Learning Forum

[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?

[Ram Gopisetti]

Hi, 

Using DEFINE_FRICTION in FS_D may not accommodate curves, as its purpose is to set the constants of the curve (FS, FD, DC) to evaluate friction based solely on the relative velocity—without accounting for pressure dependency. Typically, a contact is initially defined with FS = -2 for all pairs. Then, DEFINE_FRICTION is used for each pair assigned to PID I and PID J, where the appropriate constants are specified to establish the desired friction values within the simulation. If friction behavior dependent on both pressure and relative velocity is required, it is necessary to define the contact and assign a table via the FD parameter.

Cheers, Ram 

[zmohamma]

Hi Ram,

 

Thank you for your response. Just to confirm—if I’m modeling contact between two different materials using shell elements with pressure-dependent friction, should I assign the FD parameter directly in the contact card to reference a friction curve?

 

Best regards,

Zohreh