performance, is identified. The proposed approach enables the design of ultra-thin CTMs with optimized stability and structural integrity by promoting design decisions based on the quantitative information provided by the NN-based surrogate models. [ABSTRACT FROM AUTHOR]

In this study, the post‐buckling damage behavior of cylindrical composite tubes was examined experimentally. The samples were reinforced with glass, carbon, and kevlar fibers to obtain glass‐reinforced fiber polymer (GRFP), carbon‐reinforced fiber polymer (CRFP), and Kevlar‐reinforced fiber polymer (KRFP) cylindrical tubes. The samples were produced using 4 stacking layers with filament winding technology. In producing all composite tubes, the outer diameter was kept constant at 17 mm, and two inner diameters of 12 and 13 mm, two wall thicknesses, 5 winding angles, and two lengths were used as parameters. The load was applied to the samples until completely damaged, and the maximum post‐buckling load values obtained were measured on the testing device. The effect of different reinforcement materials, winding angle, wall thickness, and length on the load‐carrying capacity was analyzed and it was understood that they had a significant effect. It was observed that the load‐carrying capacity of GFRP samples was the highest compared to the others, followed by CFRP and KFRP samples, respectively. In all samples, it was observed that a 0.5 mm wall thickness increase increased the load‐carrying capacity, while a 50 mm length increase decreased it. The energy absorption (EA) values of GFRP, CFRP, and KFRP samples were 46.99, 25.22, and 15.48 Joules, respectively. It was understood that the energy absorption of GFRP samples was 1.86 times better than CFRP and 3 times better than KFRP. Highlights: The samples were produced using the fiber winding method, which is one of the most common production methods in the manufacture of tubes.Three different polymer reinforcement materials were used in the production of the samples.The effects of polymer reinforcement material, winding angle, length, and wall thickness on the maximum post‐buckling load were investigated.Wall thickness was found to have a significant effect on the maximum post‐buckling load.It was observed that GFRP samples had the highest energy absorption feature. [ABSTRACT FROM AUTHOR]

In this paper, the nonlinear post-buckling analysis of imperfect two-dimensional quasicrystal cylindrical shells is performed. The nonlinear governing equations are established by considering initial geometric imperfection, higher-order shear deformation theory and phonon-phason fields coupling effect. The load-shortening curves and buckling modes are obtained by the Galerkin's method. Numerical results are compared with the existing results and excellent agreements are obtained. Effects of geometrical parameters, initial imperfection and phonon-phason fields coupling effect on the critical load and imperfection sensitivity of two-dimensional quasicrystal cylindrical shells are discussed in detail. [ABSTRACT FROM AUTHOR]

Two main goals are pursued in the present work. First, the global buckling of axially loaded sandwich beams with composite face sheets and aluminum honeycomb cores under humid environments is investigated. An analytical solution with high accuracy is developed based on piecewise low-order shear deformation theory (PLSDT) to estimate the critical buckling loads. A parametric study is carried out to examine the influence of geometric parameters on the buckling loads of simply supported and clamped sandwich beams under different wet conditions. The obtained results indicate that humidity plays a significant role in the buckling behavior of honeycomb sandwich beams. As the second purpose of the present work, the weight minimization of sandwich beams is studied. The optimization variables include the face sheet thickness, core thickness, honeycomb cell size and honeycomb cell wall thickness. Moreover, different failure modes, including global buckling, face sheet dimpling, face sheet wrinkling, core shear instability, and face sheet failure are considered as design constraints. Imperialist competitive algorithm (ICA), a powerful socio-politically motivated global search strategy, is applied to handle the constrained optimization problem. The optimization results show that the presence of humidity in the environment significantly changes the optimal design of sandwich beams and makes them heavier. Furthermore, it is observed that by increasing the length of the structure, the optimal design is more affected by humidity. Moreover, it is found that ICA is a very powerful optimization tool both in obtaining the best values of geometric parameters and in reducing the computational cost. [ABSTRACT FROM AUTHOR]

The buckling behavior of tubular string is critical for safe oil and gas resource development. In practical engineering, the buckling of tubular string can appear in different development phases, such as casing putting into wellbore, BHA drilling rock, pipeline buckling, etc. Therefore, in this paper, the buckling behavior and buckling evolution of the tubular string are explored considering friction in horizontal wells. By applying the principles of static equilibrium and beam-string theory, an established theoretical model is utilized to examine the buckling behavior of tubular string. The critical load for sinusoidal buckling is determined by using both the series and trial function methods, and a comparison is made between the results obtained from these two techniques. In addition, perturbation analysis is used to obtain the angular displacement's configuration function in the helical buckling post-buckling state. To validate the model's effectiveness, a comprehensive analysis of the numerical results is performed, considering both sinusoidal and helical buckling scenarios. The research findings demonstrate that both the series method and the trial function method can effectively analyze sinusoidal buckling with high accuracy. The presence of friction significantly impedes the buckling behavior of the tubular string. Moreover, friction's influence causes a gradual decline in the efficiency of transmitting axial forces along the wellbore axis. [ABSTRACT FROM AUTHOR]

Mechanical metamaterials are valued for their diverse properties and potential applications. Due to the instability and large deformability of soft mechanical metamaterials (SMMs), geometric reorganization will occur and lead to some unusual properties. It is possible to change the properties of materials by varying the parameters. Conventional SMMs contain a periodic distribution of holes with the same size and shape, which can be changed to a lesser extent. Periodic dispersion of regular through-hole patterns of various sizes or shapes into elastomers, resulting in metamaterials with more mechanical functionality and deformation scenarios. In this paper, we investigated the influence of parameters on the buckling mechanical behavior of SMMs and the buckling mechanical behavior of structures with multiple sizes and geometric shapes. The parameters studied include geometric parameters (pore shape, porosity and area ratio) and physical parameters (Poisson's ratio and compression mode). Simulation of the buckling behavior of SMMs uses the finite element method. The finite element software ABAQUS is used, taking into account the almost incompressible characteristics of materials, the triangular quadratic plane strain hybrid element is selected (CPE6H). Numerical calculation gives the following results: Area ratio, pore shape and compression mode have obvious effects on buckling behavior, but Poisson's ratio has little effect; the influence of parameters on the buckling critical strains varied for SMMs with various pore shapes; very different buckling behaviors will result from swapping out the pattern of holes with the same size or shape for holes with two different sizes or shapes; the expression of buckling behavior is also varied when the mix of hole shapes is modified. These findings demonstrate that the design parameters may be used to achieve the desired buckling behaviors. This is a new method that can be used to control the deformation of structures; modify the properties of the SMMs without changing stiffness; simplify the structures without significantly changing the material properties. The design path of mechanical metamaterials is increased. [ABSTRACT FROM AUTHOR]

