欠陥を有するセラミックスの疲労寿命推定法

Abstract

A new method of predicting the fatigue lifetime of ceramics with various sizes of defects has been developed. In this method, first, specimens each of which has an artificial crack of constant size are used to estimate fatigue crack propagation parameters. In the vicinity of the tip of an artificial crack induced by Knoop indentation, a tensile stress field is generated. Then, the stress intensity factor acting as the driving force of fatigue crack growth was considered the sum of two terms associated with the applied stress and residual stress field. By numerical computation inserting the stress intensity factor into the power law of crack propagation, crack propagation parameters are estimated. Subsequently, using the obtained parameters, the fatigue lifetimes of the smooth specimens with fracture originating from a small defect, are predicted.This method was applied to three types of silicon nitride ceramics. As a result, the cyclic fatigue lifetimes of precracked specimens, which were set free from residual stress field by surface removal, were precisely predicted using the obtained parameters. Thus, the values of these parameters were proved to be adequate. Furthermore, the predicted fatigue lifetimes of the smooth specimens were in good agreement with the experimental results, considering the scatter of static strength.