Buckling Of Panels Research Articles

Structural design of composite stiffened panel for a flat wing micro-aircraft

In this study, the integral micro-sized composite wings are designed and manufactured by using carbon fiber reinforced plastics and low-density foam. The analytical expressions of bending stiffness of a multilayer sandwich structures for variable cross-section panel are determined. The obtained analytical bending stiffness is numerically verified using results of compressive buckling modes on wing panels from a numerical FE program and experimental tests by a series of stiffened structures which are empirically designed. Contrastive results demonstrate that the stiffener configuration tremendously affects the global buckling of the wing panels and the shapes, locations and intervals of the stiffeners which should be adjusted to construct a structure with maximum bending stiffness. Finally, with the use of the bi-directional evolutionary structural optimization method, the optimum design of the wing cross-section was determined by topology optimization method to pursue the best weight/stiffness. Compared with the initial structure, the optimum material layout of the topology structure performs better at reducing stress concentration and improving load carrying capacity of wing panels.

Design and optimization of composite sub-stiffened panels

This study concerns the buckling and post-buckling performance of composite stiffened panels with sub-stiffening structure subject to compression. The buckling response of the composite stiffened panel is first predicted and verified by experimental data available from the literature. Then sub-stiffeners are introduced into the composite stiffened panel. The distribution and stacking sequence of sub-stiffeners are optimized to improve the critical buckling load without adding weight. Further, to investigate the underlying mechanism of sub-stiffeners involved panels deformation and failure during compressive post-buckling process, different skin-stiffener interfacial parameters are considered. Results show that the introduction of sub-stiffeners to composite T-stiffened panel causes a significant improvement of buckling load (+122.66%) and induces reestablishment of the stress concentrated zone which leads to different local failure forms with different interfacial properties. In addition, the collapse load of sub-stiffened panel becomes more sensitive to interfacial parameters of skin-stiffener interface due to the presence of sub-stiffeners.

Exact solution for buckling of axially-compressed cylindrical panels with frames attached to the circular edges

This paper presents an exact solution for the boundary-value problem which describes the linear buckling of axially-compressed cylindrical panels with frames attached to the circular edges. The boundary conditions differ from the classical simply supported ones, often assumed for design purposes, in the sense that the torsion resisted by the frames are also taken into account. The quality of the results reported herein may be valuable benchmark data.

Исследование прочности и устойчивости ортотропных конических оболочек и конических панелей

Исследование прочности и устойчивости ортотропных конических оболочек и конических панелей

Buckling Load Predictions of Panel and Shell using Vibration Correlation Technique

Prediction of buckling loads is a very important phenomenon for aerospace and marine industry. In this paper buckling predictions of a submarine hull is considered by using a shell element and a rectangular panel is considered by using a plate element. The buckling load of a submarine hull can be predicted by using vibration correlation technique. Determination of these buckling loads can be carried out based on the boundary conditions of the submarine hull structure. The technique will be carried by considering both surface conditions and to determine the crippling load of a hull. This paper aims to use VCT for a submarine hull structure used in marine, ocean and can compare the results to aerospace industry by considering a rectangular panel for which buckling is predicted using vibration correlation technique . VCT is not very extensively used in case of thermal buckling. However in this paper, VCT is applied to verify the thermal buckling of a simple thin rectangular panel subjected to parabolic loading.

Numerical investigation on ultimate shear strength of long steel plate girder web panels at high temperatures

In this article, elastic shear buckling and ultimate shear strength of long steel plate girder web panels subjected to pure shear loading are investigated at both ambient and elevated temperatures by the finite element method (FEM). Ninety-six plate girders with compact, non-compact and slender long web panels are numerically analyzed and compared. From linear eigenvalue analysis, it is shown that AISC 360-16 predictions are more conservative than FEM results such that the difference is about 40% for all ranges of web panel slenderness. According to nonlinear analysis results at ambient temperature, there must be reduction factors applied to AISC 360-16 non-conservative predictions for considering the strength degradation caused by large slenderness values and effects due to initial geometrical imperfection. Furthermore, it is observed that the adopted equation of AISC 360-16 for fire situations yields values that are more non-conservative such that the difference reaches almost 18%. In this regard, the FEM results are used to develop a new equation for predicting the ultimate shear strength of long web panels by taking into account strength degradation caused by large slenderness values, high temperature and initial geometrical imperfections.

Thermo‐mechanical fluid‐structure interaction for thermal buckling

AbstractAerothermodynamical loads cause buckling and plastic deformation of thin‐walled structures under boundary conditions, which restrict the structural movement. We present the numerical computation of a loosely coupled fluid‐structure interaction for thermal buckling. The task of the research is to provide a mechanical model which incorporates the correct material behaviour and is suitable for thermal panel buckling. For this, an elasto‐viscoplastic material model with non‐linear isotropic hardening is used, which also includes nonlinearly temperature dependent material parameters. This material model is implemented into a user material in Abaqus FEA. The structural computation is coupled with the fluid computation within the fluid‐structure interaction code ifls from the TU Braunschweig. For the fluid solver TAU from the DLR is used.

