Hello,
i want to simulate the thermal conductance of two pieces of metal that are pressed together with screws. Since i want to simulate a relatively large temperature range the force/displacement pressing the pieces together would not be constant since the screws and materials elongate differently, is that possible in prepomax?
I found the option for boundarie conditions to set a fixed displacement and know how to simulate a hertz contact, but i am not too confident that those will help me because i haven’t found a way so define stuff like surface roughness that i would need for accurate results.
Thanks for the help 
You can account for thermal expansion even in a purely mechanical analysis. Temperature can be applied as defined field in a static step. Then each material will contract/expand based on its thermal expansion property.
There are two main types of thermal interfaces - tie constraint (perfect mechanical bonding and perfect heat transfer) and contact (possible sliding/separation and heat transfer based on the specified gap conductance).
Gap conductance in contact is defined as conductance vs contact pressure. It may also vary with temperature.
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Thank you, helped me a lot. I tried simulating quite a few things since my last post
Ultimately i want to simulate a coldhead in contact with a heat shield. i managed to simulate the heatshield in two variations: with the contact area to the coldhead set to a fixed temperature and a variable temperature flux. this both worked.
but in order to get accurate results i would need to have two bodies (shield and coldhead) and the coldhead would need a variable cooling power thats variable by Temperature. I found and used the amplitude function, but that is only time variable (afaik), is there a possibility to define cooling power by temperature of an object/node in prepomax?
thanks for the help
Not with built-in CalculiX features. This would likely require the use of a Fortran subroutine.