Discussion Forum

Hi,
I’m trying to modeling the indentation of a AFM cantilever with a spherical tip into a polymer thin film on a Si substrate. The geometry of the cantilever consists of 3 parts: spherical tip, cantilever, and cantilever holder (the biggest rectangular block on right), and all are set to be the same material, e.g. Si (C). The sample block set consists of a thin polymer film on thick Si (C) substrate. The separation between the lowest point of the spherical tip and the polymer surface is set 10nm. What is expected to see is the deflection of the cantilever part ONLY in Z direction when the cantilever set starts to indent into the polymer. However, except the designated Z displacement of the cantilever set, the unexpected X and Y direction movement both showed up, as shown in attached "TC_postprocess" file. The boundary conditions I set are:
1. the marked boundary was set with prescribed displacement on Rz as well as a load on Fz.
2. the all vertical boundaries and the bottom boundary of the sample block were set fixed.
3. all other boundaries were set free.
4. contact pair: lower hemi-sphere of the tip set as master; top boundary of the sample block set as slave.
5. the prescribed displacement of the cantilever holder in Z direction, Rz, was set 20nm in -Z direction from the initial position.
I’m not sure my boundary settings were set correct. Can anyone give me some suggestions on the settings for which the indentation process results in only Z direction deflection of the cantilever? Thanks.