Learning Forum

[daviderecchia]

Hi All,

I have a cylindrical rubber piece that I want to twist into a hyperboloid.
I tried fixing a circular edge, and applying a rotational displacement of 10° to the other edge but
the deformation seems quite unrealistic. I would expect the necking to happen about halfway. 
Also the required rotation is 30 deg, but solution won't converge.
Any tips on how to set up this problem is greatly appreciated.

 

Thanks

[Aniket]

Have you turned large deformations "On" in the analysis settings?

[daviderecchia]

Yes, it's turned on.

Also material is using Yeoh 1st Order model with the Elastomer Sample (Yeoh) data.

Not sure that matters much though.

[daviderecchia]

I inserted a cylindrical coordinate system and set axial and radial displacement to 0. Rotation set to 15 mm.

It sure helped, at least now the necking is happening in the middle, as expected.
Still when I look at the deformed shape (true scale) the edge expands out in radial direction:

Any ideas why this might be happening?

Also in real life when twisting the rubber sheet overlapping folds start to appear.
I was able to reproduce this by tweaking dimensions of cylinder and playing with mesh settings
but it seems a bit inconsistent. I cannot get the right result every time.

Thanks

 

[daviderecchia]

I checked the radial displacement and indeed it's really small at the top edge.
The plot scale was set 1.0 (True scale) so maybe just a visualization artifact of ANSYS?

[daviderecchia]

Somewhat improved result by adding a step to pre-tension the membrane in axial direction before twisting.
Really hard to find convergence with a refined mesh or twist angle greater than 15°

[daviderecchia]

With a little help I got it to converge for 30 deg rotation.

Some of the things that helped:

• Use QUAD8 elements to better capture curvature, by setting mesh element order to quadratic


• Use stabilization, under non linear controls, since the structure undergoes some form of instability


• Move remote point location in z top about the opposite edge


• Add more initial sub steps (100) and maximum sub steps (1000) for step 2

 

[jj77]

That's is what I would have said .

 

The cylinder is probably undergoing torsional buckling (see torsional buckling of cylindrical shells)

 

(https://www.lancemore.jp/ls-dyna/example_430.html)