Plastic deformation around indentations and their effect on fatigue cycling. (Dissertation) : Abdur-RazzaqDiss. Abstr. Int. Apr. 1989 49, (10), Pp 236

Abstract

Computational crystal plasticity (ABAQUS FE) simulations are presented for dual phase alloy Ti–6Al–4V subjected to cyclic loading in the high cycle fatigue (HCF) regime. Relations between remote loading conditions and local plasticity are discussed as a function of stress amplitude and microstructure. Based on computational micromechanics, effects of microstructure heterogeneity and R-ratio are examined in terms of their influence on cyclic microplastic strain within the microstructure of unnotched specimens. It is shown that bulk-dominated fatigue damage at high R-ratios (>0.7) is associated with the onset of percolation of ratcheting of shear strain in the HCP α phase through connected channels within the microstructure. A high cumulative plastic strain gradient across the α–β phase boundaries is the likely driving force for decohesion at phase boundaries as the manifestation of bulk damage in the HCF regime. Effects of texture are also examined using random periodic microstructure representations. Application of the same crystal plasticity model for Ti–6Al–4V in fretting fatigue contact at positive R-ratios for the bulk fatigue stress also reveals a dominance of ratcheting strain in shear bands emanating from the contact surface, ostensibly in the HCF regime.