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Stinger-like structures in living organisms evolved convergently across taxa for both defensive and offensive purposes, with the main goal being penetration and damage. Our observations over a broad range of taxa and sizes, from microscopic radiolarians to narwhals, reveal a self-similar geometry of the stinger extremity: the diameter (d) increases along the distance from the tip (x) following a power law [Formula: see text] , with the tapering exponent varying universally between 2 and 3. We demonstrate, through analytical and experimental mechanics involving three-dimensional (3D) printing, that this geometry optimizes the stinger's performance; it represents a trade-off between the propensity to buckle, for n smaller than 2, and increased penetration force, for n greater than 3. Moreover, we find that this optimal tapering exponent does not depend on stinger size and aspect ratio (base diameter over length). We conclude that for Nature's stingers, composed of biological materials with moduli ranging from hundreds of megapascals to ten gigapascals, the necessity for a power-law contour increases with sharpness to ensure sufficient stability for penetration of skin-like tissues. Our results offer a solution to the puzzle underlying this universal geometric trait of biological stingers and may provide a new strategy to design needle-like structures for engineering or medical applications.

In this study, a plane strain finite element analysis (FEA) was employed to investigate failure mechanisms of a hydrogen storage pipe system made of 316L stainless steel pipe coated with pure and functionally graded (FG) ceramic layers composed of Al2O3 and SiC. The system was studied for different common failure mechanisms, i.e., delamination, surface cracking and buckling delamination, upon cooling from an elevated stress-free temperature. Finally, the composition and thickness of the coating layers were considered as the main controlling factors and investigated for their influence on the studied failure mechanisms. It was observed that the most energetically favourable cracking mechanism for this type of system was surface cracking with the propagation of these cracks eventually leading to different failure paths. Buckling was found to be as less energetically favourable compared to surface cracking with the buckling resistance being enhanced by changing the coating thickness and composition factor. [ABSTRACT FROM AUTHOR]

In airplane structural design, creating a strong yet lightweight structure is crucial. During the preliminary design phase, structural sizing optimization is necessary to achieve an efficient and lightweight structure that meets safety standards. Composite materials offer a high strength-to-weight ratio, enabling a lighter structure without compromising strength. This work focuses on optimizing composite structure wings by considering laminae thicknesses as design variables and minimizing structure weight as the objective, using the gradient-based method. The optimization constraints include the Tsai-Hill criterion, buckling factor, and flutter speed to ensure the structure's safety against static load, buckling phenomena, and flutter phenomena. The optimization results indicate that the buckling factor is the most critical constraint, carrying the highest weight. The weight of the wing structure decreased by 53% and 79% after optimizing with static and flutter constraints, respectively. Despite minimal changes in weight after optimizing with the buckling constraint, the structure now meets the buckling safety criteria and is safe from buckling. [ABSTRACT FROM AUTHOR]

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

AbstractVarious intriguing morphological patterns emerge on the surfaces of growing, developing, or aging tissues, organs, and colonies of microorganisms. Our research draws inspiration from biological growth processes and applies differential growth to film-substrate systems. The strain mismatch induced by this approach leads to distinctive buckling patterns. Through a combination of finite element analysis (FEA) and theoretical analysis, we derive a comprehensive expression for the strain energy in a buckled film-substrate system subjected to differential growth. By solving the energy equations, our study investigates the intricate interplay of material properties, growth functions, and geometric characteristics. This exploration provides valuable insights into the deformations induced by growth in membrane structures and soft materials. Additionally, we establish a phase diagram that characterizes the buckling patterns. It opens avenues for innovative geometric design and 3D self-assembly techniques. Furthermore, our findings have the potential to inspire applications in fields such as soft robotics and flexible electronics. [ABSTRACT FROM AUTHOR]

Launch-vehicle shell structures, which can be composed of both cylindrical and conical sections, are known to be susceptible to buckling due to their large radius-to-thickness ratios. Advancements in composite manufacturing and numerical methods have enabled designers to consider more nontraditional shapes, such as connecting the conical and cylindrical sections with a toroidal transition to create a single-piece conical-cylindrical shell. This single-piece construction eliminates the need for a stiff, heavy interface ring between sections and has the potential to reduce mass. To better understand the buckling behavior of a composite conical-cylindrical shell, a laboratory-scale article was designed, fabricated, and tested. Before the test, a finite element model that included thickness variations and radial imperfections was created. The test article buckled elastically at 251.8 kN, approximately 8.8% higher than the predicted buckling load of 231.4 kN. Because the test article buckled elastically, the buckling test was repeated. The buckling load measured from the second test was within 1% of that from the first test. Continued research on conical-cylindrical structures has the potential to expand the design space for launch-vehicle structures and lead to improved designs and reduced mass. [ABSTRACT FROM AUTHOR]

