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

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

Integral buckle arrestors are regarded as the most effective arresting devices and can be perfectly adapted to innovative sandwich pipes. In the present study, hyperbaric chamber tests were performed on reduced-scale sandwich pipe specimens equipped with integral arrestors, and the effect of interface bonding behaviour on the crossover pressure was examined. Then, numerical frameworks were proposed to replicate buckling propagating and crossing phenomena under hydrostatic pressure, with a strong consistency between measurements and predictions. A broad parametric analysis on the crossover pressure was implemented covering key material properties and geometries. After that, machine learning techniques were introduced and used for predictions of crossover pressure and arresting efficiency. Four algorithms, involving Random Forest, Multi-layer Perceptron, K-Nearest Neighbors, and Support Vector Machine, were established using a dataset comprising 248 cases with thirteen variables. Based upon an evaluation of standard statistical metrics, it is observed that RF and MLP exhibit superior prediction accuracy, whereas the prediction performance of KNN is the worst. The results show that the machine learning method provides relatively reliable predictions of crossover pressure and arresting efficiency for both flattening and flipping failure modes. • Hyperbaric chamber tests were performed on reduced-scale sandwich pipe samples equipped with integral arrestors. • The effect of interface bonding property on the arresting performance was experimentally explored. • The influence of geometry and material properties on the crossover pressure was numerically examined. • Machine learning models were applied to predict the crossover pressure and arresting efficiency. [ABSTRACT FROM AUTHOR]

• Higher order FEMs are proposed for bio-inspired laminated composites plates using a quasi-3D theory for the first time. • Three different FEMs are derived based on non-conforming elements with different number of nodes and degree of freedom. • No shear locking phenomenon was observed in the analyses conducted using these FEMs. • Effects of lamination scheme, orthotropy ratio and aspect ratio on the mechanical response of the bio-inspired helicoidal composite plates are examined. A comprehensive study is carried out by employing various finite element models (FEMs) for the bending, buckling stability and free vibration analyses of bio-inspired helicoidal composite plates with various lamination schemes. A higher order quasi-3D kinematic plate theory is developed to include a shear deformation effect. The variational formulation of the problem is exploited to derive the equations of motion, element stiffness, geometrical stiffness, and mass matrices based on a non-conforming rectangular element. Three different finite elements models are derived based on non-conforming elements with different number of nodes and degree of freedom. The developed finite element model has been validated with those found in the open literature. The effects of boundary condition, lamination scheme, orthotropy ratio and aspect ratio on the mechanical response of the bio-inspired helicoidal composite plates are examined. Notably, for the lamination schemes investigated in this study, no shear locking phenomenon was observed in the analyses conducted using these FEMs. Dimensionless centre deflections, critical buckling loads and fundamental frequencies of bio-inspired helicoidal composite plates vary depending on the type of lamination scheme, boundary condition and aspect ratio. The new orientation schemes can replace the traditional ones to overcome the shear singularity and overcome the delamination defects. [ABSTRACT FROM AUTHOR]

• A new non-uniform rectangular honeycomb sandwich panel is designed based on Bezier curves to enhance material utilization. • The effective elastic constants of non-periodic honeycombs are obtained through the geometric equivalent method and the strain energy-based homogenization method. • The analytical solutions of bending and buckling responses of the non-uniform rectangular honeycomb sandwich panel are derived by using parabolic shear deformation theory. • The weight/performance multi-objective optimization design of the non-uniform rectangular honeycomb sandwich panel is conducted. Honeycomb sandwich panels have a wide range of applications in aerospace, marine and energy industry due to their high stiffness-to-weight ratio. In this study, a new non-uniform rectangular honeycomb core is presented to promote its material utilization ratio. The non-uniform wall of honeycomb core is described using Bezier curves, and the effective elastic constants are obtained by both the geometric equivalent method and the strain energy-based homogenization method. To analyze the bending and buckling behaviors of the sandwich panel, the parabolic shear deformation theory is adopted, and the governing equations are derived by employing Hamilton's principle. Then, the closed-form solutions of bending and buckling responses of the non-uniform rectangular honeycomb sandwich panel are derived. Furthermore, multi-objective design formulations are established, with the objectives of minimizing the weight and deflection, and maximizing the critical buckling load. Illustrative examples demonstrate that the non-uniform design of the honeycomb core can remarkably increase the material utilization rate and improve the mechanical performance of sandwich panels. [ABSTRACT FROM AUTHOR]

• Frameless CFSCWs can work as lateral systems in low rise long span structures. • Tension field action increases the shear strength in the post-buckling region. • Finite element models can simulate the CFSCWs under combined shear and axial loads. • Frameless CFSCWs can be designed under varying axial loads by obtained equations. This paper presents a comprehensive evaluation of a novel Cold Form Steel Corrugated Walls (CFSCWs), named Frameless CFSCWs, under combined axial and lateral loads. A series of experimental investigations were carried out on full-scale specimens. The influence of different axial loads on the buckling-failure mode, the peak force capacity, the post-buckling stiffness, and the residual force capacity are presented. Subsequently, robust finite element models were developed to simulate the complex bucking behavior of these Frameless CFSCWs. The results of the experimental and numerical investigations revealed that the lateral force-deformation response of Frameless CFSCW is highly influenced by the axial loads. A linearized backbone curve of the Frameless CFSCWs with different axial loads is proposed. Key design parameters such as overstrength and ductility ratios of the Frameless CFSCW panels are identified. The linearized backbone curve can be used by engineer to design Frameless CFSCWs under different axial loads. [ABSTRACT FROM AUTHOR]

In this paper, we propose an archetypal double-winged novel nonlinear oscillator composed of torsional springs and rigid rods which behaves smooth and discontinuous dynamics and a kind of special collision pendulum depending on the varying of a geometrical parameter. The system behaves complicated equilibrium bifurcations with different geometrical states, leading to a series of buckling phenomenon and the loss of uniqueness near the limit points. A 'collision' parameter is introduced to determine the motions near the limit points which causes a discontinuous jump of velocity and exhibits the standard dynamics as an inverted pendulum, even though the mechanic model is rather different from a pendulum. We also distinguish the coexistence of periodic and chaotic motions and also a smooth period 1 located in a small region under the presence of damping and external force using amplitude–frequency analysis and numerical simulations. This research enriches the complicated dynamical behaviors of geometrical nonlinear oscillator and provide a novel structure which is of great potential in vibration isolation engineering. • An archetypal double-winged nonlinear oscillator is proposed. • Discontinuous force and discontinuous motions are formed. • Buckling phenomenon and multiple equilibrium states are found. • Discontinuous singulars are discovered on inverted pendulum system. [ABSTRACT FROM AUTHOR]

