Material Characterization for Implementation of Hashin Tri-Axial Fatigue Failure Criteria for Unidirectional Composite Laminates

Abstract

The primary reason for popularity of composite materials is their high specific stiffness and strength enabling them to have large field of applications especially in the areas of aerospace, automobile and marine structures. Because of the intrinsic behavior of these structures, cyclic loadings come into consideration which cause fatigue failure of structures. Because of the complexity of fatigue damage mechanisms, there are many fatigue damage modeling techniques available in the literature. Fatigue life models, similar to the fatigue failure theories of metals, are one of the major categories of fatigue failure criteria for composites. Most of existing fatigue damage modeling techniques use the assumption of a plane stress state, which is only applicable for thin laminates. A few criteria are applicable for tri-axial stress state. One of the earliest fatigue failure theories is Hashin criteria. Hashin criteria have the advantage of distinguishing between two different failure modes; fiber breakage and matrix cracking. Similar to all other fatigue life models, for implementing Hashin failure criteria on a certain base material, the material should be firstly characterized to obtain its properties. In this paper the manufacturing procedure and test results for basic failure stress S-N curves are outlined as the first step for implementing Hashin failure criteria. The prepreg material is glass epoxy S2/E773 which is mostly used in the aerospace applications.