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• The elastic instability phenomenon in hyperelastic layered materials with the phases exhibiting stiffening behavior is studied • A closed-form expression for the critical stretch of macroscopic instability is derived • An analytical prediction based on Bloch-Floquet analysis for the microscopic instability is exhibited • The critical parameters and transition of instability modes are found to be highly tunable with phase stiffening This paper investigates the elastic instability behavior in soft periodic laminates subjected to finite strains, with a focus on both macroscopic and microscopic instabilities. Considering the deformation-induced phase stiffening, the Gent model with a high bulk-to-shear modulus ratio describes the behavior of incompressible phases. This non-Gaussian statistics-based model captures the non-linear constitutive results from the limited extensibility of polymeric molecular chains. This paper derives an analytical prediction for the onset of macroscopic (or longwave) instability and microscopic instability as functions of material parameters. Moreover, a numerical Bloch-Floquet analysis is imposed on identifying the instability behavior under compression. We consider a wide range of phase combinations and find that the relatively rapid stiffening of the matrix compared to the stiff layer increases the stability of laminates by decreasing the critical stretch ratio. Essentially, properly manipulating the stiffening parameters can produce an absolutely stable region without observed instability. This paper also systematically illustrates the changes in instability and the transition between macro and micro instability in fully Gent laminates, which show higher stability than fully neo-Hookean laminates with larger critical stretch ratios. The critical characteristics of instabilities, such as critical stretch ratios and critical wavenumbers, can be controlled by the choice of stiffening parameters and other material properties, enlarging the tuning of soft laminates for desired buckling patterns in practical applications. [ABSTRACT FROM AUTHOR]

This study's objective is to propose a full three-dimensional finite element modeling for examining the buckling behaviors of functionally graded (FG) porous materials with plates, spherical cap, and cylindrical shapes. An improved first-order shear deformation theory (IFSDT) is utilized in order to develop the three-dimensional solid-shell element. The governing equations are developed in a way that offers a parabolic distribution of the transverse shear strains through the FG porous shell thickness and a zero condition of the transverse shear stresses on the top and bottom surfaces. The given IFSDT solid-shell element has the ability to model any kind of shell structures and incorporates a three-dimensional material law. In this study, two types of porosity distribution functions are considered. The performance of the current IFSDT solid-shell element has been demonstrated by examining the buckling behavior of Functionally Graded Porous plates, spherical caps, and cylindrical shells. The effect of the porosity distribution, porosity coefficient, power-law index, geometrical design parameters and boundary conditions on the buckling behaviors of FG porous shells structures is evaluated. • 3-D finite element modeling proposed for buckling analysis of FG porous structures. • An improved first-order shear deformation theory (IFSDT) is presented. • IFSDT solid-shell element can model any kind of shell structures. • The shear correction factors are no longer needed. [ABSTRACT FROM AUTHOR]

• The symplectic superposition method for buckling of thick plates is developed. • New benchmark buckling solutions of TSDT-based non-Lévy-type plates are obtained. • The effects of boundary conditions and geometric dimensions are revealed. • A quantitative comparison study between TSDT and CPT/FSDT is conducted. The third-order shear deformation theories (TSDTs) are frequently employed to enhance the accuracy of mechanical behavior characterization for thick plates. However, the analytic buckling solutions based on the TSDTs are rare due to the major challenge in mathematical treatments. This study introduces an analytic symplectic superposition method to derive new benchmark buckling solutions of TSDT-based rectangular thick plates with non-Lévy-type boundary conditions (BCs), which are inaccessible using conventional analytic approaches. The governing equations are formulated in the Hamiltonian system. The symplectic framework-based mathematical techniques are manipulated, which shapes the characteristic of the method that a rational derivation is realized without any predetermined solution forms. The comprehensive buckling load factors and mode shapes of fully clamped plates and their variations are given, all of which are verified through comparison with the finite element method as well as literature results. Utilizing the obtained solutions, a comprehensive parametric analysis is conducted to elucidate the effects of BC, thickness-to-width ratio, and aspect ratio on critical buckling load factors. A comparison study is made between the results by the TSDT and those by the Kirchhoff theory and the first-order shear deformation theory, which demonstrates the superior accuracy of the former. The proposed rigorous framework offers a rational route to obtaining more benchmark buckling solutions. [ABSTRACT FROM AUTHOR]