Rehabilitation is necessary for those with restricted arm mobility to enhance arm movement efficiency and offer dynamic stability. Recent research initiatives are aimed at supporting the rehabilitation of individuals with disabilities or injuries that limit arm movement. Accordingly, the RRSS (Revolute-Revolute-Spherical-Spherical) exoskeleton mechanism for circumduction motion is proposed in this study. The objective is to ascertain the parameters of the mechanism required to accomplish or approximate a sequence of prescribed circumduction positions. When a rigid body needs to operate according to a precise displacement sequence, this design is appropriate which is considered as a nonlinear kinostatic optimization problem. The problem can be formulated with constraints concerning driven link buckling, driver static torque, and driver elastic deflection. The suggested RRSS circumduction motion production process is used to simulate and analyze the workspace of the arm and shoulder as well as muscle activity. Significant changes in the reactions of the muscles, bones, and joints movement were noted during virtual testing of the suggested exoskeleton on a human arm. Some tremendous results of exoskeleton joints and human arm fusion were found. Some computations were made for the deltoid muscles, which control arm movement in the scapular plane, the FCU (Flexor Carpi Ulnaris) muscle, which is located in the forearm and controls hand flexion and adduction, and the caput breve, a short head of biceps brachii muscles. [ABSTRACT FROM AUTHOR]

The aim of the present study is to elucidate the non-linear stability characteristics of randomly distributed carbon nanotube-reinforced fiber composite (RD-CNTRFC) beams subjected to thermo-mechanical loading. Effective material properties of RD-CNTRFC are estimated using the Eshelby-Mori-Tanaka approach and Halpin–Tsai micromechanical techniques. The material properties are considered to be temperature-dependent, and the influence of carbon nanotube (CNT) agglomeration is also incorporated in material properties estimation of hybrid matrix. The strain-displacement relations are assumed by incorporating the higher-order shear deformation theory and geometrical nonlinearity (von Kármán). The governing partial differential equations are obtained by minimizing the total potential energy of the beam. Buckling loads of beam subjected to in-plane compressive loads are estimated using Eigen value approach. Similarly, buckling temperatures are also determined by solving Eigenvalue problem iteratively due to temperature-dependent material properties. The non-linear equilibrium paths under thermal and mechanical loadings are traced through iterative Eigenvalue approach. Numerical results are presented to elucidate the influence of various parameters like CNT agglomeration, ply sequences, span-to-depth ratio, boundary conditions, and mass fraction of CNTs. [ABSTRACT FROM AUTHOR]

In this research, the optimization of the geometric parameters of a 3-layer composite plate with an elliptical cutout in the center was investigated utilizing an artificial neural network and genetic algorithm for the first time to obtain the minimum ratio of linear buckling load to weight and the ratio of the diameters of the ellipse. After completing 294 simulations in Abaqus finite element software and forming an artificial neural network with two hidden layers, the function obtained in the artificial neural network was used as the objective function in the genetic algorithm, and the optimal values for the angle of the ellipse with the horizon axis, the diameter ratio of ellipses as well as the fiber angle of the middle layer of the composite were obtained. using artificial neural networks, three algorithms, Levenberg-Marquardt, Bayesian regularization; and scaled conjugate gradient backpropagation, were compared and the number of neurons in each algorithm was compared. The results showed that Levenberg-Marquardt's algorithm is more accurate compared to other algorithms. In the end, the optimal values for the angle of the ellipse with the horizontal axis; as the fiber angle of the middle layer of the composite and, the ratio of the oval diameters as α = 12.3001 degree , θ = 5.9481 degree and D = 1.5690. [ABSTRACT FROM AUTHOR]

Analytical methods for calculating the buckling loads in laminated panels often assume uniform edge loads without any openings, overlooking real-world conditions with diverse non-uniform edge loads and varying cutout sizes. This study aims to explore the buckling behavior of composite panels with and without stiffeners under different non-uniform edge load distributions by developing a robust and computationally efficient finite element (FE) formulation. Buckling loads are determined for different plate aspect ratios, number of stiffeners under various non-uniform edge-loading cases. Furthermore, it addresses the effects of different layup schemes and stiffener eccentricities.The analysis employs a 9-noded heterosis plate element and a compatible 3-noded beam element, incorporating shear deformation and rotary inertia for both the plate and stiffeners. Additionally, due to the non-uniform stress distribution in the stiffened panels, a unique dynamic technique has been implemented to account for the stability performance by employing two sets of boundary conditions. The study demonstrates that maintaining stiffener eccentricity (est) within the range of 2.0 to 3.0 notably improves buckling strength depending on the type of edge loads. [ABSTRACT FROM AUTHOR]

