Plastic Deformation of Polycrystalline Metallic Materials Subjected to Cycle of Stress

Abstract

In a series of studies of polycrystalline metallic materials with respect to the influence of their strain history on their plastic deformation, one of the problems concerns their yield, and so the studies have been performed on their behavior of plastic deformation as they are subjected to low-cycle pulsating stresses in connection with their strain history. The present study, being the continuation of the previous study, consists of experimental examination of low-cycle pulsating stress tests under combined axial tension and torsion in which the principal axes under stress must be either rotated or fixed. From the present analytical and experimental studies, the following conclusions have been obtained. It is evident that there is larger plastic deformation of the material under the cycle of stress when the principal axes are in rotation than when they are fixed. This is due to the difference in the stress passage giving rise to variant change of the structure of the material. It is found also that the numerical value of anisotropic parameter of the material and that of parameter of the Bauschinger effect during the cycle of stress are larger when the principal axes are in rotation than when they are fixed. It is suggested moreover that the development of the structural change of the material under the rotation of the principal axes of stress, recognizing correlation between the variation Δσij of the microscopic yield stress from the mean stress and the fluctuation Δ(DE)ij of increased microscopic strain, makes much of coexistence of Δσij and Δ(DE)ij as factors to bring about changes in the location of yield surface of the material.