A rigid domain, or a rigid body, is an idealization of a body in which the deformation is neglected. In other words, the distance between any two given points of a rigid body remains constant in time, regardless of any external forces acting on it. An object can be assumed to be rigid if its flexibility is negligible in comparison to other flexibilities in the system, and when there is no need to compute internal stresses. To model a rigid domain, you can use the Rigid Material material model.

The implementation of the Rigid Material material model in the Solid Rotor interfaces differs from the other structural mechanics interfaces (for example, the Solid Mechanics interface). In the Solid Rotor interfaces, additional frame acceleration terms are always added to the include the inertial forces due to rotating.