#Surface Contacts
The interaction properties of two ContactGeometries, belonging to two different Body’s, is defined with a SurfaceContact.Model. For example, the collision between two wooden logs, and one log and one rock should be defined by two different SurfaceContact models. It is then fundamental that the geometries of the objects have the intended material assigned. If there is no SurfaceContact model declared for the material pair of two geometries colliding, the behavior should be reduced to a default definition defined by the runtime environment.
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SurfaceContact.Model defines the pairwise contact properties between geometries assigned materials. The SurfaceContact model will describe the behavior in a contact normal direction, the friction definition between the materials, and if there is any stickiness (adhesive forces) involved in the interaction. It is undefined to have more than one SurfaceContact model declared for one pair of materials, resulting in the runtime showing an error.
- NormalInteraction is a template for any definition for interactions in the normal direction of a contact between two contact geometries colliding. It requires a runtime environment that can compute the normal direction of two the geometries.
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The ElasticityType template for modeling the overlapping surface with a spring and damper model considering the contact depth. There are alternative elasticity types. The [PointwiseElasticity][PointwiseElasticity.openplx] model the surface normal interaction as individual elastic springs. The [PatchElasticity][PatchElasticity.openplx] does scale the contact stiffness to behave consistent independent of the contact area and the number of contact points.
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The RigidType defines a perfectly rigid surface contact, where the volumes of contact geometries has no ability to overlap.
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The Friction attribute define the friction forces between the two colliding surfaces. The friction acts in an orthogonal plane to the contact normal. DryFriction is a velocity independent friction which results in a force that is maximum of the friction coefficient multiplied with the normal force, while not doing any work. ViscousFriction is a fully velocity dependent friction type.
- The AdhesiveType template describes how two materials stick together, generating forces opposite to the contact normal. The NoAdhesion type declares that there are no adhesive forces active. The ConstantForceAdhesion defines a constant adhesive force active when the volumes of two contact geometries overlap.