Contact Pairs
To decide which boundaries to assign as source and destination in a contact pair consider the following guidelines:
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Make sure that the source boundary stiffness in the normal direction is higher than the destination boundary stiffness. This is especially important if the difference in stiffness is quite large (for example, over ten times larger).
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If one of the boundaries belongs to a part that is rigid, either since it is a rigid domain, or because of the constraints applied, it should be selected as the source boundary.
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When the contacting parts have approximately the same stiffness, consider the geometry of the boundaries instead. Make a concave boundary the source and a convex boundary the destination rather than the opposite.
For efficiency, include only those boundaries that can actually come in contact in the destination selection. For the source, it is often a bit more efficient to make it so large that every destination point ‘sees’ a corresponding source point. The source point is obtained by following the normal to the destination until it reaches the source boundary.
Fixed Geometry Contact
In some situations, the relative sliding between the contacting boundaries is small. This is often the case for shrink fit simulations or when mounting a component using prestressed bolts. The sliding can be considered as small if it is significantly less than the length of an element edge.
In this case, it is possible to simplify the problem by selecting the Mapping Method to be Initial Configuration in the Contact Pair node. With this setting, a certain point on the destination boundary will see the same point on the source boundary during the entire simulation. This will make the contact analysis to run faster and convergence to be more stable.
The analysis is still geometrically nonlinear when using this option, and the contact region can still have arbitrarily large displacements and rotations.
Automatic Generation of Contact Pairs
Contact pairs can be automatically generated during the finalization of the geometry sequence. When Action is set to Form an assembly, you can select Create pairs, and use Contact pair as Pair type. Boundaries which are in geometrical contact with each other will then be placed in contact pairs. When you add Contact nodes in the physics interface, you select which of these suggested pairs to actually use for the contact analysis.
The automatic pair generation will not know which side to use as source or destination. Based on the rules above, you may need to switch them using the Swap Source and Destination button in the Source Boundaries section of the pair settings.