Advancement of the Closely Coupled Probes Potential Drop Technique for Nde of Surface Cracks

Abstract: DCPD technique is powerful tool for quantitative NDE of cracks. The technique using four probes which are in close proximity to each other has been proposed for NDE of surface cracks; that is the closely coupled probes potential drop (CCPPD) technique. It has been shown that the sensitivity of the CCPPD technique is enhanced significantly in comparison with the usual method. The objective of this study was to advance the CCPPD technique. An appropriate probes distance to enhance reproducibility was found by experiment. The d-c potential fields were analyzed for many cases of crack length 2a, crack depth b and material thickness t by using FEM. By using the numerical results, the calibration equation which relate the potential drop to a, b, and t was obtained. Then the procedure to evaluate crack depth more accurately in two steps was proposed. Experiments validated the use of the technique for NDE of surface cracks.