Combined In-plane Compression Research Articles

Type I size effect and failure behavior of woven composites under biaxial flexure

This study presents an experimental investigation into the failure and size effect exhibited by woven composites under biaxial flexure, induced via the ring-on-ring plate bending test. Square-shaped, epoxy/carbon twill woven composite plates of various sizes, scaled in three dimensions are considered. The biaxial flexural response of all specimens is found to be ductile and nonlinear with failure initiation at the top surface edges under combined in-plane compression and out of plane shear. These combined compression/shear cracks propagate towards the plate center, exhibiting a four-fold symmetry, and causing the plate to deform into a cone. Elastic stress analysis is presented to interpret and support the observations. The nominal stress at the onset of non-linearity is found to obey a type I size effect law, exhibiting a marked decrease with increased plate size but approaching a constant value. This size effect must be accounted for when designing woven composite parts to be subjected to biaxial flexure.

Ultimate strength assessment of stiffened panels using Equivalent Single Layer approach under combined in-plane compression and shear

Equivalent Single Layer (ESL) approach is extended to model ultimate strength of stiffened panels under a combination of in-plane compression and shear. Ultimate strength under this combined loading depends on the loading path and could be lower than for only uni-axial compression since shear load can produce axial forces. Thus, to account for this effect, the recent ESL model is extended to include A13 stiffness component as non-zero value. Procedure to accurately obtain A13 is presented. In ESL approach, a stiffened panel is transformed into a two-dimensional (2D) single layer with the same stiffness obtained from unit cell simulations. To obtain non-linear stiffness matrix of ESL, elastic–plastic material properties and initial imperfection were applied to the unit cell. ESL responses were validated by comparing numerical and experimental results from the literature. Several stiffened panel configurations were analyzed to obtain different collapse modes. Combined loads were applied for shear to compression ratio of 0, 1, and 2. Lateral pressure loading was also considered in the simulations. Analyses were carried out based on the load sequences consisting of: 1) compression and shear loaded simultaneously and 2) shear applied first, followed by compression. The results show that the modified ESL can well capture the effect of shear load on ultimate strength in comparison to a detailed 3D FEM model of stiffened panels. The accuracy of the ESL varies depending on the collapse mode of stiffened panels.

Analytical Solution for the Ultimate Strength of Sandwich Panels under In-plane Compression and Lateral Pressure

The paper presents a closed-form analytical solution for the ultimate strength of sandwich panels with metal faces and an elastic isotropic core during combined in-plane compression and lateral pressure under clamped boundary condition. By using the principle of minimum potential energy, the stress distribution in the faces during uni-axial edge compression and constant lateral pressure was obtained. Then, the ultimate edge compression was derived on the basis that collapse occurs when yield has spread from the mid-length of the sides of the face plates to the center of the convex face plates. The results were validated by nonlinear finite element analysis. Because the solution is analytical and closed-form, it is rapid and efficient and is well-suited for use in practical structural design methods, including repetitive use in structural optimization. The solution applies for any elastic isotropic core material, but the application that stimulated this study was an elastomer-cored steel sandwich panel that had excellent energy absorbing and protective properties against fire, collisions, ballistic projectiles, and explosions.

Development of design factor predicting the ultimate strength for wide spacing in container curved bilge structures

The aim of the present study is to develop a curvature factor to estimate the ultimate strength and the progressive collapse behaviour of a stiffened curved plate under combined in-plane compression and lateral pressure. Stiffened curved plates are used in various parts of ship and offshore structures, such as bilge structures, columns and the inside structures of offshore semisubmersible rigs. The curvature of a cylindrically curved plate is found to increase the buckling strength and ultimate strength compared with a plate without curvature. Based on the numerical results of a series of nonlinear finite element calculations for all edges with symmetric curved plating with varying parameters such as slenderness ratio, stiffener size, flank angle and amplitude of lateral pressure, an empirical design factor is derived to predict the curvature influence for a fundamental scantling design by rule guidance. The outcomes can be widely referred to in basic designs to decide the required bilge thickness during local scantling.

A buckling verification approach for monolithic and laminated glass elements under combined in-plane compression and bending

Glass elements are widely used in modern buildings as structural columns, beams, stiffeners. Nevertheless, due to accidental eccentricities, additional loads, boundary conditions or imperfection factors, glass beam–columns are frequently subjected to in-plane compressive actions combined with bending moments. Because of this reason, the paper focuses on the buckling resistance of glass elements subjected to eccentric compressive loads. Based on large experimental numerical results available in literature for monolithic and laminated glass columns or beams in out-of plane bending, verification criteria for these simple loading conditions are firstly recalled from previous contributions. Subsequently, numerical static incremental simulations are performed with a finite-element model able to predict the buckling strength of imperfect glass elements eccentrically compressed. In it, also the effects of various geometrical imperfection shapes are deeply investigated. Finally, an analytical interaction curve is proposed for a conservative and rational buckling verification of monolithic and laminated structural elements.

