On the Prediction of Ductile Fracture in Flexible Roll Forming

Fracture is one of the most common defects that occur during the roll forming process. However, several process-based strategies can be employed to minimize its occurrence. This paper investigates the fracture mechanisms of AA3105 aluminum alloy sheets during the flexible roll forming (FRF) process, focusing on methods to reduce damage and prevent failure throughout forming. Experimental tests were carried out to determine the mechanical properties of the sheet and to calibrate the modified Mohr–Coulomb fracture criterion. The digital image correlation technique was used to measure the experimental strain field at the onset of fracture. Finite element simulations of the calibration tests were then performed to validate the failure criterion, showing good agreement with experimental results. After calibration, the FRF process was simulated in ABAQUS, and a user subroutine was implemented to predict fracture evolution during forming. The simulation results were validated against experimental data obtained from the FRF machine, confirming the model’s accuracy. The results revealed that increasing the sheet thickness from 0.5 mm to 1.5 mm increased the damage at the critical element by approximately 52%, whereas increasing the transition radius from 250 mm to 550 mm and the bending radius from 1 mm to 3 mm reduced the damage by approximately 28% and 13%, respectively. In addition, increasing the number of forming stands reduced the damage by approximately 10%. These findings demonstrate that both thinner sheets and multi-stage forming significantly enhance formability and reduce fracture risk in FRF of aluminum sheets.