Single-crystal and fine-grained polycrystalline samples of Cr 2 AlC were oxidized under dry air flow at temperature in the 1000–1400 °C range during 100 h. A continuous alumina layer forms on top of the Cr 2 AlC surface whereas a Cr 7 C 3 sublayer also appears. In-lab characterization of oxidized Cr 2 AlC samples shows strong damaging at the free surface, resulting from the buckling of the alumina scale. In-situ X-ray diffraction measurements under synchrotron radiations were performed to measure the lattice strain during the first hours of oxidation process and further calculate the internal stress in the Al 2 O 3 layers. Alumina layers undergo tensile stress during isothermal oxidation, showing that the buckling of the alumina scale does not result from the oxide growth. Such a tensile stress likely results from the Cr 2 AlC to Cr 7 C 3 phase transformation. During cooling, the tensile stress decreases down to compressive values, due to the thermal expansion coefficient mismatch between the film and the substrate, leading to buckling of the alumina layer. It is demonstrated that the dimensions of the buckles cannot be explained either by gas pressure or by the magnitude of the internal compressive stress in the alumina scale after cooling. The discrepancy between the experimental maximum deflection and the one predicted by the elastic theory can only be explained by a significant plastic deformation occurring in the alumina scale. [ABSTRACT FROM AUTHOR]

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

A novel meshfree local method is developed in the context of Trefftz approaches to solve eigenvalue problems related to buckling and free vibration of arbitrarily shaped thin plates, potentially having complicated cutouts. The formulation is based on Kirchhoff's assumptions for thin plates with C 1 continuity of the solution function. The mesh grid is replaced by a set of nodal points containing the degrees of freedom, located over the domain and its boundaries, thus removing the need for heavy mesh generation process. A sub-domain (cloud) centered at each node and containing several adjacent nodes is considered, in which the approximation functions are defined. The bases are made from Exponential Basis Functions (EBFs), so as to automatically satisfy part of the governing PDE and thus, removing the numerical integration procedure and increasing the solution accuracy. Due to the existence of indefinite values as the critical buckling load or the free vibration frequency, Trefftz approaches have difficulties to directly apply for eigenvalue problems. To resolve this, first the homogeneous eigenvalue problem converts into a non-homogeneous problem by moving the parts with indefinite eigenvalues to the right hand side of the equality and keeping the rest on the left. The solution to the whole eigenvalue problem is approximated using a series of EBFs. Then the solution to the homogeneous part is interpolated using another series of EBFs capable of exactly satisfying the homogeneous part of the newly defined PDE, while the particular solution is approximated using the eigenvalue solution series defined at the first step. Numerical results reveal that the proposed method can efficiently produce results with high accuracy. [ABSTRACT FROM AUTHOR]

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

We present a combined experimental and computational study of the elastic behavior of a series of highly anisotropic pyrocarbons, with crystallite sizes L a in the 2–10 nm range, under a -axis compressive load. The materials include a rough laminar and a regenerative laminar pyrocarbon, as-prepared by chemical vapor deposition and after various heat treatments up to 2600 °C, for which a -axis nanoindentation experiments have been performed, showing a significant decrease in the indentation modulus and hardness with increasing L a (or heat treatment temperature). To rationalize this behavior, molecular dynamics simulations of the uniaxial compression of accurate atomistic models of the materials as well as pristine graphite were performed, unraveling significant out-of-plane deformations in the models with increasing compressive strain, leading to elastic softening. More precisely, significant kinks were observed around extended screw dislocation-like defects in the most disordered pyrocarbon at rather large strain levels (∼ 3%). Conversely, graphite rather shows the formation of extended buckles, starting at very low strain values. Finite element modelling shows that such kinking/buckling transitions should take place in a large area under the indenter tip within usual nanoindentation conditions. Both finite element calculation and analytical approximation of the indentation modulus predict the correct trend of decreasing modulus with increasing L a when applied with the elastic tensors computed after the buckling/kinking transitions, certainly proving the importance of the latter in the observed experimental indentation moduli. [ABSTRACT FROM AUTHOR]

