Potential drop in the center-cracked panel with asymmetric crack extension

The well-known Johnson formula relates the electrical potential drop across a symmetric center crack in a current-carrying tensile panel to the crack length. To allow individual measurement of the crack growth at both ends of such a crack, the potential measured between contact points located on opposite sides and equidistant from the panel center line has been studied. Because this potential must ideally be identically zero for symmetric crack growth, it is termed the asymmetric potential. Its sign and magnitude are related to the direction and extent of asymmetric crack growth. It was found that contact points directly above the ends of the initial symmetric crack provide a signal which is well-suited to the determination of the asymmetry of the crack extension. This information is complementary to the total crack length information obtained using the Johnson formula. Experimental measurements and theoretical results were used to produce calibration formulae relating the asymmetric potential to the asymmetry of the crack dimensions in center-cracked panels. (orig.)