Rubber - Model goes unstable - how to increase damping?.

[phiga2]

Dear all,

I am modeling rubber friction at high coefficients (bigger 1.0) and at some point of sliding friction, my model goes somehow unstable and bounces up and down, with waves on the surface. Looks a bit like I modeled a liquid.

Does anybody know how I can change the damping, or put additional damping to my model?

Thanks,

Phil

 

[rstupplebeen]

Stabilization should damp your model.

However, I would start by changing the matrix storage to Unsymmetric because of the high friction.

I hope this helps.

Rob Stupplebeen

 

[phiga2]

Hi rstupplebeen,

thanks for the super fast answer. I guess "stabilization" and "matrix storage" all appear on the help manual, right?

I'll have a look for them tomorrow!

Thanks again,

Phil

 

[phiga2]

I am using Abaqus Explicit (v6.8). According to the help manual, the matrix storage option "unsymmetric" is only available in Standard, is this correct? Do you have another option in mind?

I am trying to change the critical damping factor (by default = 0.03) at the moment.

 

[rstupplebeen]

I did not know your were in Explicit. I usually assume Standard unless someone specifies otherwise. Pictures or posting our model would help.

Rob Stupplebeen

 

[phiga2]

I managed to use CIN-elements (infinite elements) in order to get "quiet" boundaries, which prevents the wave from bouncing back into my model, which is a plus. However, before hitting the infinite elements, the wave still continues throughout the model on the surface.

I am not entirely sure how that damping works, as I dont want to change the behaviour of my model.

I used both, Mooney and Neo-hookean SEF for rubber, but I doubt that putting a visco-elastic term in the model will solve the progression of the wave, would it?

Picture:

The white elements on the picture are the CIN-elements. As they are only allowed to be linear, I defined them with same properties as rubber (E=1.6MPa, poisson ratio=0.495). They seem to distort a bit, which I guess is due to the nature of CIN elements if I get it right from the Abaqus manual:

"During dynamic response analysis the infinite elements hold the static stress on the boundary constant but do not provide any stiffness. Therefore, some rigid body motion of the region modeled will generally occur. This effect is usually small."

 

[rstupplebeen]

I have never used CIN elements so I am of no help that's not in the manual.

Could you more fully explain your model. What are the boundary conditions? Is there contact? You might be going down a complex solution where a simple fix could suffice.

PS" the last post should have read YOUR model not OUR



Rob Stupplebeen

 

[phiga2]

About the CIN-elements I guess I am ok with them.

As shown in figure "wave2" my 2D model consists of a block with rubbery properties and a rigid slider.

BC's:
The block is constrained in all DOF's on the bottom side, all other sides are unconstrained (as it would be in "real life"). The slider in step 1 is indenting into the block (contact is established, defined as "surface-to-surface contact)), after that the rigid body is displaced to the left hand side.

Would that be enough for the BC's?

I would like to damp my model so that the waves shown on the surface either disappear completely or are significantly damped out.

 

[rstupplebeen]

How fast is the indentor moving down and then to the side relative to the model dimensions?

Is there a reason you can not do this in Standard? I know the sliding contact could be an issue however this is such smooth geometry that I doubt it will be that difficult.

Have you tried playing with linear bulk viscosity?

Try having the indentor move significantly slower 1/10th.

Rob Stupplebeen