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

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

Buckling is typically the governing failure mode of thin‐walled shells. In particular, geometric and material imperfections have a major influence on the buckling behavior. Small variations of imperfections have large effects on the load‐bearing behavior. However, the design of shells is still characterized by a deterministic way of thinking, in which uncertainties have not yet been sufficiently considered. Even in probabilistic approaches, false assumptions are often generated due to the small amount of experimental data. The focus of this paper is an appropriate uncertainty quantification based on the available data. Therefore, the concept of polymorphic uncertainty modeling is presented on axially loaded shells with different types of imperfections. Finally, an idea for a novel design concept for shells based on a fuzzy‐valued safety level is introduced. The paper is intended to initiate a rethinking of the methodology for the numerical design of shells with an appropriate uncertainty quantification. [ABSTRACT FROM AUTHOR]

The local stability of unsymmetric laminated structures is significantly affected by bending‐extension coupling and the comparatively low transverse shear stiffnesses, which have to be included in the structural analysis. If such structures have flat surfaces in segments, they can be investigated with the discrete plate analysis. In this analysis, the individual segments are considered as plates with rotational restraints that represent the supporting effect of the surrounding structure. The aim of this work is to improve the analytical stability of laminated plates. Therefore, Lévy‐type solutions for the buckling load of the mentioned laminated plates are considered and refined. This offers exact solutions for unsymmetrical cross‐ply laminates as well as antisymmetric angle‐ply laminates. In order to show the influence of shear deformations, the solutions for classical laminated plate theory (CLPT), first‐order shear deformation theory (FSDT), and third‐order shear deformation theory (TSDT) are worked out and compared to each other. In the context of TSDT, a new formulation for the rotational elastic restraint is presented, which affects the rotation and the warping of the plate cross‐section. This investigation presents the influence of shear deformations on different laminates and classifies the benefits of the different laminated plate theories with respect to the stability behaviour under different boundary conditions. In addition, the influence of bending‐extension coupling on different fibre angles and layer sequences is analysed. [ABSTRACT FROM AUTHOR]

Lateral buckling, an essential mechanical phenomenon observed in composite beams subjected to specific external loads and boundary conditions, is influenced by various factors including cutout dimension, shape, position, and beam thickness in woven fabric laminated composite cantilever beams. The investigation focused on examining the lateral buckling behavior of beams containing two square or circular cutouts and comparing the experimental critical buckling loads of beams without any cutouts, which yielded results demonstrating a significant level of agreement. Through the experimental analysis, it was determined that square cutouts exhibit superior lateral buckling behavior when compared to circular cutouts. Highlights: The effects of cutout shapes on lateral buckling analysis on fiber reinforced composites.The effects of cutout location on lateral buckling load on fiber reinforced composites.Comparison of the lateral buckling performances of fiber reinforced composites in relation to the type and position of cutouts. [ABSTRACT FROM AUTHOR]

Highlights Hybrid fiber‐reinforced composite sandwich panels with multi‐layer polyurethane cores are widely applied in aerospace, automotive, construction, and shipbuilding industries. This study aims to investigate the buckling performance of composite structures with varying numbers of polyurethane cores. To achieve this, the buckling loads of these structures are determined using an energy method, microscopic mechanics method, and the first‐order zigzag kinematic model. The accuracy of the equation employed in the algorithm is validated using the finite element method. Additionally, we conduct a parametric analysis to examine the influence of various parameters on the buckling performance of the structures. The results indicate that an effective strategy for improving the critical buckling loads of the hybrid fiber‐reinforced composite sandwich plate involves strategically placing fibers and matrix materials with higher elastic modulus on the skin layer. Moreover, the critical buckling load is notably influenced by the number and positioning of polyurethane layers, as well as the fiber content. An analytical model is established to predict the buckling behavior. The correctness of the model was verified using the finite element method. Effects of structural parameters on buckling performance were investigated. [ABSTRACT FROM AUTHOR]

The current study presents an experimental investigation devoted to the nano‐silica and cutout effects on the axial and lateral buckling responses of carbon/epoxy fiber‐reinforced composite laminates. To this end, specimens manufactured by vacuum bagging after hand layup technique were prepared at various amounts of nano‐silica (0.5%, 1.0%, 1.5%, 2.0%, and 3.0% by weight) incorporated into epoxy resin. Furthermore, semi‐circular and circular cutouts were opened on specimens to understand cutout effect on buckling characteristics of specimens. The results demonstrated that nano‐silica had a significant effect on buckling behaviors of the carbon fiber‐reinforced composites. Regardless of cutout presences, maximum critical axial (393.33 N, 361.67 N, 320 N for W, C and S) and lateral buckling loads (34.67 N, 33 N, 32.33 N for W, C and S), were achieved from the samples having 1.5 wt. % nano‐silica. In specimens having no cutout, maximum improvements of 72.26% in axial and 48.6% in lateral directions were achieved from the specimens having 1.5 wt. % nano‐silica content. A further amount of nano‐silica addition decreased the resistance to buckling of the specimens. Also, the presence of cutouts on the specimens led to decreases in critical loads. The decreases of 1.5 wt. % nano‐silica doped specimens without cutout in the axial and lateral critical buckling loads, respectively, were seen as 22.9% and 7.24% for circular cutout, 8.75% and 5.06% for semi‐circular cutout. It was concluded that cutout processing and nano‐silica additions should be taken into consideration in a material that may be exposed the buckling failures. Highlights: Nano‐silica impact on buckling behaviors of carbon fiber‐reinforced compositesCutout effects on buckling properties of carbon fiber‐reinforced compositesFailure modes of carbon fiber‐reinforced composites with nano‐silica particlesFindings showed that 1.5 wt. % nano‐silica inclusion exhibited the best values for buckling. [ABSTRACT FROM AUTHOR]

