不同应力状态下的高强钢板断裂机理及预测

板料成形过程的宏观断裂行为依赖于其微观断裂机理，因此成形过程模拟中的断裂准则的准确选择对于断裂预测具有重要意义。以高强钢TRIP780板料为研究对象，设计从剪切到拉伸应力状态的五种断裂试验，结合宏观拉伸试验和扫描电子显微镜（Scanning electron microscope，SEM）分析研究不同应力状态下TRIP780板料的断裂机理，得到不同应力状态下正应力和切应力与断裂机理的关联关系，引入正应力与切应力的影响构建MMC断裂准则，应用于板料压剪应力区间的断裂行为预测。结果表明，反映断裂机理的MMC准则能适用于板料压剪和拉剪变形应力状态下断裂失效的准确预测。

Research on Fracture Mechanism and Prediction of High-strength Steel Sheet under Different Stress States

The macroscopic fracture behavior of metal sheet forming process highly depends on microscopic fracture mechanism, thus establishing a ductile fracture criterion reflecting effects of fracture mechanism could ensure high forecast precision of fracture behavior. The forming processes under various stress states of advance high-strength steel TRIP780 sheet is tested and simulated. Five fracture tests ranging from shear to tension stress states are conducted and the parallel numerical simulations are also performed. The scanning electron microscope(SEM) fractographies of fracture surfaces are detected to reveal microscopic fracture mechanism. The normal stress and shear stress are obtained to correct with the evolution rule of fractographies and therefore are deemed as parameters which can describe fracture mechanism. Therefore, MMC fracture criterion is characterized by normal stress and shear stress is adopted and then extended to predict fracture behavior of in-plane compression-shear forming. The results indicate that the MMC fracture criterion reflecting fracture mechanism of TRIP780 sheet could predict fracture of forming processes under wide stress state range covering form compression-shear to tension-shear, which further proves the superiority of calibrated MMC fracture criterion.