## *CONTACT PAIR

Keyword type: model definition

This option is used to express that two surfaces can make contact. There are two required parameters: INTERACTION and TYPE, and two optional parameters: SMALL SLIDING and ADJUST. The dependent surface is called the slave surface, the independent surface is the master surface. Surfaces are defined using the *SURFACE keyword card. The dependent surface can be defined as a nodal surface (option TYPE=NODE on the *SURFACE keyword) or as an element face surface (default for the *SURFACE card), whereas the independent surface has to be defined as an element face surface. If you are using quadratic elements, or if you select face-to-face contact, however, the slave (= dependent) surface has to be defined based on element faces too and not on nodes.

If the master surface is made up of edges of axisymmetric elements make sure that none of the edges contains nodes on the axis of symmetry. Indeed, such edges are expanded into collapsed quadrilaterals the normals on which cannot be determined in the usual way.

The INTERACTION parameter takes the name of the surface interaction (keyword *SURFACE INTERACTION) which applies to the contact pair. The surface interaction defines the nature of the contact (hard versus soft contact..)

The TYPE parameter can take the value NODE TO SURFACE, SURFACE TO SURFACE, MORTAR, LINMORTAR or PGLINMORTAR. NODE TO SURFACE triggers node-to-face penalty contact, SURFACE TO SURFACE face-to-face penalty contact. MORTAR triggers the mortar method with standard dual shape functions for the Lagrange multipliers, LINMORTAR the mortar method with linear dual shape functions and PGLINMORTAR the Petrov-Galerkin method in which the usual shape functions are used to describe the variation of the Lagrange multiplier. For details the reader is referred to Section 6.7.7 and [82]-[85]. If the reader wants to apply mortar contact, it is suggested to start with MORTAR contact and to use LINMORTAR or PGLINMORTAR only if MORTAR fails. Notice that although several *CONTACT PAIR cards can be used within one and the same input deck, all must be of the same type. It is not allowed to mix NODE TO SURFACE, SURFACE TO SURFACE MORTAR, LINMORTAR and PGLINMORTAR contact within one and the same input deck.

The SMALL SLIDING parameter only applies to node-to-face penalty contact. If it is not active, the contact is large sliding. This means that the pairing between the nodes belonging to the dependent surface and faces of the independent surface is performed anew in every iteration. If the SMALL SLIDING parameter is active, the pairing is done once at the start of every increment and kept during the complete increment. SMALL SLIDING usually converges better than LARGE SLIDING, since changes in the pairing can deteriorate the convergence rate. For face-to-face contact (SURFACE TO SURFACE, MORTAR, LINMORTAR or PGLINMORTAR) small sliding is active by default.

First line:

• *CONTACT PAIR
• enter the required parameter INTERACTION and any optional parameters.

Following line:

• Name of the slave surface (can be nodal or element face based).
• Name of the master surface (must be based on element faces).
Repeat this line if needed.

Example: