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The aim of this research is to investigate the failure mechanisms of the filament-wound composite tubes under axial compressional loading by using an acoustic emission approach. First, the mechanical properties of ±45°C composite tubes were obtained experimentally. Then, failure due to the buckling phenomenon and crashworthiness characteristics were studied utilizing numerical simulation and experimental methods. Tubes were next simulated in ABAQUS software, and a continuum damage mechanics model was implemented in a progressive framework to assess the failure modes. From the macroscale view, results showed that the damage behavior of composite tubes turned out to be dominated by local buckling followed by a post-buckling field, which is generated by longitudinal cracks along the winding direction. On the micro-scale, the acoustic emission-based procedure based on the wavelet packet transform method was adopted. The hierarchical modeled assessment resulted in the identity of four clusters of AE signals. In GFRP tubes, the fiber breakage and fiber/matrix separation could mostly control the higher percentage of damage and cause to increase the energy absorption. Finally, by comparing the results obtained from micro and macro scales, the local buckling failure mode was attributed to the low content of fiber/matrix debonding in the structure. [ABSTRACT FROM AUTHOR]

This study sets out with a network-wide analysis of the risk for track buckling that concludes that track buckling relates to a few "weak points" along the track. To identify these, a numerical model to predict track buckling resistance is developed. The influences of key track parameters are evaluated and quantified using the innovative concept of an equivalent temperature. This allows to quantify the large influence of for example, curves and hanging sleepers in terms of an equivalent increase in temperature. Influence of less well-defined track parameters such as nearby fixed points or recent track work is estimated through statistical assessment of track buckling reports. Predicted influence generally agrees with empirical knowledge with some exceptions that are discussed in the report. Developed models and produced results should be valuable in identifying track sections at risk of track buckling and in assessing effectiveness of mitigating actions. [ABSTRACT FROM AUTHOR]

The present investigation underscores the efficacy of laminated plates with variable fiber spacing (VFS) in the context of internal defects. The study involves the evaluation of the variability in buckling strength when faced with multiple tiers of damage; this is achieved through the implementation of an improved first-order shear deformation theory (IFSDT) within a finite element (FE) framework. Various types of fiber distribution (DT) are being examined to evaluate the effects of damage situated at both corner and mid locations. The application of a radial basis function network (RBFN)-based surrogate model demonstrates its potential as a feasible alternative to the computationally demanding Monte-Carlo simulations (MCS) for investigating the stochastic nature of buckling; the developed surrogate model requires reduced input sampling data to quantify buckling uncertainty. This study examines the stochastic nature of different material characteristics and observed that the uncertainty in the buckling response decreases with the increased damage severity. The assessment of the probability of failure is conducted subsequently. Following this, the damage ratios are influenced by randomness, leading to the pattern that an increased damage ratio corresponds to a more pronounced deviation in buckling uncertainty. [ABSTRACT FROM AUTHOR]

The mechanical post-buckling behaviour of variable stiffness layered composite beams reinforced by curvilinear fibres subjected to compressive loads is investigated here using a sine function-based shear flexible beam model. The neutral axis stretching force stemming from the axial movement restraints is accounted for through von Karman's assumption based geometrical nonlinearity. Furthermore, the modified beam constitutive equation arising from the consideration of the Poisson's effect is introduced in the formulation for the laminated beam analysis with general lay-up or ply sequences. The governing equations incorporating the incremental stiffness matrices are formed through the minimization of total potential energy principle and are solved by numerical method. The solutions for the developed governing equations are evaluated iteratively based on eigenvalue analysis and the characteristics of post-buckling of laminated beams can be inferred through the relationship between the beam deflection level and post-buckling axial load. An in-depth analysis selecting many design parameters for instance lamina's curvilinear fibre angles, beam slenderness ratio, lay-up and edge conditions, load type and so on is dealt with in bringing out the behaviour of variable stiffness laminated beam in linear and post-buckling regions. Also, the influence of flexible end supports by restraining elastically against ends rotation is studied on the beam elastic stability behaviour. [ABSTRACT FROM AUTHOR]

Fully utilizing the post-buckling capacity of stiffened composite panels is important to reduce the weight of aeronautical composite structures. However, owing to the complex post-buckling failure modes and mechanisms, there are no effective analysis methods. This paper explores the impacts of the mode III fracture energy on the damage behavior of the stiffener–skin interface of composite stiffened panels under post-buckling conditions. To characterize the bonding interface damage, an interface damage initiation criterion considering the effects of through-thickness compression on the shear failure was used and combined with the Reeder damage extension criterion, which considers the mode III fracture. The mode III fracture toughness characteristics of the damage evolution of the stiffener–skin interface were obtained using the edge crack torsion (ECT) test method. Moreover, the compressive deformation response, buckling load, buckling modes, failure load, and failure modes of the panel were obtained by a compression test of I-shaped stiffened panels. Based on the aforementioned experimental data and numerical model, the post-buckling behavior of the I-shaped stiffened composite panels with an open cross-section stiffener was studied. It was found that the mode III fracture energy caused by the longitudinal shear stress τ 31 played a major role in the stiffener–skin interface damage extension of the stiffened panels. Therefore, the mode III fracture behavior should not be ignored in the post-buckling analysis. The numerical analysis method developed can accurately predict the damage initiation and evolution processes of the composite panel interface. The method can be effectively used for post-buckling analysis of aeronautical composite panels. [ABSTRACT FROM AUTHOR]

This study experimentally investigated the effects of nanoparticle reinforcement on the buckling behavior of composite materials. Different sizes of carboxylic acid functionalized multi-walled carbon nanotubes were used as nanoparticles. E-glass fiber-reinforced composite materials with polymer matrix in the [0°/90°/0°/90°]s cross-ply array with and without carbon nanotube reinforcement were produced by hand lay-up and vacuum bagging. Three types of carbon nanotubes in different sizes and proportions of 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% by weight were added to the epoxy resin. For the buckling test, the samples with two clamped and two free sides were attached to the universal testing machine to apply a uniaxial compressive load. As a result of the experiments, it was found that the addition of carbon nanotube in certain proportions increases the critical buckling load of composite materials. The highest increase in the critical buckling load (26.10% increase) was achieved with a carbon nanotube reinforcement of 0.2% by weight, having an outer diameter of 10–20 nm, internal diameter of 5–10 nm, and length of 0.5–2 mm. As the carbon nanotube sizes added to the epoxy resin decreased, the buckling strength increased. [ABSTRACT FROM AUTHOR]