Cristae are high‐curvature structures in the inner mitochondrial membrane (IMM) that are crucial for ATP production. While cristae‐shaping proteins have been defined, analogous lipid‐based mechanisms have yet to be elucidated. Here, we combine experimental lipidome dissection with multi‐scale modeling to investigate how lipid interactions dictate IMM morphology and ATP generation. When modulating phospholipid (PL) saturation in engineered yeast strains, we observed a surprisingly abrupt breakpoint in IMM topology driven by a continuous loss of ATP synthase organization at cristae ridges. We found that cardiolipin (CL) specifically buffers the inner mitochondrial membrane against curvature loss, an effect that is independent of ATP synthase dimerization. To explain this interaction, we developed a continuum model for cristae tubule formation that integrates both lipid and protein‐mediated curvatures. This model highlighted a snapthrough instability, which drives IMM collapse upon small changes in membrane properties. We also showed that cardiolipin is essential in low‐oxygen conditions that promote PL saturation. These results demonstrate that the mechanical function of cardiolipin is dependent on the surrounding lipid and protein components of the IMM. Synopsis: Dedicated proteins are known to control the architecture of the inner mitochondrial membrane; however, the role of specific lipids is less well defined. Here, a combination of methods including tomography and lipidomics is used to characterise the role of lipid composition in defining cristae architecture. As lipid ratios change, a critical breakpoint phenocopies the loss of cristae‐shaping proteins in the IMM of yeast mitochondria.Phospholipid saturation controls membrane mechanical properties and modulates ATP synthase oligomerization.The mitochondria‐specific lipid cardiolipin functionally compensates for increased phospholipid saturation and is required for cristae formation in low‐oxygen environments.A mathematical model for cristae membrane tubules predicts a snap‐through instability mediated by both protein and lipid‐encoded curvatures. [ABSTRACT FROM AUTHOR]

In this paper, we study the buckling problem of the drifting Laplacian on bounded domains in a complete Riemannian manifold with nonnegative ∞‐dimensional Bakry–Émery Ricci curvature. According to the property of the manifold, we obtain a family of trial functions. By making use of these trial functions, we derive a universal inequality of eigenvalues, which is independent of the domains. [ABSTRACT FROM AUTHOR]

In general, a web of the steel box girder is designed as an independent. However, in actual behaviour, since the web and the flange behave in couple, the web is considered to have a higher bending buckling strength than the designed standard due to the restraint by the flanges. Therefore, horizontal stiffeners for the web of the steel box girder might be omitted. In this study, focusing on the effect of the coupled behaviour of the web and flange on the bending buckling strength of the web of a box girder, FE analyses were carried out of steel box girder model with different structural configuration and of a panel model under identical boundary conditions as the design. From these results, it was found that the web of box girders without horizontal stiffeners have a higher bending buckling strength than the panel model due to restraint by the top of end of the web by the flange. In the case that buckling parameters of the flange are smaller than those critical buckling parameters, the influence of the bending buckling of the web of the box girder on the buckling strength of the flange is slight. [ABSTRACT FROM AUTHOR]

The "General Method" according to chapter 6.3.4 of EN1993‐1‐1 or 8.3.4 of prEN1993‐1‐1 deals with the verification of stability problems of frame and beam structures with loadings in‐plane. The "General method" according to Eurocode is intended for the general case of a combined moment and normal force. For the choice of the reduction factor χop, there are two options for applying the reduction curve, either the minimum of lateral torsional buckling (LTB) and flexural buckling (FB) or a weighted combination of both. With the use of analytical derivations, it can be shown that this approach leads to inconsistencies which can possibly lead to incorrect results. In this paper an alternative approach is presented which leads to unification and fully mechanical justification in verification. The approach allows e.g. the verification of stability of an entire frame system directly and without interaction factors (as in the equivalent member method). In addition, the issue of a consistent equivalent imperfection is addressed. With the use of this method, geometrical non‐linear analyses of structures showing out‐of‐plane instability can be omitted; only an in‐plane calculation and a determination of a linear buckling analysis is necessary. Finally, examples are presented in this paper that demonstrate the application of the approach shown. [ABSTRACT FROM AUTHOR]

Highlights This paper presents an analytical approach for buckling and postbuckling analysis for functionally graded graphene‐reinforced composite (FG‐GRC) toroidal shell segments with the trapezoidal or round corrugated core under the axial tension and compression. The considered shells are placed in a thermal environment and surrounded by an elastic foundation. Based on the von Kármán‐Donnell shell theory with geometrical nonlinearities, Stein and McElman approximation, and a homogenization technique for corrugated shells, the basic equations of shells are established. The previous homogenization technique is improved by adding the thermal forces in the internal force expressions. The shell‐foundation interaction is expressed using the model of the Pasternak assumption. The Ritz energy method is used to obtain the pre‐buckling and postbuckling behaviors of the shells, from which the critical buckling tensions and compressions can be investigated. The influences of FG‐GRC face sheets, corrugated core, and foundation on the buckling behavior of sandwich shells can be shown in the numerical analysis. Postbuckling of toroidal shell segments with the corrugated core is analyzed. A homogenization technique is improved for the thermal forces in the core. The shells are made of functionally graded graphene‐reinforced composite. The nonlinear Kármán‐Donnell shell theory and Ritz energy method are applied. Special effects of input parameters on the buckling behavior are investigated. [ABSTRACT FROM AUTHOR]

This paper presents a fiber element analysis model that simulates the structural responses of square steel‐reinforced concrete‐filled steel tubular (SRCFST) short columns under concentric compression including local buckling effects. The method of effective widths is utilized to model the gradual postlocal buckling of the steel tube walls of a SRCFST column loaded axially to failure. A new confinement model is developed for the concrete based on test results, considering the confinement induced by the embedded steel section. This confinement model is incorporated into the fiber model, and its accuracy is verified by experimental results. The accuracy of various confinement models proposed for concrete‐filled steel tubular (CFST) square columns in predicting the performance of SRCFST columns is evaluated. A parametric study is performed to investigate the performance of SRCFST columns with various parameters. The applicability of the design formulas specified in current standards for CFST columns to the design of SRCFST columns is examined. A formula is proposed to predict the strength of SRCFST short columns. The developed inelastic simulation model, confinement model, and design formula are found to yield performance predictions of SRCFST columns with good accuracy. [ABSTRACT FROM AUTHOR]

As part of the ongoing revision of the Eurocodes, design provisions in EN 1999‐1‐1 on the buckling of longitudinally welded aluminium compression members have been subjected to a critical review. The numerical investigations described in part 1 of the paper were conducted because a need for improvement was identified. In part 2 the main observations were presented qualitatively. Part 3, the final part of the paper, presents the statistical evaluation of the numerical investigations and the determination of the buckling curves. Two different approaches are conceivable for these buckling curves: conventional buckling curves with explicitly specified imperfection factor and plateau length parameters, and a modified Ayrton‐Perry approach with interpolated parameters. Both approaches are compared with the results of the numerical investigations and with test results. [ABSTRACT FROM AUTHOR]

