Probabilistic lifetime prediction for ceramic components in rolling applications

Rolling tools made of advanced ceramics have some attractive properties with respect to their wear resistance and high temperature performance but are critical due to the brittle failure mode. Lifetime predictions must be based on a probabilistic approach considering sub-critical and cyclic propagation of the inherent flaws. We will present a comprehensive reliability analysis for a rolling contact fatigue test with a silicon nitride roll using the program STAU. Based on a cyclic crack growth law, we have extended the capabilities of STAU in order to account for a complex load history typically found in the case of rolling applications. A scheme is presented for relating the failure probability to the crack density observed on the roll which allows for a quantitative comparison of predictions and experimental observations. It turns out that the water-based lubrication most critically affects the failure behaviour since water strongly promotes cyclic crack propagation.