Comparative study on characterization parameters for high temperature creep crack growth with special emphasis on dual value behaviour of crack growth rate

If the logarithms of experimental values of high temperature creep crack growth rate, log da/dt are plotted against the logarithm of C * or δ̇ (creep displacement rate), the relation or curve reveals in many cases the dual value or the nose part. This dual behaviour appears in terms of various patterns according to the materials or its processing. An analytical model has been proposed for dual behaviour of crack growth rate plotted against C * or δ̇. The methodology is to analyse the relation of creep displacement rate curve and crack growth length curve with respect to applied load time. Q * parameter projection for da/dt predicts that log da/dt is a simple monotonical increasing linear function of Q *, does not reveal dual values, and shows threshold behaviour at an early stage of crack growth.