Failure analysis of composite laminates under large deflection

This paper presents the results of the application of a procedure, developed by Reddy & Reddy [ Composites Science and Technology 1992, 44, 227–255], for the evaluation of the first ply-failure load in multilayered 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 and, therefore, allows comparison of the failure loads in both the linear 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-point behaviour. The displacement model adopted in the FEM formulation is the traditional firstorder Reissner-Mindlin plate model that takes the shear deformation effect into consideration. Concerning the failure 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 failureanalysis of thin and thick plates under a uniformly distributed transverse load. Furthermore, a comparison of the failure criteria when the shear stresses are 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 the stiffness decrease consequent to the failure, the qualitative behaviour of plates after the first non-catastrophic failure is also presented.