Basics

The Mortar contact is activated by typically appending the suffix _MORTAR to the automatic single surface, automatic surface to surface or forming surface to surface keywords. It can also be run as tied and tiebreak contacts. All Mortar contacts are segment to segment and penalty based and the tied and tiebreak contacts are always offset, i.e., the tie occurs on the outer surfaces of shells and not on the mid surfaces. For automatic contacts, edge contact with flat edges is always active. At this point, some of the more advanced features applicable to other contacts may not apply to the Mortar contact, examples are friction tables and orthotropic friction, but on the other hand it possesses features that are of particular interest to implicit and that are not available for other contacts. It is supported in both smp and mpp but the option MPP does not apply, bucket sort is performed every cycle and the smp ignore flag applies. The SOFT flag does not apply, to summarize it is a contact algorithm especially intended for implicit analysis.

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General recommendations

For the forming contact the rigid tools must be meshed so that the normals are directed towards the blank, and contacts from above and below must be separated into two or more interfaces because contact can only occur from one side of the blank for a given contact interface. For the forming contact, rigid shells on the master side have no contact thickness. This is not the case for automatic contacts, here there are no restrictions on the mesh and even rigid shells have contact thickness. For all Mortar contacts, part or part set based slave and master sides are recommended although not mandatory. If the two sides in the contact interface have different stiffness, use the weak part as slave in order to get the best possible implicit convergence behavior. This is automatically taken care of in a single surface contact. The Mortar single surface contact was up to recently rather slow even for implicit analysis but improvements have been made on the efficiency to make it practically useful in the most recent versions of LS-DYNA.