Abstract
A velocity induced eddy current probe has been used to detect cracks in both non-ferromagnetic and ferromagnetic metals. The simulation and experimental results show that this probe can successfully detect cracks in both cases, but further investigation shows that the underlying principles for inspecting non-ferromagnetic and ferromagnetic metals are actually different. For an aluminum plate, the induced eddy current density and the signal amplitude both increase with probe speed, which means the signal is caused by velocity induced eddy currents. For a steel plate, probe speed changes the baselines of the testing signals; however, it has little influence on signal amplitudes. Simulation results show that the signal for cracks in a steel plate is mainly caused by direct magnetic field perturbation rather than velocity induced eddy currents.
Highlights
Eddy current testing is a technique that has already been successfully used to detect cracks in conductive materials [1,2]
A magnetic field sensor, such as a giant magnetoresistance (GMR) sensor [3], Hall sensor [4,5], or sensing coil [6], is used to measure the magnetic field, which is the vector sum of the magnetic field produced by the current that runs in the excitation coil and the field produced by eddy currents in the specimen
The velocity induced eddy current probe has been applied to detecting cracks in both aluminum and steel plates
Summary
Eddy current testing is a technique that has already been successfully used to detect cracks in conductive materials [1,2]. In the field of nondestructive testing (NDT), velocity induced eddy current was first studied in high-speed magnetic flux leakage (MFL). The relative movement between the magnetizer and conductors will generate considerable eddy currents to influence testing signals [12,13,14]. To induce eddy current in the conductive material to be inspected, relative motion between the magnetic field source and the conductor is necessary. Because the eddy current density increases with the inspection speed, the amplitudes of inspection signals for cracks increase with inspection speed This brings up the biggest advantage of the velocity induced eddy current testing method; that is, inspecting conductive materials in systems where there is relative motion between the probe and the material to be inspected.
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