Elastoplastic Deformation of a Steel Tube Subjected to the Strain Paths Composed of Two Line Segments

Abstract

Constitutive equations play an important role for improving the accuracy of finite element analysis used in metal forming simulations. Plastic flow behavior of a steel tube is experimentally investigated in the present study. A thin-walled steel tube is subjected to linear and nonlinear loading paths. For the linear loadings, a ratio of the displacement and rotation of a grip is fixed at constant. Experimentally measured plastic flow is well predicted by the associated flow rule based on an anisotropic yield function at least for the linear loadings. In the nonlinear loadings, the specimen is subjected to the uniaxial tension followed by the simultaneous application of the axial load and torsion. The plastic flow directions in the nonlinear loadings do not agree with those for the linear loadings even though the stress states are identical. These experimental trends cannot be reproduced by the associated flow rule. We have found the linear relationship between the direction of plastic strain rate and the direction of strain rate. Therefore, the experimental data indicates that the direction of plastic flow can be represented by the direction of the strain rate as well as the stress state.