A kinematic hardening constitutive model for anomalous multiaxial ratcheting behaviors of zirconium alloy tubes under combined cyclic axial load and internal pressure at 648 K

•Uniaxial & multiaxial ratcheting tests were conducted for Zr cladding tubes at 648 K.•Negative axial ratcheting strain accumulates under symmetric uniaxial cyclic loading.•Axial ratcheting strain direction may change significantly.•A general formulation of kinematic hardening models is proposed.•Influence of the twinning-detwinning mechanism on cyclic plasticity was incorporated. Uniaxial and multiaxial ratcheting tests of zirconium cladding tubes with constant internal pressure and cyclic axial loading were conducted at 648 K, aiming to investigate the influences of axial mean stress, stress amplitude, and inner pressure. Anomalous ratcheting behaviors were observed, including negative axial ratcheting strain accumulation under symmetric uniaxial cyclic loading conditions and significant changes in axial ratcheting strain direction under certain multiaxial loading conditions. A general formulation of kinematic hardening models was proposed to decouple asymmetry and anisotropy of the kinematic hardening rule from that of the initial yielding. On this basis, a phenomenological model incorporating the effects of the {101¯2} twinning-detwinning mechanism on cyclic plasticity was formulated to simulate the observed anomalous ratcheting behaviors. The predictions of the proposed model show acceptable agreement with the test results. [Display omitted]