If you are using Bonded Contact, it will not make much difference which formulation you choose. The big impact is where some formulations allow the Iterative Solver while other prevent the use of Iterative and automatically switch to the Direct Sparse solver. If you have a very large model that won't solve with the Direct Sparse solver due to a lack of RAM, then choosing a formulation that allows the Iterative solver to run is the difference between having a result and having no result.
Here is the command to put under under a Joint: keyopt,_jid,2,1 The disappointment is that the solver still detected an MPC element and automatically switches to the Direct Sparse solver.
Here is an example bonded contact that has the formulation of MPC. The analysis settings are set to Iterative solver and it runs using the Iterative Solver.
If I suppress the Bonded Contact and use a Revolute Joint, the solver automatically switches to Direct Sparse, even though I have a Command Object to set the Penalty method.
Maybe someone from Ansys can explain why this keyopt, which is supposed to switch the method on the joint from Lagrange to Penalty, doesn't prevent the auto-switch to the Direct solver.
If you have only Bonded Contact and no Joints, you might be able to get the model to run using the Iterative solver.
Contact elements increase the size of the model and the RAM requirement compared with using no contact elements and either using Mesh Merge in Mechanical or Share button in SpaceClaim.
Contact elements hurt the RAM requirements because they connect nodes that are far away from each other in the network of elements in the model (even through the nodes are close spatially) and increase the wavefront during the solution process. When you do node merge or Shared Topology, the wavefront may be smaller than when contact elements are used.
How much RAM is in your computer? How much RAM does the motherboard support? Have you requested additional RAM to max out the RAM in your computer? If not, you should.