To reveal compression buckling, flexural buckling and torsional buckling of one-dimensional lattice truss composite columns, parameterized finite element modelling and theoretical analyses were carried out. Global and local buckling modes of six-node lattice truss composite columns in compression were revealed by finite element modelling. The buckling styles and the critical buckling forces depend on the column length, the constraints, and the bay length. For flexural and torsional lattice truss composite columns, local buckling is the dominant failure mode. The flexural or torsional buckling moment is related to the bay length and independent of the column length. The moment decreases when the bay length gets longer. Including all these factors, theoretical models were proposed based on equivalent column theory. These models correctly predict the buckling force or moment. Imperfection analyses indicate that the lattice truss column is sensitive to imperfections when the column fails at local buckling and non-sensitive at global buckling. [ABSTRACT FROM AUTHOR]

Snap-through analysis of thin, functionally graded (FG), fixed, circular shallow arches subjected to uniformly distributed vertical load is examined in this paper. The modulus of elasticity varies gradually along with the normal to the axis of the arch in alliance with the power law form. The solution of the geometrically nonlinear problem is carried out by using a numerical scheme accounting for the moderately large deflections theory based on small strain and moderate rotation in the von Kármán sense. The combined effect of the parameters that is, the power law index, the ratio of the modulus of elasticity and the modified slenderness ratio on the support reactions, the snap-buckling and post-buckling behaviors of the fixed circular shallow arches are examined. It is found that the lowest buckling load is considerably affected by the variation of these parameters. In addition, the effects of the material distribution on internal forces, deformed configurations and rotation angle are presented at various stages of the deformation. [ABSTRACT FROM AUTHOR]

Stiffened composite panels have been extensively used thanks to their ability to withstand high load and large deflection. However, their nonlinear behavior and complex damage modes during the post-buckling regime remain challenging and still require research work to improve understanding. In the current study, the buckling and post-buckling responses of a hat-stiffened panel made with carbon fiber reinforced polymer composite material are investigated experimentally and numerically with identifying the damage process and its effect on the panel stiffness. The experimental analysis is achieved by performing quasi-static multi-step compressive loading up to failure with full displacement assessment. A Structural Health Monitoring strategy is also deployed for registering and localizing the Acoustic Emission (AE) activities during each run. Matrix data extracted from the AE waveforms are processed and classified with respect to damage mechanism. Additionally, this research proposes predictive Finite Element Model based on Progressive Failure Analysis. Modified Chang-Chang failure criteria is adopted and implemented using Ansys Usermat subroutine. Numerical and experimental data have been compared and good agreement is demonstrated. [ABSTRACT FROM AUTHOR]

At present, buckling pin in the bypass of piping as pressure relief valve has been gradually utilized in the low-concentration coal-bed methane (CBM), which bends to release pressure when the main valve fails leading to pipeline blockage. However, current researches mainly focused on the buckling behavior of hydraulic cylinder rod or rod string, and less consideration was given to the operational reliability of buckling pin valves. This paper deduced the calculation formula of the critical failure load based on Euler formula in the buckling pin under buckling load. Besides, three finite element models (FEM) based on Johnson−Cook constitutive model were compared to predict failure strength of buckling pin which were verified by experiment. In addition, the defect sensitivity analysis of the buckling pin under different initial geometric defects rate was carried out. The results showed that a) the experimental value of the critical failure load in the buckling pin was 206.04 N and the bending position was in the middle of the buckling pin; b) the analysis result adopting explicit dynamic method was in best agreement with the experimental results within deviation of 0.24%; and c) the initial geometric defect of buckling pin should be controlled within 1%. This study provides an important reference to predict the critical failure load of the buckling pin valve and achieve safe transportation of low-concentration CBM. [ABSTRACT FROM AUTHOR]

This paper presents a first investigation of the mechanical behavior of porous functionally-graded material (FGM) plates reinforced with graphene platelets (GPls) nanomaterial. As a main purpose, we extend the research on GPls incorporation from single-component matrix materials to porous metal-ceramic FGMs. Four different through-thickness distributions of GPls and porosities were investigated. The effective elastic modulus of GPls-reinforced FGM was calculated using the Halpin-Tsai homogenization model, and the effect of porosities on elastic properties was considered by an exponential model that is more accurate than the common rule of mixture. A recent hyperbolic higher-order plate theory that satisfies the traction-free boundary conditions and a parabolic variation of shear stresses was used to model kinematics. The influence of various parameters was studied after method validation, and it was revealed that GPls not only can improve the stiffness and mechanical response of FGM plates, but can also eliminate the inherent transverse anisotropy of FGMs and uncouple the static response when dispersed in proper distribution pattern. This effect will result in zero mid-plane extension in bending conditions, in a similar behavior to isotropic plates. [ABSTRACT FROM AUTHOR]

The effectiveness of variable fiber spacing composite (VFSC) laminates subjected to thermal loading is compared with uniformly distributed fiber composite (UDFC) laminates. The higher-order shear deformation theory (HSDT) is adopted to develop a FE model for estimating critical thermal buckling load. Three types of fiber distribution patterns are considered to study the effect of the non-uniform spacing distribution of fiber on thermal buckling, and the results are compared with UDFC. Further, a surrogate model based on the radial basis function network (RBFN) is developed to examine the impact of composite properties uncertainty on the critical buckling response of UDFC and VFSC laminates under thermal loading. The RBFN model is found to be highly efficient and possesses a close match with Monte Carlo simulation (MCS). Though the VFSC laminates possess a large deviation (standard deviation) in the buckling temperature, the stochastic effect (standard deviation/mean) shows relatively minimal variation in VFSC and UDFC laminates. The effect of each composite property is investigated for different lamination sequences and boundary conditions. From the sensitivity analysis, the thermal expansion coefficient of matrix (α m) is found to be the most sensitive property for all the investigated cases. Lastly, the RBFN model is utilized to quantify reliability parameters for multiple stochasticity levels. [ABSTRACT FROM AUTHOR]