Fiber-reinforced elastomeric isolators (FREIs) have been proposed as a cost-effective solution for expanding the use of seismic isolation to normal-importance structures. By using lightweight fiber reinforcement and eliminating the attachment plates, FREIs reduce cost while improving the isolation efficiency and reducing tensile stresses in the rubber. However, the flexural flexibility of the fiber allows cross-sectional distortions (i.e., warping) to occur, which significantly impacts the stability of these devices. This paper evaluates the buckling of rectangular, circular, and annular FREIs, taking into account shear warping effects. A planar buckling theory previously proposed by the authors is adapted for the three-dimensional problem, and effective warping rigidities and warping-related areas are derived for the above bearing geometries, accounting for rubber compressibility. To assess the adequacy of the proposed buckling theory and derived warping properties in predicting the buckling of FREIs, a parametric finite element study is conducted. The critical load predictions of the proposed analytical formulation are found to be in excellent agreement with those of the numerical simulations. It is shown that traditional estimations of the buckling load that neglect warping are significantly unconservative. Finally, design recommendations and resources are provided for practice-oriented applications. [ABSTRACT FROM AUTHOR]

The objective of this paper is to conduct a comprehensive investigation into the buckling and post-buckling behavior of hyperelastic beams through both computational and experimental means. Natural rubber is used in the construction of a beam with a square cross-section. To determine the mechanical properties of natural rubber, a uniaxial tensile test is performed in accordance with ASTM D412. In finite element modeling (FEM), the nonlinear behavior of rubber is modeled using hyperelastic theory and the Yeoh strain energy function. The Static-Riks method is also implemented using Abaqus for the analysis of nonlinear buckling. To validate the present investigation results with FEM, an experimental test of digital image correlation (DIC) is conducted. The critical buckling force obtained via numerical methods exhibits an error of nearly 5% when compared to the corresponding results obtained from experimental testing. In order to ascertain the impact of various design parameters on the buckling behavior of the system, a comprehensive parametric analysis has been conducted. The parameters studied include the cross-sectional thickness, length of the structure, eccentric loads, as well as the mechanical properties of the materials used in the system. Consistent with the FEM outcomes, the critical buckling force exhibited by the hyperelastic beam demonstrates a positive correlation with increasing levels of hardness, cross-sectional thickness, and eccentric loads. The buckling behavior of the system is adversely affected by increasing its length. To ultimately validate the precision and reliability of the model, a supervised neural network (NN) learning method is employed. [ABSTRACT FROM AUTHOR]

A novel 3D centrosymmetric lattice that exhibits a large twist angle during compression is proposed by tailoring the twist buckling mode of a body-centered cubic lattice and a simple cubic truss to the first. The imperfections of offset and multimaterial systems are introduced to control the twist direction. Effects of geometrical parameters and material properties on twist behavior are studied. Results suggest that the buckling-driven lattice configuration can twist at an angle of 100° and an average angle per unit axial strain of 6.7°/%. The novel configurations can be used as force switches, safety devices, and temperature-controlled transmission devices. [ABSTRACT FROM AUTHOR]

AbstractThis study develops a novel analytical method to evaluate if box sections, with unequal wall thicknesses under bending, will undergo local buckling prior to reaching their yield strength since the analytical determination of critical local buckling stresses for such sections remains unexplored due to the lack of local buckling coefficients, warranting further investigation in scholarly discourse. Despite not directly computing the local buckling stresses, the developed method specifies a possible critical local buckling stress range by incorporating reference, critical, and equivalent section models, all formulated and developed with uniform wall thicknesses. The formulated method proficiently discerns the occurrence of local buckling by conducting a comparative assessment of the yield strength of the box section material against both the lower (min) and upper (max) bound stresses of the critical local buckling stress range. If local buckling persists unclear after the initial benchmark, the method reaches the final conclusion by comparing the constant wall thickness of the critical section with the web thickness of the box section. The developed method validated against finite element results obtained from linear elastic eigenvalue buckling analyses can be applied to the problem of determining whether such box sections subjected to bending will experience local buckling. [ABSTRACT FROM AUTHOR]

The lightweight fabrication of thin-walled cabin sections is popular for advanced ships, and the dimensional tolerance generated by welding buckling significantly influences the fabrication accuracy and schedule with poststraightening. A typical thin section employed in the superstructure of a high-tech passenger ship is considered the research object. Conventional fabrication procedures and welding conditions were examined beforehand with combined thermal elastic-plastic and elastic FE computations based on the theory of welding inherent deformation, while welding buckling was represented with identical behavior compared with fabrication observation. Actually, there are usually two methods to prevent welding buckling with advanced fabrication. Stiffeners with optimized geometrical features and excellent elasticity moduli were assembled to enhance the rigidity of the ship thin section, and less welding inherent deformation with advanced welding methods can be employed to reduce mechanical loading. Computational results show that either less in-plane welding inherent strain or higher structural rigidity can reduce the magnitude of welding-induced buckling, and avoid the generation of welding-induced buckling during the lightweight fabrication. [ABSTRACT FROM AUTHOR]

A family of locking-free Kriging-based Timoshenko beam elements with a new implementation of the discrete shear gap technique was recently developed (referred to as K-beam-DSG1 elements). Performance of the K-beam-DSG1 elements has been shown to be very satisfactory in the linear static analysis of beams for a wide variety of thicknesses. This paper presents further development of the K-beam-DSG1 elements to free vibration and bifurcation buckling analyses of prismatic and non-prismatic beams. Consistent Kriging-based mass matrices are used for free vibration analysis and similarly, consistent Krigingbased geometric stiffness matrices are used for buckling analysis. The results show that for most of the cases, the K-beam-DGS1 elements yield remarkably accurate natural frequencies and critical compressive loads using a reasonable number of elements to discretize the beam. For an axially functionally graded fixed-fixed supported beam, however, the elements fail to predict the critical load accurately. [ABSTRACT FROM AUTHOR]

This study investigates the elastic buckling behavior of oblate hemi-ellipsoidal shells (OHES) subjected to non-uniform external hydrostatic pressure. The virtual work-energy of OHES consists of virtual strain energy due to membrane, bending, in-plane stress resultants, and virtual work of hydrostatic pressure. For buckling analysis, the geometric stiffness matrix is obtained from the strain energy due to in-plane stress resultants. A finite element procedure via a C1 continuity axisymmetric element is applied to solve the critical hydrostatic pressure from the eigenvalue buckling problem. The buckling pressure of the hemi-ellipsoidal dome subjected to uniform external pressure is verified with the previous research and FEM commercial software. Present results also indicate that the maximum in-plane stress of the hemi-ellipsoidal shell shapes are near the apex point as the axisymmetric buckling shape. In the case of hydrostatic pressure, the critical hydrostatic pressure of OHES is determined and are in good agreement when compared with the experimental results in published research. Furthermore, the shape ratio influences the difference in critical load results between uniform pressure and hydrostatic pressure, especially when the shape ratio is higher than 0.5 and the a / t ratio is less than or equal to 100. Seawater depth limitations in subsea engineering are also presented and found that the shell thickness and shape ratio are the major factors affecting critical seawater depth. [ABSTRACT FROM AUTHOR]

