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The authors propose a mathematical model of shell structures taking into account the linear theory of hereditary material creep. This model is based on the total potential strain energy functional. Shells are reinforced with stiffeners, and the contact between the stiffener and the shell skin along a strip is taken into account. The Ritz method is applied to the functional, and a system of algebraic or integro-algebraic equations is found. The resulting system is first solved as a linear system (without account for the terms reflecting material creep), and the state of the structure under the specified load is determined. Then the iterative method is used to solve the creep problem for a given value of time. The paper presents the results of studying stiffened shallow shells of double curvature made of reinforced concrete under uniformly distributed load. The buckling of shells occurs over time as a result of the development of creep strains. Values of the buckling load as a result of material creep are found. It is shown that stresses are redistributed over the shell field over time and the maximum stress is observed near the contour of the structure. [ABSTRACT FROM AUTHOR]

This paper aims to enhance the compression capacity of underwater cylindrical shells by adopting the corrugated sandwich structure of cuttlebone. The cuttlebone suffers uniaxial external compression, while underwater cylindrical shells are in a biaxial compressive stress state. To suit the biaxial compressive stress state, a novel bidirectional corrugated sandwich structure is proposed to improve the bearing capacity of cylindrical shells. The static and buckling analysis for the sandwich shell and the unstiffened cylindrical shell with the same volume-weight ratio are studied by numerical simulation. It is indicated that the proposed sandwich shell can effectively reduce the ratio between circumferential and axial stress from 2 to 1.25 and improve the critical buckling load by about 1.63 times. Numerical simulation shows that optimizing and adjusting the structural parameters could significantly improve the advantage of the sandwich shell. Then, the hydrostatic pressure tests for shell models fabricated by 3D printing are carried out. According to the experimental results, the overall failure position of the sandwich shell is at the center part of the sandwich shell. It has been found the average critical load of the proposed sandwich shell models exceeds two times that of the unstiffened shell models. Hence, the proposed bio-inspired bidirectional corrugated sandwich structure can significantly enhance the pressure resistance capability of cylindrical shells. [ABSTRACT FROM AUTHOR]

Mechanically lined pipe (MLP) is often used for offshore oil and gas transport because of its low cost and corrosion resistance. During installation and operation, the pipe may undergo severe bending deformation, which causes the liner to separate from the outer pipe and buckles, affecting the stability of the whole line. In this paper, the buckling response of MLP subjected to bending is investigated to clarify its bending characteristics by employing both experiments, numerical simulation, as theoretical methods. Two types of MLPs were manufactured with GB 45 carbon steel (SLP) and Al 6061 (ALP) used as the outer pipe material, respectively. The hydraulic expansion and bending experiments of small-scale MLPs are conducted. In addition to the ovalized shape of the cross-section for the SLP specimens, the copper liner was found to wrinkle on the compressive side. In contrast, the liner of ALP remains intact without developing any wrinkling and collapse mode. In addition, a dedicated numerical framework and theoretical models were also established. It was found both the manufacturing and bending responses of the MLP can be well reproduced, and the predicted maximum moment and critical curvatures are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The safe and cost-effective design of wind turbine towers is a critical and challenging aspect of the future development of the wind energy sector. This process should consider the continuous growth of towers in height and blades in length. Among potential failure modes of tubular steel towers, shell local buckling due to static axial compressive stresses from the rotor, blades, and tower weight, as well as dynamic flexural compressive stresses from wind actions on the rotating blades and the tower itself, are dominant as thickness is optimized to reduce weight. As man door and ventilation openings are necessary for the towers’ operation, the local weakening of the tower shell in those areas leads to increased buckling danger. This is compensated for by tower manufacturers by the provision of stiffening frames around the openings. However, the cold-forming and welding of these frames are among the most time-consuming aspects of tower fabrication. Working towards the optimization of this design aspect, the buckling response of tubular steel towers near such openings is investigated by means of nonlinear finite element analysis, accounting for geometrical and material nonlinearity and imperfections (GMNIA), and also considering several wind directions with respect to the openings. The alternatives of stiffened and unstiffened openings are investigated, revealing that a thicker shell section around the opening may be sufficient to restore lost stiffness and strength, while the stiffener frame may also be eliminated, offering substantial benefits in terms of manufacturing effort, time and cost.

In this study, the influence of concentrated damage on the stability of beams under static loads is investigated according to a co-rotational-based large displacement approach. Well-known benchmark beam-like structures have been considered under different loading conditions and damage scenarios. The concentrated damage has been modelled by means of a cross section reduction of a beam element, following a strategy already adopted in the literature. The results have been expressed in terms of buckling loads and post-buckling responses for different damage scenarios associated with a concentrated damage characterized by different positions, intensities, and extensions.

