Assessment of back stress and load transfer approaches for rationalizing creep of short fiber reinforced aluminum alloys

Creep data from a model Al–Zn alloy reinforced with Saffil short fibers were evaluated following the threshold stress and the load transfer approaches usually employed in the creep data analysis of metal matrix composites. Experiments indicate that the short fiber reinforced material creeps with a stress exponent of 10 while the matrix stress exponent is 5. Procedures published in the literature which yield natural stress exponents and threshold stresses which decrease with increasing temperature were reproduced; however, threshold values corresponding to natural stress exponents cannot be physically justified. The procedures considered in this paper yielded no precise results. Several combinations of stress exponents/threshold values and activation energies are shown to satisfy the procedural requirements. Therefore load transfer and threshold approaches should always be combined with microstructural investigations before an attempt is made to rationalize creep behavior of MMCs.