Damage location and numerical simulation for steel wire under torsion based on magnetic memory method

Torsion tests on 50 Mn steel wire were implemented and illustrated in this research to probe into the relationship between normal components of self-magnetic-flux-leakage (SMFL) signals H-p(y) and early damage of steel wire subjected to torsional stress. Besides, a modified model with due consideration of coercivity and permeability varying with equivalent stress at elastic-plastic stage was presented to simulate H-p(y) signals of steel wire under torsion accurately. Relevant numerical simulations of magneto-mechanical coupling were performed. The results show that using zero crossing point (ZCP) of H-p(y) signals to identify defect location does not apply to steel wire under torsion. However, there is crest (or trough) showing on magnetic signal curve prior to fracture. By utilizing location of crest (or trough), damage could be positioned accurately and ultimate fracture point could be forecasted in advance as well. Furthermore, simulation results obtained from the modified model are consistent with test results. Not only can study results demonstrate that MMM technique could be used for determining early damage of steel wire under torsion, but also provide certain reference for quantitative analysis about the relationship between damage and H-p(y) signals.