To prevent overconstraint, displacement boundary conditions and other constraint equations or coupling equations (ideally) should not be applied on the contact nodes for solid-solid, shell-shell, and shell-solid assemblies, or for rigid surface constraints and coupling constraints.

The Sparse and PCG solvers are recommended to solve models with constraint equations.

The MPC-based algorithm must be used with nodal detection (KEYOPT(4) = 1, 2, or 3) for CONTA172 and CONTA174. If nodal detection is not set, the program issues a warning message and automatically sets KEYOPT(4) = 2.

MPC no-separation contact (KEYOPT(12) = 4) may cause a discontinuity when contact nodes slide from one target segment to another. However this is not the case for MPC bonded contact (KEYOPT(12) = 5 or 6).

The internal MPC option does not support rigid-flexible contact when rigid surfaces are modeled by any primitive segments (such as circle, cylinder, cone, or sphere).

The shell-solid assembly is usually used for the case where the solid mesh is fine with respect to the shell thickness. The shell-solid interface should be located in a region of the structure where shell theory is valid for an approximation. The accuracy of local stresses near the shell-solid interface (at least within the shell thickness range) is not guaranteed. Ansys recommends that you include at least two solid elements along the layer of the shell-solid interface.

Using the force-distributed constraint type of MPC with a large number of contact nodes can result in large and dense submatrices for the global stiffness matrix. This may significantly increase the peak memory required during element stiffness assembly. Consider reducing the number of contact nodes if real memory or virtual memory is limited.

The force-distributed constraint creates internal constraint equations such that the motion of the pilot node is the average of the contact nodes. For the rotations, a least-squares approach is used to define the average rotation at the pilot node from the translations of the contact nodes. If the contact nodes are colinear, then one of the rotations on the pilot node that is parallel to the colinear direction cannot be determined in terms of the translations of the contact nodes. Therefore, the associated moment component on the pilot node in that direction cannot be transmitted. When this occurs, a warning message is issued.

However, if the contact nodes have rotational DOFs, the rotational constraints on the pilot node are related to the contact node rotations in a weighted fashion, similar to those in the translational directions.

The contact related postprocessing items (ETABLE items, PRESOL,CONT, etc.) are not supported for the internal MPC option.

MPC contact generates internal constraint equations only. It does not calculate element internal force and stiffness matrices. During postprocessing, therefore, ITEM = CONT is not valid with PRNLD, NFORCE, and FSUM.

You can list the internally-generated constraint equations associated with MPC contact. You can also convert the internal constraint equations to external constraint equation after issuing SOLVE. For more information, see CELIST.

MPC contact generates constraint equations that can include constant terms, included on the right side of the system equation. Thus, they are scaled via LVSCALE when that command is used in a mode-superposition analysis. The constant terms are considered to be harmonically varying loads when included in a harmonic analysis.

MPC contact is not recommended for harmonic cyclic symmetry analysis.

The coupling constraint type (KEYOPT(4) = 3) is not supported in cyclic symmetry analysis and multistage cyclic symmetry analysis.

Internal constraint equations cannot be listed or viewed after a cyclic symmetry solution.

MPC contact with shell thickness effect included (KEYOPT(11) = 1) is not supported by the preintegrated shell section type (SECTYPE,,GENS).

The relaxation method (KEYOPT(11)=1 on the target element) has the following restrictions:

Thermal expansion of rigid surface constraints (KEYOP(12) = 1 on target element) cannot be used with primitive target shapes.

In a distributed-memory parallel solution, if one MPC contact pair overlaps any other type of contact, then the contact pairs can be decomposed into different domains. However, when two or more MPC contact pairs overlap, all the MPC contact pairs are grouped into the same domain.