Wave Velocities in Granular Materials under Microgravity
Publication: Journal of Aerospace Engineering
Volume 20, Issue 2
Abstract
Velocities of primary and shear waves in granular materials are highly dependent on confining stress. These wave velocities are related to mechanical properties of the materials such as stiffness, density, and stress history. Measurements of the wave velocities using piezoelectric sensors provide scientists and engineers a technique for nonintrusive characterization of those mechanical properties. For aerospace engineering, measuring the wave velocities under microgravity, which simulates low loading and stress conditions, has a number of potential applications. It can help the understanding of the soil mechanics and the development of appropriate materials handling technologies in extraterrestrial environments, which will be crucial to meeting NASA’s future space exploration goals. This paper presents the technique and results of experiments conducted at NASA Glenn Research Center using the drop tower. Velocities of and waves in three sizes of glass beads and one size of alumina beads were measured under initially dense or loose compaction states. It was found that under microgravity, the wave signals were significantly weaker and the velocities were much slower. The material that makes up the beads has a strong influence on the wave velocities as well. The initial compaction state also has some influence on the wave velocities.
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Acknowledgments
The writers would like to thank NASA Glenn Research Center for providing support for the research described in this paper. They would also like to thank the engineers and technicians working at the 2.2 s drop tower for their technical support throughout the project. They are grateful to Heather Angel and Phi Thanh, students from Colorado School of Mines, for their assistance in conducting the drop tower tests.NASA
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© 2007 ASCE.
History
Received: Sep 7, 2004
Accepted: May 30, 2006
Published online: Apr 1, 2007
Published in print: Apr 2007
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