Dynamic Mechanical Properties and Modification of Fracture Criteria of 6061-T651 Aluminum Alloy

In order to investigate the effects of stress triaxiality, Lode angle, temperature and strain rate on the fracture characteristics of 6061-T651 aluminum alloy materials, the mechanical property tests of materials are carried under different stress states, temperature and strain rate using universal material testing machine. Firstly, the mechanical property test results show that the fracture strain of 6061-T651 aluminum alloy material decreases with the increase of stress triaxiality. And also, the fracture strain of material related to the Lode angle parameter, especially th e effect of the Lode angle more significantly at the range of lower stress triaxiality. When the temperature less than 250 ℃, the temperature of material has significant influence on its flow stress, while the influence of temperature on its fracture strai n can be ignored. While the temperature more than 250 ℃, the temperature of material has greatly influence on its flow stress and fracture strain. Moreover, the strain rate has no significant effect on the fracture strain of 6061-T651 aluminum alloy. Subsequently, basing on the test results of mechanical properties, the Modified Johnson-Cook(MJC) criterion is obtained by modifying Johnson-Cook(J-C) fracture criterion, and the parameters of MJC and Modified Mohr-Coulomb(MMC) fracture criterion are calibrated. Finally, the impact test of sphere projectile penetrating the 6061-T651 aluminum alloy target plate is conducted on a one-stage gas gun, and also the ballistic limit velocity and failure mode of target are obtained. In order to verify the validity of the model and parameters, and the corresponding 3D model of projectile impact target is established by using ABAQUS/Explicit finite element software. The results showed that the prediction results of Lode angle dependent MMC fracture criterion is closer to th e test compared with the Lode angle independent MJC fracture criterion.