More compression strength tests of recrystallized candy
8/20/01
Click here to visit my previous work on this topic.
Or click here to jump down to the work of 8/22/01
On the way home from work, I purchased the cheapest digital bathroom scale K-Mart was willing to sell me, and arranged to use it to measure the pressure needed to cause compression failure of my 1-1/2 inch cylinder of recrystallized candy.
I used the same sample as on 8/18 and 8/19, which had already been subjected to weights of 66 pounds (concrete foundation block) an estimated 165 pounds (me) and an unknown weight (see yesterday's submission for that comedy.) The sample was compressed about 8 percent during these tests, but did not break.
As a test for my new scale, I put myself on the big scale at the supermarket, which read 167 pounds. At home, the new scale read 168 pounds while I was wearing the same clothes, shoes, and pocket lint but that makes perfect sense: attempting to solve my weight problem, I had consumed about 2/3 of a 7 ounce bag of Cheetos. That should put on at least a pound, so the dieters tell me.
Here is today's rig:
I have placed the scale on a board under the seat-stay of my picnic table, placed a bottle-jack on the scale, and piled heavy stuff on the table: the foundation blocks, a few assorted bricks and a medium-sized cat. Unfortunately, cat-weight was an uncontrolled variable in these tests.
The candy sample is placed on top of the jack and under the seat-stay,
so that it will be compressed against the weight of the table. This
way I can keep an eye on the scale as I operate the jack. Hopefully
I will be paying attention when the sample fails.
Well, the table was lifted off the ground, both feet. The scale read 265 pounds at this point. I let it stay there for about a minute.
I let everything down and measured the sample, which is now 1-5/8 inches long - compressed a bit from the previous test.
Now I pile every massive nearby thing on the table. I found two cinder blocks hiding under potted plants.
I jack it up again. The scale maxes out at 300 pounds. The table rises off the ground. I let it sit like this for a full minute, then gave everyone some relief. The blocks were weighed separately, my totals indicate that the sample was supporting 338 pounds at this point.
In case you were wondering, this clever scale zeros itself when you turn it on, so that the weight of the jack (17 pounds) is not counted. But I wonder if this much tare weight affects the accuracy of the scale.
I also wonder what kind of pressure sensor the scale uses, and if it might be adaptable as a rocket-engine thrust-gauge: might have to open it up...
Beautiful day...beautiful day.
Back in the house, the scale weighed me in at 167 pounds, indicating that it had not been damaged by these tests. Apparently I had lost my newly-gained weight. Guess I should have had a beer to "set" the Cheetos.
The cylinder is now 1-9/16 inches in length, decimal 1.56. Today's events have shortened it by about 12%. It is now 18.6% shorter than it was before compression tests started on 8/18.
In my last submission, I assumed that the sample would break with any weight greater than my own, which I estimated to be 165 pounds. Today, it sustained a weight over twice that, held it for more than a minute, and still has not broken, cracked, or suffered anything more than perhaps a migraine.
Obviously, more compression tests are required. I am considering other methods, and shall attempt to beg or borrow a substantial press. It would be interesting to see if the sample cracks, shatters, or simply continues to deform as greater pressure is applied.
Other forms of stress tests might be performed, as compression is not the only stress to which fuel might be subjected in a rocket engine. I encourage suggestions as to other tests I might perform. I would also like to see comparisons made with other fuels. Is data available on different fuels? Please let me know where I might find it.
But for now, I suggest that "low compression strength" be moved down
lower on the list of limitations for this type of propellant, at least
for fuel made by the recrystallization process.
More compression tests using same sample, 8/22/01
Overnight, I thought of another substantial weight that could be placed on the picnic table, and it would not require me to risk a hernia, just my life. So I assembled the same constellation of blocks, bricks, slabs and rocks as used before, and jacked up the table with the candy sample in the middle. The cat was unavailable.
The second picture shows me getting into position - the camera came a bit too soon. I moved forward and crouched over the blocks so that my weight was directly over the candy sample, best I could judge. I cowered in this position for a full minute.
At this point, the candy was supporting about 508 pounds.
The sample did not crack, break, chip, or hurl epithets. It did deform some. It is no longer a 1-1/2 inch cylinder, but 1-3/4 inches in diameter. Its length is now almost exactly 1-1/2 inches, about 22% shorter than when these tests began.
And yes, those blurry specks on the counter are tiny ants. Perhaps we should add one more item to the list of limitations for this type of fuel.
I look forward to hearing any and all comments, questions or suggestions.
Sincerely,
Jimmy Yawn
jyawn@sfcc.net
8/20/01
rev. 8/22/01