If a hydraulic steel tube of diameter 10mm and wall thickness 1.5mm is bent to a radius of 100mm how can I work out the reverse radius of curvature needed to straighten the tube?

I believe the only way to straighten the tube will be to apply a reverse bending moment at each end of the tube. As the tube has yielded and undergone plastic deformation then the only way to straighten this will be to 'overbend' it past straight; otherwise it it will elastically spring back to a slightly less radius of curvature (assuming that it has started to see plastic deformation again).

What I need to do is find away of ascertaining the amount I need to overbend it by. If I work out the strain required to straighten the beam then what needs to deternmined is by how much the strain needs to be exceeded by to achieve a straightened tube.

mechtr450

what are you trying to accomplish?
the tube has stretched & compressed. the outside radii has thinned wall thickness, & the inside is now compressed.
Depending on the material, The tube will need to be annealed or it will crack.
This is to my opinion a trial & error situation.
the tube is probably scrap.

mfgenggear

Agree - unless it is made out of gold or the last piece of pipe on the planet. - scrap it. You will never get right - maybe slightly close

This is most likely a futile effort. But assuming you HAVE to do it. Anneal the tube first, insert a bending spring into the tube, then start straightening using 4 degrees of springback first. Fine tune this as you get closer to straight, using U blocks, a straight edge and a press for final straightening. Good luck with this.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

Do you really think you can straighten a tube for less than the cost of a new one?

All many thanks for the replies.

This is purely a theoretical exercise so I have made the assumptions that the tube undergoes pure bending and doesn't not have any irregularities along the wall thickness where a plastic hinge may form.

I do agree though that if this was a real life situation then the tube would be scrap. I'm just looking for some pointers as to where to start with the theoretical workings. If its easier to invisage the dimensions of the tube can be whatever they want.

Theoretically I would grab each end and stretch the tube until the entire thing yielded. In reality it can not be done (unless you melt it and recast it :).

HDS, that would be the equivalent of applying an axial force which in theory would mean an infinite amount of force needed to ensure that it became completely straight? By applying a moment at each end of the tube then surely it can be worked out by how much it needs to be overbent by?

When you say this is "purely a theoretical exercise" -- is this a polite way of saying this is a classroom assignment?

Patricia Lougheed

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