Optimal Design Of Laminated CompositePlates For Maximum Buckling Load SubjectTo In-plane Restraints Using The FEM

Abstract

Optimal buckling designs of symmetrically laminated rectangular plates are presented, taking the effect of in-plane restraints along the unloaded edges into account. Restraints give rise to Poisson's effect which leads to lower buckling loads, and may cause premature instability. Moreover, the laminate behavior with respect to fiber orientations changes significantly in the presence of Poisson's effect as compared to that of a laminate with this effect neglected. This change in behavior has significant implications for design optimisation as the optimal values of design variables with or without restraints differ substantially. In the present study, the design objective is the maximisation of the uniaxial buckling load by optimally determining the fiber orientations. The finite element method, coupled with an optimisation routine, is employed in analysing and optimising the designs. Numerical results are given for five different combinations of free, simply supported and clamped boundary conditions. INTRODUCTION Laminated composites have seen increasing use as structural materials due mainly to their low weight-to-stiffness ratios. In order to realise their full potential, structures manufactured of composite materials must be optimized, which in essence increases their effectiveness as load bearing components. Such structures are often subject to in-plane loading in which case failure by buckling needs to be taken into account in the design. In the classic uniaxial buckling analysis of laminated rectangular plates, the unloaded edges (y = 0 and y = 6, Fig. 1) are assumed to be free from restraint in the plane of the plate [14]. However, this assumption is likely to lead to inaccurate and possibly incorrect buckling loads as well as optimal fiber angles [5]. In the absence of in-plane restraints, a compressive force NXO in the -direction causes a constant transverse strain ty in the y direction due to Poisson's effect. Transactions on Engineering Sciences vol 4, © 1994 WIT Press, www.witpress.com, ISSN 1743-3533