Secondary buckling and failure behaviors of composite sandwich panels with weak and strong cores under in-plane shear loading

The secondary buckling and failure behaviors of composite sandwich panels (CSPs) subjected to in-plane shear loading are studied via a self-developed quasi-conforming finite element method. The influences of key material and geometry parameters on postbuckling and failure behaviors are investigated. Numerical results show that (1) postbuckling failure is dominated by the ratio of two strengths, i.e. the through-thickness shear strength of the core and the transverse tensile strength of the lamina. In addition, two constant thresholds for this strength ratio exist in the relationship between the load bearing capacity of CSPs and the ratio, which can be used to define “weak” or “strong” core and the status of postbuckling load bearing capacity (PLBC); (2) local failures of the core and face sheets (FSs) can lead to a drastic decrease in the local stiffness of CSPs, a singularity of the tangent stiffness matrix and the occurrence of secondary bucklings of CSPs; (3) secondary bifurcation identification, branch switching and convergence improvement are all necessary to obtain reasonable paths during the path-following.

The Effects of Ply Orientation on Nonlinear Buckling of Aircraft composite Stiffened Panel

In this paper, gradual demand for curved, stiffened panels composite emerged from carbon fiber reinforced plastics (CFRP); these are structures that are frequently used in aerospace engineering. Up to 50% of the primary structure of the Boeing 787 is made up of woven graphite–epoxy. This research emphasizes the buckling analysis of stiffened composite panels using the nonlinear, finite element modeling. The stiffened panel is assumed to be subjected to a uniform axial compression load of . For the nonlinear buckling analysis, a stiffened composite panel is made of carbon fibre composite (CFC) in epoxy, Kevlar in epoxy and E-glass (EG) in epoxy. Due to the fact that there are numerous stiffened composite panels materials, this paper, therefore uses a numerical approach, to present the study and results of the nonlinear static buckling analysis of I-stiffened, on different composite panels. This research also presented the effect of the different ply orientations using Abaqus finite element analysis (FEA).

Thermal buckling and sound radiation behavior of truss core sandwich panel resting on elastic foundation

Due to high stiffness and other potential multifunctional application characteristics, truss core sandwich structure offers a promising alternative to traditional stiffened or corrugated sandwich plates used in aerospace and marine industry. And sound radiation from plate structures is a design factor indicating the power reduction, which can help the lattice truss core sandwich structure meet the acoustic requirements for practical engineering design, but the sound radiation performance of this sandwich structure remains unclear. Based on that, the thermal buckling and sound radiation behavior analyses of truss core sandwich structure resting on elastic foundation in thermal environment are presented in this paper. The mechanical behavior of structure–foundation interaction is modeled as two-parameter model including Winkler and shear foundation. The sound radiation due to a concentrated harmonic force in thermal environment is computed by solving the Rayleigh integral. By comparing with numerical simulation results calculated by commercial finite element software, the accuracy and feasibility of theoretical model developed in this paper are validated. The effects of several key parameters including the truss core radius, inclination angle and height, temperature field and elastic foundation stiffness coefficient on thermal buckling and sound radiation behavior have been subsequently investigated.

Nonlinear Flutter Suppression and Thermal Buckling Elimination for Composite Lattice Sandwich Panels

A mechanism is proposed to suppress the nonlinear flutter and thermal buckling of composite lattice sandwich panels with tetrahedral truss core in supersonic airflow by means of the Winkler–Pasternak elastic foundation. The strain-displacement relations are evaluated according to the von Kármán large deflection and first-order shear deformation theories. The aerodynamic pressure acting on the sandwich panel is formulated by the supersonic piston theory. The nonlinear equations of motion of the structure are established by Hamilton’s principle in conjunction with the assumed mode method. By using the Winkler–Pasternak elastic foundation, an effective method for eliminating the nonlinear thermal buckling of the structure is presented. The natural frequencies of the sandwich panels are validated through comparing with the published results. The parametric investigations on the shearing layer and Winkler parameters are conducted. The influences of several parameters, including ply angle of laminated face sheets, and radius and material properties of the trusses on the nonlinear flutter, and thermal buckling behaviors are investigated. The numerical results attest that the nonlinear thermal buckling effect can be completely eliminated, and the nonlinear flutter of the composite lattice sandwich panels can be effectively suppressed by adjusting the elastic foundation parameters.

