Surface-based constraints

Tie constraints are used to tie together two surfaces for the duration of a simulation. Each node on the secondary surface is constrained to have the same motion as the point on the main surface to which it is closest. For a structural analysis this means the translational (and, optionally, the rotational) degrees of freedom are constrained.

Abaqus uses the undeformed configuration of the model to determine which secondary nodes are tied to the main surface. By default, all secondary nodes that lie within a given distance of the main surface are tied. The default distance is based on the typical element size of the main surface. This default can be overridden in one of two ways: by specifying the distance within which secondary nodes must lie from the main surface to be constrained or by specifying the name of a set containing the nodes that will be constrained.

Secondary nodes can also be adjusted so that they lie exactly on the main surface. If secondary nodes have to be adjusted by distances that are a large fraction of the length of the side of the element (to which the secondary node is attached), the element can become severely distorted; avoid large adjustments if possible.

Tie constraints are particularly useful for rapid mesh refinement between dissimilar meshes.