# Linear Structural Contact

## 13 Jul Linear Structural Contact

The interaction between parts in a structure can be modelled as contacts in FEA. These contacts can be either linear or non-linear. For more information on non-linear contact, please read (https://fea-solutions.co.uk/non-linear-contact/).

When modelling these part interactions as linear contacts, there are two ways in which this is done:
– Node Sharing
– Bonded Contact

Node sharing is modelled by ensuring that there is a matching mesh on the contact faces of both parts. By using node sharing, stress averaging (https://fea-solutions.co.uk/stress-averaging/) can be done between parts. Node sharing results in more accurate stresses compared to bonded contact.

When using bonded contact, the mesh on the contact faces does not have to match. This however means that stress averaging across parts will not be possible. Bonded contact does, however, allow joining of bodies separated by a gap. It is also the only option when joining elements with different Degrees of Freedom (DOF), for example when joining a body made of surface elements (5 DOF) (https://fea-solutions.co.uk/surface-elements/) to a body made of solid elements (3 DOF) (https://fea-solutions.co.uk/solid-elements/).

There are several different formulations for bonded contacts in FEA:
– Pure Penalty – Basic contact formulation based on the penalty method.
– Augmented Lagrange – Also penalty based method, less sensitive to contact stiffness.
– Multi-Point Constraint (MPC) – Creates equations internally during solution to tie bodies together.
– Normal Lagrange – Adds additional degrees of freedom to a model, requires additional iterations to stabilise contact conditions.
– Beam – Stitches the contact faces together using massless linear beam elements (https://fea-solutions.co.uk/line-elements/).

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