Rubber cylinder to hyperboloid
Rubber cylinder to hyperboloid
(OP)
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.


Project files:
https://files.engineering.com/getfile.aspx?folder=...
Thanks
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.


Project files:
https://files.engineering.com/getfile.aspx?folder=...
Thanks
RE: Rubber cylinder to hyperboloid
Try to on nonlinear solution.
RE: Rubber cylinder to hyperboloid
For your info, I did turn on large deflection mode in analysis settings
RE: Rubber cylinder to hyperboloid
Everyone can check it.
RE: Rubber cylinder to hyperboloid
Thanks
RE: Rubber cylinder to hyperboloid
Like this:
RE: Rubber cylinder to hyperboloid
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 in ANSYS 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
RE: Rubber cylinder to hyperboloid
I don't use ANSYS, we have NX Nastran & Algor. In our world 0 described displacement and fixed are different things. 0 described displacement simply means no displacement is applied, i.e the nodes are free to move.
RE: Rubber cylinder to hyperboloid
RE: Rubber cylinder to hyperboloid
The plot scale was set 1.0 (True scale) so maybe just a visualization artifact of ANSYS?
RE: Rubber cylinder to hyperboloid
RE: Rubber cylinder to hyperboloid
I added 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°
RE: Rubber cylinder to hyperboloid
How much is the max plastic strain before the analysis stops?
RE: Rubber cylinder to hyperboloid
I thought that refining the mesh would help instead it seems to make things worse.
I didn't even bother to add self contact, because solving time goes up exponentially.
Kind of stuck at the moment...
RE: Rubber cylinder to hyperboloid
By the way, check the location of the reference node of the remote displacement boundary condition.
In this case the location does not matter though.
RE: Rubber cylinder to hyperboloid
-Use QUAD8 elements, since this is a thin body (higher order QUADS, to capture curvature better, ..). You can set that in mesh and element order (set to quadratic).
-Use stabilisation since the structure undergoes some form of instability (as seen in your image above).
-Move your remote point location in z top about the opposite edge (Z= ~0.0157 m).
With that and with more initial steps (100)+maximum steps (1000) for step 2, it is fine (solves for 32 degrees) just make sure that the stabilisation energy is not too high in the end (should be small compared to the elastic energy).
RE: Rubber cylinder to hyperboloid
RE: Rubber cylinder to hyperboloid
RE: Rubber cylinder to hyperboloid
Is there any chance it will converge?
RE: Rubber cylinder to hyperboloid
RE: Rubber cylinder to hyperboloid
RE: Rubber cylinder to hyperboloid
Eventually, I could get to twist 165° using Explicit Dynamics with damping control to remove unwanted dynamic effects.