This article presents the use of Artificial Neural Networks (ANNs) to analysis of the composite plate elements with cut-outs which can work as a spring element. The analysis were based on results from numerical approach. ANNs models have been developed utilizing the obtained numerical data to predict the composite plate’s flexural-torsional form of buckling as natural form for different cut-outs and angels configurations. The ANNs models were trained and tested using a large dataset, and their accuracy is evaluated using various statistical measures. The developed ANNs models demonstrated high accuracy in predicting the critical force and buckling form of thin-walled plates with different cut-out and fiber angels configurations under compression. The combination of numerical analyses with ANNs models provides a practical and efficient solution for evaluating the stability behaviour of composite plates with cut-outs, which can be useful for design optimization and structural monitoring in engineering applications.

The paper analyzes the influence of cutouts on the buckling of shallow shells with double curvature. Based on the Timoshenko-Reissner hypothesis, a mathematical model is presented that considers transverse shifts, material orthotropy, geometric nonlinearity and structural weakening by cutouts. Cutouts are specified discretely by single columnar functions. The computational algorithm is based on the Ritz method and the Newton method. The implementation of the algorithm is carried out in the Maple 2022 software package. To study the buckling, the Lyapunov criterion is adopted. Calculations of the buckling of flat shells of double curvature with square cuts, graphs of the dependence of deflections on loads and deflection fields are given. Accounting for the structural cutouts leads to a decrease in the critical load. At the same time, for the considered problems, it is found that the decrease in the critical load does not exceed 25 % for the cutout volume not exceeding 10 % of the shell volume.

Storage tanks are essential components in various industries, particularly in power generation, where they are utilized for oil storage. The stress developed within these tanks due to internal pressure significantly influences their useful life and buckling behaviour during service. In this study, finite element analysis is employed to investigate the stress development and buckling behaviour of a fixed, closed-rooftop cylindrical oil storage tank used in a power generation company when filled and half-filled with diesel. The stress analysis results reveal that the stress developed in the tanks under both operating conditions considered is below the yield stress of the tank material. This suggests that, under these conditions, the tank is poised to have an infinite useful life, as long as it is not subjected to external pressure. The eigenvalue buckling analysis indicates that the during buckling of the storage tank the maximum displacement in the filled tank will occur in the middle if the bifurcation point is reached while the maximum displacement in the half-filled tank varies depending on the mode being considered. Based on the finite element analysis, it is concluded that the oil storage tank, under the specified conditions, experiences stresses below the yield point, thus, ensuring an extended useful life.

This paper conducts the analytical investigation on the buckling of cylindrical shells with axially variable elastic modulus subjected to axial compressive load for the first time. First, it proves that the axially distributed elastic modulus can be expressed as the combination of constant and variable component. Then, governing differential equations for buckling analysis are derived and exactly solved by the combined perturbation method and Fourier analysis. Accordingly, the closed analytical solutions for the cylinder with arbitrarily variable elastic modulus are obtained, which reveal the explicit relations among buckling load, shell sizes and elastic modulus functions. Based on the presented analytical formulas, four types of elastic modulus variations for shell material which are uniform, periodic, linear and combined are studied in detail, and the results are also well verified. The derived analytical solutions in this paper can serve as benchmarks for buckling analyses of thin-walled cylinders with elastic modulus variations resulted from design, material manufacturing process, material imperfections and so on. [ABSTRACT FROM AUTHOR]

Double-Double (DD) laminates are discussed as an alternative to conventional laminates used in aerospace practice, which are usually composed of 0°, 45°, 90°, and −45° plies. Double-Double laminates promise advantages mainly due to simplification of design, optimization, and manufacturing processes. Stacking-sequence independent bending properties of DD laminates allow for significant simplification in context of buckling analysis, as a recent publication shows. However, not all conceivable ply-orientation combinations in DD's building block lead to it. The present short communication outlines briefly how stacking-sequence independent bending properties arise from DD's laminate architecture. The analysis reveals two valid and also a single invalid angle selection, for DD's balanced 4-ply building block. [ABSTRACT FROM AUTHOR]

This paper focuses on the size-dependent free vibration and buckling behaviors of the axially functionally graded (AFG) graphene platelets (GPLs) reinforced nanocomposite microbeams subjected to axially varying loads (AVLs). With various axial grading patterns, the GPL nano-reinforcements are distributed throughout the polymer matrix against microbeam length, and the improved Halpin–Tsai micromechanics model and the rule of mixture are adopted to evaluate the effective material properties. Eigenvalue equations of the microbeams governing the static stability and vibration are derived based on the modified couple stress Euler–Bernoulli beam theory via the state-space method, and are analytically solved with the discrete equilong segment model. The effects of axial distribution patterns, weight fraction, and geometric parameters of GPLs, as well as different types of AVLs, on the size-dependent buckling load and natural frequency are scrutinized in detail. The results show that the synchronized axial distributions of GPLs and AVLs could improve the buckling resistance and natural frequency more powerfully. [ABSTRACT FROM AUTHOR]

