Chapter 6 - Failure Criteria and Strength of Laminates

Abstract

The purpose of this chapter is to discuss the concepts of failure criteria and strength of laminates. There exist two approaches to construct the failure surface, the first of which can be referred to as the micro-phenomenological approach. The term phenomenological means that the actual physical mechanisms of failure at the microscopic material level are not considered and that we deal with stresses and strains, with conventional and not actually observed state variables. The micro-approach evaluates the layer strength using micro-stresses acting in the fibers and in the matrix and failure criteria proposed for homogeneous materials. This approach needs the minimum number of experimental material characteristics. The first type referred to as structural failure criteria involves some assumptions concerning the possible failure modes that can help us to specify the shape of the failure surface. According to the second type, which provides a failure surface of an approximate form, experiments simulating a set of complicated stress states are undertaken. As a result, a system of points is determined and approximated with some suitable surface.