Effect of a magnetic field on crack length measurement of 9NI steel by unloading compliance method

In the fracture toughness measurement of ferro-magnetic materials in high magnetic fields, it has not been clarified whether we can use the same formulas as ones used in a non-magnetic field. Therefore, it is necessary to understand the magnetic effect in the fracture toughness measurement of ferro-magnetic materials. As the first step, crack length was measured at 4 K by unloading compliance method in the testing of CT specimen of 9% nickel steel. The same formula was used in the magnetic field of 0 and 8 Tesla. They were compared with the length measured by optical fractography. The magnetic field had little effect on the crack length measurement by the unloading compliance method. The small amount of retained austenite in Q T heat-treated specimen did not exhibit a magnetic effect on the crack length measurement by the unloading compliance method