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SPRING BACK OF TUBES

SPRING BACK OF TUBES

SPRING BACK OF TUBES

(OP)
Hi,
I've come across numerous sites telling you how to calculate the springback in sheet metal when formed in a die.  But my problem is this: I need to know if there is a formula for calculating the spring back of a length of tube when,

A:It is forced through a die to reduce it's O/D, and,
B:It is drifted to increase it's I/D.

I know how to calculate interface pressures between the tool and the tube, and I know how to calculate the change in length of the tube. It is just this formula that is eluding me.  I can't find it in Roark's or Shigley either.

Can anyone point me in the right direction.

Conrad.

RE: SPRING BACK OF TUBES

Try using finite element analysis methods. The stiffness Matrix(K) is determined by the formula:  

K=EAL/2*B*BTRANS

E is modulus of Elasticity
A is Cross sectional area
L is length of the element

B is  directional vector matrix (1, -1)/L
BTRANS is the transpose of B.

This simplifies to

K=EA/L* [1  -1]
             [-1  1]

K is sort of the spring constant for the element.
If you have more than 2 nodes(properties of tube change through length you will need to prepare a global stiffness matrix.

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