Angle profiles belong to the most common steel profiles used in several types of civil engineering structures, such as in lattice towers. Although, in such towers, they are usually considered as axially loaded (truss) members, an additional bending moment develops due to the eccentricity between the point of load application and the gravity center of the profile. Therefore, this paper focuses on the buckling resistance of single-angle members subjected to combined compression and bending. The investigations have been performed through numerical parametrical studies and have been compared to different normative documents where interaction equations are provided. [ABSTRACT FROM AUTHOR]

Study Design. Experimental study. Objective. We sought to elucidate the association between ligamentum flavum thickening and tissue buckling, and the clinical and imaging factors related to buckling by comparing the ligamentum flavum thickness on MRI images and within the actual tissue. Summary of Background Data. Ligamentum flavum thickening is a main contributor to lumbar spinal canal stenosis. Buckling of the tissue may contribute to ligamentum flavum thickening along with tissue hypertrophy; however, this association has not been established conclusively. Materials and Methods. Ligamentum flavum samples (135 ligament samples) from 70 patients with lumbar spinal canal stenosis were evaluated. The ligamentum flavum thicknesses on magnetic resonance imaging (MRI) and in the tissue samples were compared to assess for the presence of buckling. The ligamentum flavum samples were divided into groups with or without buckling based on the difference between their thicknesses on MRI and in the tissues. The Pearson correlation coefficient test was used to assess the relationships between the LF thicknesses on MRI and in the tissues, MRI-tissue difference and LF thickness in the tissues, and MRI-tissue difference and LF thickness on MRI. Further, differences between the buckling+ and buckling-groups were compared using the unpaired t-test (LF thickness on MRI, LF thickness in the tissues, age, disc angle, and disc height) and χ² (disc level, disc degeneration, and receival/nonreceival of dialysis) test. Results. The ligamentum flavum thickness on MRI and in the tissues had a positive linear relationship, although the thickness was estimated to be significantly larger on MRI than in the tissues themselves. The ligamentum flavum with buckling had a larger thickness on MRI, less tissue hypertrophy, more severe disc degeneration, and was present in patients with a higher rate of dialysis. There were no differences in age and disc height, angle, or level between the two groups. Conclusions. Buckling of the ligamentum flavum coexists with tissue hypertrophy and contributes to perceived ligamentum thickening on imaging. Buckling of the ligamentum flavum tends to occur in less hypertrophied tissues and is associated with the grade of disc degeneration and the presence of other characteristics associated with spinal degeneration. [ABSTRACT FROM AUTHOR]

Current study presents a novel hybrid approach combining finite element modeling and density functional theory calculations to investigate the mechanical properties of monolayer puckered arsenene. The multiscale analysis in this study leverages finite element analysis as a distinctive approach, complementing the nano‐scale capabilities of density functional theory and molecular dynamics by overcoming limitations faced by these two methods in representing complex scenarios. Furthermore, finite element analysis demonstrates computational efficiency for larger structures, making it suitable for systems where atomistic simulations may be impractical. This hybrid methodology offers a unique framework for accurately predicting key properties, including elastic modulus and buckling force, by synergistically integrating the strengths of both computational techniques. In addition to demonstrating the effectiveness of our approach in accurately capturing material behavior, our findings shed light on fundamental aspects of nanoscale mechanics, with implications for various applications in nanotechnology, materials science, and structural engineering. By providing a deeper understanding of the mechanical response of 2D materials, our research contributes to advancing the field of nanoscale materials engineering and informs the design of innovative nanostructures with tailored mechanical properties. [ABSTRACT FROM AUTHOR]

This paper presents the process of conducting the structural analysis of AlAinSat-1 CubeSat through a numerical solution using Siemens NX. AlAinSat-1 is a 3U remote-sensing CubeSat carrying two earth observation payloads. The CubeSat is scheduled for launch on SpaceX Falcon 9 rocket. To ensure the success of the mission and its ability to withstand the launch environment, several scenarios should be analyzed. For AlAinSat-1 model the finite element analysis (FEA) method is used, and four types of structural analyses are considered: modal, quasi-static, buckling, and random vibration analyses. The workflow cycle includes idealizing, meshing, assembling, applying connections and boundary conditions, and eventually running the simulation utilizing the Siemens Nastran solver. The simulation results of all analysis types indicate that the model can safely withstand the loads exerted during launch. Also, the numerical results of the Command and Data Handling Subsystem (CDHS) module of AlAinSat-1 are experimentally validated through a vibration test conducted using an LV8 shaker system. The module successfully passed the test based on the test success criteria provided by the launcher. [ABSTRACT FROM AUTHOR]

