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Wave Velocities in Granular Materials under Microgravity

机译：微重力作用下粒状材料的波速

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摘要

Velocities of primary (P) and shear (S) 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 2.2 s drop tower. Velocities of P and S 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.
机译：颗粒材料中的主波（P）和剪切波（S）的速度高度取决于围压。这些波速与材料的机械性能有关，例如刚度，密度和应力历程。使用压电传感器测量波速为科学家和工程师提供了一种非侵入式表征那些机械性能的技术。对于航空航天工程而言，在微重力下测量波速（可模拟低载荷和应力条件）具有许多潜在应用。它可以帮助理解地球外的土壤力学并开发适当的材料处理技术，这对于实现NASA的未来太空探索目标至关重要。本文介绍了使用2.2 s落塔在NASA Glenn研究中心进行的技术和实验结果。在最初的致密或疏松压实状态下，测量了三种尺寸的玻璃珠和一种尺寸的氧化铝珠中的P波和S波的速度。发现在微重力作用下，波信号明显较弱，速度较慢。组成磁珠的材料对波速也有很大的影响。初始压实状态对波速也有一定影响。

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