Back stress evolution during creep of a metal matrix composite: an analysis by the mean-field approach and its implications

Unsteady creep behavior of a metal matrix composite has been studied by analyzing the evolution of ‘back stress’ (volume-averaged matrix internal stress) during the concurrent processes of matrix creep and diffusive mass transport along matrix-reinforcement interfaces. The matrix creep is assumed to obey the power law with a stress exponent of 3. Analytical expressions are obtained not only for the variation in creep rate with time on loading but also for the time-dependent creep strain to be recovered when the applied load is completely removed. Some numerical results are presented to illustrate the features of the analysis. A modification is also made by incorporating a threshold stress for matrix creep, whereby a possible reasoning is suggested for the ‘anomalously high’ apparent stress exponents in experimental creep data for metal matrix composites.