Reliability Engineering Approach to Cumulative Fatigue Damage of a Glass Fiber Reinforced Composite Material under Varying Amplitude Loading

Abstract

The statisitical nature of the cumulative cycle ratio, D=Σn_i/N^^∼_i, of a chopped-strand-mat glass fiber reinforced plastic under random and program loading has been studied experimentally, where N^^∼_i was the median life at the stress amplitudeσ_i as obtained from the S-N curve. In similar to the fatigue life N in constant amplitude tests, D followed a log-normal distribution approximately. The variance of log D in the random and the program load tests was approximately the same as that of log N/N^^∼_i in the constant amplitude tests. This implies that the coefficient of variation of D is approximately equal to that of N. The mean of log D was not equal to zero, hence Miner's rule did not hold statistically. A phenomenological explanation of the tests results was attempted.