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

Abstract

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. S 978-1-4244-5141-8/10/$26.00

Simulation of Real Defect Geometry and Its Detection Using Passive Magnetic Inspection (PMI) Method

“…Self-magnetic flux leakage (SMFL) is assumed to take place in the stress concentration areas of ferromagnetic materials affected by mechanical load under the Earth's magnetic field [46], and this condition can remain even after removing the load, creating detectable magnetic leakage at the material surface [47]. Measuring SMFL at the surface of the materials helps in estimating their stress-strain states (SSSs), which is an important parameter in determining a structure's reliability [48].…”

Monitoring of Local Plasticity Using Lamb Waves

“…Other researchers also have done some studies on the detection of plastic deformation by using various technologies. Yuan and Zhang (2010) studied the metal magnetic memory testing technology for monitoring the occurrence of plastic deformation through measuring the surface weak magnetic field change of ferromagnetic structures. However, this technique is limited to ferromagnetic materials and lack of theoretical support.…”

“…Moreover, reflected waves were not used in monitoring (Mostafa et al 1997). To date, none of the above mentioned methods (Mostafa et al 1997;Yuan and Zhang 2010) for detecting plastic deformation has been practically used. level, i.e., 160 MPa.…”