Syntactic foams made of hollow particles embedded in a matrix material are widely used as buoyancy materials for underwater marine structures, where both low density and high mechanical properties are desired. In most engineering materials, however, the reduction in density is often accompanied with the decrease in stiffness and strength. Such a dilemma forces us to strike a balance between them for different application scenarios, which necessitates a profound understanding of the structure-property correlations in syntactic foams. In this paper, we investigated the mechanical properties of syntactic foams subjected to triaxial compressive loading. Taking particle crushing as the primary failure mode, we develop an analytical analysis on the compressive strength of syntactic foams. For syntactic foams with high strength under hydrostatic pressure, they may fail readily in the presence of deviatoric stress. In addition, we identify the critical conditions associated with other failure modes, including particle-matrix interface delamination and particle buckling. This study not only sheds light on the structure-property relationship in syntactic foams for deepsea usage, but also provides guideline for the design and optimization of syntactic foams, which would be of great value for the development of high-performance underwater structures. • Combining engineering practice and application, the boundaries of mechanical properties for syntactic foams were explored. • Ashby diagrams showing the mechanical property vs. density relationships for syntactic foams were provided. • The critical conditions associated with interface delamination and particle buckling in syntactic foams were identified. [ABSTRACT FROM AUTHOR]

The mechanics of laminates made up of elastic alternating stiff/soft layers is dominated by bending and membrane actions in the stiff layers, while transverse shear deformations concentrate in the soft interlayers producing significant zigzag warping effects. Additionally, curved geometry and large deformations can induce an interlayer thickness strain affecting the overall response of the laminate. This work presents a rotation-free Total Lagrangian large deformation curved shell model to accurately capture such a structural response. Each stiff layer is modeled as a Kirchhoff–Love shell. Without additional DOFs, each soft interlayer is modeled as a solid-shell by expressing, in finite kinematics, the displacement of top and bottom interfaces as a function of the mid-surface displacement of the upper and lower stiff layers it couples. The model is characterized by a sparse stiffness matrix compared to high-order theories and requires a small number of DOFs (3 per stiff layer) to reproduce the 3D solution. A NURBS discretization meets the high continuity of the weak form with a patch-wise reduced quadrature to avoid locking and enhance efficiency. All thickness integrals are pre-computed just once. • A nonlinear shell model is developed for stiff/soft laminates. • It is reliable for curved laminates and large deformations. • The stiff layers are isogeometric Kirchhoff–Love shells. • The soft layers are solid-shells without independent DOFs. • Warping and thickness change are captured with minimal DOFs. [ABSTRACT FROM AUTHOR]

Wire arc additive manufacturing (WAAM) is a method of metal 3D printing which, when strategically combined with traditional methods of manufacture, has the potential to make a significant impact on the construction sector. To illustrate this potential, an experimental investigation into the flexural buckling response of 15 hot-rolled I-section columns, strengthened by WAAM, has been undertaken and is presented herein. The WAAM material was added at the flange tips and distributed non-uniformly along the member length. Complementary tensile coupon tests on the I-section and WAAM steel material were also carried out. 3D laser scanning was employed to determine the geometry and global geometric imperfections of all specimens, while digital image correlation measurements were taken to provide a detailed insight into the surface deformation characteristics of the specimens during testing. The WAAM stiffeners provided three mechanisms of strengthening: (1) increased cross-sectional area and second moment of area, (2) enhanced local buckling capacity and (3) a more favourable residual stress pattern. Disproportionately high increases in axial capacity of between 17% and 54% for relatively modest increases of mass between 2% and 26% (of the weight of the strengthened I-section column) were achieved, demonstrating, for the first time, the substantial benefits in terms of enhanced structural efficiency and material savings, that can be realised by the combination of WAAM with traditional manufacturing methods. In the best case, the efficiency of the WAAM material (in terms of increase in load-bearing capacity per unit mass) was almost eight times that of the bare steel section. The described hybrid manufacturing concept can be employed to improve the performance and reduce the environmental impact of structures and could be a game changer in both new construction and the rehabilitation of existing infrastructure. [Display omitted] • Concept of hybrid construction featuring additive manufacturing was introduced. • WAAM stiffeners were added to I-section specimens to improve their flexural buckling strengths. • Geometric characteristics of test specimens were examined via 3D laser scanning. • Minor axis buckling tests on 15 strengthened and two bare columns were performed. • All strengthened columns were shown to exhibit enhanced structural efficiency. [ABSTRACT FROM AUTHOR]

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

• HSDT is used to simulate functionally graded porous beams with uniform and non-uniform porosity distributions. • The system's dependability was evaluated using k-out-of-n system reliability analysis. • Changing gradient index and boundary conditions significantly impact the buckling characteristics of FGPB. • Clamped -clamped beams provide improved stability and support. • Governing equations are solved using KT conditions for different boundary conditions. Functionally graded materials are a class of multifunctional materials that exhibit spatial variation in composition and microstructure. This deliberate variation is designed to effectively manage and manipulate changes in thermal, structural, or functional qualities within the material. The current study explores the system reliability of functionally graded porous beams (FGPB) subjected to buckling, focusing on the interplay of gradient index (0, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10), aspect ratio (5, 10, 15, 20, 25, 30 and 35), porosity index (0, 0.1 and 0.2) and boundary conditions (simply supported, clamped–clamped and clamped-free), with a particular emphasis on the k-out-of-n system reliability assessment, employing three distinct methods such as Evolutionary, GRG Non-linear, and Lagrangian. The results show the system's sensitivity to changes in distribution parameters, with the Lagrangian method being the most robust and stable. The 10-out-of-12 system reliability analysis demonstrates that aspect ratio and even porosity distribution are reliable, while uneven porosity is not. This study enhances structural reliability analysis in FGPBs, enhancing system reliability considerations and paving the way for further advancements in structural reliability analysis. [ABSTRACT FROM AUTHOR]

