Study of the effect of interface slip and diffusion mechanisms on the creep of metal and intermetallic matrix composites

Experimental results indicate that, in general, at modest temperatures the creep strength of metal and intermetallic matrix composites is better than that of the matrix material alone. However, at temperatures higher than approximately half the melting temperature of the matrix, the composite strength is limited and in some cases the strengthening imparted by the reinforcements is completely lost despite the absence of any debonding or damage accumulation along the matrix-reinforcement interface. Slip and diffusional flow along the interface, driven by the gradient in the normal stress, are suggested as mechanisms responsible for the loss of strengthening. The composite behavior is investigated by coupling the interface diffusion and slip mechanisms with the power-law creep of the matrix.; The steady state creep strength of a continuous fiber composite under transverse loading and a discontinuous fiber composite under axial loading are investigated. In the case of discontinuous fiber reinforced composites with a diffusive interface, the critical fiber aspect ratio needed for the composite to be stronger than the pure matrix is obtained.; The two relaxation mechanisms are used to explain the temperature dependence of the strength of gamma-TiAl matrix reinforced with Ti 2AlC particles. A methodology is suggested for extracting the properties of the interface combining the experimental measurements of the composite creep strength with the corresponding finite element based strength predictions.; The strength of the leading order singularity and the angular variation of the solution within a constant around the sharp corner of a discontinuous fiber are obtained in an asymptotic study. By comparing the asymptotic and the finite element solutions the value of this constant and the region of dominance for the singular solution are obtained. The region of dominance is found to be only of the order of 5 x 10-4 times the fiber radius.; The influence of the two mechanisms on the transient stress redistribution between the composite constituents is investigated. For a composite whose matrix-reinforcement interface is either perfectly bonded, freely slipping, or rapidly diffusive, the transient solution scales with the applied load and the matrix creep viscous modulus. The transient solutions at large times are found to approach the corresponding solutions obtained from the direct steady state analysis.