A model of crack opening stresses in variable amplitude loading using smooth specimen fatigue test data for three steels

Crack growth under variable amplitude loading can be largely explained through changes in fatigue crack closure and crack opening stress. This paper presents a methodology for modeling changes in crack opening stress level and fatigue damage using data derived from periodic underload fatigue tests of smooth specimens for three steels with diverse hardness (soft, medium, and hard). The predicted crack closure stress levels are modeled under constant and variable amplitude loading (SAE Log Skidder History) and agree well with experimental measurements made with a high magnification microscope.