Development of a method for the separate measurement of the growth of internal crack tips by means of the potential drop method

Under cyclic loading fatigue cracks can arise in the vicinity of the joints of clinched structures, which behave like internal cracks. In the simplest case, the two crack tips of an internal crack grow symmetrically to the joint and it is sufficient to measure the resulting crack length with the potential drop method. However, uneven growth of the two crack tips can also occur, so that the resulting crack is no longer arranged symmetrically to the joint. In order to be able to adequately monitor even an unsymmetrical propagation of internal cracks while the test is being carried out, a new general method has been developed with which the resulting crack length and the possible different propagation behavior of the two crack tips can be registered by simultaneously measuring two potential drops. The generality of the new method is verified by applying the method to two different specimen types. A specimen with a central hole and lateral cracks with different defined lengths is used to experimentally validate the method.