Cylindrical shells with corrugation are widely used in deep sea, underground pressure structures, and other fields. It is mainly subjected to uniform and concentrated external pressure. The current research mainly includes circumferentially corrugated shells and longitudinally corrugated shells. These two kinds of corrugations improve the strength of the cylindrical shell but also have some problems such as stress concentration, buckling extension, and so on. To solve these problems, a shell with composite corrugation is proposed and it has the structural characteristics of both circumferential and longitudinal corrugations. In this paper, the numerical analysis method is used to explore the stability of the composite corrugated shell under uniform and concentrated pressures. It is analyzed by Donnell's large deflection equation. In addition, it can reduce the area of damage caused by buckling. The excellent mechanical properties of the composite corrugated shell are proven. The influence of the number of corrugations and "diameter to thickness ratio" on the buckling performance is studied by using the control variate method. It is compared with a cylindrical shell without corrugation with equal volume and weight. The concentrated pressure tests of composite corrugated shells and shells without corrugation are finished. The results show that the curve of "radial compression-reaction load" obtained by the experiment is consistent with the simulation. The ultimate load of the composite corrugated shell is 34.96% higher than the shell without corrugation. The composite corrugation can effectively enhance the compressive strength and stiffness of the cylindrical shell. Composite corrugation can make more material of the shell to be involved in resisting external deformation. This method of increasing material utilization is effective. • The advantages of the composite corrugated shell are verified from mechanical theory, finite element analysis and test. • The influence of local curvature on the buckling performance of cylindrical shell is verified. • Donnell's large deflection equation has been applied and innovated in this paper. [ABSTRACT FROM AUTHOR]

In the companion report (Telpande et al., n.d.), we discussed the impact of a weak external magnetic field (up to 0.4 T) on the electric current-induced fracture of pre-notched thin metallic conductors, revealing a linear decrease in critical current density, j c , necessary for crack propagation. This study extends the investigation to explore the effects of stronger external magnetic fields (0.6–1 T) on the fracture of pre-notched, current-carrying metallic foils. The experimental analysis reveals a substantial, albeit linear, drop (up to 40 %) in j c under stronger magnetic fields. Interestingly, calculations of the dynamic stress intensity factor, K IE,t , which assesses the interplay between applied current density and external magnetic field, indicate crack growth under a strong magnetic field even when K IE,t is below the plane stress critical stress intensity factor, K IC. A remarkable phenomenon emerges: the application of electric current pulses combined with strong external magnetic fields induces observable surface undulations near the notch tip. A comprehensive 3D finite element model, integrating linear and nonlinear buckling analyses under multiphysics stimuli, attributes these undulations to localized buckling near the notch tip. This buckling-induced stress redistribution near the crack tip contributes to an overall reduction in fracture toughness due to mode mixity, leading to the fracture of the Al foil below K IC. This investigation, along with the companion report (Telpande et al., n.d.), significantly advances our understanding of the effects of magnetic fields on the fracture of current-carrying conductors. [ABSTRACT FROM AUTHOR]

• A novel multiscale analysis is developed to assess the buckling behavior of MWCNT-reinforced laminated composites. • Integration of microstructural factors like MWCNT clustering, alignment, and curvature in evaluating composite material performance. • Comprehensive assessment of the influence of moisture and temperature on the buckling performance of MWCNT composites. • Results successfully compared and validated with existing experimental and theoretical data. • Offers significant insights for the design and optimization of MWCNT-reinforced composites. This study introduces a detailed method for analyzing the buckling behavior of laminated composite structures strengthened with multi-walled carbon nanotubes (MWCNTs). We propose a multi-scale analysis that combines analytical and computational techniques to assess the mechanical performance of MWCNT-reinforced composites under combined moisture, temperature, and mechanical stress conditions. The Halpin-Tsai equations are used to calculate the overall stiffness properties of the nano-enhanced matrix, considering factors like MWCNT clustering, alignment, and curvature. Additionally, we incorporate the nanoscopic, size-dependent features of MWCNTs into our model. The Chamis micromechanical formulas are applied to determine the individual elastic properties of the nanocomposite layers, considering the impacts of temperature and moisture. We then explore how variables such as MWCNT content and size, along with temperature and moisture levels, influence the critical buckling load of MWCNT-based laminated composite beams and plates using our multi-scale model. Our results are successfully compared with existing experimental and theoretical data to validate our approach. The developed method offers significant insights for the design and optimization of MWCNT-reinforced composites, potentially benefiting various engineering fields, including aerospace and automotive industries. [ABSTRACT FROM AUTHOR]

The buckling behaviour of combined shells fabricated from aluminium alloy and carbon fiber–reinforced polymer (CFRP) composites subjected to external hydrostatic pressure were investigated. Three sets of combined cylindrical shells with different combinations and one set of bare aluminium alloy cylindrical shells were designed and fabricated. The wall thickness of each cylindrical shell was measured. All the cylindrical shells were tested under external hydrostatic pressure, and the buckling load and final collapsed mode were recorded. Numerical models with real imperfections were established, linear and nonlinear analyses were performed to evaluate the buckling loads of cylindrical shells. The experimental and numerical results agreed favourably. On this basis, the effects of the thickness-diameter ratio, combination method and geometric imperfection on the buckling of combined cylinders were studied. This research can provide a reference for the design of combined shells made from CFRP and metal shell. • The geometry and buckling of 8 combined cylinders were tested. • The effects of the thickness-diameter ratio, combination method and geometric imperfection on the buckling of combined cylinders were discussed. • The failure mode of carbon fiber–reinforced polymer composite combined shell was discussed. • The numerical results are in good agreement with experimental results (within 8 %). [ABSTRACT FROM AUTHOR]

