Reply To: Are Non-linear contacts still Non-linear when formulation is set to MPC or Normal largrange?

[peteroznewman]

I only use MPC in Bonded Contact, so I have nothing to say about using MPC formulation in Frictional Contact, but you can read this section of Ansys Help to learn more about MPC contact.
https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v212/en/ans_ctec/Hlp_ctec_surfcon.html
Don't use MPC contact between RIgid Bodies. See this info in the Ansys Help:
https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v212/en/ans_ctec/ctecrigidbodies.html
Normal Lagrange uses the Lagrange Multiplier method.
https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v212/en/ans_thry/thy_geo6.html
Now, instead of just the deformation of nodes being the unknowns in the matrix equation, there are a number of Lagrange multipliers included in the matrix equation, which now includes a constraint that the penetration must be exactly zero. The solver iterates on the value of the Lagrange multipliers that enforce the zero penetration. This is completely different to the Penalty-based method you know about that has a Normal Stiffness to multiply with the Penetration to compute a contact Force and iterates on nodal position alone to find equlibrium.
Program Controlled frictional contact uses the augmented Lagrange Penalty-based method. Read about the pros and cons of each in this section of the help.
https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v212/en/ans_elem/Hlp_E_MPC184.html