In this study, we introduce a comprehensive investigation into the buckling behavior of carbon nanotubes (CNTs) using a combined approach of quantum mechanics and molecular mechanics methods. A novel aspect of our research lies in the exploration of the quantum effects of fine scaling on the buckling behavior of finite‐length nanotubes across various dimensions and chiralities. Specifically, we analyze the critical buckling strain variations in CNTs with distinct lengths, diameters, and chiralities, revealing pronounced differences influenced by atomic arrangement and the type of structure used in nanotube construction. Our findings elucidate that at smaller dimensions, nn2$$ \left(\ n,\frac{n}{2}\right) $$ nanotubes exhibit a higher critical buckling strain than other chiralities, while zigzag atomic arrangements demonstrate greater resistance to torsional loading at larger diameters. Additionally, we compare the buckling behavior of nanotubes obtained by wrapping armchair and zigzag nanosheets, highlighting differential resistance trends. This research not only underscores the critical role of quantum effects in determining nanotube buckling but also provides valuable insights into the nuanced influences of atomic arrangement and nanosheet type on the mechanical properties of CNTs. Thus, our work contributes a novel perspective to the field, bridging the gap between quantum mechanics and the mechanical behavior of nanostructures, which has significant implications for the design and application of nanoscale materials [ABSTRACT FROM AUTHOR]

A silo structure is usually constructed in the form of a cylindrical steel shell. It has the advantages of being lightweight, having a short construction period, and possessing a large storage space. It has been widely used in many fields of industry. Thin‐walled cylindrical shells often exhibit buckling failure and the experimental buckling load is usually lower than calculation results from classical theory and simulation without geometrical imperfection. Besides, test results with carefully conducted similar specimens still have substantial scatter due to imperfection sensitivity. The nonlinear analysis with FEM can obtain a high‐precision result comparing the experiment if the geometric parameters of the shell are fully known. However, this is almost impossible in practical engineering. The initial geometric imperfections and shell thickness of cylindrical shells are complex and random properties. Theoretically, these geometric imperfections can be described using a random field. This paper presents the experimental investigation of buckling analysis of cylindrical shells under axial compression considering the randomness of geometric imperfections and thickness. A total of 12 cylindrical shell specimens were fabricated and tested. Based on the test results, the optimal statistical distribution is obtained by the maximum entropy fitting method and the obtained results were compared with geometric imperfections based on laser scan measurements. [ABSTRACT FROM AUTHOR]

In practice, welded I‐members of steel buildings are usually made of flanges that are either wide hot‐rolled plates, or plates longitudinally divided using flame‐cuts. The residual stresses distributions resulting from both types of fabrication process are substantially different. However, the Eurocode 3 buckling design resistance of a welded I‐member in compression assumes hot‐rolled flanges, thus neglecting the beneficial impact of flame‐cuts. A parametric study is then performed regarding the out‐of‐plane flexural buckling of welded members made of flame‐cut flanges. 377 doubly symmetric members either with a uniform or a tapered cross‐section are studied. These numerical results are firstly employed to evaluate the safety and accuracy of the Eurocode 3 rules for such members by computing partial factors. The current rules proving overly conservative, two proposals are made for welded columns made of flame‐cut flanges. A first simple proposal suggests a more favorable buckling curve. A second proposal introduces an imperfection factor depending on the cross‐sectional height‐to‐width ratio. Partial factors computed for both proposals are satisfactory, the second proposal being more precise. [ABSTRACT FROM AUTHOR]

This study analyzed the flexural buckling behavior of light‐gauge built‐up compression members joined by self‐drilling screws by using the energy method. A nonconventional mechanical model that simulates the flexural buckling behavior of a built‐up member was proposed, and the contradictions of Bleich's model were described. A simple design formula that directly reflects the parameters of built‐up members was derived based on the proposed model. Furthermore, to ensure flexural buckling as a single unit member, the required stiffening stiffness and number of self‐drilling screws were proposed. [ABSTRACT FROM AUTHOR]

In the framework of the revision of Eurocode 3, Part 1–1, several amendments have been proposed and accepted in order to improve the rules for the resistance to member buckling. For clarification, a flow chart connecting the global analysis (first or second order), the imperfections and the type of verification has been implemented for ease of use. Since the publication of the standard in 2005, many research projects have been conducted across Europe on this topic and their results have contributed to provide appropriate answers to problems identified in practice. Therefore, the revised code provides new design rules for stability. Important works of calibration have been performed in these different projects to derive appropriate values of the partial factor on the resistance side. For example, a new formulation for lateral–torsional buckling has been introduced for the calculation of the reduction factor. The consequence is a reduction of the discrepancy between the results obtained by these new methods and those from experimental or numerical tests. In order to extend the scope of Eurocode 3, Part 1–1, additional methods have been implemented in an annex to cover the stability of members with mono‐symmetric cross‐section under compression axial force, biaxial bending, with or without torsion. The format of the resistance criteria remains similar to the format of the current interaction formulae so that the designers can easily identify the evolution of the rules. This article presents in a systematic way the new implementations in the formal vote version FprEN 1993‐1‐1 of the code. [ABSTRACT FROM AUTHOR]

As part of the ongoing revision of the Eurocodes, design provisions in EN 1999‐1‐1 on the buckling of longitudinally welded aluminium compression members have been subjected to a critical review. The numerical investigations described in part 1 of the paper were conducted because a need for improvement was identified. In part 2 of the paper, the main observations are presented in qualitative terms. Those observations are: the influence of the allocation of the materials to buckling classes, the influence of the imperfections plus the cross‐section geometry including the position and size of the HAZ within the cross‐section. Part 3 will conclude this paper by discussing the proposed design approaches in detail. [ABSTRACT FROM AUTHOR]

Remotely controllable photoresponsive hydrogel actuators are promising for applications in multiple fields. However, simple deformation mechanisms, which rely on the general swelling/deswelling, limit their performance and application. Herein, we report a displacement amplification mechanism based on the buckling deformation of photoresponsive hydrogel film. The on‐chip buckled architecture of the hydrogel enables actuation between a flat 2D shape and tubular 3D buckled shape with remarkable performances, including high deformation ratio (height ratio: ≈360%), tunable cycle motion frequency (0.1—1 Hz) and high cyclic stability. Moreover, localized buckling deformation, such as tube opening and closing, can be controlled in response to photostimulation. Inspired by these biomorphic shapes and motions, an intestine‐mimetic device and demonstrate segmentation with substance crushing and peristalsis motion with substance propelling were further fabricated. This study will provide a useful design principle for hydrogel actuators and shed light on diverse applications in soft robotics, dynamic microfluidics and organs‐on‐chips. [ABSTRACT FROM AUTHOR]

