Dynamic Fracture Forming Limit Curve and Modelling of AA5182-O Aluminum Alloy Sheet

The dynamic fracture of sheet metal usually occurs during the high speed forming and automobile crashing processes. The electromagnetically impacted Nakazima test was adopted with the hemispherical punch under the pressure of drive plate, and the drive plate was loaded by the Lorentz force to obtain the impact energy. Different geometries of specimen were designed to investigate the dynamic fractures of AA5182-O aluminum alloy sheet over various strain paths of tension-compression and biaxial tension. The limit strains at fracture were determined by the numerical simulation of electromagnetically impacted Nakazima test. The result showed that the dynamic fracture forming limit curve is higher than the quasi-static fracture forming limit curve. Compared with the Rice-Tracey and Oyane-Sato fracture models, the Johnson-Cook fracture model was validated to be more accurate to characterize the quasi-static fracture locus. Hence, the strain-rate-sensitive parameter of Johnson-Cook fracture model was subsequentially determined by minimizing the discrepancy between the experimental and predicted dynamic fracture locus.