The Relationship Between Fracture Of Magnesium Alloy MB2and Stress States

Magnesium alloy is a potential and lightweight engineering material, which is very rich in reserves in China. This condition provides a good material basis for the development and application of magnesium alloy in China. Nowadays, the metal resources decrease sharply in the world, and magnesium alloy as a lightweight engineering material is not fully developed. It has a broad application prospect, especially in the aerospace industry. As the theoretical basis for the design of engineering materials and structures, the fracture criterion of material is essential. At present, the fracture criterion of magnesium alloy is established for a single and simple stress state by equivalent strength, and this simple fracture criterion is usually only for some specific materials or stress states, and does not reflect the fracture behavior of the same material in different stress states. Magnesium alloy MB2is one of the most widely applied magnesium alloys. The study of fracture of this typical magnesium alloy under complex stress states and establishment of fracture criterion of magnesium alloy MB2can provide calculation condition for design of engineering structure. It is also the theoretical basis of actual engineering application of magnesium alloy MB2. So, study on the fracture behavior and establishment of facture criterion of magnesium alloy MB2have an important significance in theoretical research and engineering application.The fracture behavior of Magnesium alloy MB2is analyzed in this dissertation at different stress states through the experimental designs and the corresponding numerical simulation. The stress triaxiality as a stress state parameter can distinguish the different stress states, and for different range of the value of stress triaxiality, the experimental design and research can be carried out. Also, the breaking strength, equivalent fracture strain and fracture behavior can be studied.The work of this dissertation mainly includes three aspects:the stress triaxiality of specimens in the different experimentation is determined in the first part, including the effect of friction constraints in the low value of stress triaxiality and strain path and distribution effect in the high value of stress triaxiality. The design and analysis of experiments are conducted in the second part for different ranges of stress triaxiality including the compression test of cylinder specimens for low stress triaxiality, the torsion test of cylinder specimens for medium stress triaxiality and the tensile test of smooth and notched specimens for high stress triaxiality. Through the analysis of test and numerical analysis of the corresponding process, the fracture strength, equivalent fracture strain and fracture feature of Magnesium alloy MB2can be obtained and the value of stress triaxiality can be determined. The different fracture criteria are compared in the third part, and a more comprehensive and reasonable fracture criteria of Magnesium alloy MB2is established in the space of equivalent failure strain and stress triaxiality covering the different stress state. Besides, through the analysis of macroscopic failure phenomenon and micro fractography in the different stress state of Magnesium alloy MB2, the relationship between the macroscopic fracture characteristics and micro brittle failure mechanism will be revealed.