Multiscale Analysis of Ductile Damage In Material With Sigmoidal Hardening



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Hexagonal Closed-Packed (HCP) materials are widely used in engineering applications - from transportation to biomedical devices. Magnesium alloys are a class of HCP materials that are promising candidates because they are cheaper, more light-weight, and biodegradable, compared to titanium and aluminum. Additionally, magnesium currently expands its application to automotive and battery. However, their damage mechanism are poorly understood, because of its multi-stage stress-strain response, which often referred to as sigmoidal (or S-shaped) hardening. Therefore, the goal of this thesis will be computationally examining the material response of the sigmoidal hardening on two perspectives: macroscopic and microscopic. For macroscopic re- sponse, the higher the stress triaxitality T, or the sharper of the notch region, the postpeak nominal axial stress σeq will be higher and void volume fracture f will exponentially grows at a lower level of nominal axial strain. This can be conclude higher triaxiality will have lower strain to failure, regardless of the difference in the porosity propagate differently between power-law hardening and sigmoidal hardening. For microscopic response, stress triaxiality T related directly to the geometry shape of the void and the growth rate of the void volume. While the spherical void volume does not propagate at a low triaxiality stress, the oblate void volume yield at every triaxility stress level.



Ductile Damage, Stress Triaxiality, Void