Vilotic Marko, Sidjanin Leposava, Alexandrov Sergei, Lang Lihui
Faculty of Technical Sciences, University of Novi Sad, 21000 Novi Sad, Serbia.
School of Mechanical Engineering and Automation, Beihang University, Beijing 100191, China.
Materials (Basel). 2020 Oct 20;13(20):4667. doi: 10.3390/ma13204667.
Severe plastic deformation (SPD) processes are widely used for improving material properties. A distinguishing feature of many SPD processes is that the principal axes of the stress tensor intensively rotate relative to the material. Nevertheless, no measure of this rotation is involved in the constitutive equations that predict the evolution of material properties. In particular, a typical way of describing the effect of SPD processes on material properties is to show the dependence of various parameters that characterize these properties on the equivalent strain. However, the same level of the equivalent strain can be achieved in a process in which the principal axes of the stress tensor do not rotate relative to the material. It is, therefore, vital to understand which properties are dependent and which properties are independent of the rotation of the principal axes of the stress tensor relative to the material. In the present paper, a new multistage SPD process is designed such that the principal stress axes do not rotate relative to the material during each stage of the process but the directions of the major and minor principal stresses interchange between two subsequent stages. The process is practically plane strain, and it may be named the process of upsetting by V-shape dies. In addition, axisymmetric compression by Rastegaev's method is conducted. In this case, the principal stress axes are fixed in the material throughout the entire process of deformation. Material properties and microstructure generated in the two processes above are compared to reveal the effect of the rotation of the principal stress axes relative to the material on the evolution of these properties.
严重塑性变形（SPD）工艺被广泛用于改善材料性能。许多SPD工艺的一个显著特点是，应力张量的主轴相对于材料剧烈旋转。然而，预测材料性能演变的本构方程中并未涉及这种旋转的度量。特别是，描述SPD工艺对材料性能影响的一种典型方式是展示表征这些性能的各种参数对等效应变的依赖性。然而，在应力张量主轴相对于材料不旋转的过程中也可以达到相同水平的等效应变。因此，了解哪些性能依赖于应力张量主轴相对于材料的旋转，哪些性能与之无关至关重要。在本文中，设计了一种新的多阶段SPD工艺，使得在该工艺的每个阶段应力主轴相对于材料不旋转，但主应力的大小方向在两个后续阶段之间互换。该工艺实际上是平面应变的，它可以被称为V形模镦粗工艺。此外，采用拉斯特加耶夫方法进行轴对称压缩。在这种情况下，在整个变形过程中主应力轴在材料中是固定的。比较上述两种工艺中产生的材料性能和微观结构，以揭示主应力轴相对于材料的旋转对这些性能演变的影响。
