Effect of the Lode parameter in predicting shear cracking of 2024-T351 aluminum alloy Taylor rods

Abstract

Recent investigations have shown that the ductility of a metal may depend on not only the stress triaxiality but also the Lode parameter, especially in the relatively low stress triaxiality range. However, applications using the Lode dependent fracture criterion are few and the value of incorporating the Lode parameter into a fracture criterion to predict impact related fracture is poorly understood. In the present paper, Taylor impact test by using 2024-T351 aluminum alloy rods of 5.95 mm diameter and 29.75 mm length was firstly conducted in a one-stage gas gun in the impact velocity range of 110.8–312.7 m/s. Mushrooming and shear cracking were observed in the test with increasing impact velocity. Subsequently, mechanical tests were conducted in a universal testing machine and a SHPB test facility. By using a hybrid experiment–numerical method, a modified version of Johnson–Cook strength model, a Lode-dependent fracture criterion as well as the Johnson–Cook (JC) fracture criterion were calibrated. Finally, 3D FE model corresponding to the test was built in ABAQUS and then was adopted to predict the shear cracking of the Taylor rods. It was found that FE simulations by using the Lode dependent fracture criterion give reasonable fracture pattern predictions while that using the Johnson–Cook fracture model obviously underestimates the fracture behavior. Detailed analysis shows that the dominant stress state of the material in the projectile's fracture region in the impact event is in the range where the Lode parameter has an obvious influence on the metal's ductility. FE simulations by using virtual metals also show that the Taylor impact fracture behavior prediction is much dependent on the effect of the Lode parameter on a material's ductility.