A perfect conduction path is assumed by Pro/MECHANICA THERMAL at the interface between two mating surfaces in an assembly. This default assumption is often times the biggest mistake made in heat transfer modeling. Generally the conduction across interface boundaries is far from perfect and often the greatest temperature gradients are found in these areas. In real life this contact conductance or resistance is dependant on many uncontrollable and unpredictable parameters such as surface finish, materials and contact pressure. In most cases the flatter the surface, the softer the material and the larger the contact pressure, the lower the contact resistance will be. Since it is very difficult to accurately estimate this resistance, the best one can do is to use a value that is on the conservative side of a ballpark number. Conservative may be high or low depending on the model and what you are trying to find out. The data in the following tables should give you a reasonable starting point but you may want to setup a sensitivity design study to see how critical your assumption is.
The technique to modeling contact resistance is to create an extra part of some thickness that will be assembled between the interface surfaces. This 'interface' part will be assigned some material properties that will result in the proper thermal resistance between the two real parts. The following example shows how this may be done.
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