Shear buckling of steel foam sandwich panel resting on Pasternak foundation

Abstract The objective of this paper is to assess the inplane shear buckling of a steel foam sandwich panel that relies on elastic Pasternak foundation. The panel is a combination of solid steel face sheets and foamed steel cores. Foamed steel, that is steel with internal voids, provides enhanced bending rigidity and energy dissipation, and also, the potential to reduce local buckling. The Classic plate theory is employed where their governing equations are solved by the Rayleigh–Ritz method. Uniformly distributed in-plane shear loads are applied to the two opposite edges of the panel and all the four edges of the panel are simply supported. Finally, the effects of the panel parameters, such as the existence of a Pasternak foundation, aspect ratios, and central fraction of the steel foam core, are presented. The results showed that the optimum central fraction of the steel foam core would be 65%, so that the maximum critical shear buckling load has taken place.

Buckling and collapse analysis of a cracked panel under a sequence of tensile to compressive load employing a shell-solid mixed finite element modeling

The present study focuses on buckling and collapse behaviors of cracked steel panel by accounting for the crack opening/closure. A rectangular panel with a transverse through crack to the loading direction is selected to better understand the typical mechanical characteristics of a panel subjected to a sequence of tensile to compressive loading. When a tensile load is applied to the cracked panel, a through crack gradually opened and yielding occurs around the crack tip. When a compressive load is applied after the tensile load, the crack gradually closed and elastic/elasto-plastic buckling occur. A shell-solid mixed finite element (FE) model is adopted to effectively analyze the crack opening/closure. Shell FEs are employed in the rectangular panel (shell model), while solid FEs are partially adopted around the crack (solid model). Double nodes and contact condition are imposed on the crack face. The shell and solid models are joined together with a rigid body element (RBE). The buckling and collapse behaviors of the panel models under a sequence of tensile to compressive loading is critically examined, as well as its local behavior, i.e., crack opening displacement (COD) varying displacement amplitude, panel aspect ratio and panel thickness. The results show that the crack opening/closure strongly affect the buckling and collapse behaviors of the cracked panel.

Compression after impact behavior of composite foam-core sandwich panels

Low-velocity impact tests and compression after impact (CAI) experiments were conducted on composite foam-core sandwich (FCS) panels. The impact tests revealed that the damage depth of the FCS panels increases with an increase in the impact energy. The CAI experiments revealed that the residual compressive strength of the FCS panels decreased with an increase in the impact energy. The local buckling of the FCS panels without impact damage occurred during compression, which was observed by the strain bifurcation phenomena using electrical strain gauge measurements. However, the large strain gradient and compression failure of the FCS panels with impact damage occurred during compression, as observed by the full-field deformation using three-dimensional digital image correlation (3D-DIC) measurements. The numerical simulations using the finite element method (FEM) were consistent with the observed failure phenomena, i.e., the damage at the impact site weakening the compressive strength of the FCS panels.

Local buckling analysis of periodic sinusoidal corrugated composite panels under uniaxial compression

The critical local buckling of simply-supported sinusoidal panels subjected to uniaxial compression using the Rayleigh-Ritz method is investigated. With increased applications of thin-walled composite structures in engineering, these corrugated panels are especially popular due to their high stiffness to weight ratio and high out-of-plane rigidities. Failure of such thin-walled panels occurs mainly in buckling rather than material failure; thus, it leads to the importance of buckling failure analysis. Conventional methods are limited when analyzing these panels in local buckling because of its unique geometries. Hence, a semi-analytical solution is developed to predict the local buckling based on classical shell theory with a unit cell approach, and it shows excellent correlation with the results based on the numerical finite element analysis. A parametric study is conducted to evaluate the effects of the thickness, aspect ratio, and the corrugated amplitude of the panel on buckling. It is revealed that the derived solution can accurately capture the local buckling behavior at high thickness/radius of curvature ratios, any aspect ratios, and high corrugated amplitudes. Additionally, the effects of orthotropy, Poisson’s ratios and twisting capacities on the buckling behavior are explored. The proposed semi-analytical solution can be effectively used to aid in the efficient and accurate design analysis and optimization of corrugated panels.

Influence of modal coupling and geometrical imperfections on the nonlinear buckling of cylindrical panels under static axial load

The aim of this work is to analyse the influence of the nonlinear modal coupling and initial geometrical imperfection on the post-buckling path (perfect case) or nonlinear equilibrium path (imperfect case) of a simply supported, axially loaded cylindrical panel. The cylindrical panel is described by the Donnell nonlinear shallow shell theory and the lateral displacement field is based on a perturbation procedure, generating a precise low-dimensional model that satisfies out-of-plane boundary conditions and considers the forthcoming nonlinear modal coupling due to quadratic and cubic terms in a nonlinear equilibrium equation. The discretized equations of motion are determined by applying the standard Galerkin method. Various numerical techniques are employed to obtain the cylindrical panel’s nonlinear static equilibrium path with its structural stability analysis. The results show the influence of geometry on the nonlinear response of the cylindrical panel, unveiling an intricate competition between different types of bifurcation diagrams (stable symmetric, unsymmetrical, and unstable symmetric). Completing the presented results, the initial geometrical imperfection could change the stability of the initial nonlinear equilibrium path (from unstable to stable) depending on the applied amplitude of the imperfection and its shape. It is possible to observe that the influence of the geometrical imperfection on the nonlinear equilibrium path of the imperfect cylindrical panel is determinant.

