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• The bi-modular FGMs UMAT is developed for the first time and successfully conducted to validate the perturbation solution. • The rise-to-thickness ratio and corresponding critical load are two factors influencing the snap-through buckling. • The rotation constraint and radial constraint at the shell edge have opposite effects on the snap-through buckling. • The bi-modular FGM effect may speed up or slow down the snap-through buckling. Functionally graded materials (FGMs) enable structures to achieve a smooth transition between different material properties, providing an optimized combination of functions to meet the diversity of engineering needs. However, the presence of bi-modular effect in FGMs is often neglected due to the complexity in the analysis. In this paper, the curvature correction equivalent method based on the von Kármán theory will be applied to the theoretical study for the large deformation problem and the resulting snap-through buckling of functionally graded revolutionary shallow thin shells with bi-modular effect under different boundary constraints. Furthermore, a bi-modular FGMs user material subroutine (UMAT) is developed for the first time to simulate the real material model, thus validating the theoretical solution. The results show that except for the bi-modular effect of materials, boundary constraints of shells also have important influences on the relationship of load vs. central deflection and snap-through buckling. The research of boundary constraints brings new conclusions to snap-through buckling: the rotation constraint and radial constraint at the shell edge have opposite effects on snap-through buckling. This work will contribute to the analysis of the snap-through buckling of functionally graded revolutionary shallow thin shells with an obvious bi-modular effect and under various boundary constraints. [ABSTRACT FROM AUTHOR]

In this paper, an anti-buckling fixture was proposed to assess the deformation characteristics of DP500 and DP980 dual-phase steels, and AZ31B magnesium composite under tension–compression cyclic loading. The advantage of the device lies in the possibility of monitoring friction between the specimen and supporting blocks during the test. In consequence, it allows to avoid an error during stress determination. The full cyclic loading capacity for each material can be executed at the displacement amplitude within the range ± 2.5 mm which corresponds to the maximum strain amplitude of ± 0.2 for the specimen with the gauge length of 21.5 mm. It is concluded, that the technique proposed is promising since the thin sheet material can be tested under tension–compression in a wide range of deformation without the buckling effect. Furthermore, useful data for modelling cyclic deformation behaviour for shell structures can be obtained. [Display omitted] • Proposed fixture enables to avoid buckling during thin metal sheet compression. • The friction force is continuously registered during the test. • Complex characteristics could be successfully and precisely determined. • Useful data for modelling cyclic deformation can be obtained. [ABSTRACT FROM AUTHOR]

This paper reports the development, numerical implementation and practical application of a novel/improved approach to perform the buckling analysis of braced/restrained cold-formed steel members by means of Generalised Beam Theory (GBT). The novelty consists of a cross-section analysis procedure that incorporates elastic restraints and, therefore, leads to a set of constrained deformation modes with clear structural meaning for the member under consideration. The potential of the developed GBT-based approach is illustrated by presenting and discussing numerical results concerning cold-formed steel (i) purlins restrained by sheeting and (ii) studs braced by sheathing. For validation and assessment purposes, several GBT-based results are compared with values provided by the programs GBTul2.0 (conventional GBT), CUFSM (finite strip method) and/or A nsys (shell finite elements). It is shown that the proposed GBT-based approach is much more efficient than the conventional one, as it offers the possibility of obtaining accurate buckling results with very few (constrained) deformation modes – this feature makes it possible to derive semi-analytical formulae to calculate critical buckling loadings of braced/restrained members. This capability is used in this work to derive GBT-based semi-analytical formulae providing critical length and buckling loading estimates for cold-formed steel purlins and studs restrained by panels (sheeting or sheathing). • Novel approach for the buckling analysis of restrained members based on Generalised Beam Theory (GBT). • Restraints included in the GBT cross-section analysis, leading to constrained deformation modes. • Constrained deformation modes lead to improved structural interpretation and computational efficiency. • Application to the buckling analysis of purlins restrained by sheeting and studs braced by sheathing. • Semi-analytical formulae derived to estimate purlin lateral–distortional and stud distortional buckling loadings. [ABSTRACT FROM AUTHOR]

