Study of the Effect of Deformation on the Axes of Anisotropy

Many metal forming operations, such as rolling and tube drawing, are known to induce orthotropic anisotropy. The change of axes of orthotropy with subsequent deformation has been studied in this paper. The change in the orthotropy directions is of great importance for understanding and interpreting the subsequent yield behavior of metals. Based on Hill’s hypothesis that the orthotropy axes coincides with the principal directions of stretch, the change in orthotropy directions has been studied theoretically and experimentally. Since the grain shape and its direction of elongation is a good indicator of the principal stretches and its directions, it has been used as an experimental means of determining, not only the directions of principal stretches in an as received material, but also to determine approximately the deformation it has undergone so far from a reference state. A fully annealed isotropic state is chosen as the reference state. The directions of the axes of anisotropy, induced as a result of finite deformation applied to this reference state, are characterized in terms of the principal directions of the Cauchy’s deformation tensor. An experimental scheme has been developed to determine the varying directions of orthotropy for comparison with the theoretical model.