The crack initiation and growth under high temperature creep, fatigue and creep-fatigue multiplication

Abstract

This article concerns some of our recent studies on the crack initiation, early stage crack growth and its subsequent crack growth under high temperature creep, fatigue and creep-fatigue multiplication. The criteria for these and some new ideas are proposed. For instance, the relative notch opening displacement (RNOD) criterion for the crack initiation and the Q ∗ parameter for the crack growth are critically reviewed. Early stage crack growth and its subsequent crack growth as affected by notch tip acuity were studied. The behaviour of the tail part in the log da dN vs log C ∗ curve has been attempted to explain in terms of the curve of the creep behaviour and of the crack length against time. Furthermore it was proposed that early stage crack growth, say, the so-called first stage crack growth in terms of log da dN vs log K curve may be characterized by the parameter different from those for the so-called second stage crack growth.