Two-laser experiments to reproduce hypervelocity impacts on graphite at high temperature

Hypervelocity impacts (HVI) with millimeter or submillimeter projectiles can strike aerospace structures with relative velocities of several km/s. In the present paper, the effect of temperature, in the range of 300 to 3600 K, on the size of the craters produced by HVI on graphite targets is studied. This study was made possible by the development of an original experimental setup based on the use of two high-power lasers: a nanosecond shock laser delivering up to 40 J to simulate impacts of 260 µm diameter aluminum projectiles at velocities ranging from 2 to 4 km/s, and a continuous-wave heating laser in order to reach very high temperatures with a brief heating time and well-controlled heating ramp. This study shows that maximum depth and diameter of craters do not vary with the temperature up to 3400 K, but a slight increase of the crater volume is observed. It is explained by a more complete formation of the crater at high temperature. This behavior was not clear up to now in the literature, probably because of the effect of sublimation at high temperature which can be taken into account by the present methodology. Beyond 3400 K, a rapid decrease of crater dimensions is observed.