THEORETICAL MODEL OF MAGNETO-ELASTOPLASTIC COUPLING FOR MICRO-MAGNETIC NON-DESTRUCTIVE TESTING METHOD WITH STRESS CONCENTRATION AND PLASTIC ZONE

The metal magnetic memory micro-magnetic non-destructive testing method can detect and evaluate the damage location and degree using the local change of magnetic state caused by the stress concentration or plastic zone of ferromagnetic materials. The quantitative theoretical analysis for micro-magnetic signals can provide important guidance for its engineering application. This paper reports on the research development of the magnetic-elastoplastic constitutive relationship of ferromagnetic materials under weak environmental magnetic field and its application in micro-magnetic signal analysis for the metal magnetic memory micro-magnetic non-destructive testing method. Regarding the research on the magneto-mechanical constitutive relationship, under the weak magnetization conditions of micro-magnetic testing, an analytical expression for the ideal magnetization constitutive relationship of ferromagnetic materials subjected to an elastoplastic load is established based on the effective field theory. Then, combined with the approaching principle between magnetization and ideal magnetization, the influence of the historical process of stress and strain loading on the magnetization under a constant and applied weak magnetic field is analyzed to consider the magnetization hysteresis effect. For the micro-magnetic non-destructive testing signal analysis, based on the elasticity theory, magnetostatics theory and the newly established magnetic-elastoplastic constitutive relationship, a two-dimensional model of the surface magnetic signal induced by the elastic stress or plastic zone in the ferromagnetic specimen under a weak magnetic field is established and solved by the finite element method. Combing with the exsting experiment results, the quantitative ability of theoretical model to describe the influence of elastoplastic factors on micro-magnetic signals is confirmed, and the correlation between the characteristic parameters of micro-magnetic signals and the size of local elastic stress or plastic zone is analyzed in detail. Compared with the existing magneto-mechanical constitutive relationship, the analytical expression of the ideal magnetization established in this paper is more concise, which helps to improve the understanding and application of the magneto-mechanical coupling effect.