Learning Forum

[zmohamma]

I’m trying to better understand the methods used by LS-DYNA contact cards for calculating friction forces. Are all contact types based solely on the Coulomb friction model? If so, it seems redundant to have over 100 contact cards in the software.

 

From what I’ve gathered, LS-DYNA first calculates the normal contact force—potentially using different approaches depending on the card—followed by a friction force typically based on a Coulomb model. However, it’s unclear to me why only one friction model would be used across so many different contact types, and I haven’t found any sources that clearly explain whether other friction models are implemented.

 

Are there any references or internal documentation sources that specifically discuss the underlying friction force formulations or coding implementations for LS-DYNA contact cards?

[Dennis Chen]

there are a ton of information in the ls-dyna theory manual.  try this link or go to the Ansys ls-dyna download page - https://ftp.lstc.com/anonymous/outgoing/web/ls-dyna_manuals/DRAFT/DRAFT_Theory.pdf

You can also check in this place - https://www.dynasupport.com/tutorial/ls-dyna-users-guide/contact-modeling-in-ls-dyna

 

[zmohamma]

 

Thanks for your reply but the LS-DYNA theory manual primarily discusses the penalty-based method for calculating normal contact forces, which are used to push slave nodes back onto the master surface. These normal forces are then used in the Coulomb friction model (referred to as the “Column” model in the manual) to compute the frictional response. However, I couldn’t find any references to alternative friction formulations beyond the Column model, particularly those that consider parameters beyond the normal force.

 

Additionally, while the manual provides a general overview of the differences between contact cards, such as how normal forces are computed or which cards are suited for specific geometries, it lacks detailed guidance on selecting the most appropriate card for a given simulation scenario.

 

What I would like to understand more specifically is: Does LS-DYNA exclusively use the Column model for friction, regardless of the contact card? If so, that seems quite limited, especially considering the wide variety of contact cards available. 

 

[zmohamma]

I came across the *DEFINE_FRICTION card in LS-DYNA, which allows for defining a friction curve. However, the documentation is unclear about the nature of this curve. Is the curve representing friction coefficients as a function of some variable (e.g., relative velocity or pressure)? Or is it a friction force vs. displacement relationship?

 

Additionally, if we define a friction curve using *DEFINE_FRICTION, how does LS-DYNA apply it in simulations involving multiple parts? For instance, if we have five components interacting via pairwise contact, how is the friction curve assigned or shared between different contact interfaces?

 

Has anyone worked with this card and could share insights or examples regarding its use and implications?