This study aims to numerically investigate the buckling behaviour of externally pressurised dome caps. Following the recommendations of the European Standard EN 1993-1-6, there was good agreement between the Finite Element (FE) model and the experimental results, with an average difference of less than 7 %. Several imperfection approaches, such as (i) single load indentation (SLI) and (ii) axisymmetric outward bulge (AOB), and (iii) eigenmode-affine (EM) were used to analyse the dome cap. The EM proved to be the worst imperfection for the externally pressurised dome cap, yet the SLI is an attractive technique for simulating realistic imperfections. The imperfection tolerance was designed according to EN 1993-1-6, and the SLI was used for the realistic-case imperfection. From parametric study, a plot of the upper and lower bound curves serves as a design recommendation, similar to the NASA SP-8032 guideline. Through a regression analysis, a first-cut estimation equation of the imperfect dome cap buckling load with reliability of R2 = 0.97. A case study of shell buckling design on pressurization damage to an oil storage tank's spherical shell partition and its stress assessment are evaluated. This study provides a practical solution for the evaluation of buckling of steel domes under external pressure. • Imperfection significantly affects the buckling strength of spherical shells. • A plot of the upper and lower bound curves serves as a design recommendation. • A first-cut estimation equation of the imperfect dome cap buckling load with reliability of R2 = 0.97 is derived. [ABSTRACT FROM AUTHOR]

In recent years, concrete-encased concrete-filled steel tube (CECFST) columns have gained popularity in structural engineering. Research studies have shown that this novel type of composite columns exhibits superior strength, ductility, stiffness, and resistance to fire and corrosion property when compared to alternative types of steel-concrete composite columns. Considering the increasing use of slender columns in practice, this study investigated structural behaviour of CECFST slender beam–columns subjected to combined compression and bending. In this paper, six pin-ended CECFST slender specimens with different section configurations, load eccentricities and slenderness ratios were tested under eccentric load. Key test results consisted of buckling mode analysis, load–deformation history, moment–curvature relationship and strain response at various locations. Results generally showed that P-δ effect deteriorated structural behaviour of CECFST slender beam–columns and this unfavourable effect should be addressed properly in the appropriate design code for composite columns. In this regard, design approaches in European code and American specification were evaluated in aspects of N–M interaction curve, moment magnification factor and effective flexural stiffness (EI) eff. It was identified that both codes tend to overestimate (EI) eff , resulting in an unconservative second-order analysis. Moreover, a parametric analysis was conducted which showed (EI) eff correlates negatively to eccentricity and slenderness, but positively to steel tube size and concrete strength. However, these relationships were not reflected in the predicted (EI) eff according to European code and American specification. • DIC was applied to analyse buckling failure modes of the tested CECFST specimens. • The moment–curvature relation of CECFST beam–columns was investigated, confirming plastic hinge formation at the midpoint. • AISC 360-16 unconservatively predicts the moment magnification factor for slender CECFST columns under eccentric load. • Parametric studies were performed through FEM to study the influence of multiple factors on effective flexural stiffness. [ABSTRACT FROM AUTHOR]

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

• A sequential permutation search (SPS) optimization algorithm is presented for stacking sequence design of composite plates. • SPS is a mechanics-driven algorithm utilizing convexity of lamination parameter and stiffness sensitivity. • Buckling load of composite rectangular plates with various boundaries and load conditions are optimized by SPS algorithm. • The sign optimization algorithm (SOA) is coupled in the SPS to regulate the bending-twisting coupling effects. • Comparisons are performed among SPS, LOA, and GA, demonstrating higher efficiency and robustness of SPS. Buckling problem of composite plates is of importance since it is commonly encountered in thin-walled structural components in engineering. Buckling resistance design of composite plates involves the design of laminate stacking sequence exhibiting high dimensional discrete variables owing to the combination and permutation of ply orientations of layers. In this work, a sequential permutation search (SPS) optimization algorithm is presented for the stacking sequence design of composite rectangular plates accounting for the inherent physical-mechanical behavior of composite laminates. Owing to that the governing equation for buckling of composite rectangular plates is a linear homogeneous equation on bending stiffness parameters, the convexity of flexural lamination parameters and sensitivity of bending stiffness are utilized to construct sensitive detection techniques and linear search procedures. Moreover, to increase the robustness of SPS, a sign optimization algorithm (SOA) is coupled in SPS to regulate bending-twisting coupling effects. The SPS algorithm is applied to the buckling resistance design of composite rectangular plates exhibiting various boundaries under axial compression, where the Rayleigh-Ritz method is developed to perform the buckling analysis. Optimal results of SPS are compared against layerwise optimization approach (LOA) and genetic algorithm (GA), illustrating its reliability and efficiency. [ABSTRACT FROM AUTHOR]

We show that new kinematic equivalents with improved performance of standard flexure elements can be systematically synthesized by combination of cross-pivot flexures. Cross-pivot flexures provide a unique feature of kinematic stability under both high loading and large displacement conditions which can be exploited to synthesize a range of kinematic equivalents to standard flexure elements which retain much greater stiffness, load capacity and range capacity than the traditional elements. Cross-pivot synthetic elements provide a means to expand the performance of a large range of flexure-based structures including motion stages, manufacturing equipment and optical systems. This could result in better data collection, smaller systems, and less distortion in operation. • We show how to combinations of cross-pivot flexures can be used to synthesize kinematic equivalents to standard flexure elements. • Cross-pivot flexures provide a unique feature of kinematic stability under both high loading and large displacement conditions. • We show that cross-pivot kinematic equivalents can boost constrained direction stiffness and load capacity for a given range. • We demonstrate this enhanced performance by comparing a conventional wire flexure with its cross-pivot kinematic equivalent. [ABSTRACT FROM AUTHOR]

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

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

Hydrogen containers type IV should stand for severe operational conditions, such as temperature variations from −40 °C to 85 °C, and depressurisation from high-pressure above 95 MPa to near atmospheric pressure. There are experimental studies showing that container's liner, usually a thermoplastic material, can suffer blistering and buckling during depressurisation process. It has also been proved that elastomers under high-pressure conditions, which are submitted to a rapid depressurisation, can suffer the formation of cavities because of the dissolved gas. The formation of microscopic defects in thermoplastic materials because of rapid depressurisation is less common in scientific literature. In this paper, we evaluate by numerical means the maximum depressurisation rate a polymer sample can stand before cavitation occurs. By studying the influence of geometrical and pressure conditions, so as material's properties, we obtain algebraic equations that define maximal depressurisation rate. Results of present work serve to estimate performance of liner materials, with the scope of safe and fast container discharge. • Blistering or buckling failure is a current problem in type IV hydrogen containers. • Cavitation in polymers is considered for this type of mechanical failure. • Cavitation risk is estimated by non-dimensional parameters. • Maximum depressurisation rate is defined for liner materials and various conditions. [ABSTRACT FROM AUTHOR]