The impact test of tubular components is usually carried out by way of drop hammer impact. In fact, in many ships’ equipment, the form of load is often carried out by way of drop impact test. In this paper, the drop impact test is used to study the buckling of tubular structure under impact load, so as to make it closer to the impact form of components in actual ship structure. Firstly, the stress, strain, acceleration at each moment and the buckling deformation mode of the tubular member after the impact are obtained through the drop impact experiment, and then the impact process is analyzed. Secondly, the finite element method is used for numerical simulation of the impact process, and the accuracy of the finite element analysis results is verified by comparing with it. Thirdly, the finite element method proved to be effective and was used to simulate single and multiple drop impacts under more working conditions, and a large amount of data was obtained. Finally, according to the existing impact criteria based on the results of drop weight impact, it is applied to the drop impact process, and the accuracy of each impact criterion is analyzed and compared. This method makes up for the deficiency of the traditional experimental method of using falling weight to simulate impact, and provides a reference for the critical buckling condition of similar thin-walled cylindrical shells under impact. [ABSTRACT FROM AUTHOR]

Tissue buckling is an increasingly appreciated mode of morphogenesis in the embryo, but it is often unclear how geometric and material parameters are molecularly determined in native developmental contexts to generate diverse functional patterns. Here, we study the link between differential mechanical properties and the morphogenesis of distinct anteroposterior compartments in the intestinal tract--the esophagus, small intestine, and large intestine. These regions originate from a simple, common tube but adopt unique forms. Using measured data from the developing chick gut coupled with a minimal theory and simulations of differential growth, we investigate divergent lumen morphologies along the entire early gut and demonstrate that spatiotemporal geometries, moduli, and growth rates control the segment-specific patterns of mucosal buckling. Primary buckling into wrinkles, folds, and creases along the gut, as well as secondary buckling phenomena, including period-doubling in the foregut and multiscale creasing-wrinkling in the hindgut, are captured and well explained by mechanical models. This study advances our existing knowledge of how identity leads to form in these regions, laying the foundation for future work uncovering the relationship between molecules and mechanics in gut morphological regionalization. [ABSTRACT FROM AUTHOR]

Composite structures can achieve greater performance through variable stiffness design. In consideration of inevitable manufacturing defects introduced by the Automatic Fiber Placement machine, modified models are established to calculate equivalent properties for materials with gaps or overlaps. A modeling method for variable stiffness structures with defects is proposed based on the modified models. This approach significantly reduces the dependence on mesh size for analysis accuracy, thereby improving modeling and calculation efficiency. Upon validation of the proposed modeling method, a Hierarchical Kriging surrogate modeling is employed to optimize the buckling performance of a variable stiffness wing box with defects. The impact of different manufacturing strategies on optimization results is also investigated. The findings demonstrate that the variable stiffness design improves the wing box buckling performance under a combined torsion-bending condition. Finally, the potential of utilizing overlaps without cut-restart is analyzed for weight reduction in the design of variable stiffness wing boxes. [ABSTRACT FROM AUTHOR]

In complex cardiovascular surgical reconstructions, conduit materials that avoid possible large-scale structural deformations should be considered. A fundamental mode of mechanical complication is torsional buckling which occurs at the anastomosis site due to the mechanical instability, leading surgical conduit/patch surface deformation. The objective of this study is to investigate the torsional buckling behavior of commonly used materials and to develop a practical method for estimating the critical buckling rotation angle under physiological intramural vessel pressures. For this task, mechanical tests of four clinically approved materials, expanded polytetrafluoroethylene (ePTFE), Dacron, porcine and bovine pericardia, commonly used in pediatric cardiovascular surgeries, are conducted (n = 6). Torsional buckling initiation tests with n = 4 for the baseline case (L = 7.5 cm) and n = 3 for the validation of ePTFE (L = 15 cm) and Dacron (L = 15 cm and L = 25 cm) for each are also conducted at low venous pressures. A practical predictive formulation for the buckling potential is proposed using experimental observations and available theory. The relationship between the critical buckling rotation angle and the lumen pressure is determined by balancing the circumferential component of the compressive principal stress with the shear stress generated by the modified critical buckling torque, where the modified critical buckling torque depends linearly on the lumen pressure. While the proposed technique successfully predicted the critical rotation angle values lying within two standard deviations of the mean in the baseline case for all four materials at all lumen pressures, it could reliably predict the critical buckling rotation angles for ePTFE and Dacron samples of length 15 cm with maximum relative errors of 31% and 38%, respectively, in the validation phase. However, the validation of the performance of the technique demonstrated lower accuracy for Dacron samples of length 25 cm at higher pressure levels of 12 mmHg and 15 mmHg. Applicable to all surgical materials, this formulation enables surgeons to assess the torsional buckling potential of vascular conduits noninvasively. Bovine pericardium has been found to exhibit the highest stability, while Dacron (the lowest) and porcine pericardium have been identified as the least stable with the (unitless) torsional buckling resistance constants, 43,800, 12,300 and 14,000, respectively. There was no significant difference between ePTFE and Dacron, and between porcine and bovine pericardia. However, both porcine and bovine pericardia were found to be statistically different from ePTFE and Dacron individually (p < 0.0001). ePTFE exhibited highly nonlinear behavior across the entire strain range [0, 0.1] (or 10% elongation). The significant differences among the surgical materials reported here require special care in conduit construction and anastomosis design. [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]

Graphene platelets (GPLs) exhibit outstanding mechanical and physical properties and therefore are employed as a reinforcement in advanced polymer composite structures. The purpose of this paper is to analyze the biaxial buckling of functionally graded graphene-reinforced sandwich plates with a soft orthotropic core. A new high-order three-layer theory is developed for the accurate modeling and analysis of the sandwich structure. The sandwich plate is divided into three layers including two face sheets and a core and a different third-order kinematic assumption is dedicated to each layer. The transverse flexibility of each layer as well as the displacements continuity at the interfaces are considered. Additionally, the continuity conditions and the conditions of zero transverse stresses in the whole structure are satisfied. The plate is subjected to a biaxial compressive loading and the governing equations are derived using the principle of minimum potential energy. Analytical solutions are presented for simply supported boundary conditions to obtain the critical buckling load. The influences of plate geometry and GPL properties on buckling load are investigated. The results obtained in specific cases are compared with the published results and the validity of the present results is confirmed. It can be drawn that the use of GPL increases the buckling load of graphene-reinforced sandwich plates. [ABSTRACT FROM AUTHOR]