Generalised Beam Theory assumes the displacement field of a thin-walled member as a linear combination of deformation modes. The main family of deformation modes is constructed based on two simplifying assumptions: null membrane shear strain and null membrane transverse extension. If these modes are not sufficient for an accurate representation of the structural behaviour, two other families of modes are derived (from the main family) for which the two simplifying assumptions are eliminated. In this paper, for the special case of thin-walled cylinders, all three families of deformation modes are replaced by a new unified family, for which the membrane shear strain and transverse extension are not neglected. The derivation of the proposed modes is based on the stress equilibrium equations, and it involves the trigonometric series representation of the longitudinal modal amplitudes. The advantages of the proposed modes are highlighted throughout several linear buckling analyses with various loading and boundary conditions. • New GBT deformation modes are derived using the stress equilibrium equations. • Longitudinal modal amplitude functions are represented by trigonometric series. • Stiffness matrices are derived for linear buckling analysis. • Formulation is validated using shell finite element models. • Proposed formulation is compared with classical GBT. [ABSTRACT FROM AUTHOR]

This technical note discusses aspects related to the combination of standard Reissner–Mindlin shell and GBT-based (beam) finite elements, with the purpose of modelling, efficiently (with degree-of-freedom economy) and accurately, the structural behaviour of thin-walled members and frames with complex geometry, undergoing global-local-distortional deformation. Following the approach previously proposed by the authors (Manta et al., 2020 [1] ; 2021 [2] ; 2020 [3]), each element type is employed where it is most efficient: (i) GBT-based elements in the prismatic zones and (ii) shell elements in the geometrically complex zones (e.g., tapered, joints, etc.). While lack of compatibility obviously leads to over-flexible solutions, it is shown that full compatibility can lead to locking. Consequently, a well-balanced compatibility statement is proposed. Several numerical examples are presented to show the advantages of the proposed approach over the previous one, in linear static and buckling (bifurcation) analyses. [ABSTRACT FROM AUTHOR]

• The deformation behaviors of aluminum honeycomb sandwich panels with artificial defects of different sizes under in-panel compression were investigated using mirror-assisted MV-DIC. • Dual-surface in-plane deformation fields and through-thickness strain fields were measured. • The honeycomb sandwich panel exhibits local undulations and strain concentrations in the surface with defects. • Only defects with sufficiently large sizes leads to decreases in the buckling load. • The bending direction of the buckled specimen is influenced by the local undulations caused by the defect. Honeycomb sandwich panels have been extensively utilized in the aerospace and automotive industries for their prominent advantages of energy absorption, high strength and tailorable anisotropic mechanical properties. Nevertheless, the common presence of local core-to-skin disbonding poses an urgent need to understand the mechanical behaviors of defective honeycomb sandwich panels. The present work investigates the deformation behaviors and evolutions of aluminum honeycomb sandwich panels with varying sizes of circular artificial core-to-skin disbonding defects using mirror-assisted multi-view digital image correlation (MV-DIC). Based on the 3D profiles and dual-surface deformation fields obtained with mirror-assisted MV-DIC, it is revealed that disbonding defects induced local surface undulations with severe local strain concentrations and determined the mode of gradual bending and buckling. Defects with a diameter below 20 mm induced minor local surface undulations and slight decreases in buckling load. When the diameters of defects reach 30 mm, extensive surface convex deformation occurs and the buckling load decreases by 23 %. The results validate mirror-assisted MV-DIC as a cost-effective and practical technique for characterizing dual-surface 3D deformation of sheet composite materials and structures. [ABSTRACT FROM AUTHOR]

