LAUSR

New finite-strain elastoplastic constitutive equations are proposed toward a direct approach for simulating both monotonic and cyclic failure effects of metals. Novelties in several respects are incorporated in these new equations: (a) No yield conditions need be imposed, and therefore smooth transition from an elastic to a plastic state may be ensured without involving strong discontinuities in elastoplastic tangent moduli; (b) Complex forms of usual elastoplastic equations assuming the loading–unloading conditions may be substantially simplified in a more realistic sense of representing elastoplastic behavior of metals; (c) Failure effects in a broad case of multi-axial loading conditions may be automatically predicted as inherent constitutive features, without involving any additional variables and any ad hoc failure criteria; and (d) A new evolution equation for the back stress is introduced for effective characterization of both hardening and softening effects associated with strain-induced anisotropy. A simultaneous simulation of monotonic and cyclic failure effects of metal tubes under torsional loadings is for the first time presented for both free- and fixed-end torsion with finite rotation. Results are obtained for coupling effects of finite rotation and strain-induced anisotropy. Model predictions compare well with experimental data.