ANALYSIS OF FRACTURE DURING SUPERPLASTIC TENSION

The matter of fracture in tension is also the issue of fracture elongation. The ability of superplasticity of materials is mainly characterized by excellent fracture elongations. Since first su- perplastic phenomenon was recorded, the investigations of superplasticity have not halted. Most of the existing literatures focused on physical or microstructural mechanisms while less attention was paid to mechanical theories on the superplastic deformation. However, superplastic phenomena on large elon- gation in superplastic tension are closely related to the mechanical stability and are finally dependent on the special fracture mechanism. Correspondingly, in this article, the studies of fracture mechanism of the superplastic deformation are reviewed, which involved nucleation, growth and coalescence of cavities. Then, the literatures related to the mechanical stability in superplastic tension are classified and reviewed, which involved the mechanical analysis and numerical simulation of the fracture elonga- tion or the limit strain induced from necks initiation and development. The conclusions indicate that there has yet been no united and confirmed opinion on the superplastic fracture mechanism which has numerous versions from the microstructural or physical view, and the superplastic fracture mechanism would have maken no significant progress unless many long-term investigations will be carried out in the future. In order to interpret the essence of large fracture elongation, the current task should be thoroughly investigate the mechanical stability in superplastic tension based on the advanced technol- ogy of numeric analysis. In numeric analysis, the precise and quantitative constitutive equation should be adopted and the deformation conditons involving strain paths should be taken into account.