Interphase Shear Strength of Titanium Metal Matrix Composites at Elevated Temperatures

Abstract

A series of fiber pushout tests on thin-slice samples of a SCS-6/Timetal-21S composite were carried out to determine the load values at which partial and full debonding occurs. Finite element calculations of the stress field in the specimen were employed to assess the interphase strength of the composite as function of temperature. In these calculations, the semi-infinite thickness and the traction-free surface effects of the thin-slice samples on the corresponding stress field are considered. For each of these specimens, the distribution of shear stress along the fiber/matrix interface is determined in order to identify a region of stress localization which is taken in this study to be a measure of the interphase shear strength. This strength is then identified as the balance of forces at this localized field due to the traction-free surface of the composite section. Both contributions from process-induced residual stress and geometry-induced constraint of the traction-free surface to the strength are considered. The results of this study showed that the interphase shear strength decreases with an increase in temperature and processing-related residual stress contributes about 35 % to the interphase shear strength at room temperature. Furthermore, the interphase shear strength as calculated in this paper was found to be larger than that determined by considering uniformly distributed shear stress along a pushout fiber.