(An abstract to be submitted to the NASA Workshop on Granular Materials
in Lunar and Martian Exploration to be held in NASA JFK Space Center,
Orlando, Florida during February 2-3, 2005).

**Mechanical and Structural Behavior of Granular Material Packed Beds
for Space Life Support System Applications**

by

Ramesh B. Malla^1^ and Ganesh Anandakumar^2^

Department of Civil & Environmental Engineering

University of Connecticut

Storrs, CT 06269-2037, U.S.A.

**[Abstract]{.underline}**

Long-term human mission to space, such as living in International Space
Station (ISS), Lunar, and Martian bases, and travel to Mars, must make
use of Advanced Life Support Systems (ALSS) to generate and recycle
critical life supporting elements like oxygen and water. Oxygen
Generation Assembly (OGA) and Water Processor Assembly (WPA), critical
components of ALSS, make use of series of granular material packed beds
for generation and recycling of oxygen and water. Several granular
materials can be used for generation, recycling, processing and recovery
of oxygen and water. For example, they may include soft bed media, e.g.
ion exchange resins for oxygen generation assembly and hard bed media
such as, activated alumina, magchem (Magnesium oxide) and activated
carbon to remove organic species like ethanol, methanol, and urea from
wastewater in Water recovery/processing assembly. These beds are
generally packed using a plate-spring mechanism to provide sufficient
compaction to the bed media throughout the course of operation. This
paper presents results from an experimental study of a full-scale, 38.1
cm (15 inches) long and 3.7 cm (1.44 inches) diameter, activated alumina
bed enclosed in a cylinder determining its force-displacement behavior,
friction mobilizing force, and axial normal stress distribution under
various axially applied loads and at different levels of packing. It is
observed that force-displacement behavior is non-linear for low
compaction level and becomes linear with increase in compaction of the
bed media. Axial normal stress distribution along the length of the bed
media decreased non-linearly with increase in depth from the loading end
of the granular media. This paper also presents experimental results on
the amount of particulates generated corresponding to various compaction
levels. Particulates generated from each of the tests were measured
using standard US sieves. It was found that the particulates and the
overall displacement of the bed media increased with decrease in initial
compaction of the bed media. This effect could be attributed to the
greater tendency for inter-particle sliding/rubbing due to smaller
internal friction angles, as seen from the shear tests, at lesser
initial compacted levels. Upon unloading, it was observed that there was
no change in displacement (especially rebounding) in the bed media. This
effect could be attributed to the fact that the porous activated alumina
particles fracture/break upon increase in applied load (during loading
phase) and occupy void spaces in between the material grains; thereby
leading to settling of the media. The load-displacement curve becomes
more linear with increase in initial compaction of the bed media. It is
concluded that compaction considerably affects the load-displacement
behavior of the bed media. A series of tests were also conducted on the
packed bed media to determine the force required to mobilize the
friction between the bed media and the housing cylinder. The results
from these tests showed the existence of significant friction between
the bed media and the encasing stainless steel cylinder. Further, it was
found that friction effects were more pronounced for media with higher
initial compaction. Internal friction of the granular media was measured
using direct shear apparatus. It was observed that the internal friction
increased with increase in initial compaction of the bed media.

In this study, a computational model (CM) is also developed using finite
element software ANSYS to verify experimental results obtained for the
distribution of the axial normal stress and axial displacement along the
length of the full-scale activated alumina bed media. In the
computational model, the granular material is considered to have
appropriate failure and frictional contact exists between the wall and
the granular media. It is observed that the model predicts results
closely with the experimental method. The computational results show
that the axial normal stress distribution along the length of the
activated alumina media decreases non-linearly from the loading end and
is negligible beyond a certain depth. This can be attributed to the
existence of friction between the walls and the media and that the
friction takes up most of the applied load.

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^1^Associate Professor, Department of Civil & Environmental Engineering,
261 Glenbrook Rd, Unit-2037, Storrs, CT 06269, U.S.A. Tel: (860) 4863683
Fax: (860) 486-2298; Email: mallar@engr.uconn.edu (**Corresponding
Author).**

^2^Graduate Research Assistant, Department of Civil & Environmental
Engineering, 261 Glenbrook Rd, Unit-2037, Storrs, CT-06269, U.S.A.;
Email: anandg@engr.uconn.edu.