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Impact Spallation Experiments: Fracture Patterns and Spall Velocities

Polanskey, Carol A. and Ahrens, Thomas J. (1990) Impact Spallation Experiments: Fracture Patterns and Spall Velocities. Icarus, 87 (1). pp. 140-155. ISSN 0019-1035. doi:10.1016/0019-1035(90)90025-5.

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Spall velocities were measured for nine experimental impacts into San Marcos gabbro targets. Impact velocities ranged from 1 to 6.5 km/sec. Projectiles were iron, aluminum, lead, and basalt of varying sizes. The projectile masses ranged from a 4-g lead bullet to a 0.04-g aluminum sphere. The velocities of fragments were measured from high-speed films taken of the events. The maximum spall velocity observed was 30 m/sec, or 0.56 percent of the 5.4 km/sec impact velocity. The measured velocities were compared to the spall velocities predicted by the spallation model of Melosh (1984). The compatibility between the spallation model for large planetary impacts and the results of these small-scale experiments is considered in detail. The targets were also bisected to observe the pattern of internal fractures. The series of fractures was observed, whose location coincided with the boundary between rock subjected to the peak shock compression and a theoretical “near-surface zone” predicted by the spallation model. According to the model, between this boundary and the free surface, the target material is expected to have received reduced levels of compressive stress as compared to the more highly shocked region below.

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Additional Information:© 1990 Academic Press, Inc. Received December 8, 1986; revised February l, 1990. We have benefited from technical discussions with Jay Melosh and technical reviews from A. Vickery and A. Fujiwara. We thank Peter Schultz for his assistance in utilizing the Ames facility. This research was supported by NASA Grant NGL-05-002-105. Contribution 4405, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California.
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Caltech Division of Geological and Planetary Sciences 4405
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Official Citation:Carol A. Polanskey, Thomas J. Ahrens, Impact spallation experiments: Fracture patterns and spall velocities, Icarus, Volume 87, Issue 1, September 1990, Pages 140-155, ISSN 0019-1035, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50902
Deposited By: Ruth Sustaita
Deposited On:28 Oct 2014 16:18
Last Modified:10 Nov 2021 19:02

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