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Linear Perturbation - Buckle: Torsion on Cylinder

Linear Perturbation - Buckle: Torsion on Cylinder

Linear Perturbation - Buckle: Torsion on Cylinder

(OP)
Hello,

I'm trying to determine the critical torque required to buckle a hyperelastic cylinder after stretch and internal pressure utilizing the linear perturbation buckle feature.

I will include my CAE file but basically I have a hyperelastic cylinder and I perform the following procedures in each of the steps after creating a cylindrical coordinate system: U1=Radial, U2=Theta, U3=Z (axial)

Initial:
Fix one end in U2 and U3. I want this end to be able to expand upon internal pressure but fixed otherwise.

Stretch/Pressure: Static General w/ NLGEOM on
Apply Stretch to the opposite end by applying a BC as 25 units in the U3 direction.  Apply pressure load to internal surface.

Crit Torque:
Apply many concentrated loads in the U2 (theta) direction to the face that previously had been stretched.  The first step completes fine but then when I get to this step I get an error of "Too many iterations needed to solve the eigenvalue problem" and warnings such as "Results may be inaccurate because a perturbation analysis has been requested about an nlgeom base state which contains 1900 dloads which cause unsymmetric stiffness contributions, but the symmetric solver is being used"

Note:
I also tried using using a kinematic coupling constraint with a reference point as a control and the surface being rotated as the slave in order to keep the surface symmetric about the U3 axis but this seemed to give me more problems.

Any help would be appreciated...again I am trying to determine the critical torque after stretch and internal pressure have been applied. If you can fix mine or think of a better technique let me know.

Thanks so much!

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