SPRING BACK OF TUBES

[SOLIDMODEL1]

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.

 

[BruceL]

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.