High-Temperature cumulative damage for stage I crack growth

Abstract

The effects of cyclic shear strain-range, shear strain-rate and temperature on the accumulation of damage during constant and variable shear strain range fatigue tests on a 1 per cent Cr-Mo-V steel are reported. The hypothesis of linear accumulation of damage and the summation of cyclic fractions to unity are shown to be incorrect for interactions of time, cyclic and environmental processes which are considered in detail. Stage I cracks may be accelerated, retarded or stopped and new cracks nucleated. Nevertheless only 8 per cent of the cumulative damage tests in the high strain fatigue regime gave unsafe linear summation factors less than 0.8. None fell below 0.7.