Defining distance-dependend forces like Van der Waals force 2

[xaero24]

Hello,

I am currently trying to model the mechanics of an atomic force microscope. The basic principle is like a record player with the needle sliding across the surface. By measuring the deflection, information of the probe surface can be obtained.

Because of the small scale, forces like the Van der Waals force have to be considered.
Since I have only made normal stress analyses by now, I have a little problem on how to define these forces.

Considering a term like F=-H*R/(6d) with H and R being constants and d the distance between the probe and the tip of the needle, the needle is lowered to the probe with constant displacement increments, so the force F changes during the time until both parts are in contact.

Could anyone tell me how to model this time/distance dependend force? Any help would be apprechiated!

Thanks a lot.
Kind Regards

 

[akabarten]

Hello,

Could anyone tell me how to model this time/distance dependend force?

To control your force respect to time You can use amplitude.
Detail information how to use it You will find in Abaqus documentation:
Abaqus Analysis User's Manual, 32.1.2 Amplitude curves.

If You need to define force value base on displacement You can Use sensors to control amplitude value
(Abaqus User Subroutines Reference Manual, 1.1.19 UAMP User subroutine to specify amplitudes.)

Regards,
Bartosz

 

[xaero24]

Thank you Bartosz!!

It took me a while to figure out how to implement the routine but now it works