Passive nondestructive evaluation of ferromagnetic materials during deformation using SQUID gradiometers

Abstract

An experimental system is described for in situ passive measurement of changes in the magnetic field of ferromagnetic materials subject to tensile deformation. Changes in magnetic field during deformation are monitored using a three-axes first-order superconducting quantum interference device (SQUID) gradiometer. The gradiometer is held in a fixed position while a horizontal load frame has been constructed from nonferromagnetic materials. Results are presented for cold-rolled steel specimens. The magnetic field gradient was measured by scanning the specimen in the x-y plane while at a constant stress at a fixed distance from the tail of the SQUID dewar.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>