Graphical abstract This paper analyses the vibration and buckling responses analysis of the smart porous core sandwich plate (SPCSP) resting on the elastic foundation under thermoelectric and thermomechanical loading. The plate is a constraint with conventional and unconventional boundary conditions. The thermo-mechanical properties of the plate are graded through the thickness direction with the sigmoid and exponential laws. The sandwich plate considered geometrical nonlinearity and assumed quadratic electric potential function across the thickness direction. The Hamilton principle derives the formulation with the first-order shear deformation theory (FSDT) displacement field. A nine-node quadratic element-based higher-order finite element method with seven degrees of freedom (DOFs) is used to convert the governing equation into a set of algebraic forms and solve it computationally (using MATLAB) with a modified Newton-Raphson scheme. Buckling and vibration responses are analysed under varying plate parameters like material exponent N, thickness ratio (a/h), porous exponent with different porosity dispersion, conventional and unconventional conditions, applied electric voltage V and temperature change Δ T. It is found that the presence of the Pasternak parameter gives additional stability to structures and overcomes the instability due to porosity. Also, the proposed work is not only precise but also simple in predicting the vibration and buckling response of smart sandwich porous plates under thermo-electric mechanical loading. [ABSTRACT FROM AUTHOR]

In this paper, in order to satisfied the design and manufacturing requirements of functional materials, an investigation is carried out to study the free vibration and thermal buckling characteristics of porous P- and S-type functionally graded materials (FGM) circular plates in non-uniform thermal fields in the context of first-order shear deformation theory. FGM is formed by gradient changes in metals and ceramics, the thermomechanical properties were characterized by a gradient along the thickness direction of the circular plate by a power-law function containing porosity correction. The differential equations of motion control are derived using the Hamiltonian variational principle, and the dimensionless equations of motion and boundary conditions are solved analytically by the DTM transformation procedure. The problem has been degraded and compared with the results of the existing literature to confirm its validity. In conclusion, the influence of each parameter on the dimensionless natural frequency of the porous FGM circular plate and the influence of relevant parameters on the critical temperature rise are calculated and evaluated. The porosity weakens the overall stiffness and equivalent mass of the structure, and the foundation enhances the stiffness. The DTM calculation iteration speed is fast, and the results are highly consistent. The results can be used to provide model guidance and data support for future studies of porous FGM circular plates as well as follow-up studies. [ABSTRACT FROM AUTHOR]

In this paper, an analytical model is developed to investigate the buckling analysis of the composite sandwich conical shell with variable skin thickness under lateral pressure loading. This problem involves composite shells, which are produced during the filament-winding process, where the skin thickness varies through the length of the shell. An effective smeared method is employed to reduce the reinforced lattice core into a layer. This is done by analyzing forces and moments on a unit cell. Therefore, equivalent stiffness parameters of reinforced lattice core are determined. By superimposing stiffness parameters due to the lattice core with those of the inner and outer skins, the equivalent stiffness of the sandwich panel will be obtained. Governing equations are established based on the first shear deformation theory. The power series method is used to extract the buckling load of the stiffened shell. To verify achieved results, a 3D finite element model is provided. Comparisons showed that the analytical solution is qualified enough to study the buckling behavior of the composite sandwich conical shell. Through this study, the effects of a set of important parameters like stiffener orientation angle, number of stiffeners, semi-vertex angle, and skin lamination are investigated. [ABSTRACT FROM AUTHOR]

In this study, buckling and vibrational characteristics of a nanoshell reinforced with graphene nanoplatelets under uniform axial load are investigated. The material properties of the piece-wise graphene-reinforced composites (GPLRCs) are assumed to be graded in the thickness direction of a nanoshell and are estimated using a nanomechanical model. The effects of the small scale are analyzed based on nonlocal stress–strain gradient theory (NSGT). The governing equations and boundary conditions (BCs) are developed using Hamilton's principle and are solved with assistance of the generalized differential quadrature method. The novelty of the current study is the consideration of GPLRC and size effect as well as satisfying various boundary conditions implemented on the proposed model using NSGT. The results show that, nonlocal parameter, graphene platelet (GPL) distribution pattern, length scale parameter, number of layers, and GPL weight function have significant influence on the buckling and natural frequency of the GPLRC nanoshell. Another significant result is that nonlocal parameter does not have any effect on the buckling load for each BC. The results of the current study are useful for design of the nanoactuators and nanosensors. [ABSTRACT FROM AUTHOR]

In this work, the static, buckling, and free vibration analysis of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) beam resting on a Pasternak elastic foundation are studied. The secant function-based shear deformation theory (SFSDT) is used for this analysis. This theory fulfills the traction-free boundary conditions at the top and bottom surfaces of the beam, hence there is no need for a shear correction factor. Hamilton's principle is used to determine the governing differential equations and boundary conditions whereas Navier's solution technique is used for determining the closed-form solution. The analytical approach is used to examine the deflection, stresses, critical buckling load, and natural frequencies of the FG-CNTRC beam resting on the Pasternak elastic foundation including a shear layer and Winkler springs. To determine the material characteristics of FG-CNTRC beams, the Rule of the mixture is used. Uniform distribution (UD-beam), FG-X beam, FG-O beam, and FG-V beam are the different forms of CNT reinforcement distribution that are used in this study. Considering different span thickness ratios, the volume fraction and distribution of CNT, the Winkler spring, and the shear layer constant factors, all the structural responses are predicted. It is also observed that the present theory predicts the structural responses of the FG-CNTRC beam accurately when compared to other existing theories. A few new results are also included as the benchmark solutions for the new research. [ABSTRACT FROM AUTHOR]

This paper presents a new methodology to determine the formability limits by local buckling in thin-walled metal tubes that is an extension of a method that was earlier developed by the authors to characterize wrinkling in metal sheets. The method consists of subjecting a set of rings with different lengths extracted from the tubes to axial compression and combining experimental measurements with finite element modeling to determine the critical in-plane surface strains at the onset of buckling. Digital image correlation is used to track the experimental evolution of the in-plane strains with the normalized height of the plastic hinges and to validate the finite element model for subsequent utilization in the determination of the critical strains at the onset of buckling. Results show the effectiveness of the proposed methodology to obtain, for the first time ever, the formability limits by local buckling of thin-walled tubes in both principal strain and effective strain versus stress triaxiality spaces. [ABSTRACT FROM AUTHOR]

