THE EFFECTS OF INTERPHASE PROPERTIES ON INTERFACIAL SHEER STRENGTH INPOLYMER MATRIX COMPOSITES

The effects of interphase elastic modulus, glass transition temperatur e, and thickness on interfacial shear strength were investigated both experimentally and theoretically. Single fiber fragmentation tests wer e performed over a range of temperatures on samples with tailored inte rphases. Three different types of interphases were investigated: high modulus/high glass transition temperature, low modulus/low glass trans ition temperature and uncoated (no tailored interphase). A reduction i n interfacial shear strength with temperature was observed for all thr ee types of samples tested. The magnitude of this decrease was found t o correlate with the glass transition temperature of the interphase. T he low T-g interphase samples showed large reductions in IFSS, while s amples with a higher T-g coating showed only a small decrease. A three -phase, axisymmetric elasticity solution was developed to predict the sensitivity of the stress state to the interphase material properties and temperatures used in the experimental studies. Predictions which i ncorporated the change in modulus of both the matrix and interphase wi th temperature were in good agreement with the experimental trends. Bo th the theoretical and experimental results supported the existence of an interphase with reduced glass transition in the uncoated samples.