# Overconstrained degrees of freedom¶

Error

At least one node is overconstrained for the current settings. Please check your boundary conditions for incompatible settings.

## What happened?¶

The solver failed to run the analysis due to overconstrained degrees of freedom (DOF) of one of the entity.

## What could be the possible reason?¶

This error may occur when the slave contact surface nodes of linear or nonlinear contact are further constrained in any direction. Since during the calculation, the nodes of the slave surfaces are restricted in their movement by the deformation of the master surface, therefore, restricting slave node(s) further will lead to overconstrained system.

## What can I do now?¶

Make sure that the nodes which are part of the slave contact are not constrained in any direction. Even if you want to apply a symmetry boundary condition to the model involving contact, try to partition the symmetry face in to two so that a very small face sharing the slave contact nodes can be easily omitted from the symmetry constraint boundary condition. An example below explains the possible solution to one of the problem:

• The figure below shows two bars which are in contact with each other from the middle. The below surface of the upper bar is considered master and the top surface of the lower bar is considered slave. Now if we apply any kind of constraint (e.g. y-constraint in this case due to symmetry) over the left or right face of the bottom bar, than the edge nodes which are common between two faces become overconstrained.
• To overcome this kind of problem, we partition the face in to two and assign the slave contact and symmetry face as shown in figure below. By doing this, a small portion of the side face of lower bar is not constrained and therefore the common edge nodes are not overconstrained anymore.

Note