Thin Walled Tube around a 180deg bend

[rogueracing]

Hey guys any help you can help me solve a problem at work. I've been UV testing some polymide tubing and I need to know if it will survive one of our manufacturing processes post UV exposure. The OD is 21 (0.91 mm) thou and wall thickness is 3 (6.4 mm) thou. It will be loaded with approx 4kg, say 40N around a 180 degree bend/support of 50 mm in diameter. Now in looking for the principal stress am I looking for hoop stress * 2? Been a long day not sure why I am struggling with this one some direction would be lovely. Thanks boys n gals :)

 

[etudiant]

The dimensions need a check, 0.91 mm OD conflicts with 6.4 mm wall thickness, although 3 thou (mil?) thickness works with 21 thou OD.
Hanging 10 pounds on a thin polyimide tube will cause it to collapse. Is that an issue?
Is the tube supposed to be load bearing or is the question about internal pressure? What is the extent and duration of the UV exposure?

 

[rogueracing]

Sorry about the dimensions, I was just leaving and typed it in haste. 0.021'' OD with 0.003'' wall thickness. The tube will have a mandrel line inside, collapse is not an issue as long as the tube does not fail in being loaded with the 4kg for a short period of time on both sides. I am still working out the UV exposure but worst case scenario we are looking to loose a max of 33% in original load carrying capacity. The question is about the resulting stresses as it is in the jig and how the load is distributed.

I have attached a quick sketch to give you an idea. Thank you!

PS: Attached picture should be CW 90 degrees.

 

[etudiant]

So we have a plastic tube effectively holding about 20 pounds (2 x 4kg, with a 1/3rd capacity cut).
I'm still iffy on the tube dimensions, .003' is 3/1000 foot is about .91mm wall thickness and .021' then is the OD, about 6.4 mm, about a quarter inch.
If that is correct, it is a pretty puny tube, which I expect would surely stretch with the weight applied, but should hold, provided there are no sharp clips holding it which could start tears.
As long as some stretching is ok for your application there should be no problem, but if you need more margin, a 2 mm or thicker walled tube would give much more leeway.

 

[alphy]

Hello, thank you for reaching out for help with your problem. I understand the importance of ensuring the durability of materials during manufacturing processes. In this case, it is important to consider the stress and strain that the thin-walled tube will experience during the manufacturing process.

To determine the principal stress, you will need to consider both the hoop stress and the longitudinal stress. The hoop stress is the stress that is perpendicular to the longitudinal axis of the tube, while the longitudinal stress is the stress that is parallel to the longitudinal axis. In your case, the hoop stress will be the main concern as it is the stress that will be acting on the tube wall.

To calculate the hoop stress, you can use the formula: σ = PD/2t, where σ is the hoop stress, P is the load applied, D is the diameter of the tube, and t is the wall thickness. In this case, the load applied is 40N, the diameter is 50mm (0.05m), and the wall thickness is 6.4mm (0.0064m). Plugging these values into the formula, we get a hoop stress of approximately 625MPa.

It is also important to consider the yield strength of the material to determine if it can withstand this level of stress. If the yield strength is lower than the calculated hoop stress, then the tube may fail during the manufacturing process. I recommend consulting with a materials engineer or conducting further testing to ensure the safety and durability of the tube.

I hope this information helps guide you in the right direction. Good luck with your work!