The surrogate-based optimization of hierarchical stiffened composite shells against buckling is a typical multimodal and multivariables optimization problem. To improve the computational efficiency and global optimizing ability of the surrogate-based optimization of hierarchical stiffened composite shells, an enhanced variance reduction method based on Latinized partially stratified sampling and multifidelity analysis methods is proposed in this paper and then integrated into the surrogate-based optimization framework. In the offline step of the optimization framework, candidate pairing strategies of design variables are generated by Latinized partially stratified sampling and compared by performing priori optimizations based on the low-fidelity analysis method, and the optimal pairing strategy is therefore determined. On the basis of the optimal pairing strategy, the surrogate-based optimization is carried out using the high-fidelity analysis method in the online step. With less computational cost in the offline step, the proposed enhanced variance reduction method overcomes the limitation of Latinized partially stratified sampling that the optimal pairing strategy is not obvious in complex problems. Then, extensive optimization examples are carried out to verify the efficiency and effectiveness of the proposed optimization framework. Given an approximate computational cost, the optimal buckling result of the proposed framework using enhanced variance reduction method increases by 18.2% than that of the traditional framework based on Latin hypercube sampling. In particular, the advantage of enhanced variance reduction method in the space-filling ability is highlighted in comparison to Latin hypercube sampling. When achieving an approximate global optimal solution, the proposed framework reduces the total computational cost by 76.3% than the traditional framework. Finally, the numerical implementation of asymptotic homogenization method is used herein for the accurate prediction of effective stiffness coefficients of the initial design and optimal results. Through comparison, it is concluded that the high axial stiffness and bending stiffness are the main mechanism for the high load-carrying capacity of optimal results. [ABSTRACT FROM AUTHOR]

In this study, free and forced vibration investigations and thermal buckling analysis of three-layered centrosymmetric piezoelectric microplates are examined. To model the size effects, the size-dependent consistent couple stress theory is used. To be compatible with the modified coupled stress theory, a modification is proposed to apply to the consistent couple stress theory. Resorting to the Navier's approach, the governing equations are treated in the case of simply supported boundary conditions to extract the free and forced vibration outcomes and the thermal buckling numerical results. The verifications demonstrate the effectiveness of the proposed modification. The effects of the material length scale parameter and the flexoelectricity coefficient on the findings are investigated. Moreover, the closed- and open-circuit condition impacts on the free and forced vibration and the thermal buckling analyses are studied. [ABSTRACT FROM AUTHOR]

This paper addresses the effects of different stacking sequences and seawater on the buckling behavior of hybrid composite plates. For the buckling tests, 12-layered hybrid composite plates were produced using different combinations of carbon, E-glass and aramid fibers, with an epoxy resin system as the matrix (Araldite LY1564/Aradur 3486). The hybrid composite plates were designed at the symmetric orientation angles of [(0/90)3]s, [(30/−60)3]s, [(45/−45)3]s and an anti-symmetric orientation angle of [(0/90)3]2. The hybrid composite samples were divided into groups and were subjected to buckling tests after being kept in different settings for varying periods of time (room temperature for 90 days, Black Sea water for 90 days, Mediterranean Sea water for 90 days, Mediterranean Sea water for 150 days). In light of the data obtained from the tests, the buckling behaviors of the layered hybrid composite plates were examined. The highest critical buckling load occurred in the carbon/aramid/glass (CAG) hybrid samples with the stacking sequence of [(0/90)3]s, whereas the lowest critical buckling load occurred in the carbon/aramid/glass (CAG45) hybrid samples with the stacking sequence of [(45/−45)3]s. It was observed that the critical buckling loads of the samples immersed in seawater decreased when compared to the critical buckling loads of the samples kept at room temperature. It was also found that the critical buckling loads of the hybrid samples immersed in the Mediterranean Sea water, which has high salinity, were lower than the critical buckling loads of the hybrid samples immersed in the Black Sea water, which has lower salinity. [ABSTRACT FROM AUTHOR]

This work was carried out on the buckling effects of cold-formed perforated steel columns with base auxetic polymer stiffeners. Buckling tests were carried out for three thicknesses of steel profiles (1.5–1.8 mm) with and without base stiffeners. Loading conditions were considered to be with displacement variation of 0.1 mm/s and respective axial loads and lateral displacements were noted. Results obtained states that the lateral displacement was found to be 2.2 for 1.8 mm CFS thickness and 93 kN of axial load with the use of auxetic stiffener with 14.8% of the variation in comparison without stiffener. The strain energy of absorption for auxetic stiffener is found to be high as 0.0523 at a lateral load of 80 kN for 1.8 mm CFS thickness. The maximum resistance to local, distortional, and Euler's buckling loads was found to be high for 1.8 mm thick CFS with stiffener with 11.1%, 17.39%, and 10% in comparison without stiffener. [ABSTRACT FROM AUTHOR]

The buckling of a woven fabric influences its performance throughout processing and during actual use. In addition, this phenomenon reflects on the recovery of the textile–polymer composites. The mechanics of the buckling behavior of woven, knitted or non-woven fabrics have a large number of different approaches, and the obvious inconsistency of applying the classical beam theory to the textile problem remains. The buckling of textile materials is a deciding factor of their drape and conformability. Fabric buckling also defines the ability of a fabric to fit to a different shape object without wrinkling. An empirical approach foundation to quantitatively compare the buckling of existing and new flexible textile materials, no matter what their composition, was developed. The buckling coefficient was found to be highly correlated to the fabric modulus of rigidity, fabric Young's modulus and fabric weave design. For the twill structure, the value of twill line angle to the direction of buckling force has a significant effect. In this paper, the buckling of woven fabric with or without holes was analyzed. It has been proven that major modes of deformation in the buckling of fabrics with holes are fabric bending rigidity, fabric design and the ratio of the volume of the hole to sample volume. [ABSTRACT FROM AUTHOR]

