Default value of friction in contact 1

[ankushaggarwal2]

Hi!

I want to know what is the default value of coefficient of friction used in the contact problems. It is not specified in the manual. As well as, for defining a smooth contact, it is written to put mu=0. But should I also put TAUMAX =0 for smooth contact?

Thankyou very much in advance!

 

[Stringmaker]

To define friction you simply define a material model with a coefficient of friction and assign that material to your contact elements. If mu > 0 friction is present.

TAUMAX is the maximum stress due to friction. This would be a shear stress acting inplane on a surface. I would not specify a value. If I recall this defaults to a very large value on the magnitude of 1E+20. I wouldn't specify it unless you know the physics of your problem very well and have an actual reason to. I think you may end up complicating your life by doing so.

Unless you're relying on friction to constrain portions of your model I would not use it's absolutely necessary depending on the output you wish to produce.

-Brian

 

[ankushaggarwal2]

Does that mean that by default the contact elements dont have any friction? And for smooth contact I should use the default settings?
If not, please tell me the default value of friction present.

Regarding TAUMAX, its the maximum shear stress before tha sliding starts. So, with mu=0 and TAUMAX=default value (1E20), will it be so that there will be no sliding ever?

If you can clear me on this, I will be really very grateful.
Thanks.

 

[cbrn]

Hi,
1- there is no "default" value for MU, basically. Well, you can say that it "defaults" to zero, thus making a frictional contact behave as frictionless. BUT, when MU is defined as a material property, then the friction in the contact pair is the MU of the material belonging to the CONTACT elements
2- Warning, don't confuse things. The friction model is Coulombian, so it links the tangential force to the normal force through MU. It's a direct proportionality law. That means that, when the normal force-per-unit-area is extremely high, the tangential stress becomes extremely high altogether, and can lead to unrealistic situations. But this is only for very specific problems, such as metal forming processes. Leaving TAUMAX to "almost-infinity" is a way to make the contact problem be governed exclusively by the Coulomb law, which is the large majority of cases.
3- also see "Contact Technology Guide", 3.8 and specifically 3.8.5.

Regards

 

[ankushaggarwal2]

Got it. Thank you very much!