Contact conditions are created when an assembly is imported into the application and it detects that two separate bodies (solid, surface, and line bodies) touch one another (they are mutually tangent). Bodies/surfaces in contact:
Do not 'interpenetrate'.
Can transmit compressive normal forces and tangential friction forces.
Can be bonded together (Linear)
Able to separate and collide (Nonlinear)
Surfaces that are free to separate and move away from one another are said to have changing-status nonlinearity. That is, the stiffness of the system depends on the contact status, whether parts are touching or separated.
Use the Contact Tool to help you coordinate contact conditions before loading and as part of the final solution.