Existing conventional materials are usually difficult to achieve multiple tunable stress plateau characteristics, which hinders their multifunctional applications. This study proposes a multiple stable stress plateau metamaterial. A theoretical model for predicting stress plateaus was established, and its accuracy was verified by experimental and numerical methods. The proposed material exhibits a three-stage deformation mode owing to sequential snap-through and Euler buckling at the microscopic unit cell level under compression. The effect of geometric parameters on the stress plateau was studied. The results indicated that the first plateau stress can be tuned independently by altering the angle between the inclined thin and thick beams, whereas the third plateau stress can be tuned independently by changing the thickness of the vertical thick beams. The first and second plateau stresses can be tuned by varying the thickness ratio of the inclined and vertical thin beams. Moreover, the total number of stress plateaus and the range of each stress plateau could also be tuned by changing the thickness ratio of the inclined and vertical thin beams and the vertical thick beams. Using the energy efficiency method, we obtained the experimental and numerical plateau stresses for each specimen. Notably, the experimental, numerical, and theoretical results were in good agreement. This study is expected to provide guidance for the design of multifunctional metamaterials with multiple tunable stress plateaus. [ABSTRACT FROM AUTHOR]

[Display omitted] Cells respond to the stiffness of their surrounding environment, but quantifying the stiffness of a fibrous matrix at the scale of a cell is complicated, due to the effects of nonlinearity and complex force transmission pathways resulting from randomness in fiber density and connections. While it is known that forces produced by individual contractile cells can stiffen the matrix, it remains unclear how simultaneous contraction of multiple cells in a fibrous matrix alters the stiffness at the scale of a cell. Here, we used computational modeling and experiments to quantify the stiffness of a random fibrous matrix embedded with multiple contracting inclusions, which mimicked the contractile forces of a cell. The results showed that when the matrix was free to contract as a result of the forces produced by the inclusions, the matrix softened rather than stiffened, which was surprising given that the contracting inclusions applied tensile forces to the matrix. Using the computational model, we identified that the underlying cause of the softening was that the majority of the fibers were under a local state of axial compression, causing buckling. We verified that this buckling-induced matrix softening was sufficient for cells to sense and respond by altering their morphology and force generation. Our findings reveal that the localized forces induced by cells do not always stiffen the matrix; rather, softening can occur in instances wherein the matrix can contract in response to the cell-generated forces. This study opens up new possibilities to investigate whether cell-induced softening contributes to maintenance of homeostatic conditions or progression of disease. Mechanical interactions between cells and the surrounding matrix strongly influence cellular functions. Cell-induced forces can alter matrix properties, and much prior literature in this area focused on the influence of individual contracting cells. Cells in tissues are rarely solitary; rather, they are interspersed with neighboring cells throughout the matrix. As a result, the mechanics are complicated, leaving it unclear how the multiple contracting cells affect matrix stiffness. Here, we show that multiple contracting inclusions within a fibrous matrix can cause softening that in turn affects cell sensing and response. Our findings provide new directions to determine impacts of cell-induced softening on maintenance of tissue or progression of disease. [ABSTRACT FROM AUTHOR]

Compared with vertical wells and deviated vertical wells, the dynamic characteristics of the drill string in horizontal wells are more complicated and more prone to failure because of the drag-pressure effect under gravity. Most researchers only consider the movement of some drill strings at a certain depth and do not analyze the rotary drilling process of the whole drill string. When most researchers do drill string simulation research, the drill string system diameter of the simulation model is consistent, and the actual drill string assembly is not considered. Based on the finite element method (FEM) and the nonlinear dynamic equation of drill string, the drilling simulation model of the drilling string system in a horizontal well is established by considering the curved hole trajectory and the nonlinear impact contact between the drill string and wellbore. The buckling and dynamic characteristics of the drill string in horizontal wells are analyzed by simulating the whole drilling process, the effect of rotating speed and hook load on the buckling characteristics of the drill string, and the effect of hook load on the whole dynamic characteristics of drill string system are analyzed. The results show that in the drilling process, the buckling deformation of the drill string near the wellhead presents a trend of"Sinusoidal buckling-helical buckling-sinusoidal buckling," the "sinusoidal buckling-helical buckling "appears near the oblique section. When the hook load applied at the end of the drill string is greater than the critical value, the drill string will get stuck during drilling. When it is less than the critical value, the greater the value of the hook load, the more stable the axial feed and lateral vibration of the drill string, and the smaller the contact force between the drill string and the wellbore. With the increase in rotating speed, the vibration period of the drill string decreases, and the amplitude of the vibration increases. With the increase of drill string drilling depth, the buckling deformation of the drill string can be reduced by reducing the value of the hook load. The conclusion is that the research results can be helpful for drill string design and structural optimization. [ABSTRACT FROM AUTHOR]

In this study, the stiffener geometry was optimized using curvilinear 3D printing to enhance the buckling resistance. A bio-inspired skin/stiffener composite that mimicked spider-web structures was generated. A dataset was formulated for the regression analysis, covering buckling stresses under distinct feature values. The regression equations, crafted using a deep neural network trained on the dataset, were evaluated. The derived regression equation was subjected to sequential quadratic programming, a mathematical optimization, to determine the optimal value of the explanatory variable. This was aimed at maximizing the buckling stress-to-stiffener volume ratio, which is the objective variable. The optimized arrangement exhibited significantly improved buckling resistance, with approximately 163% higher buckling stress than conventionally designed structures with straight stiffeners of similar weight. [ABSTRACT FROM AUTHOR]