This article compares the results of estimating the buckling capacity of steel spherical shells using simple engineering formulas with the results of selected experimental studies that have been conducted over the past 70 years. It is worth noting that these studies were conducted by research centers from all over the world, and the tested coatings differed in material, manufacturing method, radius R, and thickness t. The test methods, procedures, and measurement tools were also different. The convergence of the results obtained between the proposed simple engineering approach, which is based on the provisions of EN-1993-1-6 and the recommendations in EDR5th, and the experimental studies is satisfactory, and in many cases the results obtained are almost identical. Therefore, it is possible to practically apply the developed algorithms for estimating the buckling capacity of steel spherical shells without worrying too much about the capacity reserve. [ABSTRACT FROM AUTHOR]

This paper is concerned with the electro-mechanical buckling analysis of different kinds of smart sandwich shells with functionally graded porous core and piezoelectric sensor–actuator face sheets. Different types of shallow shells with double curvature including convex shells, cylindrical shells and concave shells are analyzed. It is assumed that effective properties of the porous core are functionally graded to vary as a special function of the thickness parameter. The equilibrium equations are established for the doubly-curved smart sandwich shells using the energy method. The stability equations governing the equilibrium position of the smart sandwich shells are obtained as a set of coupled partial differential equations. Closed-form expressions are generated to obtain the critical buckling loads of the smart sandwich shells using the airy stress function. Sandwich shells under different types of electro-mechanical loadings including axial, lateral and hydrostatic pressures are analyzed. These numerical results show the effects of feedback gain, porosity coefficient and piezoelectric layer thickness on the buckling resistance of these smart sandwich structures. [ABSTRACT FROM AUTHOR]

This article aims to investigate the buckling and free vibration behaviors of nanocomposite beams reinforced with functionally graded (FG) agglomerated carbon nanotubes (CNTs) in polymeric beams matrix. In order to estimate the material properties of the FG CNTs reinforced beam, the Eshelby–Mori–Tanaka rule on the basis of equivalent fiber is employed. Moreover, the Lagrange's principle is used to achieve the governing equations under supposition of the refined higher order beam theory without need of any shear correction factor. The differential quadrature finite element method (DQFEM) as a robust and precise numerical procedure is utilized to achieve the natural frequencies and buckling loads with various boundary supports. Then, the assessment of the effects of different factors such as of CNTs agglomeration parameters, different patterns of CNTs distribution, length to thickness quotients, and mixed boundary conditions on the vibrational and buckling responses of agglomerated CNTs reinforced beam are explored. It is concluded that the current numerical solution based DQFEM is efficient and accurate for predicting the mechanical behavior of the nanocomposite structures. Moreover, the stability and vibration responses of the NC beams can be significantly affected by tailoring the agglomeration parameters. [ABSTRACT FROM AUTHOR]

The stiffened plate is one type of representative thin-walled structure consisting of plates reinforced by varying stiffeners to strengthen its resistance to buckling deformation. However, the mechanism by which stiffeners could efficiently improve the buckling resistance of such structures has not been well reported. Therefore, to investigate the mechanism and predict buckling behavior of the structures accurately, a refined Reddy-type global-local stiffened plate model (RGLS) is established firstly, which can fulfill continuous condition of in-plane displacement and transverse shear stress among the adjacent layers between the plate and stiffeners. In conjunction with the established model, a refined triangular element which can accommodate the continuous condition of transverse shear stresses at the interface between the plate and the stiffeners is constructed. Subsequently, on the basis of the unidirectional stiffened sandwich structures, the symmetric grid-stiffened sandwich structures are proposed. The buckling behavior of grid-stiffened structures is further explored by the present element. A full experimental study and a system of numerical examples have been performed to assess the reliability of the established elements. These examples demonstrate that the buckling loads could be captured by the developed element with high computational efficiency and accuracy. However, the models will significantly overrate buckling loads of the stiffened sandwich structures without considering the continuum condition of the transverse stresses at the plate-stiffener interface. [ABSTRACT FROM AUTHOR]

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

AbstractThe primary aim of this study is to analyze the buckling behavior of carbon-nanotubes (CNT) reinforced plates using a closed-form dynamic stiffness formulation. The dynamic stiffness method (DSM), typically employed for analyzing plate vibrations, is adapted here for the buckling analysis of various configurations of CNT-reinforced composite plates with internal line support and subjected to uniaxial and biaxial in-plane loads. The displacement field is based on the first-order shear deformation theory, and the analytical expressions for governing differential equations and natural boundary conditions are derived via Hamilton’s principle. The dynamic stiffness matrix is developed for individual plate elements, considering Levy-type boundary conditions. These matrices are then combined to form a global dynamic stiffness matrix, which is solved using the Wittrick–Williams (W–W) algorithm to obtain the critical buckling load. A comprehensive comparative analysis is undertaken to ascertain the accuracy and computational efficacy of the present DSM with alternative numerical methodologies, alongside detailed parametric studies to explore plate buckling characteristics. It should be noted that the DSM is known to provide accurate results as it is based on the exact governing differential equation. Therefore, the reported buckling results can serve as a benchmark for future research in this field. [ABSTRACT FROM AUTHOR]

