Nondestructive sizing of a 3D surface crack generated in a railway component using closely coupled probes for direct-current potential drop technique

The direct-current potential drop technique was applied to the quantitative estimation of the size and shape of the crack generated in railway components. First, calibration equations that relate the potential drop to the crack depth and crack length along with its location were derived where the boundary element method was used for the electric potential problem. The crack depth, crack length and its location were then determined by analyzing an inverse problem by using the quasi-Newton method which compared the potential drop obtained by the calibration equations with measurements using a carbon steel specimen containing a crack. Although the values of depths were slightly scattered because depth estimations were sensitive to the crack location and changed with even a minimal change in distance between the crack and probes, the estimations of lengths and locations were adequate.