Cratering and penetration experiments in teflon targets at velocities from 1 to 7 km/s

Abstract

We conducted impact experiments into TeflonFEP targets of widely variable thickness to assist in the interpretation of craters and penetration holes in the ∼20 m2 of thermal blankets that were exposed for 5.7 years in low-Earth orbit by the Long Duration Exposure Facility (LDEF). Soda-lime glass spheres of ∼3.2 mm diameter (Dp) were used as projectiles ranging in impact velocities (V) from ∼1 to 7 km/s.Teflon fails in a largely brittle fashion; substantial spall zones were developed at the target's front side, and especially at the rear side, if penetrated. Crater diameter (Dc) varies with V0.74. Penetration-hole diameter (Dh) depends on specific target thickness (T) and can be larger than Dc over a limited range of T(0.5 >Dp/T < 1.0), because rear spallation processes intersect the target's front at radial ranges larger than Dc. Dh becomes smaller than Dc at relative target thicknesses of Dp/T > 1, and systematically decreases as T decreases to eventually approach the condition were Dh = Dp at Dp/T > 100. Dh also increases with increasing V, yet the rate of increase depends on T, yielding a wide variety of velocity exponents that depend on Dp/T. The velocity exponent is highest for massive targets and decreases with decreasing T to approach the condition of Dh = Dp at Dp/T > 100, regardless of the velocity. The relationships of Dh, T and V are sufficiently systematic that unique solutions for projectile dimensions are possible from the diameter measurement of any penetration hole in teflon targets of any thickness. This renders the “calibration” of individual penetration holes equivalent to that of individual impact craters. Thus, improved analysis of literally thousands of penetration holes and craters in the LDEF thermal blankets seems possible.