In this study, free vibration and buckling behaviors of a functionally graded nanoplate supported by the Winkler–Pasternak foundation using a nonlocal classical plate theory are investigated. Eringen's nonlocal differential model has been used for considering the small-scale effect. The properties of the functionally graded nanoplate are considered to vary transversely following the power law. The governing vibration and buckling equations of an elastically supported functionally graded nanoplate have been derived using the principle of virtual work, and the solution is obtained using the Rayleigh–Ritz method and characteristic polynomials. The advantage of this method is that it disposes of all the drawbacks regarding edge constraints. The objective of the article is to see the effect of edge constraints, aspect ratios, material property exponent, nonlocal parameter, and foundation parameters on the nondimensionalized frequency and the buckling load of an embedded functionally graded nanoplate in a thermal environment. The study highlights that the nonlocal effect is pronounced for higher modes and/or higher aspect ratios and need to be considered for the analysis of the nanoplate. Further, it is observed that the effect of the Pasternak foundation is prominent on nondimensionalized frequencies and buckling of the functionally graded nanoplate. [ABSTRACT FROM AUTHOR]

This work deals with experimental buckling and free vibration behavior of silane-treated cenosphere/epoxy syntactic foams subjected to axial compression. Critical buckling loads are computed from compressive load–deflection plots deduced using universal testing machine. Further, compressive loads are applied in the fixed intervals until critical loading point on different set of samples having similar filler loadings to estimate natural frequency associated with the first three transverse bending modes. Increasing filler content increases critical buckling load and natural frequency of syntactic foam composites. Increasing axial compressive load reduce structural stiffness of all the samples under investigation. Syntactic foams registered higher stiffness compared to neat epoxy for all the test loads. Similar observations are noted in case of untreated cenosphere/epoxy foam composites. Silane-modified cenosphere embedded in epoxy matrix registered superior performance (rise in critical buckling load and natural frequencies to the tune of 23.75% and 11.46%, respectively) as compared to untreated ones. Experimental results are compared with the analytical solutions that are derived based on Euler–Bernoulli hypothesis and results are found to be in good agreement. Finally, property map of buckling load as a function of density is presented by extracting values from the available literature. [ABSTRACT FROM AUTHOR]

This paper presents the design optimization of filament winding composite cylindrical shell under hydrostatic pressure to maximize the critical buckling pressure. To this end, an optimization framework has been developed by employing numerical solution integrated with genetic algorithm. The design variables are fiber orientation and the corresponding number of layers. The framework is used to find the optimal design of filament winding composite cylindrical shell subjected to hydrostatic pressure. Three types of winding pattern are investigated, and the maximum critical buckling loads are increased by 26.14%, 25.82% and 20.95% compared with the base line, respectively. The influences of design variables on the critical buckling pressure are investigated. Results show that filament winding angles have more significant effect on the critical buckling pressure than the corresponding number of layers. Comparative study is carried out to verify the efficiency and accuracy of the optimization framework. Compared with the finite element analysis, the optimization framework has significant advantages in terms of calculation efficiency. [ABSTRACT FROM AUTHOR]

An exact free vibration and buckling analysis of a tapered beam-column with general connections is calculated. All structural elements are made of functionally graded material. In this study, a power function is assumed for the variation of the elastic modulus along the cross-section’s height. Extensional-coupling effects are considered in the proposed formulation. By solving the related fourth-order differential equation, the exact answers are obtained. The Bessel functions are utilized in this solution. In addition, the effect of connection flexibility is assessed by considering rotational and transitional springs at the two ends of the element. The suggested stiffness matrix can analyze the free vibration and buckling of a frame made of functionally graded material tapered beam-columns with semi-rigid connections and supports. To validate the proposed formulation, several benchmarks and novel examples are separately analyzed. All numerical findings clearly demonstrate the usefulness of the authors’ scheme. [ABSTRACT FROM AUTHOR]

FRP is gaining popularity in civil engineering applications due to their high specific strength and stiffness, lightweight and tailoring ability. Meantime, box beam applications have also been increased in bridges due to their high inherent torsional stiffness. The combination of FRP and box-beam is ideal in lightweight bridges. However, being a thin-walled structure, designs are often governed by stability. In the FRP box-beam, two types of buckling are possible, i.e. flange and web buckling. In this paper, flange buckling behaviour of simply supported FRP box-beam subjected to lateral load has been studied with emphasis on the effect of moment gradient and rotational restraint. Web buckling is precluded by adopting thicker webs. Extensive numerical studies have been conducted to identify the parameters which significantly affect the flange buckling. The significance of defined parameters has been shown with the help of generic curves and bar charts, which will be helpful to the designers at the preliminary stage. [ABSTRACT FROM AUTHOR]

In the present study, a trigonometric shear deformation plate theory was employed to perform a thermal buckling analysis of multi-directional functionally graded (FG) plates. During the manufacturing of the multi-directional graded plate, the formation of pores is abounded. Hence, the effect of porosity on the buckling performance was investigated by considering the variation of porosity in the plate for power law gradation variation of material properties. The adverse effect of porosity on the material properties was taken into account by employing the rule of mixture relation. Finite element results show that the thermal expansion coefficient is unaffected by the presence of porosity. For simply supported boundary conditions, the non-linear governing equations are solved for different thermal loads such as uniform, linear, and non-linear. A parametric study was performed in which the effect of grading parameters, aspect ratio, and side-to-thickness ratio under variable temperature change was studies. Critical material grading indices for multi-directional plates have been identified that help researchers and industry personnel in fabrication planning. [ABSTRACT FROM AUTHOR]

Natural Bouligand structure is a special class of hierarchical architectures, which have proven to be effective in enhancing its mechanical properties. In this work, we demonstrate that the thermal buckling capacity of Carbon Fibre Reinforced Plastics can also be improved by mimicking bio-inspired Bouligand architectures. A finite element approach using commercial software ABAQUS is developed to predict the critical buckling temperature of the Bouligand inspired laminated plates under thermal loading. Numerical predictions show a good agreement with analytical results obtained from the literature. The effectiveness of Bouligand-type composite laminates in enhancing thermal buckling behavior is first confirmed by comparing with unidirectional, cross-ply and quasi-isotropic laminates. We then present the effects of pitch angle and ply thickness on the thermal buckling temperature of bio-inspired Bouligand-type laminates. Finally, we conclude that the improved mechanical and thermal properties can be simultaneously achieved by the Bouligand structure of laminates as the pitch angle is increased. The present study highlights the high thermal buckling behavior of biomimetic Bouligand structure, offering a possibility in developing biomimetic composites with good trade-off between mechanical properties and thermal performance. [ABSTRACT FROM AUTHOR]

