Contact with friction

[Bugz]

Hello,

I have a problem to simulate a contact problem.

The model should describe a contact between a rigid surface non deformable (master surface) against a deformable surface of rubber material (slave surface).

I have convergence problem when I apply the friction between the two parts. The peak in the contact pressure profile is carried out by few nodes, and when the friction is applied, the high shear still carried out by only few nodes lead to high distortion of elements, and turn inside out.
I tried different type of contact definition like hard ,soft ...


My question is the following:

What can be the minimum size of my elements, knowing that they already have a 1 micros size and the pressure is around 1 MPa ?
Where is the limit with continuum mechanics ?



Do you know any experimental method to measure pressure profile with very fine accuracy ? (film sensor do not fullfil my requirement).

Thanks for your help,

Bugz

[Jorgen]

Hello Bugz,

Contact can be tricky, but you should be able to get better convergence properties than you describe.

Well, there is nothing in the mathematics of the FE method that limits the minimum element size. In fact, FE simulations are independent of dimensions: it is the user's responsibility to keep track of dimensions, the software is just crunching numbers (no dimensions)!

What is often done when simulating parts with very small dimensions is to use mm or micro-meter instead of meter as a length dimension. If you switch the dimension for length you might also need to switch force, pressure, etc. The idea of this type of unit switch is to have the magnitudes of your numbers be close to 1 (unity), in order to reduce numerical problems due to round-off errors, etc. I'll post a separate news article discussing this further.

I don't know of any easy way to measure a pressure profile with high accuracy. It is possible, however, to very accurately measure a height profile (or surface roughness) of your two parts.

Jorgen

[Bugz]

Jorgen,

Thanks for your reply.

I arealdy have a model in mm, but the big difficulty of my simulation is that the contact is driven by the bending of a large beam. The transition between the contact and the rest of the structure is a bottleneck, I can not mesh it too coarse, otherwise the shape ratio between the element will not be respected. Until now I did not find any solution to run the analysis without the complete structure.

Is there any automesh option in Abaqus standard ?
What options in the friction definition could I change to facilitate convergence ?

Thanks again,

Bye

[Bugz]

Jorgen,

Thanks for your reply.

I arealdy have a model in mm, but the big difficulty of my simulation is that the contact is driven by the bending of a large beam. The transition between the contact and the rest of the structure is a bottleneck, I can not mesh it too coarse, otherwise the shape ratio between the element will not be respected. Until now I did not find any solution to run the analysis without the complete structure.

Is there any automesh option in Abaqus standard ?
What options in the friction definition could I change to facilitate convergence ?

Thanks again,

Bye

[Jorgen]

It sounds like you have a tricky geometry that requires a lot of elements to capture appropriately. ABAQUS/Standard can do automeshing, but I think that it is currently only available for 2D problems.

As you probably know, there are many different friction implementations available for ABAQUS. Which is best will depend on the amount of sliding, geometry, materials, etc. You can always try a few different options to see if they fit your needs.

Jorgen