Application of the finite element method to laminated fiber composites

Abstract

<p>This thesis deals with the application of the Finite Element Method to the analysis of laminated fiber composites. Specifically, it addresses the problem of representing the variation of material properties through the element volume in order to reduce the number of degrees of freedom required to represent a laminated composite. This is accomplished by a modification in the evaluation of the element stiffness matrix, whereby the through thickness integration is evaluated separately for each ply of the laminate. This modification results in a significant reduction in the core memory requirements. The modification is implemented in a finite element code and used to investigate various aspects of laminate behaviour using a design philosophy based upon the laminae constituents rather than the more usual laminate properties. Problems involving lamina coupling, edge and surface deformations are solved for symmetric and unsymmetric laminates. The tensile behaviour of a particular laminate is predicted, and the ability to back calculate the specimen composition parameters is demonstrated. An explanation of the specimen size limitation for tensile tests is verified. Views of plate edge deformations are obtained that are not predicted by classical laminated plate theory, and that are currently unavailable in the literature. The modified element formulation is also used to implement a method whereby laminates of various lamination sequences may be ranked in terms of their energy absorption potential when subjected to quasistatic loading conditions by comparing the total energy absorbed before catastrophic failure. This is accomplished by the used of a damage analysis method that is based upon element integration point failure rather than the usual first ply failure criterion.</p>