Fatigue-life prediction of SiC particulate reinforced aluminum alloy 6061 matrix composite using AE stress delay concept

A study of the residual fatigue life prediction of 6061-T6 aluminum matrix composite reinforced with 15 vol % SIC particulates (SiCp) by using the aco ustic emission technique and the stress delay concept has been carried out. Fatigue damages corresponding to 40, 60 and 80% of total fatigue life were stimulated at a cyclic stress amplitude. The specimens with and without fa tigue damage were subjected to tensile tests. The acoustic emission activit ies were monitored during tensile tests. It was found that a lower stress l evel was required to reach a specified number of cumulative AE events for s pecimens fatigued to higher percentage of the fatigue life. This stress lev el is called stress delay. Approximately a linear relation was found betwee n stress delay and fatigue damage. Using the procedure defined in this stud y, the residual fatigue life can be predicted by testing the specimen in te nsion and monitoring the AE events. The number of the cumulative AE events increased exponentially with the increase of strain during tensile tests. T his exponential increase occurred when the material was in the plastic regi me and was attributed mainly to SiC particulate/matrix interface decohesion and linkage of voids. In high cycle fatigue, it was observed that the resi dual tensile strengths of the material did not change with prior cyclic loa ding damages since the high cycle fatigue life was dominated by the crack i nitiation phase. (C) 1999 Kluwer Academic Publishers.