#115: RBE3 and RBE2
RBE2 (Rigid Body Element Type 2):
Represents an infinitely stiff connection.
All connected nodes (slave nodes) follow the exact same translations and rotations as the master node.
There is no relative motion between the master and slave nodes.
Commonly used for rigid body constraints, fixtures, or modeling lumped mass regions.
Adds stiffness to the model—use with caution in flexible structure simulations.
RBE3 (Rigid Body Element Type 3):
A weighted interpolation element for distributing loads or mass.
Does not add stiffness to the structure.
Allows slave nodes to move independently; only the forces are distributed based on weights or geometry.
Often used for load transfer, interface averaging, and pressure-to-point load mapping.
Good for preserving local flexibility while enforcing consistent load transfer.
Key Differences:
Feature RBE2 RBE3
Stiffness Adds infinite stiffness Does not add stiffness
Displacement Slaves follow master exactly Slaves can deform independently
Usage Rigid connections Load or mass distribution
Structural Use Can be structural Not a structural element
Typical Use Fixtures, rigid joints Load mapping, averaging interfaces
RBE2 is a rigid element which adds “infinite stiffness” to attached nodes which means both nodes to exactly the same displacements. There will be no relative displacement between the slaves.
RBE3 is an interpolation element used to distribute mass and loads depending on the length. RBE3’s aren’t really “rigid” and shouldn’t be used as structural elements. They are for distributing loads.
RBE2 rigidly connects the master to the slave nodes. Basically, the slave nodes follow the same deformations as the master node.
RBE3 “flexibly” connects the master to the slave nodes. The master transmits a force to each slave node depending on its relative position to the master, thus allowing the slaves to deform differently compared to the master. Depending on the solver the force distribution may be weighted or altered based on DOFs.
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