An inspection of elevated temperature fatigue crack extension data in low alloy steels

The present paper describes a reasonable review of various high temperature fatigue crack growth data obtained from a range of low alloy steels under both continuous cycle conditions and those where a dwell time at maximum lo ad had been imposed. The continuous cycle data all resided below the 1/2CTO D line and were found to be primarily frequency and Delta K-2 dependant wit h all crack extensions occurring in a transgranular fashion. The dwell time fatigue crack growth data could be reasonably portrayed in terms of maximu m stress intensity K-max, prevalent at the dwell portion of the fatigue cyc le. Furthermore, it was established that the dwell time data fell roughly i nto two groups, viz., those for dwell times of 30 min or less and data with dwell times greater than this value. A comparison of similar dwell time re sults from various Literature sources indicated reasonable commonality and it was observed that in the vast majority of cases: (1) fatigue crack growt h rates resided above the 1/2CTOD line; (2) exhibited an approximately Delt a K-10 relationship; and (3) fatigue crack growth was wholly intergranular in nature. Finally the existence of some critical stress intensity conditio n and/or cavity damage condition was discussed to account for the observed abrupt switch from continuum controlled fatigue crack growth with a Delta K -2 dependence to super-continuum growth characteristics which obeyed a Delt a K-10 dependence. (C) 1998 Elsevier Science Ltd. All rights reserved.