If no restraints are defined on a part, applying a force simply pushes that part through space; the physical shape of the part does not deform. Motion that occurs without any actual deformation of the model is called rigid body motion. Because this simulation is intended to assess the deformation of products under static loads, rigid body motion is not allowed. You must define enough restraints on your model to prevent rigid body motion from occuring. If rigid body motion is detected during a simulation, the simulation fails; the existence of rigid body motion is reported in the Diagnostic Viewer. Typically a single clamp on a part prevents rigid body motion. Because a ball joint does not completely restrict the motion of a surface, it is not sufficient to apply only a single ball joint restraint to a part; a part that includes only a single ball joint can still spin freely without deforming. If there are no clamped surfaces in your part, you must apply at least three ball joints to prevent rigid body motion. However, if all of the ball joints are colinear, the part is free to spin about the axis defined by the joints and rigid body motion will still occur. If a model consists of unconnected bodies, each body must be restrained individually. The same requirement applies to a model that consists of two (or more) bodies connected by a single point or edge; because the connections between the bodies are weak, each body must be independently restrained. | |||||||||