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For Release: Sept. 18, 1996
FROM EARTHQUAKES TO SILOS, COAL TO DRUGS: SPACE MAY HOLD ANSWERS TO EARTH-BOUND PROBLEMS
Theres not so much as a grain of sands difference in the problems faced by earthquake-prone buildings, a prairie farmers silo, a West Virginia coal mine, a New York pharmaceutical company, or a sports utility vehicle careening the Colorado Rockies.
They all face problems caused by the interacting of a large number of similarly sized materials that range in size from pinheads to boulders.
And a better understanding of their problems may lie in the vastness of space.
Theyre all affected by the mysterious behavior of granular material -- whether it be sand, feed grain, crushed coal, powdered pharmaceuticals or blocks of rock -- under very low stresses.
For decades, scientists seeking to unravel the behavior of these materials under very low stress have been hampered by Earths gravity.
But scientists now believe the microgravity environment of space will allow them to see what really happens to granular materials under low-stress conditions.
During the current Space Shuttle mission they are looking for the answers that have for so long eluded them, using an experiment known as the Mechanics of Granular Materials.
Managed by NASAs Marshall Space Flight Center in Huntsville, Ala., the experiment will study the mechanical behavior of granular materials at very low stress levels -- the condition, investigators have found, that typically dominates when granular systems deform or collapse.
The experiments designers, Dr. Stein Sture, a professor at the University of Colorado at Boulder, and Dr. Nicholas Costes, a senior research scientist at the Marshall Center, have found a novel way to easily demonstrate this complex science to less-scientific Earthlings.
Costes rips open a bag of vacuum-packed coffee, exposing its brick-solid contents to air. Suddenly, the coffee grounds behave almost like liquid, shifting, collapsing and spilling from the bag.
Soil and other granular materials behave in much the same way. For what is so effectively demonstrated is a fundamental aspect of granular mechanics: A single shift in conditions can markedly change the properties of bulk material.
Look at what happens with the package of coffee. As air presses on the package from outside, coffee grains are pushed together inside the package and lock each other in place. These collective forces create a brick-like object.
But once the package is ripped open, releasing the pressures, the coffees grain assembly becomes very weak and soft, moving about freely -- much like a liquid.
To understand how such granular materials behave under low stresses, the Atlantis crew and researchers back on Earth will study three dry soil specimens under different pressures. In later missions, the specimens will be saturated with water, which cannot leave the specimens as they compress. The saturated specimens will be loaded, either by compressing them and then unloading them, or by subjecting them to "cyclic loading," a loading condition which is encountered in earthquakes.
"Testing granular material in a microgravity environment is a new and unique way of looking into the behavior of such materials under very low, confining pressures," says Costes.
And the consequences may be far-reaching: The results of the complete set of experiments aboard Atlantis and later missions could lead to improved selection and preparation of building sites, better management of undeveloped lands, and improved handling of materials in chemical, agricultural and other industries.
This research may be applied to a variety of other fields, including earthquake engineering, landslides, mining, soil erosion and the irreversible loss of enormous amounts of windblown, fertile soil.
Other fields that may benefit from the research include coastal and offshore engineering, off-road vehicle engineering, and the handling of granular materials such as grains and powders.
Sture and Costes believe one outcome of the experiment could be new methods to more effectively stabilize soils. For earthquake-prone areas, this could lead to more stable foundations for new buildings, as well as retro-fitting foundations of existing buildings.
The potential benefits of the research are myriad.
The University of Colorado researcher cites records that detail the collapse of hundreds of grain silos each year across the United States, representing great economic loss to farmers -- and great danger, as well. The key to a majority of these cases is the behavior of the grains.
"It is difficult to determine the pressures that the grain exerts on a silo," explains Sture. "The pressure can be highly non-uniform against a silos walls. Billions of grains form arches, with each arch holding the grains above it, where the pressure is tremendous. But the pressure may be next to zero below the arch."
It is when a farmer removes some of his grain from a silo -- and the grain is below the supporting arch -- that a dynamic collapse sometimes occurs, exerting tremendous pressures and instability.
"We would like to understand exactly what takes place," explains Sture, "so silos could be designed to be both economical and safe."
Findings from the Atlantis experiment may provide answers to this and other vexing questions. Just as behavior of grains in a silo can be unpredictable, so can any bulk, crushed material.
"The handling of coal, for instance, or powdered pharmaceuticals or detergents -- any material large in bulk before it is packaged -- may look simple," says Sture. "But it is very complex. Such systems designed to handle these materials, whether by conveyors or other methods, tend to jam up. Our research experiment will benefit all of these areas as we learn more about the behavior of pressure levels."
Even those who hop into a rugged, sports utility vehicle for a trek along the unbeaten path may one day see the benefits of the research by Costes and Sture.
Off-road vehicle engineers continue to study how tires interact with soil during motion, turning, slowing and braking. While were all aware of the importance of pressure inside a tire, the pressure levels under a tire, says Sture, "are very important and complex, too. Friction between the soil granules and the changing volume of the soil determine the behavior of the tires."
"This experiment," says Sture, "could lead to better-designed tires, better suspension systems and better vehicles."
The answers to many of our problems on Earth, its seems, lie in space.