A study of multiaxial fatigue damage accumulation in carbon steel

Engineering components experience multiaxial variable amplitude loading, which may be non-proportional. Fatigue design codes do not cover explicitly non-proportional paths, as cycle counting methods are rarely defined for multiaxial strains. Low cycle fatigue test results are presented here for Case A and B loads on a medium carbon steel, together with two level cumulative damage data. It is shown that life may be predicted from Stage I and II crack propagation rules for short cracks, driven by maximum shear strain range and a Rankine (Mode I) equivalent strain respectively. For physically realistic modelling, crack coalescence should be included to obtain optimum correlation. Crack propagation models provide a viable basis for life prediction under multiaxial low cycle fatigue, and offer an alternative to the widely used Miner linear damage summation rule.