Investigations on failure-to-fracture mechanism and prediction of forming limit for aluminum alloy incremental forming process

Abstract

Abstract In order to reveal the evolution mechanism of failure-to-fracture through thickness direction, quantify failure distribution of micro-crack, predict fracture forming limit (FFL) for single point incremental forming (SPIF) with high-speed tool and compare with conventional SPIF, the flow stress model and thermal ductile fracture criterion are calibrated and integrated with the numerical simulation of SPIF process for AA2024-T3 under high-speed tool rotation, and a novel numerical-analytical model is proposed to calculate the damage accumulation. The fracture behaviors appeared in SPIF process in making two typical parts are simulated and verified by experiments. It's found that damage accumulation has stepwise and incremental features, and there is a gradient of damage along thickness direction, which gradually increases so that the fracture through thickness direction can be delayed. The research also revealed that micro-crack will propagate obliquely from the outer surface to certain size along thickness direction almost at the same time at a load path cycle; Afterwards, if the forming tool passes through the failure zone again, the failure will propagate through the whole thickness, finally the fracture appears. Numerical simulation shows that FFL in SPIF with high-speed tool rotation is higher than that in traditional SPIF.