This paper describes a microstructure-based multiaxial non-proportional fatigue life prediction model with maximum shear strain and non-proportionality as damage parameters applied to A319 alloy. The materials made with different casting cooling rates and Sr modification are characterized and quantified in terms of secondary dendrite arm spacing (SDAS), size and aspect ratio of eutectic Si particles. Multiaxial non-proportional fatigue tests have been performed on six groups of A319 alloys to systematically analyze the effect of microstructure and loading path on the fatigue properties of Al-Si cast alloy. The first part of the paper is focused on microstructure quantitative characterization to determine the influence of different casting conditions, followed by stress response behavior and fatigue fracture analysis. Finally, quantitative relationship between six fatigue life parameters and microstructure characteristics is established and a new fatigue life prediction model is proposed to predict fatigue life of Al-Si alloy under multiaxial non-proportional loading condition.

This study investigated the fretting fatigue behavior and mechanism of 35CrMoA steel of different contact stresses under diamond and square loading paths in the form of curved surface contact. The results show that multiple crack sources will initiate on the subsurface of the specimen under the combined effect of contact stress and cyclic stress. Under low contact stress, only one crack source dominates, causing the instantaneous fracture zone to be biased to the other side of the main crack source. Under high contact stress, the crack sources in both fretting zones play a dominant role, making the shape of the instantaneous fracture zone into a nearly circular shape with better symmetry; At the beginning of the fretting fatigue, cracks only propagate in the cross-section where they form. When they propagate to a certain depth, a component that propagates in the longitudinal direction will be generated.