Detection of stress concentration and early plastic deformation by monitoring surface weak magnetic field change

The magnetization upon ferromagnetic samples induced by applied stresses was studied through experiments by using high sensitive magnetic sensors. The stress-magnetic coupling under cyclic tensile stress was studied during slow cyclic loading and fatigue loading process respectively. The monitoring data validated the efficiency of metal magnetic memory testing on identifying stress concentration zones. After the steel samples were stretched into plastic deformation, the surface magnetic fields of them were found reversing their polarities. This phenomenon was first proposed and discussed by introducing the theory of magnetic dipole and dislocation of metallic crystal. Based on that, a nondestructive testing method for monitoring the occurrence of plastic deformation through measuring the surface weak magnetic field changes of ferromagnetic structures was put forward and verified through preliminary experiment.