Deriving equation for third spring(bump rubbers)

[Amir929RR]

I am working on this project currently and I ended up stumbling upon a little problem.
I have rated my bump rubbers by recording the displacement vs. force, and eventually of course the force starts shooting up to infinity and displacement doesn't change anymore.
Does anyone have a clue on how exactly could I derive an equation for this so I could graph the force curve. I know I could probably do this by basically doing two separate equations, but unfortunately that won't really work or it would make it way too complicated for what I'm trying to get out of it.

If anyone could guide me in a right direction that would be great. I tried getting help from one of my calculus professors but he claimed it'd be too difficult and just to search online. I haven't been able to find anything on web though...

[silente]

so...you just have measurement points like:
x1---> Force1
x2---> Force2
.
.
.
xn---> Forcen

If this is the case, why you don´t use excel?

[stez90]

silente is right, what you need is a curve fit..

[Amir929RR]

Well more that I think about it I guess you are right. Once the bump rubber displacement stops moving I could basically just make up another infinitely big force point...
Thanks guys, appreciate the idea. I suppose it was way less complicated than I made it out to be

[Greg Locock]

A couple of points

First I often model jounce pumpers using a polynomial fit, fifth power or so.

Secondly, the rates you get (N/mm) will probably go over 5 kN/mm at high compression. This is meaningless since the rest of your system, including the body attachment points, will not be as stiff as that.