• The dynamic model of an eccentric rotating CFRP cylindrical shell using FSDT is established for the first time. • The buckling and free vibration analyses of the eccentric rotating CFRP cylindrical shell are presented. • Taking into account the influences of coriolis and centrifugal forces caused by eccentric rotation. • The critical bucking mode of the shell alters from (1, 1) to (2, 1) with the increase of rotating speed. In this paper, the dynamic model of an eccentric rotating carbon fiber reinforced polymer (CFRP) laminated cylindrical shell based on the first-order shear deformation theory is established for the first time. The buckling and free vibration analyses of the eccentric rotating CFRP laminated cylindrical shell under the axial excitation are presented. Taking into account the influences of Coriolis force and centrifugal force caused by eccentric rotation. By utilizing the Hamilton principle, the first-order shear deformation theory and the von-Karman type nonlinear geometric relationship, a system of the partial differential governing equations for the eccentric rotating CFRP laminated cylindrical shell is derived. Then, the ordinary differential equations of the eccentric rotating CFRP laminated cylindrical shell are obtained according to Galerkin method. The present method are validated by carrying out some comparisons with the existing results in the published literatures. The natural frequencies and critical buckling loads of the system are solved numerically. In this study, the influences of the eccentric distance, ratio of radius to length, rotating speed as well as the number of layers of the eccentric rotating CFRP laminated cylindrical shell on the buckling and free vibration behaviors are discussed. [ABSTRACT FROM AUTHOR]

Pseudoelastic NiTi structural components have been shown to exhibit tension/compression asymmetry. Under tension, phase transformation induces localized strains of nearly 7% that spread under nearly constant stress, while under compression the transformation leads to hardening at significantly higher stress, the strain is smaller and grows homogeneously. Bending of tubes ovalizes their cross-section, a nonlinearity that reduces the bending rigidity and precipitates instabilities that can lead to collapse. This paper uses experiment and analysis to examine the interaction of these geometric nonlinearities with the complex material behavior of pseudoelastic NiTi tubes of moderate diameter-to-thickness ratios under bending. An experiment on a tube with a diameter-to-thickness ratio of 18.7 shows that transformation causes the nucleation of several dispersed high strain banded patterns of martensite on the tensioned side. The zone where the bands coalesce into intersecting diamonds undergoes excessive local ovalization causing buckling and collapse at a relatively low overall tube curvature. The bending experiment is simulated with a finite element model coupled with a custom constitutive model of pseudoelastic NiTi that allows for plastic deformation of the martensitic phase. The analysis reproduces the moment-end rotation response, and the nucleation and evolution of the high strain diamond shaped patterns. Zones that develop such patterns exhibit accelerated growth of ovalization that degrades the local bending rigidity. In the presence of small geometric imperfections this degradation evolves into a buckle in the form of diffuse local ovalization that precipitates collapse that can negate the recoverable property of NiTi. Parametric studies show that as the tube D/t increases, the interaction between the material and geometric nonlinearities becomes stronger making buckling more imperfection sensitive. [ABSTRACT FROM AUTHOR]

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

• A simulation of multiple transverse ply cracking in laminates is presented. • Many phase-field variables are used, each one describes the crack of the layer. • Some interesting phenomenons when the cracks appear at different layers of the structure are shown out. The phase-field theory is a well-known mathematical model for solving interface problems, including crack problems in fracture mechanics. In this study, the formula is derived by variational approaches based on the Reissner-Mindlin plate kinematics and the multi-phase-field theory for simulation of the buckling phenomenon in cracked laminates. Phase-field parameters are defined independently in different plies of laminate to capture the crack behavior of each ply. Simulation is carried out to numerically investigate the stiffness reduction and buckling behavior of transverse cracked laminated composite plates. This paper focuses on the consideration of laminated composite plates, which have a crack in each layer. Therefore, this work is more complicated than the case of the plate has one crack throughout the plate thickness. The significant advancement of the phase-field approach for laminated composite plates with complex crack geometries is demonstrated. [ABSTRACT FROM AUTHOR]

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

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

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

Restraints along slender structures, such as pipes conveying fluid and beams, play important roles in enhancing their bending stiffness. The current work investigates the influence of the midpoint restraint on the buckled axial force and dynamic characteristics for the first time. A continuous model is introduced by treating the midpoint restraint force as a concentrated force using Dirac function. The influence of the midpoint restraint is discussed based on modal expansion, and a partitioned model is proposed for validation. The conclusion is that the continuous model has good accuracy. Based on this model, it finds out two stable buckled states changing with the midpoint stiffness. The first stable buckled state occurs under weak midpoint restraint and has a cambered shape. The zero- and double frequency components occur in symmetric modal shapes and the response is softened along the whole beam. However, in the second stable buckled state, it turns into a whole sine function shape. The zero- and double frequency components just occur in the second modal shape, and the soften phenomenon doesn't occur at the midpoint. With increasing excitation amplitude, a bubble appears on the primary resonance peak while another resonance peak emerges nearby it. This work explains the influence of midpoint stiffness on nonlinear resonance and enhances the study of the nonlinear behavior of buckled slender structures. • The model of a beam with the midpoint flexibly restraint is established. • It finds out two stable buckled states changing with the midpoint stiffness. • Influence of the midpoint flexible restraint on dynamics of double-span beams is studied. [ABSTRACT FROM AUTHOR]

