The influence of irregularities in the crack shape on the crack extension measurement by means of the direct-current-potential-drop method

The equations used for calculating the crack extension from the change in t he potential drop at a fracture mechanics specimen are generally derived fo r perfectly straight crack fronts. in the practice of fracture mechanics te sts the crack, however, usually grows faster in the interior of the specime n than at the exterior, leading to a curved crack front. For such a case we calculate the potential drop by means of a finite difference scheme. It is shown that for curved cracks the usual procedure of the direct-current-pot ential-drop method underestimates the red crack extension. The same finite difference scheme is then used to account for conductive bars and bridges, which sometimes are left behind the crack front. Finally, the influence of side grooves on the potential drop is investigated.