Estimation of the anisotropic plastic property using single spherical indentation—An FEM study

In this study, a method to evaluate the in-plane anisotropic plastic properties of engineering steels by single spherical indentation is proposed. This method deals with materials that obey the work hardening law and have in-plane anisotropy of the yield stress in orthogonal directions. The method thus estimates the yield stress σY, the work hardening exponent n, and the ratio of the yield stresses m. Computations were first carried out by the finite element method (FEM) in order to quantitatively study the deformation surrounding the impression, when the spherical indenter was pressed against the anisotropic plastic materials. The permanent impression that remained after fully unloading the indenter was found to be non-uniform. The pile-up height in the direction of lower yield stress becomes higher than that in the direction of high yield stress. Such differences in height were found to become larger when m is higher. Based on this characteristic, extensive FEM calculations were carried out in order to propose the method to identify the anisotropic plastic properties for various materials whose mechanical properties are available for many engineering steels. The method involves several functions that relate the indentation response (indentation curve and geometry of impression) to the anisotropic plastic property of the material. Numerical experiments were conducted in order to verify the effectiveness of the proposed method.