A mesoscale approach for growth of 3D microstructurally small fatigue cracks in polycrystals

In the high cycle fatigue regime, microstructure attributes such as grain size, shape, and crystallographic orientation usually affect fatigue crack formation and early growth. However, most computational strategies and theoretical models for assessing the influence of the microstructure on early stages of fatigue crack formation and growth rely on simple constitutive models and 2D microstructures, which limit their applicability in design of microstructure of engineering materials. This work employs finite element simulations that explicitly render the 3D microstructure of an Face-centered cubic (FCC) alloy to evaluate the change of the driving force for fatigue crack formation and early stages of transgranular growth, including consideration of growth within individual grains and stress redistribution as the crack extends. The methodology is implemented using a crystal plasticity algorithm in ABAQUS and used to study the effect of microstructure on early fatigue life of a powder processed Ni-base RR1000 superalloy at 650℃ subjected to constant amplitude loading. The effects of the microstructure in extending a fatigue crack over the first few grains are analyzed.