The analyses in this section simulate a block sliding over another block. To verify the *MODEL CHANGE capability, the models are taken through the following steps:

• In Step 1 the contact surfaces are brought together, resulting in the development of contact pressure at the interface.

• In Step 2 the slave surface slides over the master surface to generate friction forces. The sliding motion is applied with boundary conditions at the top nodes.

• In Step 3 the contact pair is removed. The contact constraint ends immediately, and throughout this step the slave surface penetrates into the master surface as the contact forces are ramped down to zero. At the end of this step there is no stress in the model.

• The contact pair is reactivated again in Step 4 with an allowed overclosure value specified with *CONTACT INTERFERENCE. This value has been specified to be equal to the actual overclosure. As this allowed overclosure value ramps down to zero, the contact surfaces come gradually into compliance throughout the step.