Hypersonic impact flash characteristics of a long-rod projectile collision with a thin plate target

Impact flash occurs when objects collide at supersonic speeds and can be used for real-time damage assessment when weapons rely on kinetic energy to destroy targets. However, the mechanism of impact flash remains unclear. A series of impact flash experiments of flat-head long-rod projectiles impacting thin target plates were performed with a two-stage light gas gun. The impact flash spectra for 6061 aluminum at 1.3–3.2 km/s collision speeds were recorded with a high-speed camera, a photoelectric sensor, and a time-resolved spectrometer. The intensity of the impact flash exhibited a pulse characteristic with time. The intensity (I) increased with impact velocity (V₀) according to I∝V₀ⁿ, where n = 4.41 for V₀ > 2 km/s. However, for V₀ < 2 km/s, n = 2.21, and the intense flash duration is an order of magnitude less than that of higher V₀. When V₀ > 2 km/s, a continuous spectrum (thermal radiation background) was observed and increased in intensity with V₀. However, for V₀ < 2 km/s, only atomic line spectra were detected. There was no aluminum spectral lines for V₀ < 2 km/s, which indicated that it had not been vaporized. The initial intense flash was emission from excited and ionized ambient gases near the impact surface, and had little relationship with shock temperature rise, indicating a new mechanism of impact flash.