Thin Walled Tube around a 180deg bend

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    Bend Tube
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Discussion Overview

The discussion revolves around the structural integrity of a thin-walled polyimide tube subjected to UV exposure and mechanical loading during a manufacturing process. Participants are exploring the implications of the tube's dimensions, stress calculations, and the effects of UV degradation on its load-bearing capacity.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant seeks guidance on calculating principal stress, specifically questioning whether to consider hoop stress multiplied by two.
  • Another participant points out a potential conflict in the dimensions provided, suggesting that the wall thickness appears inconsistent with the outer diameter.
  • Concerns are raised about the tube's ability to support a load of approximately 4 kg, with one participant stating that hanging 10 pounds could cause collapse.
  • A clarification is made regarding the dimensions, with a participant confirming the outer diameter as 0.021 inches and wall thickness as 0.003 inches, asserting that collapse is not an issue as long as the tube can handle the load for a short duration.
  • Discussion includes the potential loss of load-carrying capacity due to UV exposure, with a worst-case scenario estimating a 33% reduction.
  • Another participant expresses skepticism about the tube's strength, suggesting that it may stretch under the applied weight but could still hold, provided there are no sharp edges that could cause tears.
  • Suggestions are made regarding the possibility of using a thicker-walled tube for increased safety margins.

Areas of Agreement / Disagreement

Participants express differing views on the adequacy of the tube's dimensions and its ability to support the specified load. There is no consensus on the calculations for stress or the impact of UV exposure on the tube's performance.

Contextual Notes

Participants note limitations regarding the clarity of the tube's dimensions and the assumptions about load duration and UV exposure effects. The discussion reflects uncertainty about the mechanical properties of the material post-UV exposure.

rogueracing
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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 :)
 
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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?
 
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.
 

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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.