A simple spline finite strip for buckling analysis of composite cylindrical panel with cutout

Abstract In this study, a new sub-parametric strip element is developed to simulate the axially loaded composite cylindrical panel with arbitrary cutout. For this purpose, a code called SSFSM is developed in FORTRAN to analyze the buckling of panels. The first order shear deformation theory is used to form the strain-displacement relations. Spline and Lagrangian functions are used to derive element shape functions in the longitudinal and transverse directions, respectively. The computational cost of the SSFSM is decreased dramatically, as mapping functions of the strip element are very simple. The results obtained from the SSFSM are compared with those of the literature and the results obtained by ABAQUS to show the validity of the proposed approach. A parametric study is performed to show the capability of the SSFSM in calculating the panel buckling load. Results indicate that increasing the panel thickness and panel central angles cause an increase in panel buckling load. The cutout shape is an important factor influencing the panel buckling load. For instance, when the angle between the direction of big chord of the elliptical cutout and compressive load direction are 0 and 90 degrees, the panel buckling load reaches its minimum and maximum magnitude, respectively.

Damage assessment studies in CFRP composite laminate with cut-out subjected to in-plane shear loading

The present work focuses on the damage assessment of carbon fiber reinforced polymer (CFRP) panels subjected to in-plane shear loading undergoing large deformation. Experimental investigations are carried out to understand the buckling, post-buckling and collapse behavior of quasi-isotropic CFRP panels with and without cut-out under the shear loading. A special picture frame fixture is designed and fabricated in-house for applying shear load over the CFRP test panels with clamped plate boundary conditions. In this work, the presence of a circular cut-out and its counter effects on the structural performance, associated damage mechanisms are monitored by an integrated use of digital image correlation (DIC) and acoustic emission (AE) techniques. The whole-field displacement and strain data over the test panels are monitored in-situ using the DIC technique, and later they are used for predicting the buckling and post-buckling response. Further, the surface strain data obtained from DIC are used to study the damage initiation and propagation zones in the test panels. AE technique is employed to identify the initiation and propagation of various damage mechanisms including classification in the buckling and post-buckling regime. A detailed micrographic study is also carried out on the fractured panels to support the damage assessments done by the AE technique. Additionally, finite element modeling is done to study the post-buckling behavior of CFRP panels with and without cut-out under shear loading conditions. The finite element results are compared with the experimental observations, and the accuracy of the numerical model is validated. This study gives a better understanding of the collapse mechanism of CFRP panels under shear loading and assists in designing damage tolerant composite structures.

An empirical formulation for predicting welding-induced biaxial compressive residual stresses on steel stiffened plate structures and its application to thermal plate buckling prevention

ABSTRACTThe aim of this paper is to derive an empirical formulation for predicting welding-induced biaxial compressive residual stresses in welded steel plate panels. A test database for full-scale models of welded steel plate structures is developed. Elastic-plastic finite element method solutions, associated with thermal stresses in welded steel plate panels, are also developed. The proposed formula is derived by a curve fitting of the databases obtained from both full-scale measurements and numerical computations as a function of plate thickness and weld leg length. The paper demonstrates an applied example of the derived formulations to prevent the thermal buckling of thin steel plate panels that occurs during the welding process.

Experimental investigation of the buckling behaviour of Textile Reinforced Cement sandwich panels with varying face thickness using Digital Image Correlation

Sandwich panels with Textile Reinforced Cement composite (TRC) faces are promising structural elements for construction, as both the structural and insulating performance are merged into one lightweight construction element. In the literature, extended research has been performed to understand the bending behaviour of TRC sandwich panels, yet research into their behaviour under axial loading is scarce. Therefore, axial compression tests on TRC sandwich panels were performed; varying parameters in the tests were the materials of the TRC faces and the face thickness. Comparisons of experimental results with analytical predictions gave insight into the effect of the face thickness on the loadbearing and failure behaviour. For very thin faces the latter changed from global buckling of the sandwich panel towards wrinkling of the faces; both phenomena were clearly monitored by Digital Image Correlation. A good correlation between the analytical predictions and the experimental observations was obtained.