PROJECT TITLE: MULTISCALE MODELING OF DAMAGE IN POLYCRYSTALLINE THIN FILMS USED IN MEMS APPLICATIONS
PARTICIPANTS: FERNANDO STUMP (PHD – Now at Exxon Research), NIKHIL KARANJGAOKAR (PHD), DR. SEVERINE LEPAGE (BECKMAN INSTITUTE), PROF. IOANNIS CHASIOTIS (AE, U. ILLINOIS) AND PROF. PHILIPPE GEUBELLE
SUPPORT: DARPA MTO AND NSF CMMI
PROJECT DESCRIPTION: The key objective of this project is to formulate, implement and validate a multiscale finite element scheme to investigate the damage mechanisms taking place in thin films used in MEMS (Micro-Electro-Mechanical Systems) applications. Of particular interest are the creep and visco-plastic response of these films, which have been shown to strongly affect the performance of the mems device (see figure below).
Due to the very small size of these devices, the granular microstructure of the material is expected to play an important role in the initiation and evolution of these damage mechanisms. In particular, we aim to model the competition between intra- and inter-granular damage mechanisms taking place in these materials. to that effect, we are developing a 2d and 3d multiscale finite element framework that allows us to relate the damage taking place at the meso-scale to the macroscopic constitutive response of the material (see figure below).
The models used at the microscale are inspired by experimental observations obtained by Nikhil Karanjgaokar, a PhD student in Prof. Chasiotis’ research group in the aerospace engineering department. the experimental measurements are also used in the validation of the numerical prediction. an example of such comparison can be found in the next figure.
Lepage, S., Stump, F., Kim, I., and Geubelle, P. H. (2011) “Perturbation stochastic finite element based homogenization of polycrystalline materials.” Journal of Mechanics and Materials Science, 6 (7-8), 1153-1169.
Stump, F. V., Karanjgaokar, N., Geubelle, P. H., and Chasiotis, I. (2012) “A multiscale model of rate dependence of nanocrystalline thin films.” International Journal of Multiscale Computational Engineering, 10:5, 441-459.
- Karanjgaokar, N., Stump, F., Geubelle, P. H. and Chasiotis, I. (2013) “A thermally activated model for room temperature creep in nanocrystalline Au films at intermediate stresses.” Scripta Materialia, 68:8, 551-554. http://dx.doi.org/10.1016/j.scriptamat.2012.11.017