Fatigue crack growth measurements under spectrum loading

Abstract

Fatigue crack growth rates under variable amplitude stress cycles were measured on two center-cracked tension specimens made of SM520B steel. Four loading spectra, right-skewed and left-skewed β distributions with the minimum or maximum stress constant, were applied to the specimens. Based on the root-mean-cube stress range, the test results are compared with the fatigue crack growth behavior under constant amplitude loading with the same stress ratio. They are generally in good agreement, indicating that effect of stress ratio is generally dominant. However, when large number of stress cycles are in the low stress range region, the effect of threshold stress intensity factor range is found to be large.