RELATING HYDROTHERMAL DEGRADATION IN SINGLE-FIBER COMPOSITES TO DEGRADATION BEHAVIOR IN BULK COMPOSITES

Previous studies on single fibre composites using micro-Raman spectros copy revealed that the primary interfacial degradation mechanism in gr aphite/epoxy composites after hydrothermal exposure is mechanical in n ature. Mechanical degradation of the interface is the result of a comp lex state of stress created at the interface due to matrix swelling up on water absorption. The major component of such stresses is a radial tensile stress which causes a tensile failure of the interfacial bonds during exposure. To date, the effect of fibre volume fraction on the state of stress created at the interface due to matrix swelling has no t been considered. In this paper, finite element analysis (FEA) is use d to model bulk composites with different fibre volume fractions to de termine the applicability of single fibre composite behaviour to that of bulk composites. The analysis showed that the mechanical degradatio n mechanism can operate at all possible volume fractions and that in t he cask of a non-homogeneous fibre distribution, regions with both ver y high or very low fibre content are more susceptible to environmental degradation. Experimental results obtained from bulk composites (V-f approximate to 63-71%) confirmed the FEA results and showed that the i nterfacial degradation in that case was more severe than in the case o f single fibre composites.