In this commit, a new contact traction element was created to set the traction force to zero at the nodes that are in contact within a specified contact interaction. This feature is required in the coupling procedure with Metalub (see commit 3186 of Metafor and commit 1456 of Metalub for more details).

A ContactTraction2DElement or ContactTraction3DElement is created like a Traction2DElement or Traction3DElement. The only additional property that has to be set is NBR_CONTACT_INTERACTION, which is the number of the contact interaction. For instance,

prp = ElementProperties(ContactTraction2DElement)
prp.put(PRESSURE, -p['pMax'])
prp.put(NBR_CONTACT_INTERACTION, 3)

Hence, if nodes in this ContactTraction2DElement are slave nodes in contact (in the previous mechanical iteration) in the contact interaction 3, the traction force applied to these nodes is set to zero.

Instead of implementing the new feature directly in the TractionElement of the mtElement package, a new template class ContactTractionElement was created in the mtContact (elements) package. It had to be moved to the mtContact package (instead of the mtElement package) in order to have access to the contact features via include “ContactInteraction.h”. Moreover, the ContactTractionElement derives of TractionElement to minimize duplicate code. In a similar way to the TractionElement, 2D and 3D elements were created: ContactTraction2DElement and ContactTraction3DElement. This required to export all methods of Traction2DElement and Traction3DElement via MTELEMENTS_API (+ ELEMENT_CPP_MACRO2 extension), which only had to be added in Traction3DElement since it was already done for Traction2DElement, certainly to derive it in mtXFEM.

Some minor modifications:

• The new property NBR_CONTACT_INTERACTION was added in mtElements.h/cpp as an integer property.
• It was necessary to add ContactTraction2DElement and ContactTraction3DElement to the functions is2D and is3D in LoadingInteraction.cpp in order to be able to add them to the LoadInteraction in the Python data set.
• Untabify in ContactElement.h/cpp.
• getSlaveNode(), previously private method in ContactElement.h/cpp, becomes protected to use it in ContactTractionElement.inl.
• The method isInContactPrev() was added in ContactElement.h/cpp to get the contact status at the end of the previous time iteration. Using this contact status has the advantage that the contact traction activation/deactivation does not happen during the same time step, i.e. during the mechanical iteration. It might be possible to use the current contact status but it might introduce some undesired oscillations.