Proposal of Electromagnetic Inspection Method of Tensile Strength in Steel Without Influence of Lift-Off Between Steel and Inspection Probe

A tensile strength of steel material is measured by a tension-testing machine. It is a destructive inspection, and it is necessary to prepare a large size specimen. The conductivity of the steel with high tensile strength becomes large, and its permeability becomes small. Then, the nondestructive estimation of the tensile strength in the steel is possible by using the difference of the electromagnetic properties. The inspection method of the tensile strength in the steel is proposed using an alternating electromagnetic field. The signal, however, is also influenced by the change of the distance (lift-off: Lo) between the steel and an electromagnetic probe. In this paper, the inspection method for measuring the tensile strength which is not affected by the lift-off Lo is proposed by examining the performance of the method using the 3-D edge-based hexahedral nonlinear FEM.