MICROSTRUCTURE-SENSITIVE MODELING OF HIGH CYCLE FATIGUE

摘要

We explore microstructure-sensitive computational methods for predicting variability of low cycle fatigue (LCF) and high cycle fatigue (HCF) processes in metallic polycrystals to support design of fatigue resistant alloys.We outline a philosophy of establishing relations between remote loading conditions and microstructure-scale plasticity/crack behavior as a function of stress amplitude,stress state and microstructure,featuring calibration of mean experimental responses for known microstructures that bound the range of virtual (digital) microstructures.Based on bottom-up and top-down multiscale computational modeling,influences of microstructure-scale heterogeneities are characterized in terms of elastic shakedown,ratcheting,reversed cyclic microplastic strain conditions,and discuss HCF fatigue thresholds in terms of percolation limits for microplasticity in polycrystals and two phase microstructures.Variability of HCF behavior associated with intrinsic stochastic microstructure is distinguished from fatigue crack nucleation and microstructurally small crack growth at extrinsic features such as non-metallic inclusions.Effects of process history and resulting residual stresses are considered in certain cases of subsurface crack formation.The need to characterize extreme value correlations of microstructure attributes coupled to the local driving force (i.e.,features) for HCF crack formation is outlined,along with a strategy involving a set of Fatigue Indicator Parameters (FIPs) relevant to different mechanisms of crack formation.We describe current work involving potency of non-metallic inclusions in carburized and shot-peened gear steels,as well as microstructure-sensitive design of microstructures for HCF resistance.