Common bulkhead (CBH) propellant tanks have the advantage that its structural and space efficiency are high. The tank is a form in which an oxidizer tank and a fuel tank are integrally combined, and the oxidizer and fuel are separated by the CBH. The CBH propellant tank in which two tanks are integrated can reduce unnecessary space between the two tanks. However, there are other difficult problems regarding effectively designing the CBH propellant tanks even though there are structural and space benefit. This paper is a study on the thermal-structural characteristics of CBH tanks containing LOX/LH2 propellant. In order to conduct the thermal-structural analysis, the thermal analysis model was constructed using 2-dimensional axisymmetric elements to reflect the shape features of the tank, and the structural analysis model was built using 3-dimensional elements. The thermal-structural analysis was performed on the length of the bottom tank and the foam core thickness of the CBH. In the structural analysis of the tank, when the thermal load was ignored and only the pressure load was applied, there was a difference in the buckling load factor depending on the thickness of the CBH foam core, but as the thermal load was taken into consideration, there was also a difference in the bottom tank length. The analysis results show that the thermal-structural characteristics of the CBH propellant tank were influenced by the length of the bottom tank as well as the thickness of the foam core. • Influence of the CBH thickness and bottom tank length on the thermal-structural characteristics of the CBH propellant tank. • Increasing CBH thickness and bottom tank length decrease the amount of heat transfer through the CBH. • There is a CBH thickness where the buckling load factor is maximum. • The bottom tank length that is too long can drastically reduce the buckling load factor. [ABSTRACT FROM AUTHOR]

In this paper, the finite element method is utilized to evaluate the behavior of the armchair phosphorene nanotubes under the compressive loading. The energy equations of the molecular and structural mechanics are used to obtain the elemental properties. The critical compressive forces of various armchair phosphorene nanotubes are computed with clamped-clamped and clamped-free boundary conditions. Results show that the stability of armchair phosphorene nanotubes increases with increasing nanotube aspect ratio, particularly under clamped-clamped boundary conditions. Finally, the buckling mode shapes of armchair phosphorene nanotubes under different boundary conditions are compared. Our work offers valuable insights into how these nanotubes respond to mechanical stress, helps determine elemental properties, and investigates the effects of nanotube geometry and different boundary conditions on their stability. This knowledge has broad applications in fields like nanotechnology, materials science, and nanomechanics, advancing the understanding of nanoscale materials and their potential for various practical uses. The finite element method is utilized to evaluate the behavior of the armchair phosphorene nanotubes under the compressive loading. [Display omitted] • FE method is utilized to evaluate the behavior of the armchair PNTs under the compressive loading. • The elemental properties are obtained by the energy equations of the molecular and structural mechanics. • The buckling forces of the armchair PNTs with different radii and lengths are computed. • The stability of armchair PNTs increases by increasing the nanotube aspect ratio. • The clamped-clamped nanotubes are more stable than clamped-free ones. [ABSTRACT FROM AUTHOR]

