On the fatigue behavior of ductile F.C.C. metals

Author: Repetto, Eduardo A.

Year: 1998

Degree: Dissertation (Ph.D.)

Advisor: Ortiz, Michael

Committee Member: Unknown, Unknown

Option: Aeronautics

DOI: 10.7907/zkfb-sr87

Abstract

A micromechanically based model for fatigue crack nucleation in ductile F.C.C. metals is developed. The theory includes a model of F.C.C. crystal-plasticity in finite deformations that takes into account the Bauschinger effect, dipole annihilation in the persistent slip bands (PSBs), with vacancy generation and PSB elongation as a byproduct, as well as coupled vacancy diffusion and the attendant surface motion due to the flux of vacancies out of the body.

Finite element simulations are performed in order to establish the predictive capability of the theory. Detailed modelling of the intersection of the PSB with a free surface, enhanced by the use of remeshing and surface evolution techniques, enable the prediction of nucleation sites, life expectancy, surface profile, alternate slip between the sides of the PSB and strain localization at the grooves.

In an attempt to resolve the dislocation structures experimentally observed during cyclic loading, a theory based on the non-convexity of a pseudo-energy density is developed. Non-homogeneous minimizers are found containing variants oriented in coincidence with the dislocation walls observed experimentally. Due to the latent hardening and geometrical softening, the minimizing structures are found to consist of regions of single slip which is in accordance with the observed "patchy slip."

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