Ensuring the stability of composite structures in the marine environment is crucial. The harsh and corrosive nature of marine conditions presents unique challenges, making maintenance a top priority. In this study, the impact of seawater aging on the mechanical, buckling, structural, and thermal properties of glass fiber‐reinforced polymer nanocomposites was investigated. Composites were produced using the VARTM method with 2% nano Al2O3 and 2% nano TiO2. Aging was conducted in a seawater environment at room temperature for 120, 240, and 360 days. Mechanical properties, including tensile, compressive, flexural, impact, and buckling tests, were performed, and water absorption was determined. Structural analysis was carried out using SEM images. The experimental results indicated that the presence of nanoparticles minimized the effect of seawater. TiO2 preserved tensile strength by 10.33%, impact energy by 6.8%, and critical buckling load by 3.06% compared to the pure composite. Al2O3 reduced water absorption to 0.594% and preserved tensile strength by 6.67%, impact energy by 4.02%, and critical buckling load by 2%. Thermal test revealed an increase in thermal conductivity with aging, with the TiO2‐doped composite exhibiting the smallest increase (14.66%). The significance of the obtained results was confirmed through ANOVA analysis. Highlights: Glass fiber‐reinforced nanocomposite was produced with nano Al2O3 and TiO2.The effect of seawater aging was investigated.It showed that TiO2 nanoparticles are a good candidate against seawater aging.The experimental results showed statistical significance. [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 13 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 material tests on the conventional and WAAM steels 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 beneficial effects of the WAAM stiffeners were an increased cross‐sectional area and second moment of area, enhanced local buckling capacity and a more favourable residual stress pattern. Increases in axial capacity of between 17% and 54% for increases of mass between 2% and 26% were achieved, highlighting the tremendous potential in terms of structural efficiency and material savings that can be realised by the combination of WAAM with traditional manufacturing methods. [ABSTRACT FROM AUTHOR]

This paper presents and analyzes the nonlinear buckling responses of three types of shallow imperfect panels (cylindrical panel, parabolic panel, and half‐sinusoid panel) made from functionally graded graphene reinforced composite (FG‐GRC) on nonlinear elastic foundations subjected to axial compressive load in thermal environments. The nonlinear governing equations are formulated on Reddy's higher‐order shear deformation shell theory (HSDST) and take into account von Karman‐type nonlinearity. A new approximation technique to determine the stress function in average sense is developed and Galerkin's method is used to obtain the algebraically nonlinear equation system. Then, the simple calculation process can be used to solve the obtained equation systems, and the formulations to calculate the critical buckling loads and postbuckling load‐deflection curves are expressed in explicit form. The results can be flexibly applied to FG‐GRC panels with different curvatures in engineering designs. The effects of panel types, geometrical parameters, temperature increase, initial imperfection, and nonlinear elastic foundations on the critical buckling loads and postbuckling curves of cylindrical, parabolic, and half‐sinusoid FG‐GRC panels are discussed in numerical results. Numerical results also show a small disadvantage in the load‐carrying capacity of cylindrical panels compared to parabolic panels and half‐sinusoid shallow panels. Highlights: Postbuckling of cylindrical, parabolic, and half‐sinusoid panels are studied.The panels are made of functionally graded graphene reinforced composite.Reddy's higher‐order shear deformation shell theory is applied.A new approximation technique to determine the stress function is developed.Critical buckling loads and postbuckling expressions are explicitly obtained. [ABSTRACT FROM AUTHOR]

This study investigates the effects of nanoclay (NC) particles on the buckling behavior of carbon/Kevlar intraply hybrid composites. The laminates containing various amounts of NC particles (0.5%, 1%, 1.5%, 2%, and 3% by weight) were manufactured using hand layup stacking followed by vacuum bag molding process. The prepared samples were subjected to axial and lateral compressive loads under fixed‐fixed and fixed‐free boundary conditions, respectively, and the relevant critical buckling loads were determined. Furthermore, the failure modes were examined via microscopic views taken from the damaged areas on the samples to fully understand the influences of NC particles on buckling characteristics. The findings demonstrated that the buckling behaviors of the samples were significantly affected by the introduction of NC particles. Compared with the composite samples without any NC particles, the composite samples with 1 wt% NC particles showed an increase of 21.12% and 25.33% in the axial and lateral critical buckling loads, respectively. However, the inclusion of NC particles with an amount that higher than 1 wt% showed a decreasing trend in terms of critical loads for both buckling loadings, which can be viewed as a measure of load‐bearing capability. Moreover, the samples filled with 3 wt% NC particles exhibited a decrement on critical loads compared with those of samples without any NC particle filler. With the help of microscopic views, the failure modes were detected as matrix fragmentation and delamination for both buckling loadings. [ABSTRACT FROM AUTHOR]

The forthcoming second generation of EN 1993‐1‐5 is bringing changes in terms of buckling and interpolation curves that allow the positive effects of torsional stiffness of closed‐section stiffeners to be taken into account. Regarding the determination of the critical buckling stress for global plate buckling, analytical or numerical methods may be used. FprEN 1993‐1‐5 provides a simplified analytical equation for determining the critical buckling stress of an equivalent orthotropic plate, which can also be found in the informative Annex A of EN 1993‐1‐5. The given equation does not take into account the torsional stiffness of longitudinal stiffeners with closed cross‐sections. The latter are often used in plated structures due to fabrication and strength benefits. This paper compares two methods for determining the elastic critical plate buckling stress that consider the positive effect of the torsional stiffness of closed‐section stiffeners. First, a newly proposed analytical method that accounts for the torsional stiffness of closed‐section stiffeners is derived on the same basis as the current equation in Annex A. Secondly, a numerical linear buckling analysis is performed on a large number of stiffened panels. The advantages and disadvantages of both methods are pointed out. Finally, both values are used to determine the ultimate resistance of plates and with GMNIA results from previous studies. [ABSTRACT FROM AUTHOR]

