Experimental Investigation of Impact Flash Emission and Ejection Phenomena in Hypervelocity Impacts on Metals

Abstract A common feature of many high-velocity and hypervelocity projectile impacts is an intense burst of optical emission commonly called an impact flash. The impact flash can easily obscure observation of the earliest moments of projectile contact and penetration, making it somewhat detrimental to the experimentalist. However, the impact flash contains signatures of the earliest, most energetic processes at work during this critical phase and potentially offers valuable information for applications such as remote impact damage assessment. A multitude of mechanisms and interactions can contribute to the impact flash; a thorough understanding of the structure and nature of the flash generation itself under the experimental conditions of relevance is necessary to properly interpret any flash emission measurement. This work attempts to investigate the nature of impact flash emission for spherical impacts on metals under experimental conditions common to impact research experiments at the HyFIRE facility at Johns Hopkins. Time-resolved emission spectroscopy, photometry, and ultrahigh- speed multispectral imaging are used to identify the emission characteristics and structure of the radiating material. Under these conditions, the impact flash is observed to originate almost entirely from the rapid atmospheric ablation of jetted ejecta and debris.