In the following research, the buckling of multilayered CNT/GPL/Fibre/Polymer hybrid composite Levy-type nanoplates resting on Winkler–Pasternak support is investigated using modified nonlocal first-order plate theory. The different layers of the plate are assumed to be reinforced with functionally graded carbon nanotube composite or functionally graded graphene platelets composite. Modified nonlocal first-order plate theory is used to capture the molecular effects at nanoscale and extract the buckling equations. The along-thickness variation of reinforcing nanocomposites may be uniform or functionally graded, and functionality can be linear or nonlinear based on specific functions presented by scientists. Using a closed-form analytical solution, these partial differential governing equations are changed to a set of coupled ordinary differential equations that may be solved for the Levy-type boundary conditions (i.e., two opposite edges with simply supported and two other with edges arbitrary). The obtained results may be used as a useful benchmark for validation of other works developed in the future. [ABSTRACT FROM AUTHOR]

This paper presents comprehensive numerical studies on the instability behavior of metamaterial-based cylindrical shells (meta-shells) under axial compression. The cylindrical meta-shells are comprised of lattice-like metamaterial unit cells, including house unit cells and their variants, cuboid braced, octet truss, and octahedron. Their buckling and post-buckling behavior, effects of dimensional variations, structural mass efficiency in carrying axial compression, and the influences from damaged units are studied in this work. The results show that cylindrical meta-shells can exhibit benign or multistable post-buckling behavior rather than catastrophic unstable post-buckling commonly seen for conventional cylindrical shells with continuous surfaces. This work finds that the critical buckling loads scale with the meta-shell dimensions following a quadratic relation. However, the meta-shells' structural mass efficiencies in carrying axial load do not change or slightly increase as their sizes proportionally increase. The study on the effects of defects shows that the critical buckling loads linearly decrease with respect to the mass of total damaged units. [ABSTRACT FROM AUTHOR]

This paper introduces the Julia programming language as a dynamic, cost-effective, and efficient framework for implementing structural analysis packages. To achieve this, the finite element method was implemented for plane frames addressing the elastic instability problem through the Finite Element Method (FEM). Julia is a language open source, multiplatform, high-level and high-performance for technical and scientific computing, its compiler allows you to achieve speeds comparable to languages such as C and FORTRAN, but with more productive development dynamics due to its programming flexibility. Benchmarks between Julia and MATLAB are employed to discuss the processing costs, the programming techniques and paradigms used for computational performance. The results demonstrate that Julia performed the same analysis as the language used for comparison in 88.40% of the time, in addition to the fact that in loops comparisons case it reached 41.7% of the time for iteration, confirming its significant potential as a development tool of computational packages for structural analysis and scientific computing in general. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of an open hole on the stability of a compressed laminated composite plate. The study was carried out in two ways: using experimental tests and numerical analysis. As a result of the experiment, the buckling form and path of the plate were recorded. The form of buckling was determined using the ARAMIS non-contact measurement system. The critical load value was determined from the working path using the approximation method. The experimental results were verified by numerical analysis based on the finite element method. FEM investigations were carried out in terms of a linear eigenproblem analysis. This allowed the bifurcation load and the corresponding buckling form of the numerical model of the plate to be determined. Investigating the effect of the hole in the compressed plate at a critical state showed high agreement between the proposed test methods. No clear effect of the hole size on the buckling of the plate was observed. In contrast, a clear effect of the hole on the critical load value was determined. The maximum decrease in the critical load value was 14%. The same decrease was observed for the stiffness of the post-critical characteristics. It was shown that the [45|−45|90|0]s composite plate had more than three times lower strength compared to [0|−45|45|90]s and [0|90|0|90]s. The novelty of this article is the development of a research methodology based on new interdisciplinary research methods for describing the influence of the central hole on the stability of compressed composite plates. The ABAQUS system was used for the numerical analysis. [ABSTRACT FROM AUTHOR]

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

Copyright of DYNA - Ingeniería e Industria is the property of Publicaciones Dyna SL and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Utilising a flexible intracortical microprobe to record/stimulate neurons minimises the incompatibility between the implanted microprobe and the brain, reducing tissue damage due to the brain micromotion. Applying bio-dissolvable coating materials temporarily makes a flexible microprobe stiff to tolerate the penetration force during insertion. However, the inability to adjust the dissolving time after the microprobe contact with the cerebrospinal fluid may lead to inaccuracy in the microprobe positioning. Furthermore, since the dissolving process is irreversible, any subsequent positioning error cannot be corrected by re-stiffening the microprobe. The purpose of this study is to propose an intracortical microprobe that incorporates two compressible structures to make the microprobe both adaptive to the brain during operation and stiff during insertion. Applying a compressive force by an inserter compresses the two compressible structures completely, resulting in increasing the equivalent elastic modulus. Thus, instant switching between stiff and soft modes can be accomplished as many times as necessary to ensure high-accuracy positioning while causing minimal tissue damage. The equivalent elastic modulus of the microprobe during operation is ≈ 23 kPa, which is ≈ 42% less than the existing counterpart, resulting in ≈ 46% less maximum strain generated on the surrounding tissue under brain longitudinal motion. The self-stiffening microprobe and surrounding neural tissue are simulated during insertion and operation to confirm the efficiency of the design. Two-photon polymerisation technology is utilised to 3D print the proposed microprobe, which is experimentally validated and inserted into a lamb’s brain without buckling. [ABSTRACT FROM AUTHOR]

