Mortar Contact for Implicit Analysis

The Mortar contact in LS-DYNA[1,2] was originally implemented as a forming contact intended for stamping analysis[3] but has since then evolved to become a general purpose contact algorithm for implicit time integration. The Mortar option is today available for automatic single- and surface-to- surface contacts with proper edge treatment, and optional features include tie, tiebreak and interference. The Mortar contact is a penalty based segment-to-segment contact with finite element consistent coupling between the non-matching discretization of the two sliding surfaces and the implementation is based on [4,5]. This consistency, together with a differentiable penalty function for penetrating and sliding segments, assert the continuity and (relative) smoothness in contact forces that is appealing when running implicit analyses. The algorithm is primarily focusing on accuracy and robustness, and the involved calculations associated with this aim make it expensive enough to not be recommended for explicit time integration except for those cases where other algorithms for some reason are inadequate. While the Mortar contact is not to be seen as superior for all implicit contact situations, extensive usage and customer feedback indicate that it generally improves implicit convergence rate as well as results when compared to the contacts normally used for explicit analysis, which will be illustrated in this paper. The intention is also to provide a theoretical basis of the contact including practical guidelines on how to use it.