About 3D Contacts

3D Contact lets you define mechanical contacts between two or more bodies included in a mechanism.

This page discusses:

See Also
Creating 3D Contacts

You can select two bodies or two groups of bodies to detect kinematics or dynamics contact between them.

Note: Only the geometries of the selected products associated with a volume are taken into account during the contact detection. Surfaces, curves, and points are not considered.

Initial State Conditions

During a kinematics contact between bodies, the bodies are blocked or pushed along the degrees of freedom allowed by the joint constraints. No energy or force is applied on the bodies: a rigid body cannot move if it is not pushed by another body.

The contact between bodies is considered as rigid and nonpenetrating, and not as elastic.

To define a kinematics contact between bodies, the following initial state conditions must be respected:

  • The bodies can be in contact, but they cannot clash.
  • The constraints, drivers, and motors defined in the mechanism are satisfied and are not interfering with one another.
If one of the initial state conditions is not respected, the preview of the mechanism motion cannot be launched. For more information, see Previewing the Motion of Mechanisms.

Mesh Properties

The mesh density corresponds to the number of triangles located on the surface of the product associated with the contacting body. It depends on the size of the bounding box of the product.

The mesh density can be coarse (value of 0), or fine (value of 100). By default, the value is 35.

You can adjust the mesh density of the body surfaces. Increasing the mesh density results in a finer mesh, which usually yields more accurate analysis results. However, with a finer mesh, the analysis takes longer to run.

Damping Properties

During a dynamics contact, friction is supported through the restitution coefficient. It corresponds to the ratio of the relative velocity after collision to the relative velocity before collision. By default, the value is 0.6.

Note: You can interpret the restitution coefficient as an effective damping that describes the energy loss during an impact. For example, if you specify a restitution coefficient of 0.5, the magnitude of the normal velocity of the body after the collision is half less than the velocity before the collision.

Friction Properties

During a dynamics contact, friction is supported through the sliding friction coefficient. The coefficient is computed based on the following formula: FFric = µslide . FN, where:

  • FFric is the force of friction applied by a surface on another surface. It is parallel to the surface, and in a direction opposite to the net applied force.
  • µslide is the sliding friction coefficient.
  • FN is the normal force applied by a surface on another surface. It is perpendicular to the surface (normal).
By default, the value of the sliding friction coefficient is 0.1.

Stiffness Properties

The stiffness between bodies is computed according to the formula K/b, where:

  • b is the thickness of the elastic layer.
  • K is the material property defined according to the Young Modulus and Poisson coefficient.
By default, the stiffness values for surfaces are the following:
  • Young modulus: 210GPa
  • Poisson's ratio: 0.3
  • Elastic layer depth: 1mm

During a dynamics contact, you can define the stiffness scaling to scale the effective stiffness behavior of the contact.

Note: A value of 1 corresponds to a point contact with steel-steel material pairing.
Recommendation: You can specify a stiffness scaling above or below 1 in specific situations:
  • For conformal contact situations (large contact areas) and contacting bodies with hard materials such as steel-steel, specify a value below 1 (usually between 1e-6 and 1e-2) to make the contact softer.
  • For point contacts and bodies with very soft materials, specify a value above 1 to make the contact harder.