• An induced energy absorption structure (IEAS) with altering load transfer paths is designed inspired by the growth and deformation of tree branches. • The asymmetric buckling mode of the proposed structure exhibits higher mechanical properties compared to symmetric linear buckling. • Through the gradient design of the structures, the asymmetric buckling mode is implemented in multi-layer IEAS. Negative stiffness (NS) structures with curved beams easily experience beam fracture in small-scale designs, limiting their repeatability and energy absorption. The induced energy absorption structure (IEAS), which achieves negative stiffness by altering load transfer paths, is designed inspired by the growth and deformation of tree branches. By means of the variation method of geometric parameters, a unique asymmetric buckling deformation mode is realized in IEAS. The NS and energy absorption characteristics in IEAS are analyzed based on load distribution and major principal strain theory. Compression results demonstrate that the asymmetric buckling mode exhibits higher energy absorption and specific energy absorption compared to symmetric linear buckling, effectively improving structural toughness. Through gradient analysis of geometric parameters and comprehensive analysis of induced structure layouts, the asymmetric buckling mode is successfully implemented in multi-layer IEAS. The multi-layer IESA exhibits excellent ability of energy absorption and toughness, making it have potential applications in areas that require small-sized designs with high energy absorption capabilities. [ABSTRACT FROM AUTHOR]

In this paper, a concave-shaped unit composed of two thin-walled beams with cantilever boundary conditions is designed and fabricated. Forces are introduced through the two cantilever ends of the beams whose constraints are hinged joints to get a bi-stable axial or lateral buckled unit. Initial buckling deformations of the concave-shaped units are analyzed theoretically and numerically. Experimental and numerical methods are used to investigate the post-buckling deformations and snap-through behaviors, when the concave-shaped units are axial buckled or lateral buckled. In the case of completing downwards and upwards snapping processes, there is a hysteresis loop in the force–displacement curve for the bi-stable lateral buckled unit, while is not for the bi-stable axial buckled unit. Finally, the influence of transverse displacements and dimension parameters on the snap-through behaviors of the bi-stable lateral buckled units is studied by the simulation method. • A bi-stable lateral buckled unit is designed and fabricated. • There are two symmetric modes for the initial buckled concave-shaped unit. • Post-buckling and snap-through behaviors of the bi-stable units are investigated. • The energy dissipation capacities are influenced by beams parameters. • The assembly bi-stable units are good candidates for energy-related applications. [ABSTRACT FROM AUTHOR]

• A novel non-linear numerical model for thin-walled members is presented. • Four classes of H-section members are selected to study the hysteretic behaviour. • The comparison of test results and those of the proposed model is accomplished. • The deformation mode, buckling effects, and material nonlinearity are considered. Based on Gonçalves's geometrically exact beam theory considering cross-section deformation, the warping and distortional deformation of thin-walled members are described in this paper by means of a combination of section deformation modes. By integrating with the J2 elastic‒plasticity theory for the steel, a numerical model is established for the hysteretic behaviour of thin-walled steel members. Four classes of H-section members are selected on account of the design codes, and the influence of section warping and distortion deformation modes on the calculation of the hysteretic behaviour of components with different section types is analysed. The crucial aspect lies in the bending hysteresis behaviour around the strong and weak axes of the cross-section for H-beam steel members subjected to typical thin-walled members with relatively large widths and thicknesses. Test results on the hysteretic behaviour of H-section steel members are compared with those calculated from the proposed model in terms of the hysteric behaviour of components, strength degradation, energy-dissipating capacity, etc. These findings validate the correctness and feasibility of the established non-linear analysis model for thin-walled members. [ABSTRACT FROM AUTHOR]

• The lattice (FBCC) proposed presents salient feature of bi-plateau stress. • FBCC improved Young's modulus by 88 % than traditional body-centered cubic. • FBCC has higher specific absorption energy than most lattices. • FBCC tends to be more isotropic material than traditional body-centered cubic. • The proposed analytical model can predict the two plateau stress well for FBCC. Lattice structures are increasingly attracting attention due to their excellent mechanical properties and broad application prospects. However, most developed lattices feature single-step deformation or single plateau stress, which confine its multi-task applications. Herein, a novel body-centered cubic (NBCC) with two-step deformation based on body-centered cubic (BCC) and bionic fractal design is introduced. NBCC exhibits bi-plateau stress in the stress–strain curves. The underlying mechanism is caused by the bending and buckling deformation of the struts. The mechanical behaviors of NBCC are investigated by finite element simulation which verified by experiment. Compared with traditional BCC, NBCC has improved modulus of elasticity by 88 %, yield strength by 21.2 %, and specific energy absorption by 108 % when ρ ′ and α are 0.07 and 0.5, respectively. Moreover, the elastic modulus as well as yield strength increase with geometrical ratio α. The specific energy absorption tends to maximum at the geometric ratio α = 0.6 ∼ 0.7. From the Ashby map, the proposed NBCC lattice possesses high energy absorption, exceeding most of the existing architected materials at the same density. Furthermore, the results show that NBCC has better isotropy of elastic modulus and tends to be more isotropic material compared to BCC. Finally, theoretical model of two-step plateau stress is established based on hinge dissipation principle. This work opens up new insights into the use of element replacement design to create multi-step pathways that can be applied to design engineering structures with multiple tasks and application for impact protection. [Display omitted] [ABSTRACT FROM AUTHOR]

