Surgical Tubing spring rate?

[Tom Line]

Can anyone give me a rough spring rate on the standard FIRST surgical tubing? Normally I'd just hook it up and measure it, but I don't have access to it right now. Thanks guys!

[meaubry]

Tom,
Surgical tubing comes in varying sizes - OD and wall thickness.
Therefore, the rate will be different depending on a few variables and it is not a single value.

Mike

[Tom Line]

I understand that. In this case, I'm talking about the standard surgical tubing that FIRST supplies with the KOP. More specifically, 1/4" ID, 3/8" OD, latex surgical tubing.

[Jared Russell]

I'll look it up, but it should be pretty easy to test if you have a sample.

Measure a length of surgical tubing, put a known weight on the end, and measure the length again.

F = kx

"x" is the difference in length with and without the weight.
"F" is the weight.

Solve for "k", keeping in mind your units.

EDIT: Just saw that you said you didn't have a sample. Nevermind then! I'm still looking.

[Jared Russell]

Bah, I swore that McMaster had it listed on their site.

Anyhow, I can tell you from my own experience that it is just about 10lbs/ft.

[tbuo1]

Go to this site:

http://www.primelineindustries.com/tools.html

You can find out everything you need using the (Force calculator) spread sheet. enter the size of your tubing, the spread sheet will do the rest. Good luck.

[Tom Line]

That is outstanding! Thanks for the hint on the website to go to.

[Tom Line]

That is outstanding! Thanks for the hint on the website to go to.

[kamocat]

I think this thread will be especially useful this year as it was in 2008.

I have the spreadsheet, and it's useful for approximate calculation, but I'm interested in something a little more exact.
Here's a screenshot of the calculator:
http://content.screencast.com/users/kamocat/folders/Jing/media/89b866b4-95c9-4e4e-b9db-4787c92d1e81/00000112.png

I see down on row 36 they have whited out some text that is labeled "PSI modulus for Primeline NR compound", containing the values 105, 154, 202, 331, 460, 1100, 2800, and 4400. This corresponds to 100-900% elongation - they multiply these constants by the "CSA" value to get the estimated force.

I didn't find anything matching that sequence at http://oeis.org/.

Looking at a curve fit of that function, it appears most likely to be an exponential function, rather than a power function or polynomial.
Does that make sense?

http://content.screencast.com/users/kamocat/folders/Jing/media/077ac84f-3b5b-4f42-8bbc-9e27e5de3d45/00000113.png


Also, I was testing a similar material myself (a resistance band), and achieved permanent deformation at only 300% elongation. (In this case, it was only 16lbs weight) It wasn't a huge visible difference, but it worries me:
At what point do you achieve permanent deformation with surgical tubing? Does any elongation whatsoever cause some deformation?

[pfreivald]

Also, surgical tubing doesn't follow Hooke's Law, FYI...

Modeling the behavior of rubber bands and the like was something one of my students got into a few years ago. I don't remember the details, exactly, except that Hooke's Law didn't apply.