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# tube bending

## tube bending

(OP)
I want to use a hydraulic cylinder to bend a tube.  Is there a formula to use to calculate bend pressure of mild steel tubing.

### RE: tube bending

If you know your materials properties, then you can figure out what load it will take to exceed the yield strength of the tube.  This should be the theoretically correct force.  I would add a litle more to be certain, it bends.

sigma is in psi. so is the yield.

Let me know if you need anymore help.

### RE: tube bending

The above POST is recomending that you use the fexure formula for a beam in bending.

stress = Mc/I

M is the maximum Moment applied to the beam
c  is the centroidal distance to the top of the beam. Use tube radius
I is the moment of inertia for the tube. (pi/4)*(ro^4 - ri^4)

Look in your Machinery Handbook under Strength of Materials.

Don Leffingwell PE
dleffingwell@snet.net

### RE: tube bending

The formula referenced is applicable to bending up to the yield point of the material.  Beyond that point, plastic deformation (permanent) occurs and the formula will predict higher forces than actual which, if you are only sizing for worst case loads, should be acceptable.  Several other factors could affect your situation however.  The ratio of the bend radius to the pipe diameter will affect the loads and final shape of the bend pipe.  If the bend radius is too small, the pipe will buckle at the bend.  This ratio also affects the permanent deformation of the pipe and cracking can occur if any part of the bent pipe experiences strains in excess of its capability.  The loads are also a function of the amount of bend (degrees).  Most common steel has a relatively large region in which permanent deformation can occur without failure.  Some steels, particularly those that are high strength, have a smaller region and may crack during bending.  Pipe steels could fall into this range.  Steel tubing is designed for bending and the manufacturers will provide bending information.

Mike Van Voorhis
MJVanVoorhis@CS.com

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