Fatigue Evaluation for a Ferritic Stainless Steel (SUS430) by the Eddy Current Method Using the Pancake-Type Coil

To prevent accidents caused by the accumulation of fatigue damage, it is important to evaluate fatigue damage in stainless steel, a widely used structural material. SUS430 (ANSI430) is a ferritic stainless steel. It is well known that the electromagnetic properties of SUS430 such as permeability and resistivity, change due to fatigue damage. The eddy current method can detect change in the electromagnetic properties of SUS430. In this research, the eddy current method using the pancake-type coil was used to find fatigue damage in SUS430. The pancake-type coil was put on a specimen made of SUS430, and excited with alternating current. When a pancake-type coil and a specimen are adjacent, the change in permeability and resistivity of the specimen due to fatigue influences coil constants such as inductance
L
and phase angle ¿ of impedance. In our experiment,
L
and ¿ clearly depended on an increase in the bending stress and the number of stress cycles. It can, therefore, be said that
L
and ¿ are clearly influenced by fatigue damage. In this paper, the results of investigating the relationships between the amount of fatigue damage, bending stress,
L
, and ¿ are reported.