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Craters in aluminum 1100 by soda-lime glass spheres at 1 to 7 km/s

1995; Elsevier BV; Volume: 17; Issue: 1-3 Linguagem: Inglês

10.1016/0734-743x(95)99836-g

1879-3509

Ronald P. Bernhard, Friedrich Hörz,

Space Satellite Systems and Control

To assist in the interpretation of crater populations on space-exposed surfaces from the Solar Maximum Satellite and the Long Duration Exposure Facility (LDEF), we conducted laboratory simulations of cosmic-dust impacts into aluminum 1100 targets with ∼3.2 mm diameter soda-lime projectiles at velocities (V) between 0.7 to 7 km/s. The resulting crater diameters (Dc) conform to current cratering equations, while crater depths (Pc) are somewhat deeper, yielding typical Pc/DC ratios of 0.58 at V > 6km/s. Similar values (Pc/Dc > 0.55) are found forcraters in aluminum surfaces retrieved from the Long Duration Exposure Facility, which were produced at impact velocities as high as 20 km/s. The value of Pc/Dc = 0.5 that is being used: by many should be abandoned; a Pc/Dc = 0.58 is recommended. Similarly, we demonstrate that mass loss of the target, as determined by pre- and post-shot weight measurements, can be almost an order of magnitude less than mass losses that would be inferred from crater-volume measurements. This difference is due to substantial internal deformation of the target which permits large volumes of material to be deformed, and displaced without physical ejection and dislodgment. In addition, this study traces the behavior of the glass impactor. At V < 1.5 km/s a complexly deformed and sheared projectile resides within the crater cavity. The first projectile melts appear at ∼2.2 km/s, and mixtures of melt and debris start creeping up the crater walls at > 2.5 km/s. The radially expanding melts develop, by geometric dispersion, into thin films that tear, leaving a discontinuous melt deposit upon cooling. At V > 5.5 km/s the entire impactor is essentially molten; however, small quantities of unmelted residues still can be found at 7 km/s. Increasingly larger fractions of melt escape the crater between 5 and 7 km/s. Only modestly higher velocities would be needed to have the entire projectile escape the crater. This appears to be the case for ∼ 50% of all LDEF craters which lack detectable residues at sensitivity levels of Scanning Electron Microscopy - Energy Dispersive X-Ray analysis.