Pressure Dependent, Infrared Emitting Phenomenon in Hypervelocity Impact

Abstract

A series of hypervelocity impact experiments were conducted with variable target chamber atmospheric pressure ranging from 0.9 to 21.5 Torr. Using a twostage lightgas gun, 5.7 mg nylon 6/6 rightcylinders were accelerated to speeds ranging between 6.0 and 6.3 km/s to impact 1.5 mm thick 6061T6 aluminum plates. Fullfield images of nearIR emission (0.9 to 1.7 خ¼m) were measured using a highspeed spectrograph system with image exposure times of 1 خ¼s. The radial expansion of an IRemitting impactgenerated phenomenon was observed to be dependent upon the ambient target chamber atmospheric pressures. Higher chamber pressures demonstrated lower radial expansions of the subsequently measured IRemitting region uprange of the target. Dimensional analysis, originally presented by Taylor to describe the expansion of a hemispherical blast wave, is applied to describe the observed pressuredependence of the IRemitting cloud expansion. Experimental results are used to empirically determine two dimensionless constants for the analysis. The maximum radial expansion of the observed IRemitting cloud is described by the Taylor blastwave theory, with experimental results demonstrating the characteristic nonlinear dependence on atmospheric pressure. Furthermore, the edges of the measured IRemitting clouds are observed to expand at extreme speeds ranging from approximately 13 to 39 km/s. In each experiment, impact ejecta and debris are simultaneously observed in the visible range using an ultrahighspeed laser shadowgraph system. For the considered experiments, ejecta and debris speeds are measured between 0.6 and 5.1 km/s. Such a disparity in observed phenomena velocities suggests the IRemitting cloud is a distinctly different phenomenon to both the uprange ejecta and downrange debris generated during a hypervelocity impact.