I think that the contact surface changes under compression are going to
cause some serious problems if you are going to analyze the spring
itself. Also the spring will be undergoing 'self contact'. This
usually causes major headaches for strictly mechanical (linear FEA
code). Think of a bellows collapsing and folding in on itself without
violating the boundary of the 3D geometry.
I don't use Mechanica specifically, so I don't know its' non-linear
capabilities, but these are the things to watch out for.
Christopher F. Gosnell
FPD Company
124 Hidden Valley Road
McMurray, PA 15317