Steel-coped beams are used in industrial structures to accommodate a cluster of water mains, fire hydrants, power cables and telecommunication wires. The coped regions restrict the ultimate capacity and cause unfavorable failure modes. The current study investigates the structural assessment of the coped section in offshore topsides while their use enhances operational safety for drilling and production. The structural evaluation is done through 2D digital image correlation (DIC) experiments to quantify the influence of various cope geometries. The DIC technique illustrated the strain and deformation measurements under different loading conditions for different coped geometry. The primary failure mode observed in local web buckling is characterized by noticeable lateral displacement and the development of buckling lines over the coped web. Studies showed the influence of the cope depth on the load-carrying capacity and buckling processes for different cope geometries. The results of the DIC analysis are strongly aligned with experimental data and finite element numerical results, suggesting this technique to the structural assessment of coped section. [ABSTRACT FROM AUTHOR]

This study aims to develop semi-empirical formulas for foretelling the buckling loads of clamped and simply supported rectangular isotropic panels with central circular perforation exposed to different ratios of biaxial load conditions. The empirical formulas were developed and evaluated using Gene Expression Programming (GEP), Artificial Neural Network (ANN), and Finite Element Method (FEM). A total of 714 data set, generated using the FEM, is used to establish and validate the empirical formulas. This study investigates the effect of perforation sizes, plate aspect ratios, and biaxial load ratios on the buckling strength of perforated panels. The proposed formulas will allow a quick and easy estimation of buckling loads for perforated rectangular panels with acceptable accuracy without the need for sophisticated calculations. The results of the empirical formulas were comparable reasonably well with the results of the finite element analysis (FE) and available literature findings. [ABSTRACT FROM AUTHOR]

In this research, experimental and theoretical results for bending and buckling of a five-layer sandwich plate with composite face sheets reinforced by carbon nanotubes (CNTs), carbon nanorods, graphene platelets (GPLs), or nitinol shape memory alloy (SMA) wire and foam core are studied. The equations of equilibrium for this sandwich plate based on RFSDT and the principle of minimum total potential energy are derived, and then, the transverse displacement and buckling load are obtained. Using the rule of mixture and the Halpin–Tsai equation, the mechanical properties of the reinforced composite face sheets are calculated and also, and the constitutive equations of the SMA are presented according to the Brinson model. As well as, the influence of various parameters including thickness ratio, aspect ratio, the volume fraction of CNTs, GPLs, and nitinol SMA wire, fiber placement angle, and temperature changes are investigated on transverse deformation and dimensionless critical buckling load. Finally, tensile and buckling experimental tests were performed according to the standard tests ASTM D 3039 and ASTM C 364, respectively. [ABSTRACT FROM AUTHOR]

In the current investigation, the novelty lies in the formulation of a novel four-node rectangular finite element with six degrees of freedom per node using the strain approach and first-order shear deformation theory, therefore, this is the first article to use this approach to analyze the static, free vibration, and buckling behaviors of functionally graded. The properties of FGM vary continuously through the thickness direction according to the volume fraction of constituents defined by a simple power law function. The notion of a neutral surface is presented to prevent membrane bending coupling. The displacement functions of the suggested element which possess higher-order expressions, is based on assumed functions of strain that satisfy both rigid body modes and compatibility equations. The performance of the developed element is verified and compared with the published results in the literature and excellent agreement is observed. The influence of the geometrical, material properties, and loading types with different boundary conditions on the bending, free vibration, and buckling analysis of FGM plate are also studied and discussed for the first time using the strain-based finite element formulation. [ABSTRACT FROM AUTHOR]

