clamping and torque - relation between the 2 ?

[321GO]

Hi dear all!

what i basically want to do is transfer a torque into a pipe true a form of (pipe)clamping (a suspension arm connected to the axle to be precise).

This clamp is clamping over a certain circumference @ a certain load (pre stressing the pipe).

1 st question: is there a way to determine what clamping force is needed for a certain amound of torque transfer.

2nd question: how exactly is the amound of clamping surface to be determined? Is a larger surface clamping area better? Or a smaller area (hig local pressure points)?
Does the car tire analogy apply here? The wider the better?

Request for enlightment..

 

[desertfox]

Hi

Yes there is a way to calculate clamping force to transfer a certain torque but you're question doesn't quite make sense to me is there any chance of a sketch

 

[321GO]

Hi desertfox,

at the moment i cannot scan, but let's say the clamping is similar to this:

http://r2.cygnuspub.com/files/cygnus/image/FMS/2008/DEC/495x330/airridesuspension_10124362.jpg

I gues the clamping induces Hoop stresses which lead to a certain tangential force, correct?

Hoop stress

http://en.wikipedia.org/wiki/Cylinder_stresses

sigma = F / tl -> F = sigma t l

This would imply that the clamping force F is directly related to the thickness "t" and the length "l" of the clamp, right?

Suppose a axle is clamped using u-bolts directly, can this equation than be used to optimise the u-bolts cross section, i.e. to enhance it's torque transmitting properties?

I know my question is vage. I'm trying to understand what makes a 'good' clamp connection. I mean i see a lot of clamping connections that also incorporate some sort of spline on the axle / in the clamp itself.

 

[desertfox]

Hi Again
I've uploaded a file how I would estimate the clamping force/Torque relationship.
I've assumed that friction is independant of area which is reasonable unless the clamping pressure is very high, your biggest problem will be obtaining a coefficient of friction which I suggest you obtain by testing.
You don't say how accurate you wish to be with the clamping/torque relationship.

desertfox

 

[321GO]

desertfox, thanks for helping me out here

Don't you think mu here is influencent by the geometry of the clamp you draw? like mutual surface area / pressure distribution?

Would a small area with large contact pressure perhaps be more beneficial due to local pipe deformation, creating local indentations in the pipe?

 

[desertfox]

Hi

If I understand you're situation them mu is all you have to hold the shaft from twisting unless the two components are precision machined its unlikely you will get an area of contact around the arc.
Without more detail about you're set up its difficult, you haven't told us any forces or what torque your trying to hold or transfer

 

[rb1957]

like desertfox has outlined, torque is transfrred by friction. if you know the torque and you know mu and you know the contact area, then you know the pressure you need to apply. can the tube support this ? if not, then change one of the inputs, most likely area.