Tension influence on torsion in a pipe

[dersman]

Hi all,

A string of pipe elements clamped one side and loaded with a torsion moment results in a certain amount of rotation. Now I'm wondering if adding a tensile force to the pipe's free end results in a lower amount of rotation.

I tried to simulate this very simple problem in Ansys but rotations were equal with and without a tensile force.

Is this correct and are the two loads not coupled in any way, or am I doing something wrong here?

Thanks in advance

dersman

 

[meshparts]

I suppose the rotation ist identical in both load cases, because of the linearity assumption. Are you tanking acout of stress stiffening and/or prestress in your simulation?

Regards,
Alex

 

[dersman]

thanks for you response!

what linearity assumption do you mean? To answer your question, yes I tried both prestress and stress stiffening, both didn't change the results. The manual says about stress stiffening that it only couples bending stiffness and axial stiffness. Because there is no bending in my simulation I think stress stiffening has no effect.

dersman

 

[meshparts]

I meant that you have 2 load cases. You can solve the first load case then the second load case, and in the end you can add the displacements of both load cases to get the displacements as if you ould solve for both load cases at a time:

U(L1)+U(L2)=U(L1+L2)

This is only true for linear systems with small displacements.

You see, there is perhaps nothing wrong with your simulation, if the displacements are small.

Regards,
Alex

 

[dersman]

Thanks,

Do you agree with me that adding a tensile force should result in fewer rotation?

I understand that when you add the results of 2 seperate runs, one with torsion and one with tension, the end result will be the same amount of rotation as the run with torsion only. I just thought there would be some kind of coupling between tension and torsion.

 

[meshparts]

In the case of small displacements and linar materials, I don't think there are some kind of coupling. But what if the material is not linear. For example it has a nonlinear stress-strain relationship. That could make some deference. I ould try that.

Hope it helps!

Regards,
Alex