In this paper, the simple refined plate theory (S-RPT) is extended for the analysis of the bending and buckling behaviours of functionally graded graphene platelets reinforced composite (FG-GPLRC) plates supported by local elastic foundations under different boundaries. For the first time, an analytical method for determining the location of the local elastic foundation distribution by simple integration is extended to the analysis of the bending and buckling behaviour of plates. The method avoids complex calculations compared to previous methods for determining the position of the elastic foundation. Compared with other simplified plate theories, the displacement pattern of S-RPT is able to reflect the interrelationship between the gradient material properties and the displacement distribution along plate's thickness. The material properties of FG-GPLRC plates are affected by temperature. Using the static equilibrium method, the plate equilibrium equations are derived by directly integrating the three-dimensional elastic equations along the plate cross section. Galerkin's method is used to solve the governing equations. The accuracy of S-RPT under different boundary conditions and the accuracy of the analytical method for determining the location of the elastic foundation are verified by comparing the numerical results with the existing literature. Finally, the effects of different distribution patterns, weight fractions of GPLs, thickness ratios, aspect ratios, boundary conditions, temperature, elastic foundation distribution patterns, and elastic foundation parameters were investigated in detail. [ABSTRACT FROM AUTHOR]

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

This study presents a numerical investigation into the adhesion strength of micro fibrillar structures, incorporating statistical analysis and the effects of excessive pre–load leading to fibril buckling. Fibrils are modeled as soft cylinders using the Euler–Bernoulli beam theory, with buckling conditions described across three distinct states, each affecting the adhesive properties of the fibrils. Iterative simulations analyze how adhesion strength varies with pre–load, roughness, number of fibrils, and the work of adhesion. Roughness is modeled both in fibril heights and in the texture of a rigid counter surface, following a normal distribution with a single variance parameter. Results indicate that roughness and pre–load significantly influence adhesion strength, with excessive pre–load causing substantial buckling and a dramatic reduction in adhesion. This study also finds that adhesion strength decreases exponentially with increasing roughness, in line with theoretical expectations. The findings highlight the importance of buckling and roughness parameters in determining adhesion strength. This study offers valuable insights into the complex adhesive interactions of fibrillar structures, offering a scalable solution for rapid assessment of adhesion in various rough surface and loading scenarios. [ABSTRACT FROM AUTHOR]

Plates and curved plates are essential components in ship construction. In the design stage, the methods used to evaluate the ultimate strength required to confirm the structural safety of plates include prediction through analytical methods, finite-element analysis (FEA), and empirical formulas. However, with nonlinear buckling, the results of the empirical formula and the FEA differ for small flank angles (1~9). As a result, the prediction of the nonlinear ultimate strength of flank angle (1~9) plates still requires significant computation time and cost. To compensate for this, this study performed an ultimate strength prediction method utilizing a deep neural network together with the 4050 curved plate analysis. In addition, this paper presents the analysis results of the nonlinear finite-element method and the geometric shape and ratio of curved plates as training data. Based on the results of this study, designers can more efficiently design appropriate curved plate members by considering the ultimate strength. [ABSTRACT FROM AUTHOR]

This paper investigates stability and free vibration behaviours of bi-directional functionally graded material (BDFGM) curved sandwich beams. Simultaneous variation of material compositions along tangential and radial direction is considered. A three-node curved isoparametric beam element based on a 4-parameter global–local shear deformation theory is employed. The obtained results are verified with those from literature. Various parameters such as aspect ratio, deepness ratio, gradient indexes, boundary conditions are taken into account. Several results of BDFG curved beams are provided for benchmark purpose. [ABSTRACT FROM AUTHOR]

AbstractThis present work investigates the buckling load optimization of the laminated composite plates with the elliptical hole under different non-uniform edge loads. The design objective is the maximization of the critical buckling load by determining the optimum fiber orientations in the layers. The stability equations are derived based on the first-order shear deformation theory (FSDT) of the laminated plates. The critical buckling loads are calculated using the finite element method with the nine noded rectangular element having five degrees of freedom per node. The bonobo optimizer (BO) algorithm is employed to optimize the laminated composite plates with the elliptical hole. The computer programming is developed in the MATLAB environment. Besides, the parametric studies are conducted for different types of the non-uniform edge loads, boundary conditions, cutout radius ratio and aspect ratios and the obtained numerical results are compared. Finally, the optimum results show that these factors play an imperative role in the optimum pattern and stacking sequence of the laminated composite plates with hole. The new significant findings can aid the designers in the structural design, and other industrial applications. [ABSTRACT FROM AUTHOR]

AbstractTubular structural composites are widely used in applications where high stiffness and low weight are required. This work proposes the study and evaluation of the influence of damage on the structural responses of thin-walled structures made of composite materials, as well as the development of a buckling prediction model using artificial intelligence. The methodology is approached on a few main fronts, namely: i) numerical modeling of the direct problem of the structure in finite elements, ii) modeling and parameterization of delamination in the elliptical shell model; iii) obtaining a database through finite element updating and iv) formulation and construction of the regression and prediction model using artificial neural networks. The numerical results showed that, as expected, the presence of delamination has a significant impact on the occurrence of buckling. The study also showed that it is possible to predict buckling values, with extremely satisfactory results - an error of around 1%, provided that more complex regression methods are used, such as regression by artificial neural networks, since the relationship between damage and buckling values is not trivial. [ABSTRACT FROM AUTHOR]

