DIRECT CURRENT POTENTIAL DROP CALIBRATION OF CRACK GROWTH CURVES IN A DOUBLE EDGED NOTCHED SPECIMEN

摘要

This paper presents the direct current potential drop crack growth resistance curves for a double-edged notch specimen. The results were derived using a three-dimensional finite element heat conduction package, since the differential equation for heat conduction and direct current potential drop are the same. The finite element program was verified using, several simple heat conduction examples. A further benchmark used was the analytical solution for the potential drop around a quarter circular defect in a cube. Quarter circular and quarter elliptical cracks were modelled in the double-edged notch specimen. The quarter elliptical cracks had a maximum aspect ratio of 1.88, and were based on fatigue cracks in the D.E.N. specimen. It was found that the resistance curves are linear when the P.D. signal is measured at the optimum probe wire position, and is plotted against crack length along the plain surface. It was also established that the P.D. versus crack area relationship at the optimum probe position is independent of crack shape