Theoretical and experimental study on the hypervelocity impact induced microjet from the grooved metal surface

The dynamic process of the hypervelocity impact induced microjet from the grooved metal surface is studied theoretically and experimentally. Based on shock wave theory and Bernoulli's equation, a physical model is proposed to theoretically analyze the formation process of the microjet and predict the spike (head) velocity of the microjet. The hypervelocity impact experiments of the cylindrical aluminum projectile on the metal target with grooves are conducted through two-stage light gas gun, and the sequence shadowgraphy images of the microjetting formation are recorded by using Ultra-high-speed camera. Then, the numerical simulations of the hypervelocity impact-induced microjet are performed by a self-developed SPH (smoothed particle hydrodynamics) code to examine the velocity distribution, mass distribution and density distribution in detail. These numerical results are compared with those obtained by experiments and theoretical analysis, which verifies the validity of numerical model. The numerical results reveal that the front of the shock wave generated by hypervelocity impact is not strictly planar in the target due to the shock wave releasing from both sides of the impact interface. Thus, the shape of the multiple jets generated from the grooves resembles a “trident”, and the upper microjet and the lower microjet deflect upward and downward respectively. The jetting velocity and mass of the middle microjet is larger than that of the microjets on both sides in the impact area. Last, the variation of the spike velocity and jetting mass with the impact velocity and the target thickness is obtained.