A numerical simulation method of residual magnetic field signals for evaluating deformation-induced stress concentration in ferromagnetic materials

The metal magnetic memory (MMM) technique is a promising non-destructive inspection method that is sensitive to early damage due to stress concentration in ferromagnetic components. However, quantitative analysis methods for evaluating the stress concentration induced by local plastic deformation have not yet been sufficiently studied due to the lack of a reasonable numerical simulation method. Based on the Jiles-Atherton (J-A) magneto-plastic model, which considers the combined effects of residual stress and strain, the change in the behaviour of residual magnetic field (RMF) signals in an X80 pipeline steel specimen with an indentation is calculated in this paper using finite element (FE) simulations, while systematic experimental research is also carried out. The results show that the model-predicted RMF signals are consistent with the experimental data, which demonstrates the validity of the numerical simulation method. Moreover, the comparison indicates that the RMF FE simulations can provide an effective and reliable way to determine the location and the degree of deformation-induced stress concentration. In addition, the effect of the residual stress and strain on the surface magnetic field and the model is discussed. The results of this study help to improve the accuracy of the MMM technique for evaluating the stress concentration caused by local plastic deformation.