Graphene is a highly conductive and exceptional material that has shown potential for significantly improving the piezoelectric and mechanical properties of piezoelectric matrix. This paper examines the stability of composite plates surface bonded with graphene‐reinforced composite piezoelectric (GRCP) actuators. However, the significant differences in material characteristics at the interfaces will pose some challenges in analyzing the buckling behavior of piezoelectric composite plates by means of existing higher‐order shear deformation theories. To address this issue, a refined plate theory is developed for the buckling analysis of piezoelectric composite plates. The developed theory includes a new interlaminar shear stress field that precisely describes the distribution of interlaminar shear stresses, which differs from earlier higher‐order theories. It should be emphasized that the finite element formulation can be simplified by removing the second‐order derivatives of in‐plane displacement parameters from interlaminar shear stresses. In terms of the developed theory, a four‐node C0 quadrilateral plate element is introduced to examine the buckling behavior of piezoelectric composite plates. Furthermore, the modified interlaminar shear stress field is absorbed into the strain energy, significantly improving the ability to predict the critical loads of composite plates with GRCP actuators. The refined plate model is evaluated through the utilization of three‐dimensional (3D) elasticity solutions and results obtained from other associated theories. Numerical results demonstrate that the refined plate model is capable of producing favorable results, and a comprehensive examination is conducted to analyze the effects of significant parameters on the buckling behaviors of piezoelectric composite plates. This study sets a solid foundation for future research and development on the application of graphene‐reinforced composite piezoelectric actuators in composite structures. Highlights: Buckling analysis of composite plates with GRCP actuators is conducted.A refined plate theory with modified interlaminar shear stresses is developed.The ability to predict critical loads can be significantly improved.The finite element formulation can be simplified based on the proposed model.Comprehensive parametric studies on buckling behavior are caried out. [ABSTRACT FROM AUTHOR]

Soft and lightweight grippers have greatly enhanced the performance of robotic manipulators in handling complex objects with varying shape, texture, and stiffness. However, the combination of universal grasping with passive sensing capabilities still presents challenges. To overcome this limitation, a fluidic soft gripper is introduced based on the buckling of soft, thin hemispherical shells. Leveraging a single fluidic pressure input, the soft gripper can grasp slippery and delicate objects while passively providing information on this physical interaction. Guided by analytical, numerical, and experimental tools, the novel grasping principle of this mechanics‐based soft gripper is explored. First, the buckling behavior of a free hemisphere is characterized as a function of its geometric parameters. Inspired by the free hemisphere's two‐lobe mode shape ideal for grasping purposes, it is demonstrated that the gripper can perform dexterous manipulation and gentle gripping of fragile objects in confined spaces and underwater environments. Last, the soft gripper's embedded capability of detecting contact, grasping, and release conditions during the interaction with an unknown object is proved. This simple buckling‐based soft gripper opens new avenues for the design of adaptive gripper morphologies with tactile sensing capabilities for applications ranging from medical and agricultural robotics to space and underwater exploration. [ABSTRACT FROM AUTHOR]

This paper presents the development of flexural buckling curves for austenitic and duplex stainless steel welded I‐sections and structural hollow sections, which are proposed for implementation in the new AISC stainless steel specification. The proposed buckling curves were developed following the same type of reliability analysis employed to develop the flexural buckling curve included in AISC 360 Specification for Structural Steel Buildings for carbon steel, considering all the experimental data available in the literature and a large number of numerical results. In order to facilitate their implementation, the proposed curves follow a similar form as the AISC‐type of curve included in AISC 360, with the only differences being the addition of a yield plateau and the values of selected coefficients used to adjust the shape of the curves. Three different buckling curves are proposed: one buckling curve for circular hollow section (CHS) columns and I‐section columns buckling about the major axis; one for rectangular hollow section (RHS) columns; and one for I‐section columns buckling about the minor axis. The proposed curves represent a significant improvement with respect to the currently available stainless steel flexural buckling curve included in AISC Design Guide 27, providing an increase in strength predictions of up to 55%. [ABSTRACT FROM AUTHOR]

Buckling of the longitudinal rebar is one of the main forms of plastic hinge failure in reinforced concrete (RC) columns after an earthquake. This rebar buckling significantly impacts the seismic bearing capacity and energy dissipation capacity. To restrain the development of longitudinal rebar buckling behavior and delay the degradation of lateral strength in RC columns, this paper developed a new type of buckling restraint rebar (BRR) consisting of three components: longitudinal rebar, a restraint sleeve, and foam material. First, the BRR mechanical properties under compression and tension‐compression cyclic loading were obtained through quasi‐static loading tests. Then, the BRR compression and tension‐compression cyclic loading processes were numerically simulated based on ABAQUS finite element software. The simulated results were compared with the test results. Finally, a stress–strain constitutive model for this new BRR was proposed based on this study. Results showed that the restraint sleeve could significantly enhance the lateral stiffness and the bearing capacity of longitudinal reinforcement after yielding. The compressive performance of BRR was mainly affected by the length and wall thickness of the sleeve. The cyclic performance was mainly affected by the length of the sleeve and the clearance between the sleeve and the reinforcement. The BRR constitutive model proposed in this paper can accurately reflect the influence of restraint sleeves on the stiffness of longitudinal reinforcement after yielding. [ABSTRACT FROM AUTHOR]

The stability evaluation of structures being lifted by cranes poses a challenger for the analysts from the inherent hypostaticity that the problem presents. Usual buckling evaluation for standard structures supported by foundations are not possible and alternative modelling strategies are required. Two strategies can be defined for buckling evaluation: The Linearized Buckling Check and The Direct Analysis Method. This paper states the problem and describes both strategies along with the presentation of modelling good practices and a clear framework of codes and standards which bring light into aspects such as load factors; weight contingency; Center of Gravity imprecision, etc. A comparative study for the results obtained from both methods for a typical truss being lifted is presented. [ABSTRACT FROM AUTHOR]

The buckling of new three‐phase composite shells, which include the base material combined with macro fiber composite and reinforced with graphene (MFC‐GP), is investigated in this article. The bifurcation condition of the buckling is obtained by implementing the first‐order shell theory and wave propagation theory in conjunction with the principle of minimum potential energy. The buckling analysis is transformed into a bifurcation problem of equations. Parametric study is conducted to investigate the effects of the GP volume fraction, length, neutral surface radius, and thickness on the critical buckling loads and critical buckling modes. Furthermore, the influences of voltage and temperature change on the critical buckling displacements are explored. Reliable theoretical support for the design and manufacture of the MFC‐GP structures is provided in the results. [ABSTRACT FROM AUTHOR]

