超塑性变形的失稳比塑性变形失稳复杂得多,国内外学者在失稳的力学研究方面已发表了许多有价值的论文,对超塑性研究的进展贡献很大.由于不同学者的研究思路和研究方法不同,所得的结论也各异,因此有必要进行理论规范.本文从变形的状态方程出发,对无几何缺陷试样在恒温条件下仅由材料本身所产生的拉伸失稳,进行力学理论解析,旨在研究材料力学参数对失稳的影响.所得结果不仅与一些典型论文的失稳判据完全一致,而且从理论上论证了超塑性拉伸变形,在载荷失稳时同时不发生几何失稳,而是要经历一段均匀变形后才出现几何失稳.
Instabilities during superplastic deformation is more complicated than those during plastic deformation. Many valuable papers about mechanical analysis of instability have been published at home and abroad, which contributed much to the development of superplastic research. But their conclusions were different because of the diversity of the researchers’ thoughts and methods. Therefore, it is necessary to normalize these theories. In order to study the impact of material’s mechanical parameter on instability, tensile instability criterion of specimen without geometric defect at constant temperature, that is due to only material parameter, was analyzed based on state equation of deformation in this paper. The results not only coincided with those in some typical papers, but also proved theoretically that, during superplastic deformation, geometrical instability will happen after a period of uniform deformation which follows load instability, rather than in the mean time of load instability.
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