The combined action of subsea seismic faults and pressure loads can cause pipelines to reach the limit state. Consequently, various failure modes, such as global buckling and system collapse, can occur. In this study, the deformation of a buried subsea pipeline under different pressure-reverse fault displacement loading paths is investigated using the nonlinear vector form intrinsic finite element (VFIFE). To quantify the damage to the pipeline and identify its failure modes under accidental reverse fault displacement, the loading path 'fault displacement → internal/external pressure' was analysed first. The post-earthquake resumption and reconditioning of unpressurised and pressurised pipelines, respectively, are evaluated based on the performance criteria in terms of strain and deformation. The corresponding loading paths are simplified as 'ambient hydrostatic pressure → fault displacement → operation pressure' and 'operation pressure → fault displacement → external over pressure'. Moreover, the residual bearing capacity, weak position, and possible failure behaviour of the pipeline are comprehensively analysed for all subsequent external overpressures. The results show that the loading paths have a significant effect on structural responses, particularly on the elasto-plastic deformation. The two yield bends of a deformed pipeline under fault displacement are dangerous regions. Their inadequate relative residual strength leads to several successive local collapses and determines the occurrence and direction of buckling propagation during the subsequent external overpressure. The previous internal pressure has a significant influence on the residual capacity and failure modes of the pipeline, particularly the strain hardening effects with the influence of large seismic faults. The critical points of the first local collapse have specific characteristics, and the minimum residual resistance to external over pressure occurs when the maximum flattening parameter is 15% under initial fault displacement. The results of this study can guide the development of seismic design methodologies and engineering practice for buried subsea pipelines. • Analysis of buried subsea pipeline under different pressure-reverse fault displacement loading paths using nonlinear VFIFE. • Evaluation of post-earthquake resumption and recondition for pipelines with different initial pressure conditions. • Analysis of residual bearing capacity, weak position, and possible failure for pipelines under subsequent external over pressure. • Practical and useful distribution characteristics of the critical points of the first local collapse. [ABSTRACT FROM AUTHOR]

• Four-point bending method is applied to reproduce the pure bending behavior of diamane. • Tension-induced bending failure is observed when the carbon layer number increases. • Bending limit is slightly larger than the ultimate tensile strain. • Twisted bilayer graphene with interlayer-bonding experiences structural failures under pure bending. The intriguing physical properties of two-dimensional (2D) nanomaterials make them promising building blocks for flexible electronics. Using a four-point bending approach, this work establishes a comprehensive understanding of the bending behavior of diamane – a 2D diamond nanostructure, from elastic deformation to structural failure through atomistic simulations. The four-point bending method accurately reproduces the pure bending of the sample, and the obtained force-displacement curve fit well with the classical Euler beam theory. Structural failure is observed from diamane under bending when its thickness or the number of layers increases. Atomic insights reveal that the crack initiates from the tension side of the sample, resulting in a tension-induced bending failure. Specifically, the bending limit is found to be slightly larger than the fracture strain under tensile deformation. Additionally, the bending behaviour of the diamane analogous – twisted bilayer graphene with interlayer-bonding (TBGIB), has been investigated. Different from diamane, TBGIB bends elastically at the initial stage and then experiences structural failures with increasing bending strain. Higher interlayer bonding density is observed to result in a higher bending stiffness. Meanwhile, significant interlayer shear strain is detected during bending, which leads to interlayer bond breakage, rippling, and buckling of the graphene layer. This work provides a full description of the pure bending behavior of diamane and its analogous structure, which could be beneficial for their applications in flexible electronics. Tension-induced failure of three- or four-layer diamane nanoribbon is revealed by four-point bending simulation. [Display omitted] [ABSTRACT FROM AUTHOR]