Innovation in cold-formed steel framing systems is needed for opening flexibility and application in mid-rise buildings. Hence, this study proposes a closed built-up section using four cold-formed steel (CFS) open sections with a high load bearing capacity that potentially enables the development of high-performance cold-formed steel framing systems for these. The closed section by combining four open CFS sections using fasteners can effectively enhance the load capacity of the sections under axial loading. With a specially designed intersections gusset plate this built-up section offers more potential configurations of beam-column moment connections for CFS structures. First, a heuristic optimization was performed to identify a high-performance section based on the local and distortional buckling strengths using the finite strip method. Second, a test program was developed to investigate the load bearing capacity and failure behaviors of the optimized built-up closed section under axial and eccentric loading. Third, their load bearing capacities were compared with several other closed sections such as the rectangular hollow tube (RHS) of equal cross-sectional area or equal moment of inertia to highlight the high material efficiency. This study paved the groundwork for exploring high-performance cold-formed steel framing systems with this unique closed built-up section. • Proposed a closed built-up section for two-way cold-formed steel framing systems. • Investigated the compression behavior and strength of specimens under axial and eccentric loadings. • Achieved a high load-bearing capacity of the closed built-up section. • Conducted a comparable analysis with equivalent rectangular hollow tube sections numerically. [ABSTRACT FROM AUTHOR]

High strength steel has been attracting attention in the building industry due to its superior mechanical properties. The accurate design of high strength steel structures is crucial to boost its wide application. In this paper, an accurate and unified design approach for high strength steel I-section columns with different material grades, boundary conditions, geometric dimensions (including cross-section sizes and member lengths) and failure modes is proposed based on machine learning. Firstly, 871 experimental and numerical data were collected from the literature to establish a database. Then, seven machine learning algorithms, including Decision Tree, Random Forest, Support Vector Machine, K-Nearest Neighbour, Adaptive Boosting, Extreme Gradient Boosting and Categorical Boosting, were applied to establish machine learning regression models to predict buckling resistances of high strength steel I-section columns. The model performance was then evaluated through statistic indices, with the evaluation results indicating that the Categorical Boosting trained model yields the highest level of accuracy. Based on the data in the collected database, the regression model trained by Categorical Boosting and existing codified design provisions, as given in the European code and American specification, were assessed and compared. The European code and American specification were found to yield scattered and inaccurate failure load predictions, while the Categorical Boosting trained model led to substantially more accurate and consistent failure load predictions for high strength steel I-section columns with different material grades, boundary conditions, geometric dimensions and failure modes. • A database including 871 structural performance data on high strength steel I-section columns was established. • Regression models were developed by using machine learning algorithms to predict load-carrying capacities. • The regression models were evaluated and the Categorical Boosting model provided the best performance. • The machine learning design method yielded improved design accuracy than the existing design codes. [ABSTRACT FROM AUTHOR]

• Novel mechanical characteristics of metamaterials are studied by theoretical analysis. • Dissipated energy per buckling event is studied. • Static and dynamic(re)programming characteristics are studied. • Potential energy landscape of programmable structure is studied. Metamaterials derive promising properties mainly from an internal micromechanical mechanism, rather than their chemical composition. Many interesting mechanical behaviors can be obtained by orderly assembling buckling elements. Elastic programmable properties, corresponding potential energy landscape and dynamic dissipation mechanism of elastic beam structures are studied in detail. To accomplish this work, a combination of theoretical models and extensive numerical calculations are applied to investigate a single element as well as homogeneous and gradient structures. This comprehensive investigation not only provides insights into the complex internal buckling behaviors and mechanisms of a specific unstable structure but also establishes conclusions that are applicable to other unstable structures having similar buckling behaviors. The potential energy of a serial combination of unstable elements is extremely wiggly, enabling multiple equilibrium configurations and resulting in multistable transformations and energy dissipation with elastic deformation and loading timescale independence. To the best of our knowledge, the most of programming properties investigated in this paper, the complex energy landscape, the deformation of internal elements, and programmable dynamic responses of gradient unstable structures have not been reported in previous papers. [Display omitted] [ABSTRACT FROM AUTHOR]

