Effect of Varying Inspection Parameters in Crack Depth Measurements Using Potential Drop Method

When working with industrial clients, the NDE Group of Company Assistance at Iowa State University often straddles the area between research and application. For example, it is well known that the potential drop method may be used for measure crack depth in metallic specimens. But of interest to our manufacturing clientele is how much sample preparation and data interpretation might be needed if they apply a commercially available off-the-shelf (COTS) device to their particular inspection need. In this paper, a commercially available device that used alternating current potential drop (ACPD) to measure crack depth was applied to a variety of samples having known cracks and notches. These included samples with varying contact area geometries and surface conditions, and were intended to simulate the range of demands of industrial conditions for applying such measurements. The results discuss to what degree the industrial user can expect to get meaningful performance out of such test devices under various conditions, and guidelines are offered for surface preparation needed.

References
1. Lugg, M. C., “An Introduction to ACPD,” Technical Software Consultants Ltd., TSC/MCL/1146, United Kingdom, 20 February 2002. 2. Saguy, H. and Rittel, D., “Flaw detection in metal by the ACPD technique: Theory and experiments,” NDT&E International 40, pp. 505-509, Elsevier Ltd., 2007. 3. Lugg, M.C., “Data interpretation in ACPD crack inspection,” NDT International, Vol. 22, No. 3, June 1989. 4. “The Potential Drop Technique & Its Use In Fatigue Testing,” Matelect Application Note Reference FPD04, London.
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