Difference between Kinematic coupling in Abaqus and Rigids in Nastran

Kinematic coupling (KINCOUP) ties the displacement (motion) of node 2 to node 1, using a function such as Tx2 = function (Tx1), where T means translation, and x means global x axis. In its simplest form, the above kinematic coupling function could be Tx2 = Tx1, which means node 2 follows exactly the displacement of node 1.

Another way to achieve Tx2 = Tx1 is to use a rigid bar finite element, such as RBAR or RBE2. A rigid element rigidly welds the parts together.

 It is important to keep in mind; RBE3 is not a rigid element. RBE3 creates force equilibrium, but not displacement compatibility. Use RBE3 only if you want to distribute a force or mass from a node that has no other element connected to it, but you do not want a valid displacement compatibility between the parts.