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Gravity Flow of Powder in a Lunar Environment (In Two Parts). 1. Property Determination of Simulated Lunar Soil.
NTIS: PB 203 654 :34 pages
This report investigates the mechanical behavior of fine soils in a lunar environment in engineering gravity-flow bins. The ultra-high vacuum, absence of moisture, and a lunar gravity one-sixth that of earth gravity represents a unique environment, both advantageous and detrimental to these systems. On earth, moisture and gases contained in powder masses can be responsible for complex descriptions of gravity flow. Their absence appear to simplify the lunar soil behavior. However, simulation of the lunar gravity and vacuum complicates the development of experimental data for designing bins. The properties of a dry soil powder, its behavior under one-dimensional compression, and its torsional and direct shearing strength under earth atmosphere are described in part 1 of this paper. These properties provide the parameters for a finite- element analysis to optimize the design of bins, to be described by Dr. William Pariseau in part 2. Shear tests assess the failure criteria for the material. Compression tests provide modules and (ko) stress-ratio values from the loading portion of the compression cycle, duplicating the condition of a bin at rest with the discharge closed. During the unloading portion of the compression cycle (soil overconsolidated), the residual ko values rise. It is postulated that this phenomenon creates a high-lateral stress in bins when they approach incipient flow. Assessment of the ko value, overconsolidation ratio, and the void ratio state is proposed as a criterion to determine the flowability of powder.
IH; Report of Investigation;
NTIS Accession No.
NTIS: PB 203 654
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division