In the notched structures, to achieve maximum buckling resistance in comparison with structural weight, the optimal design of a stiffener is very important. In this research, after a review of the existing literature, nonlinear buckling behavior of composite plates containing the cutout with three different designs of stringer was investigated. The considered stiffeners are planer, longitudinal, and ring types. The buckling experiments were carried out on the stiffened plates containing a circular notch. Moreover, to achieve an efficient prediction of the buckling in the stiffened laminate with the hole, a finite strip method is developed based on the Airy stress function and von Karman's large deformation equations. Studies show that there is a good agreement between the postbuckling behaviors derived from developed finite strip method with experimental results. Fast convergence of the considered finite strip method compared with the finite element results shows its efficiency for prediction of buckling behavior in laminated composites. The results show that the buckling load-bearing capacities of perforated plates with a longitudinal and planer stiffener are higher compared with the other stiffener, respectively. The detailed parametric study on the effects of thickness of the plate and stiffener and opening diameter on buckling behavior was performed using experiments and modeling. [ABSTRACT FROM AUTHOR]

Local buckling analysis of thin walled composite beams is presented, where the flanges are stiffened at their free edges. The web and the flanges are modelled by rotationally restrained long orthotropic plates. Explicit expressions are developed for the calculation of the lowest buckling load. For the stability of the flange distortional buckling, plate buckling (or local buckling) and their interaction are considered, while the stabilizing effect of the web is taken into account by elastic constraint. Web buckling is modelled with a long plate, whose edges are constrained by stiffeners with warping stiffness. The accuracy of the method is demonstrated through numerical examples. [ABSTRACT FROM AUTHOR]

This paper focuses on the buckling problem of cylindrical shells under combined non-uniform axial compression and external pressure. To obtain buckling loads, a completely new method called two-parameter perturbation method is established. Using this method, governing differential equations are solved and buckling loads expressed by load functions, load parameters, and shell dimensions are derived for the first time. Comparative studies show that buckling loads by the analytical formulas coincide with those for combined uniform loads or single wind load in literatures. Buckling of a cylinder subjected to combined bending and wind loads is analyzed, and confirmed by the Galerkin method for the case of small load variations. Therefore, the presented formulas are adequately validated. The numerical calculations are carried out to analyze the effects of non-uniform load parameters on buckling load coefficient. The obtained results in this paper can be applied to evaluate buckling loads for cylinders subjected to combined non-uniform loads in actual engineering. [ABSTRACT FROM AUTHOR]

Thermal buckling deformation can significantly impact the operating performance of hydro-viscous drive. A thermal buckling finite element shell model was established with the nonlinear radial temperature as the thermal loading condition. The thermal buckling behavior of friction pairs was investigated under three different boundary constraints. Moreover, the influence of thickness and material parameters on the critical buckling temperature was discussed. The simulation results coincide with the failure modes of friction pairs in practice, and the most common ones are the coning mode and the potato chip mode. The ability to resist thermal buckling deformation can be improved as the thickness increases. In addition, the steel disc with outer edge simply supported is more prone to thermal buckling, because the critical temperature is minimum. The thermal expansion coefficient is the primary factor in thermal buckling study, which is inversely proportional to the critical temperature. These provide a theoretical basis for avoiding thermal failure of friction pairs in a hydro-viscous drive. [ABSTRACT FROM AUTHOR]

Crucial buckling loads of composite laminates are typically determined by employing analytical techniques based on the presumptions that the plates are susceptible to uniform edge loads, ignoring the fact that the practical assemblies are regularly exposed to different non-uniform edge loads. The current research paper is centered on the buckling behaviour of different patterns of trapezoidal composite laminates with cutouts under the application of non-uniform in-plane edge loads by employing finite element technique. To achieve this, the panel is discretized by using 9-noded heterosis plate element by employing the impact of shear deformation and rotary inertia. For a given load and the shape of panel, the stress concentration within the panel is highly non-uniform in nature. Hence, a dynamic approach has been employed to calculate the buckling loads. The accuracy of the method is verified by relating the obtained results with existent research. The impact of various variables including the size of the cutout, non-uniform edge loads, boundary conditions, ply alignments and panel trapezoidal shape ratio has been considered to examine the buckling behavior of trapezoidal panels. Buckling load factor optimization using CCD and RSM has also been carried out in detail. [ABSTRACT FROM AUTHOR]

Analysis and numerical results for the axisymmetric vibrations of two-directional functionally graded circular plates under the action of an in-plane force have been presented on the basis of classical theory of plates. The mechanical properties of the plate material are assumed to vary in both radial and transverse directions. Generalized differential quadrature method has been employed to obtain the frequency equations from the differential equation governing the motion of such simply supported and clamped plates. The lowest three roots of these frequency equations have been reported as the first three modes of vibration. The effect of volume fraction index, in-plane force parameter, heterogeneity parameter and density parameter has been studied on the natural frequencies of vibration. By allowing the frequencies to approach zero, the critical buckling loads for both the plates have been computed. Three-dimensional (3D) mode shapes for specified plate have been plotted. A comparison of results has been presented. [ABSTRACT FROM AUTHOR]

On the purpose of improving the structural efficiency of stiffened panels, which is widely used in engineering, three promising layouts of sub-stiffened thin-walled structures were optimized in view of structure's initial buckling and further analyzed through post-buckling and imperfection-sensitivity analysis. The optimization tasks were carried out using an integrated framework, which is based on the multidisciplinary optimization platform Model Center and finite element method software ABAQUS. The particle swarm optimization algorithm was applied to optimize layout parameters. Three optimal sub-stiffened panels were then evaluated based on their performance on critical buckling loads and post-buckling ultimate strength under uniaxial loading. Imperfection-sensitivity analysis was also conducted to investigate the stability behavior of the proposed panels with defect. The results indicate that the introduction of sub-stiffeners into the traditional stiffened panel can achieve significant improvements on the panel's buckling loads and ultimate strength under uniaxial loading, which are favorable to expand design space for engineering structures under requirements of lightweight with high bending stiffness and bucking resistance. [ABSTRACT FROM AUTHOR]

