Simulation of closure: Effects on crack detection probability and stress distributions

It is well known that partial contact of two rough crack surfaces will lead to transmission of an acoustic signal across the crack, thus giving rise to a reduced probability of detection (POD). To explore the effects and consequences of such partial contact, impression experiments--using small spheres--have been performed to determine the effects of contact area on the amplitude transmitted. The results have been compared with a theory described elsewhere in these proceedings. Based on the experimental results it will be speculated that the residual stress field responsible for the crack closure may be calculated based on a determination of the size and separation of the contact areas