Yield Surface Evolution and Elastoplastic Model with Cubic Distortional Yield Surface

We conducted a series of axial-torsional strain-controlled experiments on thin-walled tubular specimens of aluminum alloy Al6061 in our lab, examining carefully the probed yield points in axial-torsional space. On the basis of the experimental findings, a rate-independent flow elastoplastic material model featuring an evolving cubic distortional yield hypersurface, which is articulated with two Mises hyperspheres, characteristic of internal symmetry of two elements of the projective proper orthochronous cubic distortional yield hypersurface in the plastic phase, is proposed. Associated with each Mises hypersphere in stress space is a normality plastic flow rule and a mixed-exp-AF's rule, referring to a combined isotropic-kinematic rule of hardening-softening, which combines the isotropic exponential rule of degree 2 and the kinematic rule of Armstrong-Frederick. The model needs a total of 10 material constants. An identification procedure is presented for estimating the 10 material constants of the model from the experimental data. The cubic distortional yield hypersurface estimated by the probed experimental data of yield points and the evolving yield hypersurface simulated by the proposed model along with the identified material constants was validated satisfactorily. © 2022 American Society of Civil Engineers.