Buckling of thin walled tube with external pressure

[cm603]

Hi all,

I'm new here so please correct me if I'm posting in the wrong place etc.

I have a car silencer which I'm effectively putting a hose clamp round and securing a heatshield. There is a thin wall (~0.1mm) surrounding insulation, which surrounds the actual exhaust pipe.

I want to work out if the hose clamp (when tightened to a specific force) will crush / buckle the silencer wall. I'm doing some FEA of the strip of tube in contact with the hose clamp, and I'm getting up to 1.5MPa stress, and very little deformation (of course, pressure is even all the way round).

Are there any other ways I can determine if the wall will buckle?

The wall material is not smooth, it's like an embossed heat shield

 

[TimSchrader2]

HELLO

If you did the FEA on a "STRIP" and not the full length that is a conservative assumption. 1.5Mpa is not too much. At first I was thinking you may need to do some buckling estimates, but for the looks of the picture it looks like is corragated, so will have a equivalent thickness that is more then .1mm. It should have the highest stresses at the bends in the corragation, which is tehnically a bending stress and not a true buckling of thin material. Not sure how deep the corragation is. Unless its pushing against the pipe then there is local buckling of the ridges of the corragation

 

[EdStainless]

One big issue is the uniformity of loading.
If your clamp dosen't fit smoothly this can lead to buckling.
Watch the hose clamp and make sure that the rigid piece under the screw fits the shape smoothly.
If you keep it round these loads should not be an issue.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[JStephen]

I would think the easiest and best way to determine that would be by actual testing.

 

[Compositepro]

Why are any calculations needed? The embossing of the heat shield allows it to survive extreme temperature changes without fatiguing due to CTE. The clamp will crush the shield until it touches and clamps onto the pipe or muffler. The embossing again make the contact "soft". So, no problem.

 

[cm603]

Thanks for all the replies!

TimSchrader2 I ended up doing some more FEA of the longer tube; fixing it at the ends where the diameter changes. The results were a bit more realistic looking here; the tube deformed at the clamp. I don't have much info on the corrugation as the exhaust comes from an external supplier, so I'm not too sure how I could approximate it here.

EdStainless in terms of non uniform load; I did end up adding a force directly down on the clamp contact area; to represent an acceleration (car going over a bump etc), which should also be a good indication of if the clamp was not evenly loaded.

JStephen we may end up doing that!

Compositepro there's a decent gap between this heatshield material and the actual pipe, as it's filled with some form of insulation. We can't really intentionally deform the outer wall in this case.

 

[3DDave]

A hose clamp doesn't have enough strength to damage the exhaust pipe. If there is going to be a problem it will be from differential thermal expansion as the exhaust pipe is exposed to a higher temperature change than the hose clamp does.

Of course, I am stupidly assuming you mean the sort of hose clamp that everyone else calls a hose clamp rather than a pipe clamp or any of the other 10,000 kinds of things that clamp around round things.

One factor you don't seem to appreciate is that the heated part of the exhaust will increase and decrease in length by a noticeable amount making axial fixity your major problem. By firmly clamping the heat shield in place you will also be clamping the corrugated sleeve in place, inducing loads that it was not designed to resist.

 

[EdStainless]

Dave makes a good point, make sure that you aren't clamping too many places too tightly.
With systems that see rapid cyclic heating and cooling you either have to allow motion and deflection, you will have it tear itself apart. The stresses have to go somewhere.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube