General Contact
Use the General Contact node to define mechanical contact between parts in an assembly as defined by a General Contact Pair.
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Mechanical contact contributions and properties are defined by adding one or several Contact Model subnodes.
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A No Contact subnode can be used remove contact contributions for selected boundaries.
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The geometrical properties of boundaries can be adjusted by adding an Offset subnode.
If general contact pairs are present and active in the model component, a default General Contact node is added to the physics interface with all pairs selected.
The pairs selected in a General Contact node are exclusive, which means that if a pair is selected more than once, only its last occurrence in the physics tree will be active.
The General Contact node is only available with some COMSOL products (see www.comsol.com/products/specifications/).
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In order to specify contact conditions, one or more General Contact Pair nodes must be available in the Definitions branch.
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A contact mapping always occurs from a source to a destination. For General Contact, the same boundary can simultaneously act as source and destination.
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All boundaries included in a General Contact Pair are referred to as source boundaries.
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Source boundaries that intersect with the selection of the General Contact node are referred to as destination boundaries.
When a General Contact node is present in the model, all study steps are geometrically nonlinear. The Include geometric nonlinearity checkbox in the study step Settings window is selected and cannot be cleared.
For the default General Contact node, selecting Disconnect pair removes the above requirement and makes it possible to clear the Include geometric nonlinearity checkbox.
When at least one Contact, General Contact, or Interior Contact node is active in the model, a Contact Force plot group is added to the list of result templates. The plot group contains one vector plot showing the contact pressure for each contact node. If a Friction node is present, then there will also be a vector plot of the tractions caused by friction.
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Contact Modeling
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Contact Analysis Theory
General Contact
Select the Exclude constrained boundaries to omit boundaries that are constrained from the selection of General Contact, effectively omitting any contact contributions from such boundaries. Here, constrained boundaries include both boundary constraints such as Fixed Constraint, Prescribed Displacement, or Roller, and boundaries that are adjacent to a domain constraint such as Fixed Constraint or Prescribed Displacement. By default constrained boundaries are excluded.
Excluding constrained boundaries removes them from the destination boundaries. However, they remain part of the source boundaries as defined by the general contact pair. A contact search from another boundary can thus still identify them as a valid contact mapping.
Quadrature Settings
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog.
Typically, the expressions in the contact weak equations include discontinuous functions. It is sometimes preferable to use a high integration order to improve the accuracy of the numerical integration of such expressions.
Select the Integration order — From displacement field; From displacement field, reduced; or User defined.
When selecting From displacement field, the numerical integration of the contact weak equations is twice the shape function order of the displacement field.
When selecting From displacement field, reduced, the numerical integration of the contact weak equations is the same shape function order of the displacement field.
When selecting User defined, specify a custom integration order, which can be an integer value between 0 and 41.
Advanced
The equations for the contact conditions can be implemented differently in order to influence the robustness and stability of the discretized system of equations and its linearization. This can be controlled by the Jacobian Contribution setting.
When the Jacobian Contribution is set to Nonsymmetric, the variations of the normal vector on the source boundary are excluded. This is the most robust implementation for cases where the source boundary undergoes large deformation. However, it has the drawback of causing the global stiffness matrix to become nonsymmetric, which increases the memory requirement and solution time in the linear solver.
The Symmetric option can be used instead when this is problematic for the linear solver. For this option, the main contact equations does not force a nonsymmetric stiffness matrix, although some subnodes may still do so. Variations of the normal vector on the source boundary are excluded also for this option, but it is not as robust as the Nonsymmetric option.
When the Jacobian Contribution is set to Automatic, the Nonsymmetric option is used for contact pairs using the Deformed configuration mapping method, while the Symmetric option is used for the Initial configuration mapping method.
Location in User Interface
Context Menus
Solid Mechanics > Pairs > General Contact
Solid Mechanics, Explicit Dynamics > Pairs > General Contact
Multibody Dynamics > Pairs > General Contact
Ribbon
Physics tab with Solid Mechanics; Solid Mechanics, Explicit Dynamics; or Multibody Dynamics selected:
Pairs > General Contact