In this article, the numerical and experimental results for buckling analysis of a nanocomposite beams reinforced by nanorods are studied and compared. The Chebyshev-Ritz method is used to calculate the buckling numerically and compare it with the buckling test. Epoxy resin, glass's fiber, and nanorods are used to make composites. These nanorods are made using recycled materials. Also, bending and tensile tests are used to obtain the properties of these composites. In addition, the effect of various parameters such as Young's modulus, temperature change, Poisson's ratio, and boundary conditions, the strain gradient parameter, and different shape function is investigated. The addition of nanorods increases the strength and stiffness of composites and increases the critical buckling load. Actually, the made nanorods are used as a reinforcement in matrix, thus in the made nanocomposites, fracture and buckling tests are done and the results indicate that the inclusion of nanorods (0.32%) increases the critical buckling load by 16.4%. A facile hydrothermal method to synthesis the nano rodes has a less cost with the other methods, thus by adding a small percentage of it to the composite, the stiffness of the structure increases. According to the results and the significant increase in Young's modulus and critical buckling load and the cost-effectiveness of carbon nanorods (CNRs) made from recycled materials, these environmentally friendly reinforcements can be used in various industries such as machine body construction, automobile manufacturing, shipbuilding and construction of type's turbines. Highlights • Using potato peels and hydrothermal methods, CNRs produced. • These CNRs are useful, and production is cheap and no harm environmental. • Buckling sample include of glass fiber, without and with CNRs and epoxy resin. • Third order shear deformation beam theory and Chebyshev-Ritz are used • Theoretical and experimental buckling critical load are compared. [ABSTRACT FROM AUTHOR]

Buckling of a simple supported and cantilever nano‐rod and under action of self‐weight was modeled, taking into account the surface effect according to two models of surface elasticity – Gurtin–Murdoch and Steigmann–Ogden. The size effect under the buckling was studied by the Ritz method using two kinematic hypotheses, known as the rod theories of Euler–Bernoulli and Timoshenko. The simulation results were compared depending on the accepted surface elasticity model and the kinematic hypothesis. [ABSTRACT FROM AUTHOR]

Grid‐stiffened composite cylinders are widely used in a variety of applications and are subjected to static, dynamic, and impact loads. In terms of buckling strength, these structures outperform simple layered and sandwich composites of the same weight, and the presence of unidirectional fiber ribs contributes to their delamination resistance. The purpose of this research is to look into the buckling behavior of grid‐stiffened composite cylinders under low‐velocity and high‐energy axial impacts. The tests were carried out at room temperature using a 35 kg impactor with an impactor fall height of about 2.75 m. This study builds on previous research and considers the samples' thin skin, indicating that skin buckling is the primary buckling mode in such scenarios. According to static loading research, three types of buckling can occur in grid‐stiffened composite cylinders: local shell buckling, local rib buckling, and general buckling, and each of these can be controlled by adjusting the geometric properties. But, based on the loading speed in the weight‐drop test, controlling the specific type of buckling that occurs during impact loading is difficult. Examining residual structural effects can help determine the type of buckling and damage sustained during impact events. According to the results, the forces that cause buckling in grid‐stiffened composite structures under impact loads are 1.5–2 times greater than static loading conditions. Notably, once the forces are removed, these structures can return to their original positions, however with less stiffness. As a result, they absorb a significant amount of impact energy. Highlights: Composite cylinders with spiral ribs have higher static compression resistance.Dynamic loading increases local buckling forces in grid‐stiffened structures.Despite being damaged, grid‐stiffened cylinders bounce back quickly after impact.Skin buckling is a common mode of failure for grid‐stiffened composite.The global buckling force is greater than the local buckling force. [ABSTRACT FROM AUTHOR]

A design concept is proposed for the building block, a dot, of programmable braille readers utilizing bistable shell buckling, magnetic actuation, and pneumatic loading. The design process is guided by Finite Element simulations, which are initially validated through precision experiments conducted on a scaled‐up, single‐shell model system. Then, the simulations are leveraged to systematically explore the design space, adhering to the standardized geometric and physical specifications of braille systems. The findings demonstrate the feasibility of selecting design parameters that satisfy both geometric requirements and blocking forces under moderate magnetic fields, facilitated by pneumatic loading to switch between the two stable states. While the study is focused on experimentally validated numerical simulations, it is also identify several manufacturing challenges that need to be resolved for future physical implementations. [ABSTRACT FROM AUTHOR]

The steel plate shear walls (SPSWs) are reckoned as one of the lateral load‐resisting systems with a high ductility and strength as well as a great energy dissipation capacity, which have been widely used in the recent years. One of the most important drawbacks of the SPSWs concerns their shear buckling due to which the behavioral parameters of this system is considerably undermined. To overcome this issue, the buckling‐restrained (BR) SPSWs have been developed, which have succeeded in resolving the drawbacks of the conventional SPSWs. This paper has investigated behavior of the BRSPSWs subjected to the cyclic loadings. To examine the nonlinear static behavior of the BRSPSWs, four experimental specimens including the specimen without concrete panel, the specimen with concrete panel and gap width equal to zero (directly connected to the steel plate) and the specimens with gap width 20 and 40 mm, were built in the laboratory with a scale of 1:2 and then subjected to the cyclic loadings. Afterwards, the specimens were numerically simulated considering the gap widths 0, 20 and 40 mm. After the process of verification, a parametric study was performed, in which cyclic performance of the specimens subjected to the reversed loadings according to ATC‐24 protocol was investigated. Based on the obtained results, the specimen without concrete panel has the lowest energy dissipation capacity, which is due to the local and lateral buckling. Additionally, the pinching phenomenon was significant in this specimen. In contrast, the specimens with gap width 20 and 40 mm exhibited an energy dissipation capacity six times greater than that of the specimens without panel or even gap. Moreover, it was observed that the shear capacity of the specimens with the concrete panels increased by nearly 50%. [ABSTRACT FROM AUTHOR]

