Micromechanical investigation of the influence of defects in high cycle fatigue

• Finite element analysis of smooth and notched polycrystalline aggregates of an electrolytic copper are conducted.
• Effects of cubic elasticity and crystal plasticity are investigated.
• The cubic elasticity strongly affects the distributions of normal and shear stresses.
• A pronounced influence of the crystal plasticity on the shear stress is observed only in notched microstructures.
• The predictions of three fatigue criteria are evaluated for two defect geometries and several defect sizes.

This study aims to analyse the influence of geometrical defects (notches and holes) on the high cycle fatigue behaviour of an electrolytic copper based on finite element simulations of 2D polycrystalline aggregates. In order to investigate the role of each source of anisotropy on the mechanical response at the grain scale, three different material constitutive models are assigned successively to the grains: isotropic elasticity, cubic elasticity and crystal plasticity in addition to the cubic elasticity. The significant influence of the elastic anisotropy on the mechanical response of the grains is highlighted. When considering smooth microstructures, the crystal plasticity have has a slight effect in comparison with the cubic elasticity influence. However, in the case of notched microstructures, it has been shown that the influence of the plasticity is no more negligible. Finally, the predictions of three fatigue criteria are analysed. Their ability to predict the defect size effect on the fatigue strength is evaluated thanks to a comparison with experimental data from the literature.