Superplastic Tensile Test And Comparative Analysis Of Superplastic Bulging By Finite Element Analysis

After nearly 100 years of development, superplastic forming has become an important research content in the fields of international materials science and technology, and plays an important role in modern manufacturing. While the materials in the superplastic state, it has good plasticity and the small deformation resistance during the process of forming. What's more, the parts have good forming quality and stable dimension. There is no rebound phenomenon caused by strain hardening effect after forming. Such makes the superplastic forming technology been widely used in the fields of modern manufacturing. However, the superplastic deformation theory is lack of studying deeply, it can not fully reveal the superplastic deformation rules, and it can not gave scientific guidance to the practical production effectively either. So in recent days, many scholars at home and abroad pay more attention to the research of superplastic deformation theory and its practical application.The superplastic deformation is closely related to the stress state, the loading path and so on, the stress state of the material is complex during the process of superplastic forming,especially two-dimensional forming(bulging) and three-dimensional forming(extrusion,torsion, etc.). Therefore, previous studies on the superplastic phenomenon and theory is mainly based on one-dimensional tensile test, including the establishment of the constitutive equations for deformation, the measurement of the strain rate sensitivity exponent m, strain hardening exponent n and other important material parameters. When it comes to the practical application of superplastic forming analysis, the empirical constitutive equation is usually established by tensile test, m and n are usually regarded as constant, which is deviate from actual situation. The superplastic materials have strong structural sensitivity,the measured constitutive equation changes according to different stress states, even different deformation paths, both m and n are also variables in the process of deformation. Therefore, we must take the constitutive equation between the contact aboutsuperplastic materials under different stress states and different deformation paths into consideration, and combine with superplastic tensile test to establish the accurate mechanical model and accurate measurement of material parameters, which will guide and carry out the actual superplastic forming application analysis.In this paper, we use Zn-5%Al material as the research object to analyze the actual application of superplastic bulging by one-dimensional tensile test. Main contents includes:1. The superplastic tensile test is carry out at 340?. On the basis of the theory about superplastic deformation, the material parameters m()??(5) and n()??(5)were also measured accurately by the numerical simulation method; Based on the differential equation of state,the tensile constitutive equation of material is established under two deformation paths of constant strain rate and constant load. The results show that the m and n measured by the superplastic tensile test are not constants.2. Depend on the application of the secondary development function with Marc finite element simulation software, we carry out simulation and analysis of superplastic free bulging process by using the constitutive equation of variable parameters with tensile test.Afterwards we make a comparision and analysis of simulate results about Marc software comes with the empirical constitutive equation. The results show that: the simulation and analysis results are different on the constitutive equation of test and the software comes with the constitutive equation. For a certain kind of superplastic material, it is necessary to establish an accurate constitutive equation to guide its superplastic deformation under a certain deformation path.3. We established the formula of equivalent relationship between one-dimension tensile and two-dimension free bulging by the tensile test data, in order to control the quality of the bulging part better.