Most studies have focused on determining optimal dimensions of metal- or composite-based rectangular hollow sections (RHSs) by considering only the design requirement of strength. Different from those, an analytical procedure for the determination of optimal sectional dimensions of polymer-based RHS beams by accounting for both adequate-strength and local buckling for the first time has been presented in the context of this study. Analytical expressions which give the optimal sectional dimensions simultaneously satisfying the adequate-strength and local buckling conditions have been derived for two different loading configurations such as a pure major axis bending and a combined axial compression and major axis bending. The analytical procedure proposed in this study depends on the idea of preventing the polymer-based RHS from buckling prior to its compressive strength. This has been achieved by increasing the critical buckling stress of the RHS up to its compressive strength via optimizing its sectional dimensions. During the optimum design, different elastic and plastic material behaviors of polymers in tension and in compression have been taken into calculations. The results attained analytically have been validated against numerical predictions obtained from linear elastic eigenvalue buckling and postbuckling analyses implemented in Abaqus engineering finite element code. Thus, the analytical procedure reported in this study can be used as a benchmark in identifying the optimal dimensions of RHS members manufactured from polymers. Communicated by Davide Spinello. [ABSTRACT FROM AUTHOR]

• Nonlinear torsional buckling of toroidal shell segments is presented using the Ritz energy method. • The corrugated core sandwich toroidal shell segments with FG-GRC coatings are considered. • The thermal forces are added to improve the homogeneous model for the corrugated core. • Ritz energy method, Donnell shells theory, and Pasternak's foundation model are applied. • Effects of corrugated core, material and geometrical parameters on the buckling behavior of shells are investigated. An investigation on the nonlinear torsional buckling of corrugated core sandwich toroidal shell segments with functionally graded graphene-reinforced composite (FG-GRC) laminated coatings in temperature change is mentioned in this paper using the Ritz energy method. The complex configuration of sandwich toroidal shell segments with double curvatures and the combination of the corrugated core and the FG-GRC coatings create the special behavior of structures. A homogenization model for corrugated structures and the extended Halpin-Tsai model can be applied to estimate the stiffnesses of shells. The effects of uniform temperature change are taken into account by supplementing the thermal forces into the total forces of shells. The Donnell shell theory and Pasternak's foundation model are used to establish the total potential energy of the structures. Ritz energy method is applied, and the closed condition and circumferential stress are taken into account, the postbuckling curve expressions of torsion-deflection and torsion-twist angle are obtained in explicit forms. The numerically obtained examples can show the significantly beneficial effects of FG-GRC laminated coatings and corrugated core on nonlinear buckling responses of structures. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of friction on the buckling behavior of a thin, shallow, elastic spherical shell under uniform external pressure based on an axisymmetric model of the finite element method. The study examines a combination of different geometric parameters with three different types of boundary conditions: clamped, hinged, and frictional ends with a wide range of friction coefficients. Friction has a significant influence on the buckling response of the spherical shell for all geometric parameters. In general, the critical pressure decreases as the friction coefficient or geometric parameter decreases. The buckling behavior of the frictional end with small friction coefficients presents an obvious difference compared to the results of high coefficients. For certain geometric parameters, the buckling mode of the spherical shell is transited because of changing the friction coefficient. A buckling map that describes the dependence of critical pressure on both friction coefficient and geometric parameter combined with buckling mode is generated. This map can be applied to the design of the spherical shell against buckling. [ABSTRACT FROM AUTHOR]

The ability of biomolecules to exert forces on their surroundings or resist compression from the environment is essential in a variety of biologically relevant contexts. For filaments in the low-temperature limit and under a constant compressive force, Euler buckling theory predicts a sudden transition from a compressed state to a bent state in these slender rods. In this paper, we use a mean-field theory to show that if a semiflexible chain is compressed at a finite temperature with a fixed end-to-end distance (permitting fluctuations in the compressive forces), it exhibits a continuous phase transition to a buckled state at a critical level of compression. We determine a quantitatively accurate prediction of the transverse position distribution function of the midpoint of the chain that indicates this transition. We find that the mean compressive forces are non-monotonic as the extension of the filament varies, consistent with the observation that strongly buckled filaments are less able to bear an external load. We also find that for the fixed extension (isometric) ensemble, the buckling transition does not coincide with the local minimum of the mean force (in contrast to Euler buckling). We also show that the theory is highly sensitive to fluctuations in length in two dimensions and the buckling transition can still be accurately recovered by accounting for those fluctuations. These predictions may be useful in understanding the behavior of filamentous biomolecules compressed by fluctuating forces, relevant in a variety of biological contexts. [ABSTRACT FROM AUTHOR]

This article considers a bidirectional functionally graded (BDFG) beam with various distributions of volume fraction. The impact of these distributions on the buckling and bending response of BDFG beam with general boundary conditions is investigated via a quasi-3D solution. It is assumed that the beam is exposed to a set of in-plane varying compressive loads and there mechanical characteristics change in both directions. Also, the BDFG beam is considered to be exposed different external mechanical loads. Hamilton's principle is employed to derive the governing equations, which are then solved using analytical solution to obtain buckling and bending characteristics. The precision of the current formulation is investigated via a comparison with available data in literature. Some numerical results are presented and discussed to assess the effect of different parameters such type of volume fraction, boundary condition, varying load, and beam geometry on the buckling and bending of BDFG beam. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) offers new possibilities to fabricate and design lightweight lattice materials. Due to the superior mechanical properties of these lattice structures, they have the potential to replace honeycombs as cores in sandwich panels. In addition to the advantage of the integral fabrication thanks to AM, additively manufactured lattice core sandwich panels may be also used as heat exchangers, enabling a multifunctional use of the core. To ensure a reliable and safe structure, the mechanical response of lattice core sandwich panels under given load conditions must be predictable. In conventional sandwich panels subjected to compressive loads, the sandwich's global buckling and the face sheets' local buckling are the dominant failure modes. In constrast, core strut buckling may be the critical failure mode in lattice core sandwich panels. Therefore, an analytical 2D model to predict the local buckling of lattice core struts is considered in this study. Furthermore, the critical load for global buckling is obtained based on the first-order shear deformation theory. Thus, the transition from local buckling to global buckling depending on the length-to-thickness ratio is captured by the presented model. The comparison with finite element modeling of the sandwich model with truss cores has proved the accuracy of the derived model. [ABSTRACT FROM AUTHOR]

In this paper, buckling and nonlinear post-buckling behaviors of a bidirectional porous (BDP) beam are investigated under bidirectional hygrothermal environment. Euler–Bernoulli beam theory with the von Kármán nonlinearity is employed to derive the nonlinear variable coefficient governing differential equations based on Rayleigh quotient method. Analytical solutions of critical buckling load and load–deflection equilibrium path in post-buckling are deduced for the single directional varying (SDV) porous beam. The general numerical solutions for bidirectional varying (BDV) porous beam are obtained by differential quadrature finite element method (DQFEM) with Newton–Raphson iteration method based on the variation principle. The high accuracy of the present numerical method with higher computing efficiency is verified by comparison with published reports and the analytical results in this work. Parametric analysis on effects of the porosity bidirectional distributions, porosity coefficients, distributions of hygrothermal environment and boundary conditions on buckling load and post-buckling response is carried out to enhance the buckling and deformation resistances in design, manufacture and usage of porous structures. The results show that the bidirectional porosity pattern, linear and nonlinear hygrothermal distribution and boundary conditions play a significant role on buckling critical external load and critical hygrothermal increments, buckling form and post-buckling path. [ABSTRACT FROM AUTHOR]

