Fracture Mechanics of Crack Growth During Sonic-IR Inspection

In past studies, we showed that cracks synthesized under carefully controlled conditions will propagate when subjected to sonic IR testing. The extent or severity of the propagation observed depended on several parameters including the stress intensity factor (which corresponds to crack growth rate) under which the crack was synthesized, the tightness of the crack closure, and the initial crack length. Furthermore, we showed that crack propagation during sonic IR testing occurs for 2024 aluminum, titanium and 304 stainless steel specimens. In this study, we extend the range of experimental conditions for synthesizing cracks to further elucidate their effect on the crack propagation, and we focus more specifically on the stress intensity factor. The stress intensity factor not only determines the rate of crack growth, but it has two profound effects on crack characteristics: the establishment of plastic zones around the crack tip and the variation of the topography of the mating crack surfaces. These two factors strongly affect crack propagation.