The limited past research on light-weight cold-formed steel (CFS) composite sections have indicated their success in addressing the buckling instabilities, but have been confined to flexural members. Thus, there is a need to extend this research to columns as well. In the first part of this study, an experimental investigation was carried out on lightweight CFS composite built-up battened columns composed of channel sections, connected in the face-to-face configuration. Two series of tests were performed to evaluate the axial compression capacity and stability response of built-up sections formed using various light-weight materials like GFRP and timber, as composites with CFS channels. The structural performance of these composite built-up battened columns was assessed in terms of their peak loads resisted, load–displacement response, axial stiffness, failure modes and strength-to-weight comparison. The second part deals with the theoretical analysis of the lightweight CFS composite built-up sections using the current codes for checking their adequacy. The third part presents the finite element simulation of the lightweight CFS composite built-up sections for validating the test results. • Light-weight CFS composite built-up columns are developed using GFRP and timber. • Monotonic tests performed to explore the structural behaviour of composite columns. • FE simulation of the behaviour of such composite built-up columns is carried out. • Theoretical strengths were determined and compared with the test strengths. • Large improvement in the strength, stiffness & strength-to-weight ratio is achieved. [ABSTRACT FROM AUTHOR]

A new type of braced frame structure with a double-cylinder arc energy dissipator is proposed in this paper. The energy dissipator is composed of an inner cylinder, an outer cylinder, and a stiffener fabricated and connected to a steel beam and column by welding, and the double cylinder arc energy dissipator is connected to a steel beam and steel column by welding. The seismic performance of the braced frame structure with a double-cylinder arc energy dissipator was analyzed by Abaqus. The results indicated that seismic energy could be dissipated through the deformation of the outer cylinder, inner cylinder, and rib plate. However, the double-cylinder arc energy dissipator could avoid the out-of-plane buckling deformation of the brace. Further, it exhibited properties similar to those of concentrically and eccentrically braced frames. The deformation of the braced frame with a double-cylinder arc energy dissipator mainly occurred on the dissipator and energy-dissipating beam (between the dissipator and column). During the loading process, the stiffener, outer and inner cylinders, and beam gradually yield. The height, thickness, and spacing of the stiffener of the double-cylinder arc energy dissipator were observed to significantly influence the seismic performance of the proposed braced frame. In contrast, the effect of the thicknesses of the inner and outer cylinder arcs on performance was negligible. • Seismic performance of braced frame structure with double cylinder arc energy dissipation was studied. • The initial stiffness, linear stiffness, and bearing capacity of the structures under monotonic load were studied. • Energy dissipation capacity, degradation property, failure, and deformation modes under low-cyclic loading were studied. [ABSTRACT FROM AUTHOR]

Confining with an outer sleeve is an effective means of enhancing the load-bearing and deformation capacity of compression struts. The outer sleeve and compression strut, i.e., inner core, constitute a sleeved core-loaded member, where the latter ideally bears all the axial compression under the lateral restraint of the former. Additionally, an extension segment of the inner core is typically required as the allowance for contraction. However, the unrestrained extension segment is prone to excess flexural deformation, dramatically decreasing the overall load carrying capacity of the sleeved member. In this paper, first, an analytical investigation of the behaviour of the sleeved member with pinned ends is presented. Second, a numerical study was conducted to determine the limit state of the localized flexural failure and to propose the corresponding design criterion combining the analytical model. Last, the design criterion was further validated by compressive tests, indicating that the proposed method accurately predicted the localized​ flexural failure of both seamless-sleeved members and members with assembled outer sleeves. • A theoretical model on the localized flexural failure of sleeved members is built up. • The corresponding design criterion is proposed combining numerical cases. • The unrestrained length ratio of the core and the gap width exhibit notable effects. • The theory is validated by tests on both seamless- and assembled-sleeved members. [ABSTRACT FROM AUTHOR]