Postbuckling Strengths of Composite Laminates with a Central Circular/Elliptical Cutout Under In-Plane Combined Loads

Abstract

This paper deals with the effect of cutouts (i.e., circular and elliptical) aspect ratio on the buckling and postbuckling strengths, and failure characteristics of a simply-supported quasi-isotropic composite laminate subjected to in-plane shear and uni-axial compression combined with in-plane shear loads. The present study is carried out using self developed finite element program. The finite element formulation is based on the first order shear deformation theory and von Karmans assumptions to incorporate geometric nonlinearity. The resulting nonlinear algebraic equations are solved by Newton-Raphson method. The postbuckling strength of the laminate is defined in terms of the first-ply failure load of the lamina predicted by tensor polynomial form of the 3-D Tsai-Hill criterion. It is observed that for maximum buckling and first-ply failure strengths of the laminate with a cutout, it is preferred to have elliptical shape of the cutout as compared to the circular shape of the same area. It is also found that irrespective of load conditions and cutout shapes and sizes, shear load direction has significant effects on buckling and postbuckling stiffness of the laminate; although buckling stiffness is greater under negative shear, but the laminate shows stiffer postbuckling response under positive shear load.