Semi-crystalline polymers is an important group of materials that is used in a vast array of products. In this study, the rate-dependent properties of high-density polyethylene (HDPE) are investigated, both experimentally and theoretically. Experimental compression testing of a three-dimensional HDPE structure is performed and analysed numerically by use of the finite element method. In addition, an Eulerian constitutive material model for isotropic, semi-crystalline polymers is proposed. The model is able to account for such essential phenomena as strain-rate dependence, work hardening, pressure-dependence of inelastic deformations, and damage. The proposed material model was implemented in Abaqus as a VUMAT, which is an explicit implementation. The material model was calibrated by use of uniaxial tensile tests performed on HDPE dog-bone shaped samples, and the model was further explored by applying the VUMAT implementation to the compression tests of the HDPE structure. The simulation model was able to reproduce the experimental results well, both the uniaxial tests and the compression tests. In particular, the friction present in the compression tests seems to play an important role in determining the buckling mode of the structure. • Experiments on high-density polyethylene: compression testing of a 3D structure. • Modelling of rate-dependent inelasticity and damage of semi-crystalline polymers at finite strains using an Eulerian formulation. • Analyses of rate-dependent buckling of the 3D structure. [ABSTRACT FROM AUTHOR]

The possible emergence of a localized buckled configuration for a simple supported linear elastic beam on an elastic foundation subject to axial compression is analyzed numerically. Beams on a softening foundation and, for comparison purposes, beams on a linear elastic foundation are considered. The critical bifurcation mode involves periodic lateral displacements for both foundations. Calculations are carried out for imperfections that can have a component in the shape of the critical periodic bifurcation mode as well as a component with a localized shape. For beams on a softening foundation, the buckled configuration obtained in the calculations depends on the magnitudes of the periodic and localized imperfection components: (i) for a wide range of imperfections, a rather abrupt growth of localized lateral displacements occurs after a load maximum, even if the imperfection magnitudes are such that the critical periodic mode is suppressed; or (ii) if the magnitude of the periodic imperfection component is sufficiently large, the buckled configuration with a localized imperfection involves lateral displacements that are oscillatory but not periodic. For beams on a linear elastic foundation, a calculation with a sufficiently large magnitude localized imperfection gives a localized buckled configuration under increasing load. For beams on both types of foundation, the main features of the lateral displacements in the localized buckled configuration are similar, for example, involving both positive and negative lateral displacements even if the localized imperfection only involves non-negative deflections. • A beam on a softening foundation with periodic and localized imperfections. • A localized buckled shape can occur by a bifurcation after a load maximum. • A localized buckled shape can occur without any periodic imperfection. • A large periodic imperfection acts to suppress emergence of the localized shape. • A localized buckled shape can develop with no softening under increasing load. [ABSTRACT FROM AUTHOR]

To date, many studies have been conducted on the experimental behaviors of circular and square hollow section braces. In those studies, the effect of material properties, cross-sectional shape and loading history on the performance of braces were investigated independently of each other. In this study, the effects of the combined actions of these variables on the performance of steel braces were examined. For this purpose, approximately 1/3 scaled 12 specimens (6 circular and 6 square), which were cold formed from carbon/stainless steel sheets, were experimentally and numerically investigated under 3 different cyclic load effects representing far field and near fault loadings. The buckling strength, energy dissipation capacity and displacement ductility of the specimens were evaluated. In addition, parametric studies, using 198 FE analyses verified with current study, were conducted. Experimental results indicate that the buckling strength limits provided in AISC 360–22 and EN 1993-1-1 for carbon steel braces are significantly influenced by the cross-section, loading protocol and material properties. On the other hand, it has been determined that the buckling strength limits given in AISC 370–21 and EN 1993-1-4 for stainless steel braces are safe for far field loadings, but insufficient for near fault loadings along the full slenderness range. It has been seen that the most disadvantageous results for the buckling strength, energy dissipation capacity and displacement ductility of the braces can only be obtained by applying different loading protocols. Moreover, It has been determined that the effect of material properties on the performance of braces varies considerably depending on the cross-section geometry. • Stainless steel braces tested under near-fault loadings for the first time. • Combined effect of material properties, cross section and loading history on the performance of braces has been investigated. • The experimental and numerical results are discussed. • Important differences with the previous studies were pointed out and discussed. • Parametric studies were carried out across a range of global and local slenderness ratios. [ABSTRACT FROM AUTHOR]

This paper delivers a comprehensive analysis of the thermomechanical behavior of steel–concrete (SC) composite elements under elevated temperatures, up to 200 °C, as these can be encountered in accidental scenarios within nuclear power plant operations. The focus lies on the thermal buckling of external thin steel plates. We undertake an integrated approach, combining an experimental campaign and numerical simulations, to investigate thermal buckling phenomena. Using these findings, along with principles from thermoelasticity and thin plate theory, we establish an analytical model to guide preliminary SC element design. The efficacy of this model is ascertained through rigorous comparisons with experimental and numerical results. The paper concludes by demonstrating the model's practical utility for thermal buckling verification through a relevant case study. • Local thermal buckling in SC elements was studied via experiments and simulations. • Database expansion and key buckling factor identification conducted numerically. • Analytical formulas for SC design were derived from thermoelasticity and plate theory. • Formulas were validated against numerical and experimental data for reliability. • Significance of diagonal connector spacing in SC walls was demonstrated. [ABSTRACT FROM AUTHOR]

Grid-stiffened structures have excellent performance, such as high specific stiffness and strength, and are widely used as critical load-bearing structures in aerospace equipment, including launch vehicles and spacecraft. It is now a well-established fact that curvilinearly stiffened panels with curved stiffener paths and varying stiffness distributions significantly improve load-bearing efficiency. However, existing methods are usually designed based on two clusters of approximately orthogonal stiffeners, which may limit the design flexibility and load-carrying potential of such structures. In the proposed design method, various complex variations of curved stiffener layouts can be characterized with a simple set of variables by establishing a database of stiffener unit cells and feature dimension reduction, as well as using coordinate transformation and monotonicity preserving interpolation methods for geometric dimension reduction, respectively, which allows simultaneous selection of basic stiffener unit cells and adjustment of stiffener paths. Based on the structure characterization with high design flexibility, the hyperparameter dimension reduction of the Kriging model is introduced, thereby forming an optimization framework through multi-level dimension reduction, while ensuring the efficiency of the optimization process. Moreover, an accurate geometric modeling based on NURBS is proposed to meet the needs of designing stiffened structures on various types of complex surfaces. In two typical aerospace cases, the developed structural concept and design method can improve structural performance by over 80 % compared to initial design schemes with straight stiffeners and constant stiffness. The results demonstrate that both the developed structural concept and design methodology effectively enhance the upper performance design limit of stiffened structures. These findings are practically significant for the application of advanced lightweight thin-walled structures in aerospace equipment. [ABSTRACT FROM AUTHOR]