Eurocode 3 design rules for the lateral stability of welded I‐members are based on the assumption of hot‐rolled flanges. In practice, a large amount of welded I‐section members is made of flame cut flanges. However, residual stresses of hot‐rolled and flame‐cut flanges are quite different. The latter are more favourable with respect to out‐of‐plane buckling. The beneficial effect of flame‐cuts commonly performed at the flanges tips is then neglected in design standards. A literature review of lateraltorsional buckling tests on welded I‐members with flame‐cut flanges highlights a scarcity of results on mono‐symmetric and/or non‐uniform members. In addition, tests are generally performed on stocky cross‐sections while welded members are usually slender. Lateral‐torsional buckling tests have thus been conducted on four S355 slender welded members made of flame‐cut flanges: two uniform beams and two tapered beams. Within both couples of beams, one had a doubly symmetric cross‐section, the other one being mono‐symmetric. Experimental results highlight the impact of tapering and/or increasing the compression flange thickness whatever the beam type. These experimental tests are then modelled with shell finite elements considering imperfections, residual stresses and material laws measured experimentally. The results are in good agreement with experimental tests. Additional finite element analyses are performed varying the residual stresses distribution. A significant impact of the flange fabrication process is confirmed, flame‐cuts increasing substantially the lateral‐torsional buckling resistance. [ABSTRACT FROM AUTHOR]

A thermoplastic matrix composite flat panel stiffened by induction welded stringers, according to a typical aerospace configuration was tested. A Poly‐Ether‐Ether‐Ketone (PEEK) matrix reinforced by carbon fibers was adopted. The aim of this study was to investigate the shear buckling, a load condition that is very common for the aerospace structures, of the panel obtained using a non‐conventional approach for its fabrication, that is, induction welding. A finite element (FE) model capable to describe the buckling and the postbuckling behavior of the stiffened panel was also developed and compared with experimental results. Testing was performed using fixtures suitably designed to transmit a pure shear to the panel, and strain gauges were mounted on the external surfaces to measure the deformations. [ABSTRACT FROM AUTHOR]

Distortional buckling is a characteristic failure mode of compressed C channels with an intermediate unbraced length in the range of 4 to 7 times the web depth. The usual codified design method to calculate the buckling resistance by Eurocode EN 1993‐1‐3 proceeds through the determination of an effective cross‐section with reduced thicknesses of the stiffener zones working against distortional buckling. To calculate the slenderness of the compressed stiffener zones Eurocode gives simple formulas, applicable separately for end stiffeners and intermediate stiffeners. The identification of the part of the cross‐section to be used in these formulas can be doubtful. It can be demonstrated that these formulas will predict unreliable critical stresses being often on the unsafe side. EN 1993‐1‐3 allows to use more reliable values based on FEA or other approaches without giving a detailed, applicable design methodology. This paper presents a method which is able to assign cross‐section buckling modes calculated with the help of finite strip analysis to compressed stiffener zones of a compressed general C section. Assignment is based on the determination of deformation energy balance. The proposed approach finds the zones of the section which tend to buckle during distortional buckling and the zones which are responsible to restrain this buckling. Additionally, it gives guidance on how to determine the exact area where the calculated thickness reduction shall be applied around the stiffener. For the thickness reduction the buckling curve given in the actual EN 1993‐1‐3 will be used. The proposed method is part of a larger research project which aims to provide a complete Eurocode compatible design methodology considering local, distortional and global buckling of general shaped cold‐formed members subject to 3D loading and support condition, to be implemented in computer software programs working with 7DOF beam finite elements.. [ABSTRACT FROM AUTHOR]

Flexible wearable sensors have the characteristics of flexibility, comfort, and wearability, and have shown great potential in future electronic products. Despite significant efforts in developing stretchable electronic materials and structures, the development of flexible strain sensors with a wide temperature range, high sensitivity, broad detection range, and good interface stability remains challenging. Here, strain sensors with buckled structures are fabricated using high and low‐temperature resistant material Ti3C2Tx MXene/graphene, PDMS 184. The conductive material Ti3C2Tx MXene/graphene exhibits excellent interface interaction with PDMS 184, addressing not only the poor compatibility issue between the conductive material and the flexible substrate, but also demonstrating good stability and cycling performance. Buckled structure improves the stretchability and linearity of strain sensors. The fabricated strain sensor is suitable for a wide temperature range (−40 to 120 °C) and exhibits high stretchability (120% strain). The strain sensor demonstrates rapid response times at different temperatures: −40 (72.6 ms), 0 (62.7 ms), and 120 °C (52.7 ms). The strain sensor exhibits high sensitivity at different temperatures: −40 (GF = 0.38), 0 (GF = 0.24), 40 (GF = 0.66), and 120 °C (GF = 1.47). The strain sensor has a wide detection range (0.1% to 120%) and excellent cycling stability. In addition, Ti3C2Tx MXene/graphene strain sensors can accurately capture various human activities, such as blinking, speaking, finger bending, and wrist bending. [ABSTRACT FROM AUTHOR]

This study investigates the buckling of microbeams with variable cross‐sections and middle supports in a thermal environment. Based on classical theories and modified couple stress, the size‐dependent behavior of the microbeam is modeled, and the intermediate support is simulated elastically. A temperature‐dependent relationship will also be assumed for the material properties of the microbeam. The governing equations will be derived using Hamilton's principle based on the modified Couple stress theory and the nonlinear thermal field. Using an analytical approach, buckling loads and deformation of microbeams will be determined. The accuracy of the answers will be investigated to demonstrate the effectiveness of the method used and the correctness of the results obtained. A comparison will be made between the obtained results and the results available in the scientific literature to prove the accuracy of the formulation and the method used. A parametric study will then be conducted to determine the effect of boundary conditions, the flexibility of the middle support, temperature distribution, and geometric characteristics on the buckling loads of microbeams. [ABSTRACT FROM AUTHOR]

As part of the ongoing revision of the Eurocodes, design provisions in EN 1999‐1‐1 on the buckling of longitudinally welded aluminium compression members have been subjected to a critical review. Numerical investigations were conducted because a need for improvement was identified. This part 1 of the paper describes the individual steps of the revision and the modifications discussed, which include the introduction of longitudinally welded members. Before going into the numerical investigations in more detail, previous observations are presented regarding buckling classes and plateau lengths. In part 1 of the paper, explanations of the numerical investigations are limited to presenting the modelling of the geometry, the mechanical properties and the imperfections as well as their respective variation in the context of the parametric studies. The results of the numerical investigations and the proposed design approaches will be presented in detail in parts 2 and 3. [ABSTRACT FROM AUTHOR]

