Distributed Coupling for Bolts

Distributed coupling allows the faces attached to pin and bolt connectors to deform, which delivers a more realistic representation of a connector’s behavior.

When you set Connection Type to Distributed, a distributed coupling formulation connects a reference node (beam element node of a bolt shank) to a group of coupling nodes inside the imprint regions of a bolt's head and nut. Distributing coupling constrains the motion of the coupling nodes to the translation and rotation of the reference node. Nodes located inside the head and nut imprint areas can deform relative to each other.

This constraint is enforced in an average sense in a way that enables control of the transmission of loads through weight factors at the coupling nodes. For example, the constraint distributes a bolt's pre-load such that the sum of the forces at the coupling nodes is equivalent to the total pre-load at the reference node. Uniform weight factors are applied in this case.

The distributed connection produces more realistic stress and displacement fields at a bolt's head and nut contact areas.

A rigid connection produces stress hot spot areas inside the head and nut regions of the connected components, because rigid bars introduce high stiffnesses. A distributed connection eliminates these high stresses.

The image shows two cylindrical components connected by a bolt with a prestress load of 1,000 N. No-penetration contact exists between the two components.

Results of a static analysis using rigid and distributed connection for this bolt.
Rigid Bolt Connection Distributed Bolt Connection
von Mises stress plot with hot spot at the head imprint region. von Mises stress plot with smoother gradients at the head imprint region
Rigid Bolt Connection Distributed Bolt Connection
Resultant displacement plot showing uniform deformation at the head imprint region Resultant displacement plot showing smoother distribution at the head imprint region