High-speed photography and stress gauge studies of jet impact upon surfaces

Experiments were conducted to investigate the mechanisms of damage to brittle materials by liquid–jet impact as seen in cavitation or simulated rain erosion. In this work, a liquid–jet of 3 mm in diameter and speed ca. 600 m s-1, produced using the single–impact jet apparatus (SIJA), was impacted on a polymethylmethacrylate (PMMA) target, chosen as a representative brittle solid. Damage was produced by the liquid jet both near the surface of, and within the bulk of the target. These failure phenomena, which proceeded in several stages, were observed in detail by means of a high–speed camera and with the aid of schlieren visualization techniques. The damage introduced resulted from the interactions of stress waves (compressive, tensile and shear) within the target. A surface ring crack was produced behind a propagating release wave. A central crack along the axis of the jet was also produced by interaction of these waves and, in the case of targets of finite thickness, spall damage was observed at the rear surface. A further crack was opened by the interaction of a shear wave with a reflected release. All the failure mechanisms resulted from wave interactions induced in the target and occurred within a few microseconds of impact.