The present study is focused on the numerical and experimental investigation of the non-linear buckling behavior and ply-failure analysis of a hybrid composite shell under uniform hydrostatic pressure exposed on its outer surface. Laminated composite shells made of glass fiber reinforced polymer (GFRP) composites with and without multi-walled carbon nanotubes (MWCNT) reinforcement are considered for the investigation. The critical buckling pressure is numerically determined by performing a buckling analysis on a hybrid composite shell with consideration of various non-linearities such as material non-linearity, geometric non-linearity, and geometric imperfection using the commercially available software ANSYS®. The governing non-linear differential equations of composite shell structures are solved using the arc-length approach and non-linear finite element analysis. The nanotubes dispersion, distribution, structural integrity, aspect ratio, functional group, and purity level of CNT reinforcement with epoxy matrix materials are quantified using field emission scanning electron microscopy (FE-SEM). The elastic and plastic properties of the GFRP lamina with and without MWCNT reinforcement are experimentally determined based on ASTM D3039. The critical buckling pressure obtained through experiments on a GFRP composite shell with and without MWCNT reinforcement is compared with the results obtained from the numerical analysis to validate the effectiveness of the present numerical model. Parametric studies are undertaken to investigate the first ply failure analysis, the effect CNT reinforcement, aspect ratio of MWCNT, and different lamination sequences on the critical buckling pressure of the composite shell. It was observed that the Von-Misses stresses developed on the composite structures with ply angles of either all layers as 0° or combination of ply angles with 0° and 90° is always less than those of the structures having ply-angles such as 45° and 60°, irrespective of CNTs reinforcement. Furthermore, the highest critical buckling pressure was obtained with reinforcement of 1.5 wt% MWCNT in the composite shell with ply orientation of [90°]4s. [ABSTRACT FROM AUTHOR]

THIS PAPER IS DEVOTED TO AN ASYMMETRICAL SANDWICH BEAM with a functionally graded core with three different variants of boundary conditions. An analytical model of this beam, considering individual nonlinear shear deformation theory, is developed. Based on Hamilton's principle, two differential equations of motion for this beam are obtained. These equations are solved analytically, and as a consequence, the critical forces and basic natural frequencies for each beam support variant are determined. Detailed calculations are carried out for selected exemplary beam structures, and their results are compared with numerical FEM analysis. [ABSTRACT FROM AUTHOR]

The current article presents the modeling and investigation of thermo-mechanical buckling behavior for the porous functionally graded (FG) plates of rectangular and skew geometry. In this article, the modified rule of mixture and power law distribution is incorporated in the Third order Shear Deformation Theory (TSDT) to establish the governing equations using principle of minimum potential energy (PMPE). Finite element meshing is introduced using four node rectangular elements to discretize the FG plate for stability analysis. The constituents of the FG plate are continuous and vary over the thickness in accordance with modified power-law. Porosity is associated as locally distributed density and estimated using modified power law. To ascertain the effective boundary restraints skewness to the FG plate is imposed via transformation matrix. The computation of the critical non-dimensional buckling load for the structures subjected to uni-axial compressive and different thermal loads is executed via Gauss numerical integration. The assessment of the present formulation is performed against the buckling parameter available in the reference literature. Stability characteristics is evaluated under three different temperature distributions. The impact of material compositions, different thermal load, porosity distributions and various other parameters on the stability characteristics of porous FG structures are thoroughly investigated. [ABSTRACT FROM AUTHOR]

The main, well-known scientific results were obtained by outstanding scientist Yu. N. Rabotnov in the field of creep theory, hereditary elasticity, damage mechanics, technical theory of shells. However, in the last years of his life, the academician Yu. N. Rabotnov was keen on some problems in the field of mechanics of fiber-reinforced composite materials. He proposed new, original strength criteria, simplified methods for ply-by-ply calculation of composite laminates. One of Yu. N. Rabotnov's scientific passions were connected with description of specific fracture modes of layered fibrous composites having the types of delamination and splitting. On the base of energy fracture criterion, it's possible to estimate the scale effect of strength – the dependence of critical stresses on the absolute sizes of composite members. Such models of specific fracture modes make it possible to estimate the danger of such technological defects as thin polymeric film between composite layers. [ABSTRACT FROM AUTHOR]