Buckling of composite stiffened cylindrical shell panels having cutout is analyzed using the finite element approach. Shell panel and stiffeners are modeled using first-order shear deformation theory and considering displacement compatibility at the stiffener-panel interface. Convergence and validation studies are conducted to establish the accuracy of the present approach. An attempt is made to maximize the uniaxial and biaxial buckling loads by varying the lamination, boundary conditions, load position, depth of stiffeners, and their arrangements. Parametric studies show that buckling load and mode shapes depend on the size of cutout, ratio of shell width to thickness, degree of orthotropy, and fiber orientation angle. The parametric variations considered here may help the practicing engineers to have an elaborate design aid for improving the buckling strength of such shell panels. [ABSTRACT FROM AUTHOR]

The external hydrostatic buckling behavior of fiber metal laminate (FML) composite cylinders was investigated numerically. The critical buckling pressure predicted by eigenvalue analysis was compared with experimental results. The numerical results showed different modes of buckling and buckling deformation for cylinders of different fiber orientation when subjected to external hydrostatic loading. FML cylinder with 0°/90° fiber orientation exhibited higher buckling strength and lower buckling deformation as compared to FML cylinders of 60°/30°, ±45°, and ±55° fiber orientations. The orientation of fiber has significant influence on the performance of FML composite cylinder as compared to fiber-reinforced plastic thickness. The correlation between numerical and experimental results is discussed in terms of buckling strength, circumferential stiffness, and buckling deformations. It was observed that the cylinders were less sensitive to initial imperfections irrespective of fiber-reinforced plastic thickness. In addition, the results of finite element analysis and experimental results indicate good matches. [ABSTRACT FROM AUTHOR]

CCF300/5228A aero composite stiffened panels achieved absorbing saturation in hygrothermal condition (70℃ distilled water), whose absorbing process followed the Fick law. Many debonding and gaps of matrix to fibers could be observed after hygrothermal exposure by scanning electron microscope (SEM). Compressive experiments were conducted on unaged and aged composite stiffened panels. Failure modes of the two types of specimens are quite similar with several major ways, including the debonding and fracture of stiffeners together with the splitting and ripping of panel. Buckling patterns for both types of specimens are similar and characterized by buckling of panels between stiffeners and buckling of the middle two stiffeners. However, the bending direction of buckling mid-panel for aged specimens is opposite to that of the unaged at same position panel, which shows that hygrothermal condition influences the bending direction of buckling mid-panels seriously. There still exists a post-buckling process for aged specimens under axial compression, whose average buckling load and failure load decrease by 3.1% and 22.2% respectively, comparing to that of unaged specimens. [ABSTRACT FROM AUTHOR]

The solution for the buckling problems of fibre metal laminates is usually based on the assumptions that the plates are subjected to uniform edges loads without any discontinuity or damages. Nevertheless, in practice the plates are subjected to various kinds of nonlinear/nonuniform edge loads along with various sized and positioned openings. The present work mainly focused on the vibration and buckling performance of inter laminar hybrid fiber metal laminates (HFMLs) with and without cutouts subjected to different kinds of nonlinear loading conditions by utilizing finite element approach. Towards this a 9-noded heterosis plate element has been used to discretize the plate by taking into account the effect of shear deformation and rotary inertia. Since the stress distribution within the plate is highly non-uniform in nature, the dynamic approach has been used to solve the buckling problems. The present study consists of aluminum metal face sheets bonded with four layered symmetric hybrid cross-ply laminates, in which six different hybrid configurations have been considered. The performance of each hybrid configuration along with different sized and positioned cutouts is well investigated under various nonlinear loading conditions. [ABSTRACT FROM AUTHOR]

This paper aims to carry out sensitivity analyses to study how the effect of each design variable on the performance of self-centering buckling restrained brace (SC-BRB) and the corresponding buckling restrained brace (BRB) without shape memory alloy (SMA) rods. Furthermore, the reliability analyses of BRB and SC-BRB are performed in this study. Considering the high computational cost of the simulation methods, three Meta-models including the Kriging, radial basis function (RBF), and polynomial response surface (PRSM) are utilized to construct the surrogate models. For this aim, the nonlinear dynamic analyses are conducted on both BRB and SC-BRB by using OpenSees software. The results showed that the SMA area, SMA length ratio, and BRB core area have the most effect on the failure probability of SC-BRB. It is concluded that Kriging-based Monte Carlo Simulation (MCS) gives the best performance to estimate the limit state function (LSF) of BRB and SC-BRB in the reliability analysis procedures. Considering the effects of changing the maximum cyclic loading on the failure probability computation and comparison of the failure probability for different LSFs, it is also found that the reliability indices of SC-BRB were always higher than the corresponding reliability indices determined for BRB which confirms the performance superiority of SC-BRB than BRB. [ABSTRACT FROM AUTHOR]

In this study, an optimization procedure is proposed to find the optimum stacking sequence designs of laminated composite plates in different fiber angle domains for maximum buckling resistance. A hybrid algorithm combining genetic algorithm and trust region reflective algorithm is used in the optimization to obtain higher performance and improve the quality of solutions. As a novelty, Puck fiber and inter-fiber failure criteria are directly implemented to the optimization problems as nonlinear function constraints, which have allowed more consistent and feasible results. The performance of the hybrid algorithm is demonstrated by comparing with the individual performances of genetic and trust region reflective algorithms via test problems from the literature. Also, a study is performed to exhibit the effectiveness of the selected failure criterion as constraint among the other common criteria. The proposed procedure is used to solve many problems including various design considerations. The results indicate that reliable stacking sequence designs can be achieved in specific configurations even for the composite plates subjected to superior buckling loads when Puck physically based (3D) failure theory is considered as a first ply failure constraint in the buckling optimization. [ABSTRACT FROM AUTHOR]

