Plasticity-induced crack closure under thermomechanical fatigue loading: Influence of phase relationship and plasticity model on crack closure, CTOD, ratchetting and numerical stability

In this work, plasticity-induced crack closure is studied under strain-controlled in-phase and out-of-phase thermomechanical fatigue (TMF) loading using the finite element method. The influence of the TMF phase, the applied strain ratio and the material model on the crack opening stress and the crack tip opening displacement is investigated. Therefore, a plane strain penny- shaped crack under large-scale yielding and four temperature-dependent viscoplasticity models with different numbers of backstresses with or without modification for an improved description of ratchetting are considered. The results show that crack closure is strongly determined by the TMF phase and not significantly affected by the strain ratio. Moreover, the plasticity model strongly influences the results, suggesting the need for the appropriate description of ratchetting effects and hardening behavior for large plastic strain ranges typically occurring at and around the crack tip.