Purpose: This article presents a Legendre-Ritz solution for free vibration and buckling analysis of porous microbeams. Background and Method: The beam model is based on the modified couple stress theory and higher-order shear deformation theory. Three porosity distributions of the beam, including uniform, symmetric, and asymmetric porosity distribution, are considered. The equation of motion is established from Lagrange's equation. The Legendre polynomial, which possesses the orthonormal and recursion properties, is developed to approximate the displacement field, and the Ritz procedure is used to find the porous microbeam's natural frequency and critical buckling load. Result: Numerical examples are conducted to assess the present method's efficiency and investigate the effect of the material length scale parameter, boundary condition, and porosity ratio on porous microbeams' frequency and critical buckling load. Conclusion: The study indicates that the Legendre-Ritz solution is simple and effective for analyzing porous microbeams' vibration and buckling behaviors. [ABSTRACT FROM AUTHOR]

Cold-formed steel (CFS) sections constructed with high-strength steel have gained prominence in construction owing to their advantages, including a high strength-to-weight ratio, shape flexibility, availability in long spans, portability, cost-effectiveness, and design versatility. However, the thin thickness of CFS members makes them susceptible to various forms of buckling. This study focuses on addressing and mitigating different types of buckling in columns and beams by manipulating the lip length (d) and the ratio of inside radius to thickness (Ri/t) in CFS C-sections. To achieve this objective, a comprehensive analysis involving 176 models was conducted through the Finite Element Method (FEM). The findings reveal that an increase in lip length leads to a corresponding increase in critical elastic buckling load and moment ( P c r l , P c r d , P c r e , M c r l , M c r d , and M c r e ). It is recommended to utilize a lip length greater than or equal to 15 mm for both columns and beams to mitigate various buckling types effectively. Conversely, an increase in the ratio of inside radius to thickness (Ri/t) results in an increase in critical elastic local buckling load ( P c r l ) and moment ( M c r l ). Thus, lip length (d) significantly influences column and beam buckling, whereas Ri/t exhibits a relatively impactful effect. Subsequently, the experimental test results were used to verify finite element models. These insights contribute significant knowledge for optimizing the design and performance of CFS C-sections in structural applications. [ABSTRACT FROM AUTHOR]

No theoretical model effectively explains the blistering process, which provokes functional distress in asphalt pavements worldwide. This study focuses on the possible causes of blistering, the physical processes that drive blistering, the role of asphalt properties, and the uncertainties and gaps in the current knowledge. This paper analyzes peer-reviewed studies on pavement blistering published between 1959 and 2022 retrieved in a systematic literature review to justify and model this distress observed on sidewalks, airports, and bridges. According to the scientific literature, high surface temperatures due to solar radiation are the common factor responsible for uplifting, but several causal mechanisms have been investigated. Indeed, chemical reactions, evolutionary materials, thermal buckling, and physical reactions are the generally recognized causes. Their effects on pavement smoothness vary according to the various interdependent geometrical, physical, and mechanical properties of asphalt mixtures and the boundary conditions. Both the mix design and construction processes can hinder the blistering process that occurs during daytime hours of the hot season, right after the work is finished or a few years later. Further research should identify measures to prevent bulges whose management after uplift is difficult but necessary to avoid safety and functional issues. [ABSTRACT FROM AUTHOR]

New or in-service truss bridges, with or without upper bracing systems, may display instability phenomena such as general lateral torsional buckling of the upper chord. The buckling of structural elements, particularly in the case of steel bridges, can be associated with the risk of collapse or temporary/permanent withdrawal from service. Such incidents have occurred in the case of several bridges in different countries: the collapse of the Dee bridge with truss girders in 1847 in Cheshire, England; the collapse of the semi-parabolic truss girder bridge near Ljubičevo over the Morava River in Serbia in 1892; the collapse of the Dysart bridge in Cambria County, Pennsylvania in 2007; the collapse of the Chauras bridge in Uttarakhand, India in 2012; and the collapse of a bridge in Nova Scotia, Canada (2020), and such examples may continue. Buckling poses a significant danger as it often occurs at lower load values compared to those considered during the design phase. Additionally, this phenomenon can manifest suddenly, without prior warning, rendering intervention for its prevention impossible or futile. In contemporary times, most research and design calculation software offer the capability to establish preliminary values for buckling loads, even for highly intricate structures. This is typically achieved through linear eigenvalue buckling analyses, often followed by significantly more complex large displacement nonlinear analyses. However, interpreting the results for complex bridge structures can be challenging, and their accuracy is difficult to ascertain. Consequently, this paper aims to introduce an original method for a more straightforward estimation of the buckling load of the upper chord in steel truss bridges. This method utilizes the theory of beams on discrete elastic supports. The buckling load of the upper chord was determined using both the finite element method and the proposed methodology, yielding highly consistent results. [ABSTRACT FROM AUTHOR]

