NONDESTRUCTIVE CHARACTERIZATION OF BIFURCATED CRACK BY POTENTIAL DROP TECHNIQUE

Abstract A method was presented for the nondestructive evaluation of a crack bifurcated from a horizontal crack in a rail. The method was based on the measurement of the difference and distribution of d.c electrical potential on the top surface of thc rail.First, a problem of current flow in a plate, which contained horizontal and bifurcated cracks 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 both ends of thc horizontal crack. Also the relation between the vertical component of the bifurcated crack and the total potential difference above the horizontal crack was revealed to be independent of the combinations of the cracks. Next, in order to characterize the cracks in actual rail based on the 2-D numerical analysis, a method was introduced for obtaining a rectangular section elecirically equivalent to the section of actual rail. Finally, it was verified by experiments using rail specimens that the cracks were characterized quantitatively through the present numerical results together with the usc of the equivalent section. keywords: Potential drop techniquebifurcated crackrailfinite clement method