Measurement of plasma for elucidation of crater formation mechanism on aluminum foam under high speed impact

Abstract

It has been reported that when a high-speed projectile collides with aluminum foam, a unique crater with a narrow entrance and large cavity is formed, shaped like a turnip. In the case of a material with higher porosity, it is considered that a debris cloud is produced by the impact, and the crater is created by scattering the debris cloud inside of the target material. In addition, melting traces have been observed, and it is predicted that these are caused by the heat created by the impact. It is conceivable that the temperature of a plasma induced by high-speed impact is associated to indicate the temperature at impact, although this relationship has not yet been proven. Measuring temperature at impact point is difficult since the measuring device will have to avoid collision with the projectile. Therefore, it is essential to measure plasma apart from impact point and observe diffusion of plasma. In this paper, high-speed impact experiments in which plasma was measured with a triple probe and a high-speed camera was performed to confirm the above. The high-speed impact experiment was performed with a vertical gas gun at Ritsumeikan University's Impact Engineering Laboratory. The impact speed was 400 m/s, and the target material was A5052. The high-speed camera had a maximum frame rate of 1.4 Mfps and a minimum exposure time of 1.0 μs. Plasma signals were measured by the triple probe method, and at the moment of impact, the flash was recorded by the high-speed camera.

Keywords

• high-speed impact
• plasma
• triple probe method
• temperature
• aluminum foam
• crater