This paper aims to analyze the effects of porosities, tangential constraints of boundary edges and elevated temperature on the buckling and postbuckling behaviors of thin functionally graded cylindrical shells subjected to uniform torsion. The porosities are assumed to exist within functionally graded material (FGM) according to even and uneven distributions. The properties of constituents are assumed to be temperature dependent and effective properties of porous FGM are determined using a modified rule of mixture. Mathematical formulations are established within the framework of classical shell theory taking into account von Kármán–Donnell nonlinearity and elasticity of tangential edge constraints. Multi-term analytical solutions are assumed to satisfy simply supported boundary conditions and Galerkin method is used to determine buckling torsional load and load–deflection relation for postbuckling analysis. Numerical results show that porosities have remarkably deteriorative influences on the torsional buckling resistance and postbuckling load capacities of FGM cylindrical shells. This study also reveals that tangential edge constraints have pronouncedly beneficial and detrimental effects on the postbuckling strength of torsion-loaded porous FGM cylindrical shells at room and elevated temperatures, respectively. [ABSTRACT FROM AUTHOR]

A new utilization of entropy in the context of buckling is presented. The novel concept of connecting the strain energy and entropy for a pin-ended strut is derived. The entropy of the buckling mode is extracted through a surrogate model by decomposing the strain energy into entropy and virtual temperature. This concept rationalizes the ranking of buckling modes based on their strain energy under the assumption of given entropy. By assigning identical entropy to all buckling modes, they can be ranked according to their deformation energy. Conversely, with identical strain energy assigned to all the modes, ranking according to entropy is possible. Decreasing entropy was found to represent the scaling factors of the buckling modes that coincide with the measurement of the initial out-of-straightness imperfections in IPE160 beams. Applied to steel plane frames, scaled buckling modes can be used to model initial imperfections. It is demonstrated that the entropy (scale factor) for a given energy roughly decreases with the inverse square of the mode index. For practical engineering, this study presents the possibility of using scaled buckling modes of steel plane frames to model initial geometric imperfections. Entropy proves to be a valuable complement to strain energy in structural mechanics. [ABSTRACT FROM AUTHOR]

Negative Poisson's ratio in auxetic structures plays a crucial role in energy absorption and impact mitigation. Origami-based lattices within the realm of auxetic structures offer the advantage of facile fabrication and design. Nevertheless, the utilization of periodic lattices in origami-based auxetic structures constrains the available design space for achieving diverse mechanical properties. Addressing this limitation, our study introduces origami-based auxetic structures with functionally graded thickness, utilizing origami-based lattices known as Tachi–Miura polyhedra. We investigated the impact of functionally graded thickness on buckling behavior and force responses through dynamic loading experiments employing 3D-printed test pieces. The experimental results indicate that functionally graded thickness induces partial auxetic deformation in lattices, and the resulting nonsymmetric deformation prevents global buckling, thereby averting bounded forces observed in structures with uniform thickness. These findings extend the applicability of auxetic structures, spanning from energy absorption to the design of cushioning structures. [ABSTRACT FROM AUTHOR]

To meet the complex and diverse demands for low-stress mechanical measurements of fabrics and other flexible materials, two integrated multidimensional force sensors with the same structure but different ranges were explored. They can support both rapid and precise low-noise, high-precision, low-cost, easy-to-use, reliable, and intelligent solutions for the complex measurement of fabric mechanics. Having analysed the mechanical relationship of the parallel beam theory, and considering the specific requirements of fabric measurement, a novel multi-dimensional force sensor is designed, capable of measuring tensile, shear, and buckling properties. Finite element analysis is used to simulate the mechanical performance of this sensor for fabric-loading/unloading measurement, and the sensitivity of the mechanical quantity transfer, the amount of sensor deformation, the stress distribution, and the degree of inter-dimensional coupling have been investigated and verified. The basis for subsequent digital processing is achieved by a low-offset, low-temperature-drift, low-power-consumption analogue front end, 24-bit ADC circuit, and signal conditioning electronics, suitable for the measurement of fabric mechanics under low stress, which is like the end-user requirements. The sensor information channel is supported by a host microcontroller with a DSP and a floating-point processing instruction set. Information processing is performed in time-sharing with the support of a multitasking real-time operating system. The purpose of designing this sensor is to facilitate the development of a new testing instrument, which will adopt the advances of current instruments whilst eliminating their shortcomings. [ABSTRACT FROM AUTHOR]

In the current research, we delve into the intricate realm of bifurcation analysis for Föppl–von Kármán plates, employing a precise numerical tool. This innovative numerical approach melds the power of spectral discretization with the prowess of a high-order continuation method-based Taylor series development (HODC). It is worth noting that combining the high-order continuation method with such discretization techniques offers an efficient path-following approach, complete with adaptive step lengths, capable of tackling a wide array of nonlinear problems. Despite the extensive applications of nonlinear elasticity, the spectral method remains relatively uncharted territory within this context. However, our deep-rooted understanding and expertise in the field drive us to embrace this method alongside high-order development continuation for bifurcation analysis of Föppl–von Kármán plates. The governing equations governing thin elastic plates experiencing significant elastic deflections manifest as a pair of coupled nonlinear differential equations, famously known as the von Kármán (vK) equations, presented in a strong form with two principal unknowns: deflection (w) and the Airy stress function (F). Leveraging Chebyshev decomposition matrices, we approximate these fourth-order elliptic nonlinear partial differential equations. Subsequently, we harness high-order development continuation techniques to morph these nonlinear systems into linear ones. Our rigorous evaluation and validation of this numerical approach's precision and performance come to fruition through a comprehensive buckling analysis encompassing multiple illustrative examples. [ABSTRACT FROM AUTHOR]

Welding buckling deformation is one of the foremost failure modes of thin plate welded structures. It is important to estimate welding buckling for structural design and process optimization. Inherent strain-based welding buckling evaluation methods have been proved to be valid, but the existing methods have low efficiency due to requiring multiple inherent forces. In this study, a novel welding buckling evaluation method based on longitudinal shrinkage force was established. The effectiveness of the proposed method was validated using a butt welded joint. In addition, this method was applied in a large-scale thin plate structure for evaluating the structural stability, the effects of heat input, welding manner, and external constraints on welding deformation and buckling were also discussed. The results reveal that the proposed inherent strain-based welding buckling evaluation method can be used to judge whether welded structures are buckled. The reduction of welding heat input and the use of single-sided welding can mitigate welding deformation. Increasing external constraints can not only reduce the welding deformation, but also improve the welding critical buckling load for preventing welding buckling. [ABSTRACT FROM AUTHOR]

