Penetration experiments in aluminum and teflon targets of widely variable thickness

Abstract

A 5 mm light‐gas gun was used to fire spherical soda‐lime glass projectiles from 50 to 3175 μm in diameter (Dp), at a nominal 6 km/s, into aluminum (1100 series; annealed) and Teflon (TeflonTFE(R)). Targets ranged in thickness (T) from infinite halfspace targets (T≂cm) to ultra‐thin foils (T≂μm), yielding up to four orders of magnitude variation in absolute and relative (Dp/T) target thickness. This experimental matrix simulates the wide range in Dp/T experienced by a space exposed membrane of constant T that is being impacted by projectiles of widely varying sizes.Penetration hole size (Dh) decreases systematically with decreasing target thickness. Relative hole size (Dh/T) may be used to extract projectile diameter Dp from individual penetration holes in space‐exposed surfaces, provided one assumes an impact velocity. The condition of Dh=Dp mandates Dp/T≳50 in both targets. The ballistic‐limit thickness (TBL), at 6 km/s, occurs at Dp/T=0.29 for our aluminum, and at Dp/T=0.16 for the Teflon. While these thicknesses define the onset of physical perforation, they are not synonymous with the transition from cratering to penetration processes; this transition is gradual and occurs over a wide range of T. Consideration of the shock‐pulse duration (t) in both the projectile (tp) and target (tt) identifies the condition of tp/tt=1 as the real transition between cratering and penetration processes. This transition, at 6 km/s, takes place in our aluminum and Teflon targets at a Dp/T=0.83 and 0.62, respectively (i.e., at target thicknesses some factor of 2–3 thinner than the ballistic limit). Consideration of pulse duration is readily extended to impact velocities beyond those simulated in the laboratory; it may assist in understanding the velocity scaling of penetrative impact events.