• The proposed model satisfied the consistency condition of the plastic multiplier under any loading patterns. • Results of the proposed model were consistent with the material and structural test results. • The proposed model had equivalent convergence to existing models. Mild steels are frequently used in building structures because of their high strength, productivity, processability, and weldability. One key feature of mild steels is their yield plateau, which is followed by a hardening region in the stress–strain relationship. During large earthquakes, building members can experience a large plastic strain whose amplitude is difficult to predict beforehand. Constitutive equations applicable to the full-range strain field are necessary for accurate structural safety evaluation. This study provides novel constitutive equations for the plateau region, capable of reproducing a yield plateau. A set of hardening constants was proposed to satisfy the consistency condition of the plastic multiplier under any loading pattern. The closed form of the stress–strain relationship was derived to calibrate the material constants. The material constants were calibrated using two types of material test results. The results of the proposed model were consistent with the material test results under cyclic loading at various strain amplitudes. This was validated by comparing the shear buckling and lateral torsional buckling test results of an H-shaped beam with the finite element analysis (FEA) results. The numerical demonstration also highlighted the significance of not only material constitutive laws but also the introduction of residual stress and initial imperfections in reproducing the pre- and post-buckling behaviors. The convergence of the residual force for the proposed model was equivalent to those of the authors' previous model and the Chaboche model. These results indicate that the proposed model can predict hardening phenomena at the material and structural levels in the plateau and hardening regions. [ABSTRACT FROM AUTHOR]

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

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

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

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

In this paper, 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]

• 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]

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]

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 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]

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]

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]

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]

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

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

Steel jacket structures subjected to environmental impacts exhibit severe dynamic responses, potentially causing local fatigue failure, plastic damage, and even catastrophic collapse. Therefore, a structure with adjustable stiffness and large damping is ideal for coping with complex environmental loads and dissipating kinetic energy. A novel programmable damper was designed by connecting N -layer coupling elements composed of a linear spring, wire ropes, and an asymmetric column. Analytical models for the elastic buckling behavior of the damper were derived and mutually verified with finite element analysis (FEA). Based on the analytical models, the dependence of the mechanical responses of the damper on the number of elements and the spring stiffness was investigated for design guidance. The results indicate that the N -layer damper has 2 N different stiffnesses, and the total dissipation capacity increases by approximately 2.6 N times compared with a single asymmetric column. For potential applications, the dynamic decay responses of representative jacket structures assembled with the damper were simulated using the FE software ABAQUS combined with user-defined-material (UMAT) code, which demonstrated that the programmable damper is an advanced device that simultaneously achieves adjustable stiffness and significant damping. • Design a novel programmable energy absorber. • Achieve arbitrary programmable stiffness and large damping. • Impact protection and vibration suppression for jacket structures. [ABSTRACT FROM AUTHOR]

The reinforcement in marine RC structures will inevitably be corroded under long-time erosion of chloride ions, which will weaken steel mechanical properties and then structural seismic resistance. The new metallurgical technology is adopted for manufacturing high-strength steel bars (HSSB), but that may affect the corrosion resistance of steel bars at the same time. This paper experimentally investigates the effects of corrosion on monotonic and low-cycle fatigue properties of HSSB HTRB600 and normal strength steel bars (NSB) HRB400E. The HRB400E and HTRB600 steel bars were corroded to different corrosion rates by electrochemical accelerated corrosion technique. The monotonic tensile and compressive, as well as low-cycle fatigue tests of corroded steel bars were conducted to investigate the effects of corrosion on steel mechanical properties, of which corrosion levels (0–20% target corrosion mass loss), slenderness ratios (L / D =6, 8, 10, 12) and strain amplitudes (2%, 4%) are considered. Test results show that, the corrosion morphology of steel bars under electrochemical accelerated corrosion is basically consistent with that observed under natural corrosion. Compared with uncorroded HRB400E and HTRB600 steel bars, 20% corrosion mass loss leads to 38% and 35% decrease in tensile strength, as well as 33% and 28% reduction in buckling stress, respectively. The HTRB600 steel bars present slightly superior monotonic tensile and compressive corrosion resistance than HRB400E steel bars. Corrosion obviously decreases the low-cycle fatigue (LCF) life of steel bars, resulting in reductions of 44% and 36% in LCF life at 20% corrosion mass loss for HTRB600 and HRB400E steel with a L / D of 6, respectively. Moreover, the HTRB600 steel bars present more significant corrosion degradation in total hysteretic dissipated energy, compared with HRB400E steel bars. The combined effect of corrosion and inelastic buckling further exacerbates the deterioration of LCF performance of steel bars. The corresponding deterioration models are proposed to determine the LCF life and energy dissipation capacity of corroded steel bars. • Carry out monotonic and low-cycle fatigue tests of corroded HTRB600 and HRB400E steel bars. • Compare corrosion morphology between electrochemical accelerated and natural corrosion. • Establish mechanical deterioration model of corroded steel bars. • Investigate and compare the effects of corrosion on monotonic and LCF performance of HTRB600 and HRB400E steel bars. [ABSTRACT FROM AUTHOR]