Hybrid fibre reinforced polymer (FRP)-timber (HFT) thin-walled structural members are a novel technology developed recently as a sustainable alternative to thin-walled steel and aluminium structures. HFT structures are made by forming thin timber veneers and FRP laminates into efficient cross-sectional geometries. While existing studies have demonstrated the potential of HFT thin-walled members to be used as structural elements, a systematic study to investigate the behaviour of HFT thin-walled structures is yet to be carried out. This paper presents a study aimed at investigating the behaviour of HFT C-section columns under concentric axial loading. In total five HFT C-section specimens each from 700 mm to 2000 mm lengths were fabricated and tested. It was found that shorter HFT C-section columns failed due to local buckling while increase in length changed the failure mode to global buckling. Effect of GF orientation and density on load carrying capacity of the HFT C-section columns was investigated numerically. It was found that it's necessary to provide adequate GF volume in transverse to axis direction, but further increase in GF volume in transverse direction did not significantly increase the load carrying capacity. Increase in GF density in parallel to axis direction increased the load carrying capacity. [ABSTRACT FROM AUTHOR]

This article is the first attempt in the open literature to investigate the impact of uncertainty in material properties on the critical buckling speed of rim-driven rotating laminated plates. The formulations are constructed using the isogeometric approach (IGA) and higher-order shear deformation theory (HSDT). Coriolis and centrifugal forces resulting from rotation are taken into consideration. The results of the current formulation are compared to the previous results and validated. The accuracy and flexibility of the RBFN-based surrogate model, designed for uncertainty analysis, is verified by comparing the result with Monte Carlo simulation (MCS). Through a variety of parametric experiments, the critical buckling speed of rotating laminates driven by a rim is stochastically analyzed. Variance-based sensitivity analysis is employed to identify the influence of individual material properties on the critical buckling speed. Further, the impact of sensitive properties on the probability of structural failure is estimated. This research can be used to forecast the probability of failure of a structure at various levels of material uncertainty associated with it. [ABSTRACT FROM AUTHOR]

This paper aims to evaluate the seismic response of multitiered buckling-restrained braced frames (MT-BRBFs), assess the design provisions specified by the 2022 AISC Seismic Provisions for multitiered BRBFs, and propose improvements to these provisions. A set of 17 frames is first selected by varying bracing configuration, frame height, number of tiers, and tier height ratio. The frames are then designed in accordance with the 2010 and 2022 AISC Seismic Provisions. A numerical parametric study is performed under scaled ground motion accelerations. The results of the parametric study show that when the frames are designed to the 2010 provisions, the frame inelastic deformation tends to concentrate in the tier(s) undergoing tensile yielding due to their lower postyield stiffness, compared to BRBs yielding in compression, which creates unequal story shear, contributed by braces, in adjacent tiers with BRBs in tension and compression and engages column flexure to compensate for unbalanced brace story shears between tiers. Columns experience yielding and even buckling in several cases due to combined flexural and axial load demands. MT-BRBFs designed to the 2022 AISC Seismic Provisions exhibit a more uniform deformation response between tiers and relatively lower flexural demands in their columns. However, these provisions may overestimate column in-plane flexural demands (on the order of 3), resulting in potentially uneconomical design solutions. On the basis of the numerical simulations, modifications are proposed to compression BRBs' adjusted strength to better estimate column in-plane flexure and tier deformation while achieving an economical column design. The proposed improvements are validated using dynamic analyses. [ABSTRACT FROM AUTHOR]

Introduction: Compare the anatomical and functional outcomes, operation duration, and complication rates between standard scleral buckling (SSB) and chandelier-assisted scleral buckling (CSB) for phakic eyes with rhegmatogenous retinal detachment (RRD). Methods: PubMed, Embase, and Cochrane Library databases were searched from inception to June 2024. The primary endpoint will be set as a final success. The secondary endpoint will be primary success, operation time, and final BCVA. Results: Our meta-analysis showed that there is no statistical difference between CSB and SSB for the final success rate (RR = 1.00, 95% CI = 0.97–1.03). For the primary success rate, there is no statistical difference between CSB and SSB (RR = 1.00, 95% CI = 0.94–1.06). For operation time, our meta-analysis showed that the CSB group is less than the SSB group (pooled MD = −15.8, 95% CI = −22.60 to −9.00). For postoperative complications, our study shows that the CSB group presented with lower pooled risk than the SSB group (RR = 0.59, 95% CI = 0.41–0.89). There is a trend that the ERM formation risk is higher in the CSB group if there is no routine suture for the sclerotomy (p = 0.08). Conclusion: CSB showcases a significantly reduced operation duration and less postoperative complication in contrast to the SSB group, maintaining comparable primary and ultimate anatomical success rates as well as final BCVA. [ABSTRACT FROM AUTHOR]

The real-time judgment and screening of the dangerous parts of the whole structure is always one of the very difficult problems in the process of structural strength verification. As an important monitoring index in the static test of aircraft structure, the identification and judgment of the buckling position determines the degree of control of the field test personnel on the overall test. In the static strength test of aircraft structure, the test risk is more and more difficult to control, and unexpected structural failure occurs from time to time. In order to realize the identification of structural buckling parts accurately and efficiently, a buckling real-time detection system was designed and realized. The system realized real-time acquisition of collected data based on timer technology, and completes buckling position judgment based on nonlinearity, and finally visualized the buckling parts through two-dimensional and three-dimensional forms. The system has been applied in the test site, and the effect is remarkable. [ABSTRACT FROM AUTHOR]

A simplified column-buckling model is developed to understand the buckling mechanism of thin-walled strips restrained by uniform lateral pressure in the milling process. The strip is simplified as two rigid columns connected by a rotation spring, resting on a smooth surface, restrained by a uniform pressure and loaded by an axial force. Two loading cases are considered, i.e., the dead load and the follower load. Analytical solutions for the post-buckling responses of the two cases are derived based on the energy method. The minimum buckling force, Maxwell force and stability conditions for the two cases are established. It is demonstrated that the application of higher uniform pressure increases the minimum buckling force for the column and thus makes the column less likely to buckle. For the same pressure level, the dead load is found to be more effective than the follower load in suppressing the buckling of the system. The effect of initial geometric imperfection is also investigated, and the imperfection amplitude and critical restraining pressure that prevent buckling are found to be linearly related. The analytical results are validated by finite element simulations. This analytical model reveals the buckling mechanism of strips under lateral pressure restraint, which cannot be explained by the conventional bifurcation buckling theory, and provides a theoretical foundation for buckling-prevention strategies during the milling process of thin-walled strips, plates and shells commonly encountered in aerospace or automotive industries. [ABSTRACT FROM AUTHOR]

This technical note presents the optimal shape of an arch carrying a central point load to two pinned supports for maximum in-plane bifurcation buckling load. The arch shapes considered are triangular, parabolic, circular, catenary, and ogival. It is assumed that the arches are elastic and inextensible and their flexural rigidity is uniform throughout the arch length. The Hencky bar-chain model was used for elastic buckling analysis. It is found that the optimal arch shape depends on the arch apex height to length (h/L) ratio. The optimal arch shape changes from circular to catenary to parabolic and finally to triangular from h/L=0.1 to 1. This shows that the funicular triangular arch shape for the central point load is not the optimal arch shape against in-plane buckling when h/L is less than 0.528. For maximum buckling load, one may use either the circular, catenary, or parabolic arch with h/L approximately equal to 0.3. [ABSTRACT FROM AUTHOR]