Buckling behavior of laminated composites are entirely depends on the geometry and stacking sequence of layers. The different fiber paths as a result of the stacking sequence can affect the buckling properties of laminates. The aim of this paper is to determine the effect of fiber path on the buckling behavior of laminated composites using Yarn Interlacing Matrix (YIM). Different fiber paths were implemented by making hybrid/uniform laminates. Glass woven fabrics with different yarn architectures and epoxy resin were used to fabricate the 8-plies laminated composites in 25 × 25 cm2 with 25 × 8.5 cm2 aluminum sheet in middle layer by vacuum infusion process (VIP). The buckling test was carried out on the prepared samples using DARTEC testing machine with five replicates. In addition, the buckling behavior of laminates was simulated using ABAQUS software. The novelty of this study is to use the YIM in theoretical model and investigate the critical buckling load of hybrid laminate composite in pattern of weave and understand the effect of geometrical hybridization on critical buckling load. It showed that the critical buckling load for hybrid samples are larger than the uniform ones. Comparison between theoretical and experimental results of the critical buckling load showed a maximum error of 16% in predicting the critical buckling loads. Also, comparison between theoretical and experimental results of the critical buckling load showed a maximum error of 59.7% in predicting the critical buckling loads. The main outcome of this research is that the fiber path has a greater effect on the buckling behavior than the elastic modulus of the laminates; so that despite the lower elastic modulus, the critical buckling load of laminates with hybrid reinforcement is higher than that of laminates with uniform reinforcements. [ABSTRACT FROM AUTHOR]

This study investigated the effect of an auxetic structure, positioned as the central layer in a three-layered cylindrical shell, on its buckling behaviour. The material for all three layers is aluminium. The covers are assumed isotropic. Axial and static loads are modelled as pressure on the shell's surface. In this study, modified shear deformation theory and Galerkin's numerical solution method were used, and the effect of the presence of an auxetic core on the buckling behaviour of a three-layered cylindrical shell was investigated. The assumed structure for the auxetic cell was a 2D Re-entrant honeycomb. Finally, we explore how the length-to-radius ratio, core thickness-to-total thickness ratio, and cell angle of the auxetic structure impact the system's stability, presenting the results. The distinguishing feature of the current work compared to previous studies lies in its mathematical approach. We present the system's equations as comprehensively as possible. Finally, the effect of the length-to-radius ratio, the auxetic layer's thickness relative to the whole shell's thickness, and the cell angle's size on the buckling load were investigated. In short, with the increase of both ratios, the amount of load required for buckling decreases, or in other words, system stability is reduced. Also, the size of the cell angle has little effect on the system's stability. [ABSTRACT FROM AUTHOR]

This manuscript concerns the investigation of the influence of the open hole on stability of the compression plate made of carbon-epoxy composite. Experimental tests carried out on the real plate resulted in a postcritical path from which the critical load value was determined using appropriate approximation method. In parallel, an independent study was carried out based on a numerical analysis using the finite element method (FEM). Investigations were conducted in terms of a linear eigenproblem analysis, from which the value of the bifurcation load was determined for the FEM model of the plate. Its values resulting from the numerical analyses were validated against the experimental results, thus confirming the adequacy of the designed FEM model of the plate. The paper shows that the incremental increase of the hole in the plate monotonically influences the decrease in the critical load of the plate. The largest decrease was observed for the specimen with the largest hole analysed and was 13.5% compared to a plate without a hole. The newness of the paper is the application of interdisciplinary investigation methods to describe the influence of the open hole compression (OHC) on the stability of composite plates. ABAQUS® was used as the tool with which the numerical analyses were realised. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The woven structure made of naturally curved (in-plane) ribbons has smooth geometry and fewer geometric imperfections, but there is no study of its buckling mechanical properties under vertical loads. The aim of this paper is to investigate buckling mechanical properties of spherical woven structures. Three spherical woven structures with different ribbon types and six new spherical woven structures with different ribbon widths and thicknesses were designed and the quasi-static vertical compression tests were carried out. The buckling load of spherical woven structures were studied by nonlinear finite element and ring buckling theory. Results indicate that the failure mode of the spherical weave structure under vertical loading can be divided into two stages, where a flat contact region forms between the spherical weave structure and the rigid plate and inward dimple of ribbons. Spherical weave structures using naturally curved (in-plane) ribbon weaving have better buckling stability than those woven with straight ribbon. Based on theoretical and finite element analysis, we propose a buckling load equation and buckling correction factor equation for the new spherical weave structure under vertical compression load. The formula is validated and has good agreement with the test results, which could help to design the stability of spherical weave structures with in-plane ribbons. [ABSTRACT FROM AUTHOR]

