Dynamic Impact Over a Subsurface Crack: Applications to the Dynamic Tear Test

Dynamic fracture is often studied by means of the dynamic tear (DT) test, which involves transverse impact by a mass on a beam. This process generates a complicated elastic wave pattern in the beam which, however, consists of two wave types: impact waves and reflected waves. The former are the compression wave radiating from the impact line and its diffractions at the notch end, while the latter are all waves originated by reflections from the beam surfaces. To gain insight into the role of specific waveforms in generating the fracture at the notch end in this process, the effects of the impact waves on the dynamic notch end stress field is studied. For both an idealized and an experimentally determined impact force, these waves are shown to initially place the notch end in compression. Moreover, even when a tensile stress state is eventually achieved, the stress intensity factor levels lie well below experimentally determined fracture toughness values. These results suggest that reflected waves generate the fracture, which agrees with experimental evidence.