Based on the surface elasticity theory combined with the theories of Kirchhoff plate and Mindlin plate, the influences of surface effects on the buckling and post-buckling behaviors of nano-laminates are studied. Analytical solutions for critical buckling loads under uniaxial and biaxial compressions are obtained. Furthermore, approximate solutions for critical post-buckling loads under moveable and immoveable edge conditions are provided by using the Galerkin's method. Numerical examples are given to study the influences of thickness, number of layers, surface parameters and the length of the nano-laminates on buckling and post-buckling critical loads. Results obtained indicate that the surface/interface energy is connected with the number of layers. In addition, the effects of the surface/interface energy on the critical loads enhance through increasing the length of the laminates but reduce by increasing the thickness. Mechanical model, analytical method and conclusions of this work are helpful for designing and examining the stability of the nano-laminates and nanoscale devices. [ABSTRACT FROM AUTHOR]

AbstractIn the present work, a generalized finite element formulation is established and implemented for the free vibration and buckling characteristics for temperature dependent carbon nanotube (CNT) reinforced plate. The uniform and functionally graded distribution of CNT is assumed in the plate and the plate is modeled in non-polynomial axiomatic framework. The extended rule of mixture is employed for computing the equivalent material parameters which are temperature dependent. Further, an eight-noded C0 continuous element with seven degree of freedom is adopted for discretization of the plate domain. The convergence and comparison studies are carried out to ensure the accuracy and effectiveness of the proposed formulation. As temperature conditions significantly influence structures integrity, on that account, thorough parametric studies are performed to examine the influence of volume fraction (VCNT), span to thickness ratio (a/h), CNT distribution and boundary conditions on the FG-CNTR plate for the different temperature conditions. The results demonstrate that the efficient use of CNT distribution and boundary conditions can consequently improve free vibration and buckling characteristics of the temperature dependent FG-CNTR plates. [ABSTRACT FROM AUTHOR]

A topology optimisation approach that accounts for buckling resistance and manufacturability using fibre-reinforced composites is presented. This approach combines topology optimisation and fibre orientation optimisation to achieve a design with maximum buckling resistance. To ensure the optimal designs can be manufactured using 3D printing, constraints based on the continuity of fibre orientation and fibre path generation are applied. A compressed column, a stubby cantilever and an MBB beam are designed to demonstrate the response of the topology and fibre orientation when accounting for buckling resistance, as well as the compromise due to the inclusion of manufacturing constraints. The results show that the presented approach successfully guarantees manufacturability with a significant increase in buckling resistance. [ABSTRACT FROM AUTHOR]

This study focuses on variations in the hysteretic behavior of buckling-restrained braces (BRBs) configured with or without out-of-plane eccentricity under cyclic loading. Quasi-static experiments and numerical simulations were carried out on concentrically and eccentrically loaded BRB specimens to investigate the mechanical properties, energy dissipation performance, stress distribution, and high-order deformation pattern. The experimental and numerical results showed that compared to the concentrically loaded BRBs, the stiffness, yield force, cumulated plastic ductility (CPD) coefficient, equivalent viscous damping coefficient and energy dissipation decreased, and the yield displacement and compression strength adjustment factor increased for the eccentrically loaded BRBs. With the existence of the out-of-plane eccentricity, the initial yield position changes from the yield segment to the junction between the yield segment and transition segment under a tensile load, while the initial high-order buckling pattern changes from a first-order C-shape to a second-order S-shape under a compressive load. [ABSTRACT FROM AUTHOR]

Highlights The engineering structures with cutouts should consider both buckling and stiffness. Inspired by the multi‐level leaf veins, in this paper, the skeleton of the grid‐honeycomb sandwich structure was designed in the hierarchical form, and combined with the cutout characteristics of the side walls of the railway vehicle body, the multi‐objective stiffness and mass optimization of the skeleton layout under buckling constraints was achieved. The cutout honeycomb sandwich structure was designed with orthogonal grids in the stiffness design area and curved grids based on the quadratic polynomial in the buckling design area. The optimization model also included the linear angle hierarchical grid, the constant angle hierarchical grid, and the single‐level orthogonal grid. The multi‐objective optimization framework based on the Radial Basis Function (RBF) surrogate model and the Non‐dominated Sorting Genetic Algorithm (NSGA‐II) was developed. The optimization results indicated that the hierarchical grid provided the more extensive design space. The optimal solution of the quadratic polynomial hierarchical grid had the highest stiffness and stiffness per unit mass compared to the rest of the grid layouts, which were 23.28% and 30.47% higher than the single‐level orthogonal grid, respectively. Finally, the multi‐order eigenvalue buckling was analyzed based on the optimal structure. Layout of hierarchical grids proposed inspired by multi‐level leaf veins. Orthogonal grids ensure stiffness and curved grids inhibit buckling at cutouts. Apply the hierarchical grids as skeletons to honeycomb sandwich structures. Stiffness and mass optimization subject to buckling constraints is performed. [ABSTRACT FROM AUTHOR]

This study proposed novel designs for achieving self-centering (SC) behavior using superelastic shape memory alloy (SMA) buckling-restrained plates (BRPs). Compared with previous studies relying on small-diameter SMA bars, this study employed large-dimensional SMA plates that could provide sufficient strength for real construction projects. The design concept and configurations of SMA-BRPs were first introduced. Corresponding tests were then conducted. Three specimens were tested, including one that was unsatisfactory and two that were acceptable. Based on the initial examination of the behavior and failure mode of the unsatisfactory trial specimen, the corresponding modifications were made to achieve the improved performance of two acceptable specimens. Subsequently, the hysteresis and SC behaviors, energy dissipation capacity, and yielding strength degradation of the two acceptable specimens were investigated. Both specimens exhibited high-quality flag-shaped behaviors in their tension–compression cycles, with their strengths reaching around 200 kN under tension and more than 310 kN under compression, representing one of the largest strength values shown by a single SMA element in the literature. Asymmetric behavior was observed under tensile and compressive loadings, primarily due to the asymmetric behavior of the SMA base material, high-mode inelastic buckling under compression and friction between the SMA core plate and buckling-restraining device. After the tests, finite element models were developed to obtain an in-depth understanding of the detailed behavior of SMA-BRPs. The studies showed that SMA-BRPs successfully achieved the SC buckling-restraining design target. The design incorporating end restrainers was preferred due to its flexibility, which reduces application restraints. [ABSTRACT FROM AUTHOR]

