Stress transfer in the fiber/matrix interface of titanium matrix composites due to thermal mismatch and reaction layer development

Abstract

It is well known that the difference in the coefficient of thermal expansion of the components of titanium matrix composites with the SCS-6 SiC-fiber gives rise to substantial residual stresses. Due to the fact that the fiber/matrix bond strength is low (as long as there is still a substantial thick carbon protection layer) fiber/matrix stress transfer is realized partly through interfacial friction enabled by the residual radial compressive stress at the fiber/matrix interface. Fiber matrix reactions usually lead to a volume change. In the present investigation this volume change is investigated analytically as well as experimentally on the SCS-6/IMI834 system. It was determined analytically with the aid of a two-dimensional stress analysis that fiber/matrix reaction leads to a reduction of the residual stresses. Experimental results on composite specimen diameter change indicate an increase of the residual stress caused by an unexpected shrinkage of the matrix. Another source for residual stress is an unequal (inwards and outwards) radial growth of the reaction layer if the diffusion rate of the reacting species through the reaction layer differs from the stoichiometric relation for the reaction.