Proposal of slack inspection method of high tension bolt of hexagon head using alternating magnetic field

Abstract

The development of the inspection technique of detecting the slack of the high tension bolt is desired. The permeability inside the side of the bolt head is changed since the bolt head is compressed by bolting a plate. Therefore, the evaluation of the slack of the bolt is possible by detecting the difference of the magnetic characteristics. In this paper, the inspection method for measuring the slack of the steel high-tension bolt of hexagon head using a small electromagnetic non-contacting sensor is proposed. The distribution of stress, flux density and eddy current density near the bolt head is estimated by 3-D nonlinear electromagnetic finite element method (FEM) analysis taking account of the electromagnetic property under various compressive stresses. The results showed that the non-destructive inspection of the slack of the high-tension bolts is possible by detecting the change of flux density in the side of the bolt head.