Empirical formulations for estimation of ultimate strength of continuous stiffened aluminium plates under combined in-plane compression and lateral pressure

The present research was undertaken based on the results obtained by the same authors in a sensitivity study on the buckling and ultimate strength of continuous stiffened aluminium plates. Empirical expressions are developed for predicting ultimate compressive strength of welded stiffened aluminium plates used in marine applications under combined in-plane axial compression and different levels of lateral pressure. Existing data of the ultimate compressive strength for stiffened aluminium plates numerically obtained by the authors through the previously performed sensitivity analysis are used for deriving formulations that are expressed as functions of two parameters, namely the plate slenderness ratio and the column (stiffener) slenderness ratio. Regression analysis is used in order to derive the empirical formulations. The formulae implicitly include effects of the weld on initial imperfections, and the heat-affected zone.

Sensitivity analysis on the elastic buckling and ultimate strength of continuous stiffened aluminium plates under combined in-plane compression and lateral pressure

In this paper, the results of an investigation into the post-buckling behaviour of high-strength aluminium alloy stiffened plates subjected to combined axial compression load and different magnitudes of lateral pressure using non-linear finite element approach is presented. Both material and geometric non-linearities have been taken into account. The principal variables studied are the plate thickness, boundary conditions and the stiffener geometries beside the geometrical imperfection, the width of the welding heat-affected zone (HAZ) and welding residual stresses. The influence of these variables on the post-buckling behaviour and ultimate strength of such stiffened plates has been investigated in details.

Analytical Solution for the Ultimate Strength of Metal-faced Elastomer-cored Sandwich Panels under In-plane Edge Compression and Lateral Pressure

This paper presents a closed-form analytical solution for the ultimate strength of simply supported sandwich panels with metal faces and an elastic isotropic core under combined in-plane compression and lateral pressure. By solving the geometrically nonlinear governing differential equations of imperfect isotropic sandwich panels with a relatively soft core using the ordinary Galerkin method, the stress distribution in the faces under uniaxial and lateral pressure loads is obtained. The ultimate strength equations are then derived on the basis that collapse occurs when yield has spread from the middle of the concave face plate to the mid-length of the unloaded sides of the face plate. The solution is validated by a detailed nonlinear finite element analysis using three alternative models. Because the solution is analytical and closed-form, it is rapid and efficient and is well-suited for use in practical structural design methods, including repetitive use in structural optimization. The solution applies for any elastic isotropic core material, but the application that stimulated the study is an elastomer-cored steel sandwich panel that has excellent energy absorbing and protective properties against fire, collision, ballistic projectiles and explosions.

複合荷重を受ける薄板の座屈後耐力

The objective of this study is to obtain the post-buckling strength of thin-plates under combined loads by FEM analysis. At first, the post-buckling behaviors of thin-plates subjected to in-plane compression and bending, in-plane compression and shear, or in-plane bending and shear are discussed. Finally the formula of post-buckling strength under combined in-plane compression, bending and shear is proposed in terms of the interaction equations. The validity of the proposed formula is examined by the further numerical analysis.

The buckling performance of composite stiffened panel structures subjected to combined in-plane compression and shear loading

In this paper a study is made of the buckling behaviour of some composite stiffened panel structures subjected to in-plane compression and shear load combinations. The finite strip method, a computer aided engineering analysis procedure, is employed to determine the buckling solutions. Since the prediction of structural performance is quickly and accurately determined through computer simulation, the analysis capabilities of the finite strip method promotes the examination of many design alternatives. The designer is encouraged and indeed readily aided to make the most efficient use of materials and thus the development of highly reliable structural components, which are able to operate at optimised performance levels, can be achieved. A basic strip formulation for composite material construction is presented which is able to predict the complex buckling modes associated with in-plane load combinations. The buckling displacement fields are represented by algebraic polynomials across the strip and trigonometric functions along the strip length. The inclusion of sufficient harmonics in the appropriate displacement representations provides the required flexibility of the strip formulation to accommodate the more elaborate buckling modes associated with the presence of in-plane shear loading. The results presented in the paper are those pertaining to the buckling capabilities of stiffened panels manufactured from high strength carbon-epoxy composite material. The results illustrate, graphically, the effect on buckling performance of changes in stiffener geometry. Interaction curves are presented in the paper which detail the limiting boundaries for critical load combinations of specific structural configurations.