SimScale CAE Forum

Bending of an optical fiber


#1

Hello, I’m trying to simulate the bending of an optical fiber with initial tension to determine the additional stresses the fiber experiences during bending. The project is found here https://www.simscale.com/projects/aplank/fiber_bending/

To bend the fiber I applied a rotating motion the right end of the fiber and let it rotate for 90 degrees.
Regarding this project I have this question:

  • When I ran the simulation with a simpler model the end of the fiber had a displacement of 15 mm when done bending. A small displacement is to be expected but this seems to be large considering I didn’t apply any stress. This seems to be caused by my choice of position of the rotating base point. I tried different base point positions but I could not find a solution for this large displacement. What would a good base point be?
    The origin of the model is circled in the picture below.

Kind regards


#2

Hi @aplank!

That reminded me of that project: https://www.simscale.com/projects/ahmedhussain18/copper_wire_bending_analysis_1/ - maybe you can have a look at it and see how that was set up :slight_smile:

Also you can use some solids inside the fibre to get a more realistic behavior. Tagging the @FEA-SQUAD as well here.

Cheers and enjoy your weekend!

Jousef


#3

Hi there!!

Are you sure this behavior is not realistic? There could be an interaction between the two materials of the fiber causing shear stresses and torsion. Some pretension might give more rigidity to the fiber, mitigating the effect.

Some steps I would take to further investigate on the matter:

  • Refine the mesh on the fiber to see the influence on the lateral displacement.
  • Restrict the lateral movement on the face, and see the effect on the solution.
  • Get rid of most of the die body to cut on resource consumption, leaving just a quarter ring for example. You can invest this elements on refining the fiber, which is too coarse right now in my opinion.

#4

Thank you for your reply!

I had a look at the project you linked and I’ll try to bend the fiber with an extra part like in the simulation (the roller). Maybe this will solve the displacement as the rotating motion is not applied directly to the fiber.
I’ll post my results when I have them.


#5

Hi @ggiraldo,

I do expect a small displacement in the fiber, but one as large as here seems unrealistic to me since I applied no stress to it.
I’ll refine the mesh of the fiber and remove unnecessary parts of the body.

What would be the best way to add pretension? I tried to apply stress as an initial condition and then apply the same stress to one end of the fiber to keep this tension. When I do that I get an error message stating that a constant non-zero boundary condition was defined for a nonlinear analysis and that I should ramp up my load. But if I ramp the load it would not be a pretension and it would not be the same for the duration of the simulation or am I seeing this wrong?

Thank you for the tips you’ve given me.


#6

To add pretension, you can use a ‘Follower Pressure’ load on the moving end. Please try and let me know.


#7

I changed my model to include an extra part to apply the bending to the fiber. This fixed the problem with the displacement of the fiber.
Thanks for the tips!


#8

I tried to apply a Follower Pressure to the moving part of the fiber. I also ramped it up with time. After I start the simulation i get an error stating that there was a problem in physical contact solution. I applied a rather big pressure since that is the stress of which I want to know the effect on the fiber. Should I make it smaller just to see what happens?