Nondestructive magnetic detection of plasticized area using superconducting quantum interference device

The relationship between the magnetic and structural changes induced by the application of a tensile load to a carbon steel specimen was investigated by correlating the change in the spatial second-order gradient component of the magnetic flux density d(2)B(z)/dr(2) With the appearance of the Luders bands on the specimen surface. The magnetic change was measured using a no ndestructive evaluation (NDE) system with a concentric second-order superco nducting quantum interference device (SQUID) gradiometer of low temperature superconductor. The area where peaks and folds appeared in the 3-dimension al map of d(2) B-z/dr(2) corresponded to the area where Luders bands appeas ed on the specimen surface, The dimensions of the area where peaks and fold s appeared had a strong correlation with the residual strain of the specime n. It was concluded that the magnetic NDE using SQUID has the ability to de tect the area plasticized by fine deformation in ferromagnetic materials.