Modelling of TMF crack initiation in smooth single-crystal superalloy specimens

In this paper the TMF crack initiation behaviour of the single-crystal nickel-base superalloy MD2 is investigated and modelled. TMF tests were performed in both IP and OP for varying mechanical strain ranges in the [001] crystallographic direction until TMF crack initiation was obtained. A crystal plasticity-creep model was used in conjunction with a critical-plane approach, to evaluate the number of cycles to TMF crack initiation. The critical-plane model was evaluated and calibrated at a stable TMF cycle, where the effect of the stress relaxation had attenuated. This calibrated critical-plane model is able to describe the TMF crack initiation, taking tension/compression asymmetry as well as stress relaxation anisotropy into account, with good correlation to the real fatigue behaviour.