This study is devoted to analyzing the thermal buckling behavior and natural vibration characteristics of a uniformly heated rectangular thin plate with two adjacent in-plane frictional sliding edges. These sliding edges are initially at a stick status under the friction forces, and may slightly slip due to the thermal expansion of the plate until the sliding edges contact the stops, i.e. the bounds of the clearances. In the study, both temperature dependencies of material properties and friction coefficients are taken into consideration. For each case, the explicit equations for the buckling temperature rise and the natural frequencies of the plate are derived. Then, some parametric studies are made to reveal the influences of both normal forces and clearances on the critical buckling temperature rise and the natural vibration characteristics of the plate. The results show that both normal forces and clearances have significant influences on the critical buckling temperature rise and the natural frequencies of the plate, especially for the square plate, which has repeated natural frequencies. These results enable one to adjust the normal forces and the clearances in design in order to improve the mechanical performance of a heated rectangular thin plate. [ABSTRACT FROM AUTHOR]

The present study introduces a novel higher-order shear deformation theory for assessing buckling and free vibration characteristics in laminated composite and functionally graded porous beams. The proposed theoretical framework effectively considers three variables and eliminates the need for a shear correction factor. The governing equations are derived from the Lagrange principle, while Legendre-Ritz functions are utilised to solve the resulting problem. Various types of laminated composite beams with arbitrary lay-ups and functionally graded porous beams with symmetric or unsymmetric configurations are analysed. To validate the accuracy and efficiency of the proposed theory, several numerical examples are conducted and compared against the results of existing research endeavours. [ABSTRACT FROM AUTHOR]

In this study, buckling behavior of adhesively patch repaired composite plates was investigated experimentally and numerically. Unidirectional carbon/epoxy composite plates with circular cutout were repaired with an adhesively bonded patch. Critical buckling loads of composite plates were researched without cutout, circular cutout, single patch-repaired, and double patch-repaired conditions. In addition to circular hole dimensions, patch length and adhesive thickness were used as geometrical parameters. Numerical study was performed in ANSYS finite element software three dimensionally. As a result, the critical buckling loads of single and double patch-repaired composite plates were increased from 96 and 263 ratios higher than circular-cutout composite plates. The percentile errors between experimental and numerical studies were determined from 2 to 11.5. [ABSTRACT FROM PUBLISHER]

This article presents free vibration and buckling analyses of functionally graded blades with variable thickness subjected to mechanical and thermal loading using isogeometric analysis as a powerful numerical method. The proposed method is based on deployment of Hamilton’s principle to the two-dimensional kinematics of blades. The governing equations are derived in the context of a modified form of higher order shear deformation plate theory that merely needs C0 -continuity (C0 -higher order shear deformation plate theory). Without the necessity of defining a shear correction factor, the theory can accurately predict the solution for different thickness-to-length ratios. The numerical predictions for the buckling loads and natural frequencies are successfully compared with the available solutions in the published articles and in the lack of relevant results, finite element analysis using ANSYS is used for verification of the model. The effects of variable thickness and aspect ratio on the natural frequencies and mode shapes known as the frequencies loci veering phenomena are assessed for the first time, which is an important design factor for the blades. The proposed method uses non-uniform rational B-spline element, which is able to approximate linear and nonlinear thickness distribution and the couple modes with an excellent numerical consistency. The influences of aspect ratio, thickness variation, taper ratio, volume fraction exponent, and boundary conditions on the free vibration and buckling of variable-thickness functionally graded blades are also examined. [ABSTRACT FROM AUTHOR]

This article is provided to investigate the free vibrational behaviors accompanied by buckling characteristics of carbon nanotube-reinforced conical shells via the Haar wavelet technique. For a better performance in the thermal environments, materials used in the structure obey the temperature-dependent relations. On the other hand, carbon nanotubes are embedded across the thickness uniformly or functionally. Using Hamilton's principle through the first-order shear deformation theory yields governing equations. Both dynamic and stability states are evaluated in the vicinity of equilibrium state and are also derived with regard to initial thermal stresses that are obtained via linear membrane technique in static analysis. The obtained partial differential equations are converted into ordinary ones with the aid of separating variable technique. Subsequently, the Haar wavelet approach is used to discretize the equations meridionally and transform them into new algebraic ones. Capability of this approach in calculation of frequencies with only a few numbers of the collocation points is demonstrated. Finally, to verify the integrity and precision of the proposed approach, some comparison studies are made with those of relevant results in the literature primarily. Thereafter, some effective parameters such as the geometry of nanotube, different boundary conditions, temperatures, and material properties are studied. [ABSTRACT FROM AUTHOR]

To reveal the compression failure modes of one-dimensional hierarchical double-shell octagonal lattice truss composite structures (DLTCSs), finite element modeling and equivalent continuum models were developed. DLTCS has three typical failure modes: (a) fracture of the strut, (b) global buckling, and (c) local buckling. Failure mode maps were constructed. It is found that column of long enough length will collapse at global buckling. When the column length decreases, the failure mode will turn to local buckling and strut fracture successively. Bay length greatly influences the buckling mode. Longer bay length could change the buckling mode from global buckling to local buckling. Compared with single-shell lattice truss composite structure, DLTCS has advantage in load carrying when the column fails at strut fracture or global buckling, while local buckling tolerance of DLTCS is smaller. [ABSTRACT FROM AUTHOR]

Laminate composites contain holes as a means of connection in industrial applications. A better understanding of the mechanical properties of open-hole components is necessary. Herein, progressive damage postbuckling analysis models are proposed for investigation of tensile damage and compressive buckling behaviors of open-hole laminate composites. The progressive damage model is based on failure criteria provided by the continuum damage mechanics model; virtual crack closure technology was employed to calculate the energy release rate for crack delamination in compressive postbuckling analysis. The models were utilized to analyze variations in the tensile and compressive mechanical properties, failure process, and buckling evolution of open-hole laminate composites using finite element analysis. The tensile failure patterns and failure processes of plies with different open-hole laminate composite angles were obtained and analyzed. Buckling characteristics, as well as the progression of buckling onset, buckling propagation, crack delamination, unstable delamination, and global buckling, were investigated. The influence of delamination crack length and crack distribution on the buckling properties of open-hole laminate composites are discussed in detail. Additionally, unstable and stable buckling characteristics were examined. The numerical results were in good agreement with theoretical and experimental results; damage initiated at the edge of a hole propagated to two sides with the onset of matrix damage, followed by fiber damage. The fiber damage of a 0°-ply led ultimately to laminate failure. The laminate with a symmetrical crack distribution showed stable buckling, whereas a short, nonsymmetrical distribution of cracks usually led to unstable buckling and delamination. [ABSTRACT FROM AUTHOR]