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

摘要

The equations used for calculating the crack extension from the change in the potential drop at a fracture mechanics specimen are generally derived for perfectly straight crack fronts. In the practice of fracture mechanics tests the crack,however, usually grows faster in the interior of the specimen 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 usualprocedure of the direct-current-potential-drop method underestimates the real 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, theinfluence of side grooves on the potential drop is investigated.