Kresling origami, a representative variant of origami, exhibits several distinctive features such as multistable states, changeable stiffness, and compression-torsion coupling deformation. The first focus of this study involves examining the mechanical properties of origami structures, specifically, the equivalent modulus and critical buckling stress during the deployment process are evaluated. Subsequently, the collapsibility of the Kresling origami structure is explicated with regard to energy and strain. In the folding process, when the Kresling angle is 0.0135 rad, the maximum torque is 959 Nmm, and the structure will occur snap-through instability, which is the nonlinear critical buckling load of the failure. After that, the torque decreases rapidly, and then gradually increases slowly. The mechanical model is developed and subsequently evaluated in terms of its flexibility and adjustment of stiffness. The present study investigates the buckling modes and vibration properties of Kresling origami structures, as well as their combination structures. For the buckling of Kresling origami structure, the critical buckling load of Euler buckling is 0.023 N and that of local buckling is 0.67 N. In short, the critical buckling load of the column shell is greater than that of the Kresling origami structure, which is due to the small local stiffness of structure. [ABSTRACT FROM AUTHOR]

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

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

Surface instability, termed wrinkling, might occur in compressed bilayer systems constituted by an external rigid skin resting on an internal soft substrate, where wrinkling is favored by the rigidity contrast between the two layers. In this paper, the same instability mechanism is explored by considering a substrate characterized by an orthotropic elastic response. By varying the orientation of the principal axes of the substrate's material, the critical strain of wrinkling and the wrinkles' wavelength can be tuned during compression. Theoretical formulations for wrinkling are discussed along with the results obtained by linear bifurcation and geometrically nonlinear analyses carried out with two-dimensional finite element models. To experimentally validate the results, the intrinsic properties of Fused Deposition Modeling (FDM) 3D printing technology are leveraged: bilayer objects are manufactured by printing continuous outer shells (corresponding to the rigid skin) along the borders, while the inner raster is shaped with a porous infill pattern, forming a substrate with an orthotropic elastic response. [Display omitted] • Wrinkling of a compressed isotropic skin on an orthotropic substrate is studied. • A single material is used, leveraging the intrinsic properties of FDM 3D printing. • The stiffness mismatch is achieved varying the rastering orientation of the substrate. • Eigenvalue buckling analyses and experiments validate the governing equations. • Tunable wrinkling strain and wavelength are obtained. [ABSTRACT FROM AUTHOR]