This study presents the Equivalent Anisotropy Orientation Tensor (EAOT) algorithm as a novel approach for the integrated design of thin-walled structures composed of composite materials. The EAOT algorithm is designed to enhance the buckling load of structures by efficiently optimizing the distribution of strain energy density. In addition, the algorithm considers the fiber orientation and stiffener structure as orthogonal isotropic material, providing an innovative design methodology that surpasses conventional approaches. The EAOT algorithm incorporates a weighted function to account for the effects of different buckling modes, which solves the problem of mode overlap and exchange that affects the optimization effect. Utilizing the optimization results from the EAOT algorithm enables the realization of effective material-structure integrated design. Two case studies demonstrate the superior performance of designs based on this algorithm compared to conventional methods, resulting in a substantial increase in the critical buckling load by 15.3 % to 34.7 %. [ABSTRACT FROM AUTHOR]

The behavior of prestressed carbon fiber reinforced polymer (CFRP)-reinforced steel columns is intricately linked to CFRP stiffness and stress; when the system is exposed to fire, the performance is more complex because of the degradation of CFRP mechanical properties. Therefore, transient fire tests are first conducted on four prestressed CFRP-reinforced steel columns under axial preloading using the ISO 834 standard curve to investigate their high-temperature performance. The entire failure process is revealed, three significant time points (i.e., CFRP failure time, buckling time, and critical time) influencing system behavior are identified, and the effect of preload and prestress level on the time points is elucidated. It is observed that CFRP plates fail with a final hair-like rupture; steel columns undergo symmetric and asymmetric failure modes, related to the initial imperfection. Subsequently, the finite element models (FEMs) are established and validated by test results, followed by a parametric analysis. It indicates that the high-temperature behavior of the prestressed CFRP-reinforced steel columns is dependent on the preload, CFRP prestress level, and initial imperfection; the buckling and critical time of such columns decrease with increasing preload and initial imperfection, while an increase in prestress leads to an increase in the buckling and critical time. Moreover, even CFRP plates without protection, and prestressed CFRP plates can improve the high-temperature performance of steel columns when the preload is not very large or the initial imperfection is not very small. These findings serve as a valuable reference for applying such columns when considering fire issues. • Transient fire tests are conducted on prestressed CFRP-reinforced steel columns using ISO834 standard curve. • Three significant time points influencing the system behavior are identified. • Effects of initial imperfection and preload on high-temperature behavior and reinforcing efficiency are discussed. [ABSTRACT FROM AUTHOR]

Metamaterial structures that exhibit negative stiffness (MSNS) behavior have shown the potential to be used as energy dissipation systems in different applications. Negative stiffness honeycomb structures consist of multiple pre-buckled beams that snapping through from one pre-buckled mode to another buckled mode, when subjected to transverse loads, displaying negative stiffness, and dissipating a significant portion of the input energy. This paper presents finite element models (FEMs) developed to investigate the performance of negative stiffness pre-buckled beams and honeycombs. The FEMs were validated using experimental results of single pre-buckled beams and honeycomb structures. The experimental testing of the pre-buckled beams was presented in the current study while the results of the honeycomb were available in the literature. The FEMs have the ability to capture the transition of the elements from one mode of buckling to another mode as well as the force thresholds, energy dissipation values, and residual displacements. The FEMs were extended to investigate the effect of different parameters such as boundary condition, apex height-to-beam thickness ratio, and constraining the second mode of buckling on the behavior of negative stiffness honeycombs. • Metamaterial structures that exhibit negative stiffness (MSNS) have potential for use in energy dissipation systems. • Finite element models (FEMs) are presented to study the performance of MSNS beams and honeycombs. • FEMs are validated using experimental results from single pre-buckled beams and honeycomb structures. • FEMs can accurately predict transitions between different modes of buckling, force thresholds, and energy dissipation. [ABSTRACT FROM AUTHOR]

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

• The paper presents a novel approach for calculating the elastic critical moment of corrugated web girders. • The results obtained with the new proposal significantly enhance the outcomes of previous methods. • The new proposal is based on closed-form formulas to determine equivalent section properties. Using corrugated web girders offers several advantages, including increased resistance to lateral-torsional buckling. Researchers have proposed various methods for determining the critical moment value as a function of the cross-sectional geometry. Previous studies have suggested that the enhanced critical moment is attributable to a larger warping constant. In this paper, we present the results of a systematic numerical study using finite element analysis on girders with various corrugated web shapes. Bending along the weak axis demonstrates that corrugated web girders possess a higher moment of inertia. Furthermore, our torsion linear analysis indicates that the increase in the critical moment is primarily due to a larger torsional constant. We compare the elastic critical moment values obtained using finite element linear buckling analysis to those derived from theoretical expressions that introduce equivalent section properties. Our results illustrate that the equivalent section properties method provides values that closely resemble those obtained using finite elements. Finally, we provide closed-form expressions that can be used to estimate equivalent section properties for any girder with a corrugated web. Our findings suggest that employing these expressions to calculate the critical moment yields results that are satisfactory when compared to those obtained through finite element linear buckling analysis. [ABSTRACT FROM AUTHOR]

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

The study aimed to analyse the stability and load-carrying capacity of compressed thin-walled composite columns subjected to axial compression. The subject of the survey was composite columns with closed square cross-sections made of carbon-epoxy composite. Different lay-ups of the composite material characterised the test specimens - several cases of lay-ups were considered. The application of the subject of the research is closely related to the use of these elements as load-carrying elements of aerospace and building structures. The requirements for such structures are closely related to the provision of a large reserve of load-carrying capacity after buckling. Experimental testing was carried out using a universal testing machine and other testing techniques, where acoustic emission, an optical deformation measurement system, and a digital microscope, among others, were used. Numerical simulations using the finite element method were carried out parallel to the experimental studies. In the case of FEA simulations, original numerical models were developed considering known failure models of the composite material. For both empirical studies and FEM simulations, an in-depth analysis of the buckling and post-buckling states was carried out, considering the failure phase of the composite material. The novelty of the present work was the development of original FEM models, allowing faithful reproduction of experimental studies conducted on physical models, as well as the use of research methods to determine the load-carrying capacity of composite structures. [ABSTRACT FROM AUTHOR]

