FAILURE ANALYSIS OF COMPOSITE LAMINATES UNDER LARGE DEFLECTION

This paper presents the results of the application of a procedure, dev eloped by Reddy & Reddy [Composites Science and Technology 1992, 44, 2 27-255], for the evaluation of the first ply-failure load in multilaye red composite plates. The procedure, which is based on the use of the finite element method (FEM) and which is suitable for the analysis of generally loaded plates, uses the non-linear von Karman formulation an d, therefore, allows comparison of the failure loads in both the linea r and the geometrically non-linear behaviour. Nevertheless, the use of the Newton-Raphson technique in searching the non-linear equilibrium points restricts its application to the case of plates without limit-p oint behaviour. The displacement model adopted in the FEM formulation is the traditional first-order Reissner-Mindlin plate model that takes the shear deformation effect into consideration. Concerning the failu re criteria, the analysis is based on a tensor polynomial criterion to which all other polynomial and independent criteria are brought back as particular cases. The study refers to the failure analysis of thin and thick plates under a uniformly distributed transverse load. Furthe rmore, a comparison of the failure criteria when the shear stresses ar e evaluated by means of the constitutive equations and by means of the local equilibrium equations is carried out. Finally, adopting a very simple degradation model of the mechanical properties to account for t he stiffness decrease consequent to the failure, the qualitative behav iour of plates after the first non-catastrophic failure is also presen ted. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.