POTENTIAL DROP TECHNIQUE FOR NONDESTRUCTIVE EVALUATION OF BIFURCATED CRACK IN RAIL

Abstract The potential drop technique was applied to nondestructive evaluation of a crack bifurcated downwards from a non-planar crack in a rail, since the case of non-planar cracks is more often observed than that of horizontal cracks. The method of evaluation was based on the measurement of the distribution of d.c. electrical potential on the top surface of the rail. A problem of current flow in a plate, which contained non-planar and bifurcated cracks modelled in practical shape and was subjected to a uniform current, was analyzed numerically by using a 2-D finite clement method. The potential distribution on the measuring surface of the plate was obtained for various combinations of the cracks. The potential distribution showed a remarkable change in its slope just above the tips of the non-planar crack. Also the relation between the vertical depth of penetration of the whole crack and the total potential difference above the non-planar crack was revealed to be independent of the combinations of the cracks. It was verified by experiments using rail specimens that the cracks were characterized quantitatively through the present 2-D numerical results together with the use of the equivalent height of the rail.