When a tube is being bent is the internal radius still in original length or the centreline is original length

My name is Gai Abraham, an automotive engineer trying to build a little LEV (low emission vehicle)





I have contacted you previously and I wish to ask further help on the bending of steel tubes.





Namely I have designed a chassis from bent steel tube, the technical sheet on S.S. astm 301 allows, depending on the hardness of the tube, to have elongations ranging from 40% (for annealed) up to 9% (for full hard) from original length.





The issue I am trying to solve is whether the original length is the midline of the tube, giving during bending, compression on the inlay and tension on the outlay for final plastic bending





or the original length is the inside radius of the curved tube and gradually all the tube stands deformation up to a maximum value on the outer side?





I think that if the tube is held in position and supported on the inside while curving it, the original length is the inside radius since it was not able to compress.





thank you


Gai


ga5aq@yahoo.com|||The inside will compress some. The outside with stretch a little more. And the tube will flatten slightly.


For most tolerance requirements the centerline length will work.|||in draughting the centre line retains the origin length





in practical terms the error is small





concentional :- (eg bending copper tubes up to 25 mm)


you need to bend a tube with the outside or inside held concentric with an internal or external spring