In the realm of aircraft design, there is a prevalent need for surrogate modeling techniques capable of efficiently and accurately modeling objects with high evaluation costs and uneven sensitivity distributions, such as those encountered in the nonlinear buckling of thin-walled structures and aerodynamics at transonic speeds. However, the non-stationary Gaussian Process Regression (GPR) model requires extensive hyperparameters or judicious assumptions, limiting its applications in such tasks, and the commonly used K-Fold methodology suffers from inherent instability. Addressing these issues, this paper proposes an active learning method for surrogate modeling in systems featuring uneven sensitivity distribution, integrating non-stationary-noise GPR and K-Fold Artificial Neural Network (ANN) methodology, namely NSN-GPR-KF. Instead of relying on a non-stationary kernel function, the algorithm regards noise as a non-stationary factor within a stationary GPR framework, with noise levels estimated via the K-Fold ANN methodology, allowing GPR to efficiently adapt to non-stationary systems while avoiding the aforementioned requirements for non-stationary GPR. Case validations, performed on two test functions with pronounced uneven spatial sensitivity, demonstrate that NSN-GPR-KF outperforms commonly used stationary GPR and pure K-Fold methodology. It synthesizes the exploration capabilities of GPR with the exploitation proficiency of the K-Fold methodology, achieving comparable global accuracy with reduced sample sizes—up to 26 % and 22 % less than the other two algorithms, respectively. The algorithm was successfully applied to predict the buckling load of thin-walled pipe beams, demonstrating accelerated convergence and approximately 25 % greater accuracy compared to pure K-Fold model. These results suggest that NSN-GPR-KF can serve as an efficient and precise modeling tool for engineering tasks with high evaluation costs and complex sensitivity distributions. [ABSTRACT FROM AUTHOR]

What are the geometrical and mechanical properties ruling bistability of Kresling origami metamaterials? How can we tune the magnitude of their axial-torsional coupling? Complete answers to these compelling questions cannot be found in the scientific literature, as the intertwining between bistability, axial-torsional coupling and an other significant behaviour, namely transverse dilation/contraction, remains mostly uninvestigated. This contribution aims at shedding light on this intertwining, through the use of a discrete model of Kresling origami that takes into account folding resistance. The present study is mostly computational and involves both pre- and post-critical analyses. It is based on displacement controlled tests — shearing and axial shortening/lengthening. Single-storey Kresling origami's are first considered, preliminarly to multiple-storey tubes, where buckling is observed. Several parameters are taken into account such as the number of storeys, stretching and folding stiffnesses, and – for shearing tests – the prescribed displacement direction in the transversal plane. The ultimate goal of the paper is to provide evidence that can be useful in the construction of homogenised continuum models of Kresling origami metamaterials. • We present some numerical simulation concerning metamaterials based on Kresling tube pattern. • Numerical analyses of some selected tests clarifies the mechanical behaviour of metamaterials based on Kresling pattern. • Numerical simulations address the homogenised model of Kresling tubes. [ABSTRACT FROM AUTHOR]

This study uses the FGP-GPLs (functionally graded porous metal reinforced by graphene platelets) to rehabilitate the egg-shaped liner-pipe system. The water penetrates the cracked pipe and surrounds the thin-walled liner, resulting in hydrostatic pressure that may contribute dominantly to the buckling of the thin-walled liner. The critical buckling pressure is derived analytically by combining the thin-walled shell theory, a refined displacement function, and the energy scheme. It is found the egg-shaped FGLs liner sustains higher buckling pressure than the circular FGP-GPLs one. Furthermore, a finite element model is developed to verify the theoretical solutions. The results indicate the numerical equilibrium paths agree well with the analytical ones. In addition, the present analytical predictions are compared successfully with other close-formed solutions. Finally, parametric analyses indicate that the addition of GPLs may significantly improve the stability of the egg-shaped liner, while the increase of pores decreases the stability of the liner. The thickness of the GPLs has a slight effect on the stability of the liner when the volume of GPLs is constant. Thus, thick GPLs may be recommended in engineering practices to reduce the manufacturing cost. • An egg-shaped pipe is used to improve the hydraulic efficiency of the cross-section. • FGP-GPLs liner are employed to rehabilitate the cracked egg-shaped pipe. • Analytical schemes are developed to describe the stability of the egg-shaped liner. • The equilibrium curves are plotted for the egg-shaped FGP-GPLs liner. [ABSTRACT FROM AUTHOR]