Strain Energy Based Method for Metal Magnetic Memory Effect of Tensile Tested Structures

The metal magnetic memory (MMM) technique has been widely regarded as an effective method to locate stress concentration zones and to identify structural defects. To study its applicability in prognostics of structure damage, a series of static tensile tests and MMM measurement were carried out on the commonly used Q235 steel. The experimental results show that the normal component of self-magnetic-flux-leakage signals Hpzis linear with the position in loading direction x and the gradient Gz,x increases with an increase in the external load. 2D magnetostatic finite element analyses indicate that the variations of Gz,x should be due to the change in relative permeability of the specimen after the effect of mechanical loading under geomagnetic field. The strain energy density in the structure during loading is found to be exponentially determined by Gz,x with an adjusted R-squared value of 0.9984. The monotonous correlation enables prediction of structure damage using the MMM technique.