Microjet formation from the grooved surface of aluminum under shock waves with different pulse durations

The shock-induced microjet phenomenon has attracted much attention due to its importance in shock compression science and technology. The existing researches have shown that shockwave profile has a significant effect on the microjet formation. This work investigates the influence of shock pulse duration on the microjet systematically based on smoothed particle hydrodynamics simulations and theoretical analysis. In fact, when the pulse duration of shock wave is more than 7.31 times the time of shock front passing through groove, the microjet mass and its time-space evolution will be consistent with the case under supported shock. It is shown that there is a critical value for the shock pulse duration (about 4.21 times the time of shock front passing through groove), below which the effect of shock pulse duration is distinct. With decreasing the shock pulse duration, the mass from spike to bubble experiences a rapid increase due to the increase of the velocity gradient behind the free surface, while the mass from spike to the theoretical free surface experiences a gradual reduction because the shock energy reduces. As a result, the spike becomes very thinner and the bubble amplitude is lengthened. The damage will be localized around the groove region. Besides, with the interaction between the release stage of incident waves and the release waves from the groove, the cavities and different low-density fragments are observed.