A new type of buckling-restrained brace (BRB), called induction-hardened buckling-restrained brace (IHBRB), is proposed in this study. The IHBRB uses a round bar as the core steel and a hollow round section as the restrainer. The core steel undergoes partial induction hardening, which makes its strength lower in the middle but higher at the two ends. This strength difference along the length is expected to trigger energy dissipation in the middle but keep the ends undamaged. The restrainer has an inner diameter similar to that of the core steel, which minimizes the gap between them and avoids time-wasting grouting. This study introduces experimental and analytical research on four types of IHBRB. Tensile coupon tests revealed that the core steel of the IHBRB-600 series satisfied the target yield strength of 600 MPa in the middle and 1,200 MPa at both ends. The core steel of the IHBRB-800 series also satisfied the target yield strength of 800 MPa in the middle and 1,200 MPa at both ends. The ascending cyclic loading test showed that the IHBRB exerted a load capacity of over 1,000 kN as designed and exhibited tensile-compressive symmetric hysteresis behavior. IHBRB-600L, the specimen that failed by tensile fracture, showed that the high-strength brace end succeeded in remaining elastic as planned, while the low-strength brace middle showed a higher-order mode buckling. However, unexpected overall buckling at the joint occurred on other specimens. The low cycle fatigue specimens showed large cumulative inelastic deformation ratios of more than 200. A three-dimensional finite-element model of IHBRB-800L built by ABAQUS/Explicit (Dassault Systèmes Simulia Corp., Paris) captured the experimental results well. A parametric study revealed that the longer restrainer fixed at one side of the core steel end was one of the solutions to guarantee the great seismic performance of the IHBRB. [ABSTRACT FROM AUTHOR]

The utilization of functionally graded graphene platelet-reinforced composites (FG-GPLRC) and honeycomb sandwich constructions is prevalent in the field of engineering. Therefore, it is crucial to investigate the buckling and vibration properties of these materials under heat circumstances. This paper specifically focuses on the vibration and thermal buckling characteristics of a novel multi-arc concave honeycomb sandwich plate (MACHSP) equipped with an adjustable positive-negative Poisson's ratio. The governing equations of motion for the system are derived based on the first-order shear deformation theory in conjunction with Hamilton's principle. The formulation of the system's characteristic equation involves the establishment of displacement functions that satisfy distinct boundary conditions. Using computational programming, natural frequencies, mode shapes, and critical buckling temperatures of MACHSP with three different FG-GPLRC distributions under thermal influences are determined. Subsequently, these results are compared with outcomes from finite element simulations and findings from previously published literature. Additionally, the amplitude-frequency response characteristics of the structure under harmonic excitation are analyzed, followed by a discussion of the impact of structural parameters on its buckling and vibration characteristics. The results indicate that the established theoretical model for predicting the buckling and vibration characteristics of MACHSP with FG-GPLRC distribution aligns well with simulation models and prior research. In contrast to solid plates, MACHSP not only achieves a substantial reduction in weight but also demonstrates a significant increase in natural frequency. Furthermore, graphene platelets have the potential to enhance the structure's natural frequency values and critical buckling temperatures. Lastly, various structural parameters exert a notable influence on the structure's performance. [ABSTRACT FROM AUTHOR]

Thin-walled structures, i.e. the wing-upper-skin panels, are prone to buckling accompanied by a significantly large out-of-plane deflection. The computational efficiency of the conventional finite element based full-order method is not satisfactory for nonlinear buckling problems of the structure. In this work, the skin panels on the upper surface of the wing butt box are selected using a sub-modeling technique based on the nonlinear structural analysis. A reduced-order method is proposed to trace the geometrically nonlinear response of the single and double-curved skin panels in a stepwise manner. A predictor-corrector strategy is developed using the Koiter-perturbation-theory based reduced-order model and Newton iterations. The high-efficiency of the proposed method is validated by comparing the number of path-following steps and iterations with the full-order method. A fairly large step size is achieved to significantly reduce the computational cost in a nonlinear buckling analysis. The influence of the number of closely-spaced modes on the numerical accuracy and efficiency of the proposed reduced-order method is also studied. Different boundary condition, location, and thickness of the wing-upper-skin panel, are considered to further demonstrate the favorable performance of the proposed method. • Nonlinear buckling analysis is applied to skin panels with single and double-curved shapes on the wing upper surface. • A reduced-order method is adopted to trace geometrically nonlinear responses in predictor-corrector based stepwise manner. • Influence of the number of closely-spaced modes on numerical accuracy and efficiency of the proposed method is investigated. • Numerical accuracy and high-efficiency of the proposed method are validated for skin panels con- sidering various parameters. [ABSTRACT FROM AUTHOR]

Composite sandwich double‐curved shells (CSDCS) have been extensively employed in the engineering domain of variable temperature environments; consequently, it becomes very significant and essential to present the thermal buckling characteristics of CSDCS to supply some valuable numerical results. The no‐linear strain–displacement relationship due to temperature variation has been taken into consideration based on the Von‐Karman non‐linear strain theory, and Hamilton's principle is adapted to derive the buckling differential equations of the CSDCS. The Navier method is employed to solve the eigenvalue problem for obtaining the critical buckling temperature. Finally, through studying the variation rule of thermal buckling temperature (CBT), several interesting findings on thermal buckling of the CSDCS are shown, as follows: As the h3/h1 rises, the CBTs of CSDCS first decrease then increase. With the increase of radius value, the CBTs of spherical shells decline, the CBTs of models (1,1) and (2,2) of hyperbolic paraboloidal shells are essentially unchanged, but the ones of models (1,2) and (2,1) decrease. As the h2 increases, the CBT progressively grows after the initial reduction. With the increase in aspect ratio, the CBTs for modes (1,1) and (2,1) of CSDCS gradually increase, and the ones of modes (1,2) and (2,2) shows an increase after an initial decrease. The CBTs of CSDCS gradually increase as the shear module of damping layer increases. Highlights: Thermal buckling of composite doubly‐curved sandwich shells was studied.A solution was proposed to derive the buckling differential equations.The change rules of critical buckling temperature were obtained. [ABSTRACT FROM AUTHOR]

Thin-walled composite cylindrical shells are nowadays widely used as primary structures in the aerospace industry. The so-called variable stiffness (VS) composite cylindrical shells with flexible stiffness tailoring characteristics have been made possible by existing AFP techniques. Considering the inherent imperfection sensitivity property of axially compressed thin-walled cylindrical shells, the buckling behaviors of the axially compressed VS composite cylindrical shells with initial geometric imperfections and delamination imperfections are investigated respectively in this paper. The design buckling loads of the axially compressed VS composite cylindrical shells are first determined by the probing method, which is verified by comparing with the existing test data and numerical simulation results. Additionally, a parametric study is conducted to investigate the effects of delamination imperfections on the buckling loads. The constraint delamination sizes of the VS composite cylindrical shells based on the design buckling load in this paper are given. Furthermore, the effects of continuously variable fiber angles on the buckling loads are investigated considering the imperfection sensitivity. The specific VS composite cylindrical shells with both high- buckling loads and low-imperfection sensitivity are obtained. Results indicate that the effects of imperfection sensitivity need to be carefully considered in buckling design of the axially compressed VS composite cylindrical shells. [ABSTRACT FROM AUTHOR]