Even though the simulations used to describe the failure of laminates are becoming more and more predictive, complex testing under multiaxial loadings is still required to validate the design of structural parts in a wide range of industrial domains. It is thus essential to assess the actual boundary conditions to allow for an objective comparison between testing and calculations, in particular since the structural tests are complex and often leads to buckling. Therefore, accurate estimation of force and moment fluxes applied to the specimen is critical. In this context, stereo digital image correlation (SDIC) has proven to be an important measurement tool and provides very well‐resolved surface displacement fields, but the exploitation of such measurements to calculate fluxes remains problematic when testing composites. The first objective of this study is both to reduce the uncertainty associated with fluxes determination on a complex test and to simplify the extraction process with respect to existing procedures. The second objective is to make this methodology robust to geometrically non‐linear deformations. In this paper, we propose a new methodology that extracts minimal boundary conditions in the form of 3D mechanically admissible displacements fields. The approach developed uses a finite element SDIC (FE‐SDIC) method regularized by means of mechanical behaviour admissibility equations. Results show that the new methodology outputs much more accurate fluxes than classical data generated from multiple differentiations of the displacement fields. Excellent noise robustness is obtained and quantified. Numerical predictions have been satisfactorily compared with experimental data from one structural‐scale composite specimen under complex testing. [ABSTRACT FROM AUTHOR]

Wire and Arc Additive Manufacturing (WAAM) is one of the promising metal 3D printing techniques, with the ability to produce large‐scale structural components with high speed and low cost. However, there is a lack of research on the structural performance of WAAM members. To this end, numerical modeling and design of WAAM stainless steel circular hollow section (CHS) stub columns has been conducted. Finite element (FE) models considering both as‐built material properties and rough geometry were proposed and verified by the existing experimental studies. By using the FE models, parametric studies on the local buckling resistance of WAAM CHS stub columns were conducted to consider a wider range of specimen geometries. Based on the FE results, the applicability of the current column design provisions in EN 1993‐1‐4 and AISC 370 to WAAM stainless steel CHS stub columns was assessed. At last, a new modified method was proposed to predict the local buckling resistance of WAAM stainless steel CHS stub columns. This study provides a novel approach for the FE modelling of WAAM components. [ABSTRACT FROM AUTHOR]

Optimizing the core thickness of a sandwich structure can be a computationally expensive task. In this work, an optimization approach for slender columns is presented. The approach iteratively determines the optimal thickness distribution using the second derivative of the eigenmodes as an input for the shape function. To demonstrate its capabilities, it is applied to simple columns constrained according to Euler's buckling cases. The optimization results are validated with detailed finite element models and compared to those from a nonlinear least squares‐based optimization. [ABSTRACT FROM AUTHOR]

The post‐buckling strength, which is simply called as crippling, is investigated for laminated composite structures in this study. L profiles that had various stacking sequences of carbon fiber reinforced epoxies were tested. Three different layups configurations were used by changing flange‐to‐thickness ratios. The main objective of this research was to show that flange‐to‐thickness ratio was not the only effecting parameter for crippling. Therefore, a new parameter, EGY number, was developed by considering the positions of 0° and 45° plies. Depending on EGY number, a new semi‐empirical formulation was presented to calculate crippling strength of the laminated composite structures. One of the test results was employed to verification of EGY number. In addition, the test results were validated with finite element analyses. Static, Riks and Dynamic, Explicit computational results were compared to simulate the experiments. Highlights: Determination of crippling strength both experimentally and theoretically.Comparison of numerical models: Static, Riks versus Dynamic, Explicit.Developing a new parameter called as EGY number.Developing of a new analytical semi‐empirical formula for crippling strength. [ABSTRACT FROM AUTHOR]

The axial buckling load of single carbon fiber or composite strands is typically predicted using Euler's formula, developed for isotropic materials. This study introduces anisotropy in a mechanical carbon/epoxy Z‐pin model under axial pressure. It examines the influence of compressive modulus, shear modulus, off‐axis angle, and aspect ratio on its buckling behavior. Results show that the axial instability performance of the Z‐pin decreases with lower compression, shear modulus, and aspect ratio while keeping the tensile modulus fixed. Anisotropy decreases buckling load by up to 14% compared with Euler's formula, which only considers tensile modulus. Additionally, the impact of the deflection Angle between the pressure and pin‐axis can be ignored when it is less than 3°. Highlights: Euler formula overestimates composite Z‐pin buckling force under axial pressure.Anisotropy decreases buckling load by up to 14% for carbon/epoxy.Shear modulus is more influential on Z‐pin with a small aspect ratio.For off‐axial compression angles <3°, influence can be ignored. [ABSTRACT FROM AUTHOR]

Aim: To evaluate the bending, buckling and torsional resistance of ProGlider (PG) (Dentsply Sirona, Ballaigues, Switzerland), R‐Pilot (RP) (VDW, Munich, Germany) and WaveOne Gold Glider (WOGG) (Dentsply Sirona). Methodology: Ninety instruments were used: 30 PG (size 0.16,.02v taper), 30 RP (size 0.125,.04 taper) and 30 WOGG (size 0.15,.02v taper). The bending resistance test was performed on 10 randomly selected instruments of each system according to ISO 3630‐1 specifications. For the buckling resistance test, a loading was applied in the axial direction of each instrument using a universal test machine, with a 20 N cell and 15 mm min−1 speed, in the axial direction. When a lateral elastic displacement of 1 mm occurred, the force was registered. The torsional resistance test was performed according to ISO 3630‐1 specifications. Statistical analysis was performed using one‐way anova and post hoc Student–Newman–Keuls test (P < 0.05). Results: WOGG had the lowest bending resistance, whilst RP had the highest bending resistance (P < 0.05). RP also had the highest buckling resistance, and WOGG had the lowest (P < 0.05). PG had intermediate results regarding bending and buckling resistance, with significant differences to RP and WOGG (P < 0.05). RP had the highest torsional strength and the lowest angular deflection when compared to PG and WOGG (P < 0.05). No differences in the torsional strength and angular deflection were observed between WOGG and PG (P> 0.05). Conclusion: The glide path instruments had different behaviours in term of bending, buckling and torsional resistance. [ABSTRACT FROM AUTHOR]

This paper presents the state of art in the field of composite shells with focus on stress analysis, buckling and post‐buckling responses under mechanical and thermal loading. Many researchers have investigated the buckling and post‐buckling responses of cylindrical, conical, spherical, thin and thick composite shells with single and doubly curved shells under mechanical and thermal loading. From the literature it can be inferred that hydrostatic pressure, axial compression and thermal environment influence the buckling behavior of laminated composite shell significantly. An effort is taken to review the research on buckling and post‐buckling responses of cylindrical and conical shaped shells under mechanical and thermal loading and their behavior during buckling and post‐buckling conditions. POLYM. COMPOS., 39:4231–4242, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]