G.-Q. He’s research while affiliated with Tongji University and other places

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.

Based on the microstructural investigation of low cycle fatigue under multi-axial non-proportional loading of 316 L stainless steel, the distance within which dislocation moves freely was measured, while its distribution rule was analyzed. The quantitative relation between the macroscopic effective saturated stress and the statistical mean distance within which dislocations moves freely was given. The new definition of non-proportionality of loading path was presented on the basis of the statistical mean distance within which dislocation moves freely, which is considered as entering uniaxial cyclic constitutive equation to describe the stress and strain behavior under multiaxial loading.