This article discusses the influence of technological defects on the mechanical behavior of carbon-fiber reinforced polymer (CFRP) during buckling under compression. The study found that the presence of defects affected the elastic modulus and maximum load of the CFRP samples. Acoustic emission signals and digital image correlation were used to monitor the delamination process and fiber fracture. Another related study explores the effect of elevated temperature and preliminary thermal aging on the residual mechanical properties of a structural fiberglass, using acoustic emission signals to assess changes in mechanical behavior. Both articles provide valuable insights into the performance and durability of these materials. [Extracted from the article]

A large part of functionally graded materials is influenced by pores. By gradually expanding the distribution of pores from the surface to the interior, many features can be added. The amount and distribution of porosity have an impact on the materials Young's modulus and tensile strength. 2D-functionally graded porous beams are exposed to different sets of boundary conditions using a third-order shear deformation theory. According to the power-law distribution, the properties of the beam's material vary in both the axial and thickness directions. Axial and transverse deflections with in the cross sections could be written in polynomial formulations to calculate buckling load. Auxiliary functions are combined with the displacement functions to meet the boundary criteria. Three boundary conditions are taken into account: simply-supported, clamped-free, clamped–clamped. The results obtained are compared to prior attempts at convergence and verification studies. On buckling reactions of 2D-functionally graded porous beams, the impact of various aspect ratios, boundary conditions, and gradient indices is examined. [ABSTRACT FROM AUTHOR]

A parametric investigation of several unbraced steel frames with regular and irregular geometry subjected to elevated temperatures is carried out in this study to determine the most accurate procedure and buckling lengths to be considered during the structural design under a fire situation. In such conditions, the stiffness and strength of steel decrease considerably due to high temperatures, and uncertainty remains in the application of the fire design rules of Eurocode 3 Part 1-2 (EN 1993-1-2) for unbraced frames as no information is given regarding the treatment of the deformed geometry (the so-called second-order effects). More precisely, it is unclear in the norm whether the verification based on the buckling length concept could be used or if a second-order analysis to calculate the internal forces is sufficient to ensure the stability of the frame in case of fire. Based on the linear buckling analysis of the steel frames accounting for the temperature development during a fire, recommendations for the appropriate buckling lengths to be used are given. Finally, it is demonstrated that using the recommended buckling lengths together with the design rules of EN 1993-1-2 leads to results in favor of safety when compared to the results obtained with the finite element method. On the other hand, it is concluded that using second-order internal forces and the real length of the columns as the buckling length, as suggested for room temperature design, yielded results outside safety when compared with the finite element method, and this analysis and verification procedure should not be used for the case of fire. [ABSTRACT FROM AUTHOR]

The set of critical points of a simple mechanical device undergoing static or quasi-static evolution is investigated. When the system is fully elastic open bifurcation problems in the static case remain only for special structures or loadings. But the state of the art is different in the case of elastic-plasticity when addressing general solids or structures and general loadings where many difficult problems remain and where a relatively complete bifurcation diagram has been obtained only for a very simple mechanical system. The present paper focuses on the same simple system but in the case of damage which turns out to be very different since a part of the static equilibrium equations turns to be non-local. [ABSTRACT FROM AUTHOR]

Abstract This work introduces a novel metastructure designed for quasi-zero-stiffness (QZS) properties based on the High Static and Low Dynamic Stiffness mechanism. The metastructure consists of four-unit cells arranged in parallel, each incorporating inclined beams and semicircular arches. Under vertical compression, the inclined beams exhibit buckling and snap-through behavior, contributing negative stiffness, while the semicircular arches provide positive stiffness through bending-dominated behavior. The design procedure to achieve QZS is established and validated through finite element analysis and experimental investigations. The static analysis confirms a QZS region for specific displacement. Dynamic behavior is analyzed using a nonlinear dynamic equation solved using the Harmonic Balance Method, validated experimentally with transmissibility curves showing sudden jump down with effective vibration isolation. Parametric studies with varied payload masses and excitation amplitudes further verify the ability to of metastructure to attenuate vibrations effectively in low-frequency ranges.

The research focuses on examining the impact of technological defects, specifically "dry-spot" and "wrinkles," on the mechanical behavior and buckling resistance of structural composites. The investigation of the buckling phenomenon was carried out through a compression test on a thin plate fabricated from carbon-fiber-reinforced polymer (CFRP) laminate. This test was performed using a specialized fixture designed in accordance with ASTM 3410 standard. For the analysis, the study employed a three-dimensional digital optical system, Vic-3D, in conjunction with the AMSY-6 acoustic emission system. The research showcases findings from acoustic emission signals that verify the shear-based mechanism of buckling in plates constructed from CFRP featuring "dry-spot" type defects. In the case of "wrinkles" defects, it was observed that transverse shear transpires at the stress concentration points created by the "excess" layers.