A 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 al loy Al2024T3 sheet. Microscopic examination has shown that the damage of th e aluminium alloy is due to the nucleation and coalescence of micro-voids u nder high strain. The damage, causes degradation in the effective elastic p roperties of the material, and may be considered as the first stage of frac ture. A second order continuity tensor psi has been used to quantify the da mage of the aluminium alloy. The principal values required for the determin ation of the continuity tensor have been obtained experimentally under diff erent magnitudes of tensile pre-strain. Thus, the values of the continuity tensor have been calculated using an expression derived recently by the aut hors. The minimum principal continuity psi(II) has been taken as a governin g parameter to establish the damage evolution equation. Assuming a power-la w type material constitutive relation and using a damage-based fracture cri terion, the fracture limit cure (FLC) of the Al2024T3 sheet has been comput ed. A series of experiments has been performed to obtain the FLC of the alu minium alloy sheet. The experimental FLC is found to be in agreement with t he predicted one. In addition, the experimental results show that ductile f racture of the aluminium alloy sheet occurs while the minimum principal con tinuity psi(II) reaches a critical value. (C) 1999 Elsevier Science S.A. Al l rights reserved.