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How to calculate composite modulus 2

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SunTrustFan

Mechanical
Joined
Jun 16, 2010
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Location
US
Hello,

I am currently working on a problem, and am having trouble calculating a value. I need to be able to calculate the composite modulus of a co-extruded tube (Nylon inner, TPU outer). The tube is being pressed into a Polycarbonate fixture, and I need to be able to calculate the composite modulus of the tubing in order to approximate the sress on the Polycarbonate fixture.

If anyone could help me come about how to calculate this value, I would appreciate it. Thank you!
 
look up "rule of mixtures" ... transform the section to a single E
 
Rb's method will get you close, and is the technique to start with, but I'd be a little leery of the results given that the two elements are not loaded in parallel, to borrwo an electrical term. A better result might come from modelling the two tubes via hand calcs (thick wall cylinders in plane strain or plane stress - exact solutions for your problem exist). The solution technique predates us all, it was used to figure out the autofrettage of big artillery cannons in WW 1. Or, you could use an FEA solver.
 
One more suggestion, since you are using polycarbonate - you have an opportunity to directly "read" the stress using birefringence patterns. Look thru a polarizing filter as the fixture is loaded/unloaded, count the number of moire lines...more stuff to google.
 
"photo-elastic" stress analysis ... outside the lab !
 
Rb,

You must've had the same labs we did at our uni. Aero dept. Now every time I see some clear plastic molded thingamabob, I'm always looking for my polarized sunglasses. And then people walk by my office wondering why I'm wearing dark glasses, squeezing a plastic gizmo and chortling. Well, wondering more than they usually do.
 
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