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AEM Microgravity Materials Team


Team Name: Metrology Junkies

Supervisor: Dr. Thomas Shield
shield@aem.umn.edu 612-626-7793


Effects of Microgravity on Random Close Packing Arrangements


ABSTRACT:

The packing of spheres in a box can be used to model the packing of particles in a composite material. Our experiment will provide physical data concerning the volume ratio of ball bearings in a box as one of the box’s walls is moved inwards. By measuring how the volume ratio varies with the wall velocity, we will determine a relationship between wall speed and average packing volume ratio at the system’s maximally jammed state. We will then compare this relationship to the current computational models of random close packing. By conducting this experiment in microgravity, the biasing effects of gravity can be considered negligible, as the computational models require.


EXPERIMENT DESCRIPTION:

The experiment consists mainly of about 5,800 one-quarter inch diameter steel ball bearings within a 4"x4"x8" box made of 1/4" LexanŽ. One wall of the containment box is attached to a pneumatic cylinder so that the wall can be moved inwards to create a minimum containment dimension of 4"x4"x4". A secondary outer wall, made of 1/8" LexanŽ, surrounds all experimental components, excluding the laptop computer. This outer wall ensures that, should the moving wall or any other portion of the inner box fail, the steel ball bearings will not disperse themselves into the aircraft, possibly endangereing the safety of those onboard.

The movable wall is driven by a pneumatic cylinder that compresses the balls until the maximum packing factor has been reached. The cylinder has a stroke length of 10 inches. A pressure transducer will be used to measure the exact pressure within the cylinder during the compression. This data will be sent to a laptop computer via a data acquisition card. The velocity of the wall can be controlled by using one of three three-way valves that are mounted on the outer containment box. The three-way valves are connected to needle valves that control the flow rate into the pneumatic piston. The final piece of this pneumatic setup is a pneumatic jet that is inset into the inner LexanŽ box. This can be fired briefly just before the onset of stable micro-gravity to randomize the ball bearings.

A linear potentiometer will measure the total distance that the wall moves. A Linear Variable Differential Transducer (LVDT) will also be used during the last inch of wall travel to allow precise calculation of the sphere packing ratio. The potentiometer and LVDT will represent the distances with voltages. These voltages will be sent through the data acquistion card and recorded by the laptop.

A digital camera will be used to record all of the data on a video stream. In addition to providing a good visual understanding of the jamming procedure, the camera will also act as a backup data acquistion system. A ruler will be attached to the LexanŽ box in the field of view of the camera, providing a backup distance measurement to the potentiometer and LVDT. Similarly, an analog pressure gauge will be placed in the FOV of the camera to provide a backup pressure measurement to the pressure transducer.


THE TEAM:



Top Row: Bryan Henneman, Ryan Wold, Professor Tom Shield, Dave Kubat.
Bottom Row: Jenni Bonin, Adam Creuziger, Richard Russell


This year's team members are:

CURRENT WORK:


26. APRIL 2002:
Tremendous appologies for the delay in updating the website. The team flew down to Houston, TX on April 3 and returned on April 12. Truly, the trip was an experience of a lifetime from beginning to end. We would like to offer endless thanks to the wonderful people at NASA as well as our own AEM department for allowing us this terrific opportunity.

Here are some NASA-oriented highlights of our trip, including some of the pictures that NASA took before and during our two flights. Thanks once again to the NASA camera people. I will attempt to put some of our own pictures online once we get them scanned in...

Chamber Flight:
Prior to going up in the KC-135, every student needed to pass a physiological training course in NASA's pressure training chamber. The Chamber is basically an enclosed room in which the air pressure can be accurately controlled. Each student is seated in the room and given an oxygen mask. Once everyone has their mask on, the Chamber is "taken up to 25,000 ft." In actuality, the room does not move. Rather, the air pressure is lowered to a level like that at 25,000 ft altitude. And then they ask you to take off your oxygen mask for five minutes...

Please note that at above about 10,000 ft, surplus oxygen is needed to allow for typical physical and mental behavior.

At 25,000 ft, each student noticed some aspect of hypoxia -- the deficiency of oxygen in the body. For some, this only resulted in discomfort, dizziness, or tunnel vision. For others, the effects included severe mental impairment, shaking, or loss of awareness of their surroundings. As the test intended, each individual recognized his own symptoms, whether large or small.

The "Snoopy" masks we got to wear were probably the most amusing visual part of the Chamber Flight...



Ryan, Shirin, and Bryan, wearing their fancy headgear.



Phil, Nenad, and Jenni masquerading as elephants.

Test Readiness Reviews:
On Monday the 8th, the Test Readiness Reviews (TRR) were held. The TRR involved perhaps a dozen NASA personnel asking questions concerning the construction and safety of the experiment. Fortunately, our experiment passed with flying colors.



The experiment under scutiny


Team leader Bryan strutts his stuff


Flight I:
On Tuesday, April 9, the experiment -- and the experimenters -- got their chance to fly in zero gravity. Overall, things ran alright. The data acquisition system took too long to run, and needed to be tweaked for the next day's flight, but the experiment itself ran well. As for the experimenters...



Bryan and Jenni smile at the camera -- who needs the floor!?



The best positions to run the experiment in!


Flight Team I: Jenni Bonin and Bryan Henneman

Flight II:
With only a few minor adjustments needed, team and experiment were ready for a second day of testing on April 10. The experiment ran flawlessly. More important for the experimenters, for the second day in a row, the University of Minnesota fliers all kept their lunches inside...



"No hands!" says Dave with a laugh.



After much experimentation, Ryan finds the ceiling of the KD-135!



Flight Team II: Dave Kubat and Ryan Wold


And the experiment?
Overall, the experiment ran remarkably smoothly. Although the data analysis is incomplete, we believe that there is some packing improvement in the balls under microgravity compared to Earth gravity. Future analysis will show how much, and whether the speed of packing affected this packing ratio.



The fully packed state in zero-gravity.



In microgravity, the stir jets helped randomize the balls, sometimes even pushing them to the top of the containment box.




Click here to check out our PAST WORK on the project!


 


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