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气压成形(材料承受双向拉应力)是应用极为广泛的一种超塑性成形方法。单向拉伸(材料承受单向拉应力)是材料试验中应用最普遍的一种方法。由于在上述两种变形过程中材料所承受的应力状态不同,因而,由单向拉伸试验所测得的材料超塑性性能指标还不能简单地直接用来指导制定超塑性气压成形工艺参数(如:加压规律及成形极限分析)。本文建立了气压自由胀形过程与单向拉伸变形过程之间的等效关系。并在此基础上建立了超塑性自由胀形极限变形面积比计算公式。试验结果表明:理论与实际有良好的吻合。
Air pressure forming (materials subject to bidirectional tensile stress) is a very broad application of a superplastic forming method. Uniaxial stretching (the material is subjected to unidirectional tensile stress) is one of the most common methods used in material testing. Due to the different stress states of the material during the two deformation processes, the superplasticity index of the material measured by the uniaxial tensile test can not simply be directly used to guide the formulation of superplastic pressure forming process parameters : Pressure regulation and forming limit analysis). In this paper, the equivalent relationship between free bulging and uniaxial tensile deformation is established. On this basis, the calculation formula of the ultimate deformation area ratio of superplastic free bulging was established. The experimental results show that there is a good agreement between theory and practice.