[Dem.Pet]

Hey guys! This is my first post here. I 've searched a lot about this and haven't found any answer. Am trying to simulate the response of a conical spring. My issue is that i always get a linear response instead of both linear and non-linear (see attached image). I am trying to determine the k constant for a range of force from 10-200N. For every stacked coil of the spring, the k constant should grow. I tried with several springs. with 5 active coils and with more. At the end, i am getting the max deformation for the force. and then i draw the chart F=f(x). Thanks for any help