In-situ observation of critical damages in presence of microporosity under tension in Al-Cu-Li alloys

In-situ observations of critical damage evolution during uniaxial tensile of Al-Cu-Li alloys were performed by using micro-X-ray computed tomography (X-CT). The effects of microporosity nucleation and growth on microstructural damage failure were explored, and the fracture mechanism was eventually revealed. The digital volume correlation (DVC) technique is used to analyze the strain concentration effect during fracture. As for the multi-porosity (high porosity) microstructure, there is radial linking and merging of microporosities during tensile loading, and the predicted values of the McClintock model are in good agreement with the experimental values. Furthermore, the fracture failure of the alloy is highly correlated with the size and morphology of the microporosities. Microporosities with equivalent diameter D_eq>50 μm and sphericity S < 0.25 are effective sites for crack initiation, which is the main microscopic mechanism causing fracture failure of the alloy. The linkage between microporosities during tensile loading is a preferential path but not a dominant factor in crack propagation. The DVC results indicate that during tensile-dominated loading, the value of the destructive strain at the largest microporosity (crack initiation strain) is 3–6 times higher than the experimentally observed value.