Application of Digital Particle Tracking and Schlieren Imaging to Study Debris Cloud and Shockwave Formation During Hypervelocity Impacts

Abstract

The study of hypervelocity impacts (HVIs) is of increasing interest in numerous engineering applications involving micrometeoroids, orbital debris, hypersonic vehicles, and hypervelocity weapons systems. The associated relative velocities are typically in excess of several kilometers per second. The experimental and modeling studies of HVIs are instrumental in damage estimation and designing protective armor for personnel and hardware. In typical HVIs, debris clouds are formed at the front and rear of the target and propagate outwards. By unraveling the physics of these debris clouds, it is possible to gain a fundamental understanding of the energy of the impact, energy absorption and dissipation, and material failure mechanisms. Such knowledge also helps to determine the feasibility of materials for protective applications. Innovative optical diagnostic techniques can be applied to study the temporal and spatial evolution of these debris clouds. In this work, we use digital particle tracking and schlieren imaging to analyze HVIs produced by a two-stage light gas gun that can launch metal or polymer projectiles of 2–10 mm in diameter at speeds of 2–8 km/s. The target material in these experiments is ultra-high molecular weight polyethylene (UHMWPE). A dynamic delay generator system was developed to obtain synchronized ultra-high-speed videos at frame rates greater than 1M fps of the formation and expansion of the debris cloud. A particle tracking code enables the estimation of particle size and velocity from these videos. Additionally, a lens-type schlieren imaging system is used to track the density gradients produced by the shock waves formed by the fragments. These results are vital to better characterize, develop, and validate materials failure models during HVI events.