Nondestructive sizing of three-dimensional surface crack in wheelseat of shinkansen vehicle axle using D. C. potential drop technique

摘要

D.C. potential drop technique is applied to the quantitative estimation of the size and shape of a fretting fatigue crack generated in the wheelseat of a Shinkansen vehicle axle. First, a series of calculations were performed using the boundaryelement method for each half-space by specifying one of three-dimensional semi-elliptical surface cracks in turn from those of various sizes and shapes to obtain the relationship between the potential drop on the surface and the crack depth, crack lengthalong with its location when a constant d-c current is applied between two points near the crack. The calibration equations were derived from the results. The crack depth, crack length and its location were then determined by the analysis of an inverseproblem using the quasi-Newton method which compares the potential drop obtained by the calibration equations and measurements using a carbon steel specimen containing a slit simulating a crack. The convergence to the solution was good. Although thevalues of depths are slightly scattered because depth estimations are sensitive to crack location and change with even a minimal change in distance between the crack and the sensor, the estimations of lengths and locations are adequate.