Energy distribution characteristic of impact flash of metallic target impacted by hypersonic projectile

The impact flash as a physical phenomenon of hypervelocity impact has been widely studied for decades, but these ballistic impact researches related to impact flash of low-mass particles were mostly concerned with hypervelocity impact at a speed beyond 4 km/s. In comparison to the substantial literature on light emission from hypervelocity impact events, our knowledge of light signatures from hypersonic impact is relatively limited presently, especially for those occur in air and associated with explosively accelerated fragments, which typically have maximum velocities in the range of 1-2 km/s. This study attentively investigates the impact flash generated by hypersonic projectile impacting metallic targets from the perspective of energy distribution. Firstly, series of hypersonic impact tests were conducted using the two-stage light gas gun, and the wavelength-resolved flash signals and optical data in the band of 200-1000 nm under different impact conditions were simultaneously measured, where the target plate made of 6061 aluminum, pure aluminum and 45 steel were impacted by projectiles made of the same material over a velocity range of 1-2 km/s, and the ambient pressure (AP) varied from 100 Pa to 105 Pa. The flash signal composed of components of low frequency with high amplitude and high frequency with low amplitude was split. The cumulative integration of flash intensity over the wavelength range was calculated to derive its energy distribution. Besides, the probability distribution characteristic of flash intensity was obtained through computing its probability density function. The influences of impact velocity, ambient pressure and target parameter on energy distribution of impact flash were discussed. The above research findings may promote deeper understanding of the energy release and transition of hypersonic impact process.