Theory Manual Version 3.4
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Subsection 7.4.1: Contact Integral Up Section 7.4: Multiphasic Contact Subsection 7.4.3: Penalty Method

### 7.4.2 Gap Function

The gap function , representing the distance between the contact surfaces, is defined by The linearization of variables associated with motion, pressure, and concentration, is given by where with and .
Subsection 7.4.1: Contact Integral Up Section 7.4: Multiphasic Contact Subsection 7.4.3: Penalty Method