Holistic Approach on the Research of Yielding, Creep and Fatigue Crack Growth Rate of Metals Based on Simplified Model of Dislocation Group Dynamics

Abstract

The simplified model of numerical analyses of discrete dislocation motion and emissionfrom a stressed source was applied to predict the yield stress, dislocation creep, and fatigue crackgrowth rate of metals dominated by dislocation motion. The results obtained by these numericalanalyses enabled us to link various dynamical effects on the yield stress, dislocation creep, andfatigue crack growth rate with the experimental results of macroscopic phenomena, as well as tolink them with theoretical results obtained by the concept of static, continuously distributedinfinitesimal dislocations for the equilibrium state under low strain or stress rate conditions. Thiswill be useful to holistic research approaches with concern for time and space scales, that is, in atime scale ranging from results under high strain rate condition to those under static or low strainrate condition, and in a space scale ranging from meso-scale to macro-scale mechanics. Theoriginality of results obtained by these analyses were found by deriving the analytical formulationsof number of dislocation emitted from a stressed source and a local dynamic stress intensity factorat the pile-up site of dislocations as a function of applied stress or stress rate and temperaturematerial constants. This enabled us to develop the predictive law of yield stress, creep deformationrate, and fatigue crack growth rate of metals dominated by dislocation motion. Especially, yieldingphenomena such as the stress rate and grain size dependence of yield stress and the delayed timeof yielding were clarified as a holistic phenomenon composed of sequential processes of dislocationrelease from a solute atom, dislocation group moving, and stress concentration by pile-up at thegrain boundary.