Arrangement of probes for measuring case depth by means of four-point probes

In the present paper, the suitable arrangement of probes to measure case depth of shaft-like materials by using four-point probes method was considered. In the induction hardening process, case depth is essential for its quality control. It needs great time and labor to measure hardness distribution in the sectional area with cutting the samples. In the previous paper, we have proposed a procedure to evaluate case depth of shaft-like materials by using four-point probes method. This study was aimed at enhancement of sensitivity of evaluation. The potential drop for various probe arrangements on the surface of shaft-like materials was analyzed by using finite element method. The surface hardened shaft was modeled as a two layered structure having different electrical resistivity in surface hardened layer and inner untreated part. The value of resistivity obtained from experiment using carbon steel was used for numerical calculation. The effect of probe arrangement in axial direction or circumferential direction, distance between current input-output probes, and distance between current input-output probes and potential measuring probes, on change in potential drop by case depth was shown. From the results, suitable probe arrangement for sensitive evaluation was considered.