基于微结构分析定义应变路径非比例度

DEFINITION OF NON-PROPORTIONALITY OF STRAIN PATH BASED ON MICROSTRUCTURES ANALYSIS

对316L不锈钢进行了单轴及多轴非比例循环加载低周疲劳实验及其微结构的观察,研究了非比例循环附加强化对应变路径依赖性的微观机理,分析了位错自由运动间距的分布规律,结果表明:316L不锈钢在非比例循环加载下产生的附加强化与材料中的多滑移位错结构的形态与尺寸直接相关,滑移面上的位错自由运动间距服从正态分布,位错自由运动间距的统计平均值与宏观等效饱和应力幅值之间呈现线性对数关系,基于上述研究结果,以位错自由运动间距统计平均值给出了应变路径非比例度的定义,结果表明:在单轴循环应力-应变关系式中引入新的非比例度的定义可以较好地描述应变路径对材料非比例循环变形行为的影响。

The tests of low cycle fatigue of 316L stainless steel under uni-axial and multi-axial non-proportional loading were carried out, and the microstructures in this material were observed also. The micro-mechanism of the dependence of non-proportional cyclic additional hardening on the strain path was studied. The distributive rule of distance within which dislocations move freely is analyzed. The results show that the non-proportional cyclic additional hardening of 316L stainless steel is directly related to the shape and size of the multi-slip dislocation structures. Distance within which dislocations on slip planes move freely is normal distribution. There is the logarithmic linear relationship between the macro effective saturated stress amplitude value and the statistical mean distance within which dislocations move freely. Based on the above results, the new non-proportionality of loading path is defined with the statistical mean distance within which dislocations move freely. The result show that the new non-proportionality defined in this paper is considered as entering uni-axial cyclic constitutive equation, which can describe the effect of the strain path on the non-proportional cyclic deformation behavior of the material.