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Mechanical analysis of temperature impact on stability during superplastic tensile deformation

Science China(Technological Sciences) 2006年第6期49卷 641-654页

作者： song yuquan guan zhiping wang minghui song jiawang Superplastic and Plastic Research Institute Jilin University Changchun 130025 China Superplastic and Plastic Research Institute Jilin University Changchun 130025 China Superplastic and Plastic Research Institute Jilin University Changchun 130025 China Superplastic and Plastic Research Institute Jilin University Changchun 130025 China

Based on state equation that stress is the function of strain, strain-rate and temperature, the paper establishes the differential constitutive equation used for analyzing load-stability and the variational constitutive equation used for analyzing geometry-stability during superplastic tensile deformation, which contain strain hardening index, strain-rate sensitivity index, temperature sensitivity index introducted for the first time and temperature undulation index introducted for the first time in the paper. And then, based on the universal condition of plastic elementary theory, the paper analyzes load-stability and geometry-stability under continuously rising temperature and under the non-uniform temperature along the axes of specimen respectively. The results prove the impact of continuously rising speed and non-uniform value of temperature on deformation stability is that the faster temperature rises and the more non-uniform temperature is, the smaller the corresponding uniform strain of load-stability and geometry-stability are; strain hardening index is the necessary condition of stability during superplastic tensile deformation, and geometry-instability will not happen when load-instability occurs, but happen when uniform deformation has lasted after load-instability; in the superplastic temperature field, constant temperature is not necessary condition of superplasticity, but during the deformation, the slower temperature rises and the more uniform temperature is, the more stable deformation is.

关键词： superplasticity, temperature, tensile deformation, stability.

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Theoretical and metrical standardization of strain rate sensitivity index

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Science China(Technological Sciences) 2007年第6期50卷 714-735页

作者： song yuquan guan zhiping LI ZhiGang wang minghui Superplastic and Plastic Research Institute Jilin University Changchun 130022 China Superplastic and Plastic Research Institute Jilin University Changchun 130022 China Superplastic and Plastic Research Institute Jilin University Changchun 130022 China Superplastic and Plastic Research Institute Jilin University Changchun 130022 China

Strain rate sensitivity index m is one of the vital mechanical parameters for deter- mining material superplasticity. In this paper, the existing formulae for measuring m value are reviewed, and it is found that the m values can be classified into three classes: mi under constant length, mv under constant velocity, and mP under con- stant load. The constraint equation of the generalized m value is established ac- cording to the tensile constitutive equation and the basis theory for plastic me- chanics. Based on three typical deformation paths, the m value is redefined. Fur- thermore, from the formula of generalized m value, the formulae for measuring mi, mv and mP are theoretically deduced. The precise methods with numerical simula- tion are presented. The results prove that the m value is a non-constant and its dependence on ε changes with the deformation path. Under different deformation paths, the m values calculated from the same formula are different. Using different formulae, the m values under the same deformation path are also different. There- fore, deformation path and corresponding formula should be given during the measurement of the m value. Moreover, it is explained theoretically and experi- mentally that why the mv value under constant velocity is sometimes negative but the mP value under constant load is sometimes lager than 1. The aim of the analysis and measurement of the m value is to facilitate the study on the relationship be- tween macroscopical mechanical laws and microscopic physical mechanisms during superplastic deformation.

关键词： superplasticity, strain rate sensitivity index, tensile deformation

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拉伸变形应变硬化指数的理论和实验规范

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金属学报 2006年第7期42卷 673-680页

作者：宋玉泉管志平马品奎宋家旺吉林大学超塑性与塑性研究所长春130025

从应力为应变和应变速率函数的状态方程出发,导出了超塑性拉伸变形的微分本构方程,从而解释了方程中应变硬化指数的力学涵义．导出了应变硬化指数的约束方程,定义了典型变形路径的应变硬化指数,导出了它们之间的相互关系．导出了典型变... 详细信息

从应力为应变和应变速率函数的状态方程出发,导出了超塑性拉伸变形的微分本构方程,从而解释了方程中应变硬化指数的力学涵义．导出了应变硬化指数的约束方程,定义了典型变形路径的应变硬化指数,导出了它们之间的相互关系．导出了典型变形路径应变硬化指数的测量公式和数值模拟的精确测量方法,以此为依据对应变硬化指数进行了实验测量,对测量方法和测量结果进行了精细分析．研究结果判明:应变硬化指数不仅不是常数,而且与应变的变化规律及变形路径有密切的联系;在一定变形路径下还与所用的测量公式有密切关系．因此,在引用应变硬化指数时,应该标明所对应的变形路径;在测量应变硬化指数时,应采用所对应变形路径的测量公式．

关键词：超塑性应变硬化指数力学解析实验测量

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