This study introduces multi-objective genetic algorithms for optimizing the stacking sequence of lightweight composite structures. Notably, significant emphasis is placed on adhering to engineering design guidelines specific to stacking sequence design. These guidelines are effectively integrated into the optimization problem formulation as either constraints or additional objectives. To enhance the initialization process, a novel strategy is proposed based on mechanical considerations. The method is then applied to optimize a composite laminate in terms of weight, inverse reserve factor, and buckling load factor. Three laminates were considered, and the influence of the design and the material composition on their mechanical properties were studied. This research demonstrated that a new stacking sequence [906/454/06] resulted in improved optimum designs compared to the traditional stacking sequence comprising plies at 0°, 45°, and 90° angles. These outcomes can be deemed the optimum stacking sequence, making them valuable for future applications in unmanned aerial vehicle (UAV) structures. [ABSTRACT FROM AUTHOR]

To maximize the capabilities of nano- and micro-class satellites, which are limited by their size, weight, and power, advancements in deployable mechanisms with a high deployable surface area to packaging volume ratio are necessary. Without progress in understanding the mechanics of high-strain materials and structures, the development of compact deployable mechanisms for this class of satellites would be difficult. This paper presents fabrication, experimental testing, and progressive failure modeling to study the deformation of an ultra-thin composite beam. The research study examines the deformation modes of a post-deployed boom under repetitive pure bending loads using a four-point bending setup and bending collapse failure under eccentric buckling. The material and fabrication challenges for ultra-thin, high-stiffness (UTHS) composite boom are discussed in detail. The continuum damage mechanics (CDM) model for the beam is calibrated using experimental coupon testing and was used for a finite element explicit analysis of the boom. It is shown that UTHS can sustain a bending radius of 14 mm without significant fiber and matrix damage. The finite element model accurately predicts the localized transverse fiber damage under eccentric buckling and buckling stiffness of 15.6 N/mm. The results of the bending simulation were found to closely match the experimental results, indicating that the simulation accurately shows deformation stages and predicts damage to the material. The findings of this research provide a better understanding of the structure characteristics with the progressive damage model of the UTHS boom, which can be used for designing a complex deployable payload for nano-micro-class satellites. [ABSTRACT FROM AUTHOR]

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 x ~ dn, 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. [ABSTRACT FROM AUTHOR]

This paper presents the analytical process of porous functionally graded graphene-reinforced truncated conical shells subjected to hydrostatic pressure and axial tension. Three types of graphene platelet (GPL) dispersion and three patterns of porous distribution were considered. A modified model, in which the volume fraction of the pores is regarded as the essential parameter, was built to evaluate the material properties. The static stability equations of the shells, coupled with the effect of the combined forces, were derived. The Galerkin integrate technique was employed to obtain the critical buckling hydrostatic pressure and axial tension. After the present method was validated, the influences of pores, GPLs, and shell geometrical characteristics were investigated in the parametric studies. The results show that the critical hydrostatic pressure and axial tension can be elevated by increasing the porous coefficient, semi-vertex, and length–thickness ratio. On the contrary, the critical pressure and tension are decreased with the rise of GPL mass fraction. [ABSTRACT FROM AUTHOR]

In order to study the buckling behavior and post‑buckling behavior of stiffened panels with different opening sizes in aircraft structures under compression load, the corresponding test method and test fixture are designed and the compression test of the panels is completed. The buckling/failure loads, instability processes and failure modes of stiffened panels with different opening sizes are obtained. The results show that the buckling mode of the stiffened panel is the opposite deformation of the interbar skin and the outer skin, and the buckling mode changes several times with the increase of load. The compressive failure mode of stiffened panel is based on the buckling deformation with obvious deformation. The finite element simulation for stiffened panels with different opening sizes is carried out. The buckling and failure modes obtained are consistent with the experimental results. The error of buckling/failure load and test results is less than 4%, which verifies the validity of the finite element model. The simulation results show that with the increase of the opening size, the yield load of the stiffened panel decreases slowly at first and then increases rapidly, the failure load of the panel decreases gradually, and finally the structure loses the post‑buckling bearing capacity. [ABSTRACT FROM AUTHOR]

This paper presents an analysis for the dynamic stability of sandwich beams/wide plates subjected to periodic axial loads. The formulation of the problem is done by use of the Extended High-order Sandwich Panel Theory (EHSAPT). The equations of motion are derived from Hamilton's principle and are expressed in terms of seven generalized displacements. A sandwich panel with simply supported edges is studied as an example, and the equations of motion for a given harmonic n are further derived. Two time-variations for the axial forces, namely, harmonic axial forces and step-wise periodic axial forces, are considered in this work. By considering the features of these two periodic load profiles, Floquet theory and Bolotin's method are adopted to perform the dynamic stability analysis. Sandwich panels with different face-to-core thickness ratios are studied. Stability maps for varying frequency and amplitude of the forces are presented. Numerical examples show that when a sandwich panel is subjected to periodic loads, it is possible that it can experience dynamic instability even when the dynamic loads are much lower than the static critical loads. [ABSTRACT FROM AUTHOR]

