A Micromechanics-Based Fatigue Damage Process Zone

A primary issue in high cycle fatigue life prediction is the appropriate definition of damage process zone (i.e. volume influencing fatigue crack initiation) for notched components. Several definitions of the process zone have been proposed based on stress distributions obtained using homogeneous elastic or elastic-plastic finite element analysis. It is generally accepted to be the region, adjacent to the surface of the specimen, where peak stress is highest and fatigue crack initiation occurs; assumed as perhaps several mean grain diameters in spatial extent. However most of these existing techniques have not yet been related to fatigue failure mechanisms via computational micromechanics studies. Therefore they do not address the role of microstructure explicitly in fatigue life prediction. In this study, computational micromechanics is used to clarify and distinguish process zone for crack formation relative to scale of notch root radius and spatial extent of stress concentration at the notch. A new nonlocal criterion for fatigue damage process zone based on the distribution of a shear-based fatigue indicator parameter is proposed and used along with a probabilistic mesomechanics approach to obtain a new microstructure-sensitive fatigue notch sensitivity index, thereby extending notch sensitivity to explicitly incorporate microstructure sensitivity and attendant size effects via probabilistic arguments. The probabilistic approach presented in this study predicts the general trends of notch sensitivity obtained from experimental results in literature. © 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM11