Damage-based criterion for fracture prediction in metal forming processes: a case study in Al 2024T3 sheet

In the present study, a damage-based criterion derived by continuum damage mechanics (CDM) has been used to predict the fracture limit of aluminium alloy Al2024T3 sheet. Microscopic examination has shown that the damage of the aluminium alloy is due to the nucleation and coalescence of micro-voids under high strain. The damage, causes degradation in the effective elastic properties of the material, and may be considered as the first stage of fracture. A second order continuity tensor ψ has been used to quantify the damage of the aluminium alloy. The principal values required for the determination of the continuity tensor have been obtained experimentally under different magnitudes of tensile pre-strain. Thus, the values of the continuity tensor have been calculated using an expression derived recently by the authors. The minimum principal continuity ψIIhas been taken as a governing parameter to establish the damage evolution equation. Assuming a power-law type material constitutive relation and using a damage-based fracture criterion, the fracture limit curve (FLC) of the Al2024T3 sheet has been computed. A series of experiments has been performed to obtain the FLC of the aluminium alloy sheet. The experimental FLC is found to be in agreement with the predicted one. In addition, the experimental results show that ductile fracture of the aluminium alloy sheet occurs while the minimum principal continuity ψIIreaches a critical value.