Modeling of ductile damage evolution in roll forming of U-channel sections

Abstract

In this study, the modified Mohr-Coulomb (MMC) ductile fracture criterion was employed to investigate the ductile fracture during the roll forming process of the AA6061-T6 aluminum alloy. To this aim, the MMC fracture criterion was calibrated based on the tension tests and was integrated into the commercial finite element (FE) Abaqus/Explicit using an appropriate user subroutine. The experimental procedures were designed based on two distinct forming strategies, namely single-stage and multi-stage roll forming processes. The results indicate that the calibrated fracture model based on tension tests is capable to predict the fracture initiation in the single-stage roll forming process at an error rate of 4.47%. Meanwhile, the numerically predicted fracture initiation during the multi-stage roll forming process is inconsistent with the experiments. Hence, a nonlinear damage accumulation rule together with the additional test (multi-stage L-bending) was utilized to predict the onset of fracture throughout the multi-stage roll forming process, considering the effect of deformation mechanics and nonlinear loading path during the process. The results reveal that the fracture onset during the multi-stage roll forming process can be accurately predicted when the MMC fracture criterion with the nonlinear damage accumulation rule is used in the numerical fracture model (with an error of about 9%).