Fatigue Lives Simulation in Sintered Silicon Nitride Based on Probability Distribution of Defects Size and Micro-Crack Propagation Behavior

Abstract

In this study, a computer simulation taking into account the defects size distribution and the micro-crack propagation behavior was conducted by using virtual bending specimens. The defects size distributions in the virtual specimens were estimated by using a Monte-Calro technique based on a large number of defects diameter (approximately 72000) measured on the Si3N4 specimen surface. The effects of two types of scatter−one is defects diameter, the other is micro-crack propagation rate−on fatigue lives were estimated separately. It is proved that the scatter of fatigue life mainly originated from the scatter of defect size. For the cases of the simulation using micro-crack propagation behavior, estimated fatigue lives were always shorter than that of using long-crack propagation behavior. Recognizing simulated fatigue lives Nf as crack propagation lives Np, we can define a crack initiation life Ni. As the applied stress decreases, estimated value of Ni/Nf increases. It is remarkable that this tendency shows a good agreement with the experimantal value of Ni/Nf. It is concluded a crack initiation life and its scatter are very important to discuss the fatigue lives in ceramic materials.