Piezoelectric vibration simulation in FreeFEM

Hi, I am interested in simulate piezoelectric vibration by FreeFEM. I see an example on the website. I am curious about the capability of 3D vibration model with preload on the piezoelectric material. If multiple materials are assembled, how do the preload and the interaction properties between surfaces be configured? I am willing to simulate piezoelectric vibration by an open source tool.
Thanks.