Influence Of Stree Triaxiality On Material Fracture

In this paper, based on the test phenomenon and theory analysis, the fracture mechanism and fracture angle are studied. Stress field near crack tip of I-II mixed mode of ductile is systematically analyzed. Combining phenomenon analysis of conventional and mixed mode fracture tests of LY12-CZ and LY12-M, fracture laws of ductile materials under different stress states are investigated. last two decades, lots of experimental and theoretic research on the hardening behavior and flow characteristics With the result datum of uniaxial tensile tests of three materials, their critical values of stress triaxiality of tension fracture and shear fracture are calculated using Bridgman formula. New mixed mode fracture criterion is established using stress triaxiality as the fracture parameter. Stress and strain distributions at the minimum cross-section of three materials with different notch root radius are analyzed through the FEM calculations. The main results are as follows.1. With change of stress triaxiality, There exist two kinds of fracture modes for LY12 alloy aluminums. That is to say, there exist a critical value of stress triaxiality for ductile fracture, the fracture mode is tension fracture when the Rσvalue is above the critical value, and the fracture mode is shear fracture when the Rσvalue is below the critical value.2. The critical values of stress triaxiality between tension fracture and shear fracture of alloy steel 14CrNiMov,45 steel and A3 steel are 0.462,0.472,and 0.587 respectively.3. Mixed mode fracture criterion combining stress triaxiality, test validation, actual parameters confirmation.4. Bridgmans equations are inaccurate. The material properties and specimen geometry do have a very important influence on the value of stress triaxiality. The stress triaxiality and equivalent plastic strain distributions at the minimum cross-section of specimens with different notch root radius are similar for such three kinds of materials. The stress triaxiality is highest at the middle of the minimum cross-section of the notched specimens with R≥2mm; and at the notch root with R<2mm...