I want to measure insertion force!

Hi, I'm the student in Korea. I need some helps..!

I'm doing a simulation of insertion force of needle type electrode using COMSOL 4.2a.
But I have some problems..

What I want to do is measuring insertion force of needle type electrode while the electrode inserted in brain with constant velocity. Therefore I chose the "Solid Mechanics" and after modeling the electrode and brain. Then, make the electrode part move toward brain model with constant velocity(using prescribed velocity). And then as the result, I plot the 1D point graph of von Mises stress at tips. I think that there should be clear increase of stress at the moment of penetration through the brain model. But the result showed linear increase irrelevant to brain model.

And also I want to know how much stress will be given to brain model as insertion of electrode. How can I get the result??

Lastly... Can I get the "force" result rather thank von Mises stress?? I wanted to get "force" data. But I couldn't find it.
(In y-axis Data expression of the settings of point graph, I could't find the "force" in categories...)

I attached my comsol file.
Please give me some advises...!! :)