Hyperelastic Settings

[aba24]

Hi, I'm using Abaqus 6.13 to model a Silicone chamber deformation with an internal pressure of 0.15MPa. The material is Ecoflex 0050 of which I have imported stress/strain curve and used Ogden to model the behaviour.
I used as step Dynamic explicit and added an amplitude at the load. The simulation takes very long times to reach a result.
I tried to change some settings, but the simulation doesen't work if Dynamic Explicit with amplitude is not set.
Do you have any advices on what are the best settings for the hyperelastic simulations? I mean about step settings, where I think to make mistakes.
thank you all

 

[rstupplebeen]

Can you please describe what you are tying to model a little more. Is it a dynamic test such as an explosion or is it a static pressure of 0.15MPa? If it's the latter then Abaqus/Standard may be more appropriate. For Abaqus/Explicit try ramping up the pressure similar to the actual test. 'Smooth Step' is substantially linear but has a toe in region which helps with convergence. I hope this helps.

Rob Stupplebeen

http://www.optimaldevice.com

 

[aba24]

Sure. I'm modeling a small device made of ecoflex. This device contains a chamber which have to be insufflated with air. When I model the static pressure, I use as step the generic, static one but the simulation doesn't work and an error message appears: with hyperelastic material hybrid element should be used (something like this). I don't understand which is the setting to solve this problem. I tried to change the step, using dynamic, explicit one and imposing for the load (internal walls pressure of 0.15MPa) an amplitude, tabular, like this: Amplitude data,first row= 0 0; second row= 1 0.001; Baseline correction: none. In such a manner the simulation works but it takes more than a hour and a huge deformation is shown already at the middle of the simulation. I think I'm making some mistakes in setting the steps, the time of sim, the incrementation, and the amplitude too. Tank you for the help and the answer, hope to solve soon.

 

[rstupplebeen]

In the mesh module go to mesh>element type select the body with the hyperelastic material properties. Here there should be a check box for 'hybrid'.

Modeling as a 'fluid cavity' may work for your needs as well.

I hope this helps.

Rob Stupplebeen

http://www.optimaldevice.com

 

[aba24]

Thanks for the help, but I made an important step towards the solution. I made a partition of my part to allow a hexhaedrical mesh. In such a manner the simulation takes less than 10 minutes to be completed, with optimal results. Just a question about timing. I need to simulate the isufflation of the chamber, I set 1 second of simulation with a smooth step amplitude, but still don't know if my assumpions are correct. Imposing such an amplitude I'm supposing that my load (internal pressure of 0.15MPa) is augmenting from time 0 to time 1 of 0.001? if yes, at 1 sec (the ending time of the simulation) what is the pressure applied on the internal walls? the one I set up (0.15MPa)?
Maybe have some confusion about dimensioning in Abaqus. If I build my part considering mm scale, what value I have to apply for the pressure 0.15MPa? Is it correct to write 0.15 for the load?
Thank you so much for the answer and sorry if my question are quit stupid, but I'm using Abaqus since only one week

 

[rstupplebeen]

If you are in N,mm,s then yes MPa is appropriate. I suggest using this excellent table over at polymerfem.com.

http://polymerfem.com/polymer_files/FEM_Dimensions.pdf

I have put this up in every office I've ever worked in. I hope this helps.

Rob Stupplebeen

http://www.optimaldevice.com