Damage mechanism of ductile metals based on stress state parameters

Loading spectrum, integrating Von-Mises yield criterion with Tresca yield criterion, described the loading state in order to research the effects of loading mode on micro-crack initiation and growth at microscopic scale. A microcosmic view field model containing an elliptical inclusion was investigated in 5052 aluminum alloy and the inclusion was regarded as cohesive elements based on the loading spectrum. The stress state parameters were applied to explore the crack type and the initial location of crack under various loading modes. The results show that the micro-crack firstly initiates at brittle phase, and the main reason is the inconsistent stress condition between matrix and inclusion. The overall scalar stiffness degradation (SDEG) predicts the crack nucleation location and the stress state parameters comprehensively describe the crack type. The same strain but the difference at crack nucleation shows that diaxial compression loading mode doesn't easily induce crack and pure shear loading mode is easier to initiate crack than the other loading modes. The analysis results agree with the experimental results.