Some Fundamental Fracture Mechanisms Applicable to Advanced Filament Reinforced Composites

Abstract

The object of this study is to establish experimentally the critical fracture modes of an epoxy matrix in the vicinity of a break in a high modulus, high strength filament simulating the effect of tensile loading on unidirectional composites. Three distinct failure modes were observed to occur and the nature of these three modes is explained through an analysis of the stress state in the matrix. A single filament embedded in an epoxy novolac was used to examine the fracture process. The advantage of using this type of resin arises from its ability to be modified to varying degrees of crack sensitivity. The effects of varying gross strain rate were evaluated and the study was then extended to specimen configurations containing more than one filament. This approach permits the examination of the interaction of nearby filaments with localized fracture processes. Filaments of boron on tungsten (B/W) boron on Silica (B/SiO 2), boron carbide on B/W and tungsten wire were used with epoxy novolac (DEN 438).