Detecting Contact

The first step is to decide if the materials at the node are actually in contact. NairnMPM allows a simulation to use various combinations of the following three contact detection criteria:

1. If the total volume at the node is less than some fraction of the total volume expected for an internal node (a parameter Vmin), the materials at that node are assumed to not be in contact. If the volume is greater than Vmin, the contact detection continues. This check can be skipped by setting Vmin = 0 (because all nodes with materials will have volume greater than zero).
2. Next, the normal to the material contact surface is calculated and it is used to determine the velocity of approach for the two material surfaces. If the surfaces are moving apart, the node is assumed to not be in contact. If they are moving toward each other, the contact detection continues.
3. Finally, if enabled, the displacements for each material at the node are calculated. If the two materials overlap, the node is in contact. If not, the node is assumed to not be in contact. There are two ways to find displacements. The method is selected with the ContactPosition command (where details on the methods are given).