Mesoscale modelling of crack nucleation from defects in steel

Defects such as pores and non-metallic inclusions have a significant influence on the long-life fatigue strength of high strength steels. The largest of these defects in a critical material volume is in the range of tens of micrometres which is on the same size scale as the grain size. At this scale materials are non-homogeneous since each grain in a polycrystalline material will have a different orientation. Finite element-based mesoscale modelling has been used to model the stress and strain in individual grains in the vicinity of a spherical defect. Microcrack nucleation and propagation models based on shear stress and plastic shear strain have been applied. Especially for low stress amplitudes near the endurance limit, critical grain orientation and defects are both essential for cracks to initiate and propagate.