Fatigue crack coalescence in discontinuously reinforced metal matrix composites: Implications for reliability prediction

This paper examines aspects of the distribution of the longest possible mic rocracks in specimens of a fatigued aluminum-matrix silicon carbide whisker composite and the probability of coalescence in general. The length of the longest microcracks in this material is determined largely by coalescence and making reasonable assumptions is bounded and an upper bound can be calc ulated. This upper bound is used to fit sample data to an asymptotic extrem e value distribution from which reliabilities based on an arbitrarily chose n critical length are calculated. It is shown that for reliabilities corres ponding to failure probabilities less than even 10(-10) the mere presence o f an upper bound on microcrack length can determine the extreme value distr ibution independent of the actual value of that bound provided that the exp erimental data supporting the extreme value distribution are entirely chara cteristic of actual service and that a loading criterion is met.