This paper presents a simple methodology for determining the optimal design of an elastic funicular arch under point loads and selfweight for maximum in-plane buckling capacity. This class of optimization problem has hitherto not been investigated. The cross-section of the arch is assumed to be geometrically similar and constant through its entire length. The arch is assumed to be inextensible. The supporting points of the arch may be either pinned or fixed. The methodology for determining the optimal arch shape involves first finding the funicular shape of the arch under point loads and selfweight. Next, the arch is modelled by the Hencky bar chain model (HBM) for the buckling analysis. The HBM is adopted because it eliminates the requirement for formulating the governing equation for buckling and it is a straightforward model to comprehend and implement in a computer code. Each funicular arch shape is specified by a horizontal force value, and it has to be optimally selected to maximise the buckling capacity of the arch. As it is a single parameter optimization problem, the Golden Section search was used to determine the optimal horizontal force, and hence the optimal funicular arch shape. The methodology is illustrated by solving two example problems: (1) an arch under a point load and selfweight and (2) a symmetric arch under two equal point loads and selfweight. By solving the self-buckling problem of a catenary arch, the maximum spanning capacity of the catenary arch can be obtained as shown herein. • Paper outlines a method for designing elastic funicular arches to optimize buckling capacity. • Arch supportings can be pinned or fixed, offering design flexibility. • Method finds funicular arch shape under seflweight and point loads for analysis. • Paper uses Hencky bar chain model for buckling analysis, simplifying governing equations. • Method demonstrates with two examples: an arch under point load and selfweight, and a symmetric arch under two equal point loads and selfweight. [ABSTRACT FROM AUTHOR]

Due to their outstanding physical and mechanical properties, double-network (DN) hydrogels have gained a most attention among various synthetic tough hydrogels. The Mullins effect and buckling instability are two frequent phenomena that may occur simultaneously in slender DN hydrogel structures as high load-bearing candidates. The swelling/deswelling degree of the DN hydrogel affects the coupling phenomena. It is essential to understanding the interplay between these behaviors. In this work, a physically based damage constitutive model for a DN polymer under water-diffusion equilibrium and cyclic loadings is developed. This theory of coupled swelling and load-induced deformations show good capability in capturing the Mullins effect of swollen DN hydrogels and the corresponding swelling ratio. The model parameters are determined by fitting experimental data of a freely swollen DN hydrogel under cyclic compression. Based on the constitutive model and determined parameters, the buckling instability of DN hydrogel beams is studied via the analytical formula of incremental modulus. The stability diagrams of the DN hydrogel beams under virgin loading and reloading are presented. The influences of stress softening, strain stiffening and chemical potential on buckling conditions for compressive stress and slenderness ratio are thoroughly analyzed. It demonstrates that the stress softening is dramatically against the stability of the beam, but the strain-stiffening effect would conversely help widen the stable range. Besides, it is found that a DN gel beam immersed in a sufficient low chemical potential environment has better buckling stability. These theoretical results are valuable in the preparation and structural design of DN hydrogels for repeated use purpose. • A constitutive model for double-network (DN) polymers under swelling and cyclic loads. • Global instability diagrams of DN hydrogel beams with various damage degrees. • Analysis of impacts of the Mullins effect and water content on buckling conditions. [ABSTRACT FROM AUTHOR]

• New buckling solutions of truncated conical shells are obtained. • Pre-buckling nonlinearity is incorporated for accurate buckling analysis. • A quasilinearization-precise integral method is developed for nonlinear PDEs. • The effects of size parameters and boundary conditions are quantitatively revealed. The pre-buckling nonlinearity is found to have a remarkable effect on both the buckling loads and modes of shells according to the previous studies. In this study, we present a novel accurate buckling analysis of the truncated conical shells under broad boundary constraints incorporating the pre-buckling nonlinearity by a quasilinearization-precise integral method (Q-PIM). Specifically, the nonlinear buckling equations of the shells are transformed into several linear ones by the perturbation and quasilinearization, and they are then solved by the PIM. The produced state transition equations by the PIM are assembled into a global matrix equation, involving the boundary conditions (BCs), to yield the buckling solutions of the shells with or without incorporating the pre-buckling nonlinearity. The convergence study and benchmark buckling solutions verified by the refined finite element method are presented. The quantitative effects of the size parameters and BCs on the nonlinear critical buckling loads as well as the pre-buckling nonlinearity are investigated. [ABSTRACT FROM AUTHOR]

The composite honeycomb sandwich with auxetic reentrant honeycomb (CSP-ARH) is a typical negative Poisson's ratio structure, which has better mechanical properties than composite structure with positive Poisson's ratio. In this study, a 2D asymptotic equivalent model (AEM) based on the variational asymptotic method (VAM) is proposed and used to analyze the vibration and buckling problems of CSP-ARH incorporating CFRP facesheets and an aluminum honeycomb core. After validation with 3D finite element results, a particle swarm optimization (PSO) algorithm is applied to optimize the mesoscopic size of composite facesheets and honeycomb core. The primary objectives of the optimization process involve maximizing the buckling load and natural frequency, minimizing the mass while satisfying specific mechanical properties requirements. Moreover, a few additional optimization iterations are performed to find the optimal shape coefficients of the curved fibers in the CFRP facesheets for variable stiffness composite sandwich panels. The shape of the curved fiber is defined using a cubic polynomial function f (x , y) and is described by a 20 × 20 grid of discrete elements. The results indicate that CSP-ARH with optimal curved fibers shapes exhibit superior performance compared to those with straight fibers, with buckling load and natural frequency increased by 8.18% and 7.09%, respectively. • VAM is extended to establish 2D-AEM of CSP-ARH, and verified by the 3D-FEM. • 2D-AEM reduces the DOFs of the CSP-ARH and improves calculation efficiency. • The PSO algorithm is applied to optimize the structural parameters of CSP-ARH. • The buckling and free vibration behaviors of CSP-ARH and CSP-ARH-CLF are studied. • Optimizing curved fiber direction improves the mechanical properties of CSP-ARH-CLF. [ABSTRACT FROM AUTHOR]

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