This paper presents a set of experimental results concerning the evolution of yield loci for anisotropic materials in the course of finite shear deformation history. Thin walled tubes of SAE 1020 steel are tested under triaxial loading conditions – tension, torsion and internal pressure, at room temperature. The specimens were prepared from cold-drawn tubes which had a prominent fibrous grain structure. They showed considerable amount of in-plane anisotropy and orthotropic yield properties with respect to the longitudinal and circumferential axes. The as-received specimens were further pre-strained by imposing simple shear which causes the change in orientations of these elongated polycrystalline grains. Our previous experimental results [1] have verified that the principal directions of the total stretch of the current grain shape match with the directions of orthotropy, and in this work, the subsequent yield loci for the pre-strained material are determined with respect to the new reference frame fixed along these directions of orthotropic symmetry. By utilizing the unique triaxial loading scheme of our servo-hydraulic testing system it has been possible to create the principal directions of a biaxial state of stress in a specified direction. The changes in the size and shape of the yield loci in the stress space are critically analyzed in this paper.

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