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### Mortar Contact

Mortar contact is a consistently weak formulation of the contact conditions. For details of the method the reader is referred to [28] and [25]. It is a surface-to-surface method which usually leads to better convergence and a more uniform stress field. In the author's experience the iterations take longer (higher computational effort), however, fewer are needed to obtain convergence. The contact definition in the input deck is similar to penalty contact except for:

- The contact surfaces (both slave and master) must be face-based.
- On the *CONTACT PAIR card the parameter TYPE=SURFACE TO SURFACE must be specified to trigger Mortar contact (default is penalty contact).
- The SMALL SLIDING parameter on the *CONTACT PAIR card has no effect. The Mortar implementation is such that the pairing of the slave and master surface and the calculation of the normals to the slave surface is done at the start of each new increment. It is not repeated for each iteration.
- The *SURFACE BEHAVIOR card needs only one parameter: the spring constant.
- The *FRICTION card is needed to specify the friction coefficient. The stick slope is irrelevant since the stick range for the present Mortar formulation is zero (infinite stick slope).

Next: Materials Up: Boundary conditions Previous: Penalty Contact Contents