An infinitely long elastic plate is under compression and adhering to a flat rigid base. Many studies have investigated such a layer with a pre-existing flaw in the bond (i.e. an initially de-bonded region) which may then lead to buckling and possibly to delamination. The present investigation considers the possibility of spontaneous de-bonding and simultaneous buckling, followed by delamination, in an initially homogeneous stress field without a pre-existing flaw. It is shown that a sufficiently large pre-stress can lead to this sequence of events. This limiting pre-stress depends on the plane strain elastic modulus, the layer thickness and the stiffness characteristic of the adhesion law. These results lead to theoretical limits on the pre-stress for the prevention of de-bonding, buckling and subsequent delamination under ideal bond conditions. [ABSTRACT FROM AUTHOR]

A non-probabilistic reliability topology optimization method is proposed based on the aggregation function and matrix multiplication. The expression of the geometric stiffness matrix is derived, the finite element linear buckling analysis is conducted, and the sensitivity solution of the linear buckling factor is achieved. For a specific problem in linear buckling topology optimization, a Heaviside projection function based on the exponential smooth growth is developed to eliminate the gray cells. The aggregation function method is used to consider the high-order eigenvalues, so as to obtain continuous sensitivity information and refined structural design. With cyclic matrix programming, a fast topology optimization method that can be used to efficiently obtain the unit assembly and sensitivity solution is conducted. To maximize the buckling load, under the constraint of the given buckling load, two types of topological optimization columns are constructed. The variable density method is used to achieve the topology optimization solution along with the moving asymptote optimization algorithm. The vertex method and the matching point method are used to carry out an uncertainty propagation analysis, and the non-probability reliability topology optimization method considering buckling responses is developed based on the transformation of non-probability reliability indices based on the characteristic distance. Finally, the differences in the structural topology optimization under different reliability degrees are illustrated by examples. [ABSTRACT FROM AUTHOR]

Based on the nonlocal theory, a ID layered nano-quasicrystal (QC) simply supported beam model was established to investigate the free vibration, buckling behavior, and bending deformation of nano-QC beams. The pseudo-Stroh formula was used to derive the governing equations for the nanobeam. Using the transfer matrix method, exact solutions of the natural frequency, the critical buckling load, the generalized dis- placement and the generalized stress for bending problems of layered nano-QC beams was obtained under sim- ply supported boundary conditions. The effects of the height-span ratio, the layer thickness ratio, the stacking sequence, and the nonlocal effect on the natural frequency, the critical buckling load and the bending deformation of layered nano-QC simply supported beams were analyzed. The results show that, the natural frequency and the critical buckling load decrease with increasing nonlocal parameter. The bigger the outer-layer quasicrystal elastic constant is, the higher the natural frequency and the buckling critical load will be. The stacking sequence has a significant effect on the mechanical behavior of nano-QC beams. The obtained exact solution pro- vides a reference for various numerical methods and experimental results of nanoscale beam structures. [ABSTRACT FROM AUTHOR]

We previously developed a simplified finite element (FE) "unit" model to reproduce the mechanical interaction between the smooth muscle layer and elastic lamina (EL) in the aortic media. Nevertheless, whether this simplified FE model can represent the structure of a real medial wall and whether its modeling technique can help in developing a highly sophisticated and structure-based aortic FE model should be determined. Therefore, this study aimed to computationally represent EL buckling in the aortic medial ring at an unloaded state based on the integrated unit models and reproduce transmural variations in EL waviness across the vascular wall. We confirmed that the inner and outer layers of the medial wall were relatively subjected to compressive and tensile residual stresses, respectively, at the unloaded state, implying that the ring model will open spontaneously when it is radially cut. In addition, the residual stresses computed under such a stress-free condition were comparable to the analytically estimated values, partially supporting the validity of our modeling approach. Although further study is still required, the information obtained in this study will greatly improve the understanding of basic aortic physiology and pathophysiology and provide a basis for performing more sophisticated computational modeling of the aortic wall. [ABSTRACT FROM AUTHOR]

Artificial intelligence is increasingly used in various branches of engineering. In this article, artificial neural networks are used to predict the crush resistance of corrugated packaging. Among the analysed packages were boxes with ventilation openings, packages with perforations and typical flap boxes, which make the proposed estimation method very universal. Typical shallow feedforward networks were used, which are perfect for regression problems, mainly when the set of input and output parameters is small, so no complicated architecture or advanced learning techniques are required. The input parameters of the neural networks are selected so as to take into account not only the material used for the production of the packaging but also the dimensions of the box and the impact of ventilation holes and perforations on the load capacity of individual walls of the packaging. In order to maximize the effectiveness of neural network training process, the group of input parameters was changed so as to eliminate those to which the sensitivity of the model was the lowest. This allowed the selection of the optimal configuration of training pairs for which the estimation error was on the acceptable level. Finally, models of neural networks were selected, for which the training and testing error did not exceed 10%. The demonstrated effectiveness allows us to conclude that the proposed set of universal input parameters is suitable for efficient training of a single neural network model capable of predicting the compressive strength of various types of corrugated packaging. [ABSTRACT FROM AUTHOR]