Examination of electromagnetic inspection of surface hardness: 3-D nonlinear FEM analysis considering nonuniform permeability and conductivity

The inspection of surface hardness of the hardened steel is important in keeping the quality of automobile parts, etc. The permeability of hardened steel decreases when the hardness is increased. Therefore, the surface hardness evaluation is possible by detecting the difference of the magnetic characteristic using the electromagnetic inspection method. However, the surface hardness inspection is not easy, because the relative permeability and conductivity of the hardened steel are usually nonuniform compared with that of the normal steel. In this paper, the technique for reducing the effect of the nonuniformity of the permeability and the conductivity on the large magnetic noise, and measuring the surface hardness is examined using three-dimensional edge-based hexahedral finite element method. In addition, the experimental verification is also carried out.