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The size scale plasticity and fracture subgroup focuses on variations in
material properties at the micro and nanoscales.
Thin films for MEMS and NEMS applications typically exhibit yield stresses
significantly larger than their bulk counterparts. This is attributed to specimen
size and has been experimentally characterized through techniques such as micro-
and nano- indentation. A Membrane Deflection Experiment (MDE) has been recently
developed to investigate the tensile behavior of freestanding polycrystalline FCC
metallic films in the absence of macroscopic deformation gradients. Several size
effects were observed including yield stress variations with film thickness.
In-situ TEM/SEM experiments are also being performed to characterize and understand
the deformation mechanisms leading to the observed size effects. For this purpose,
a MEMS device was developed in our Nanotechnology laboratory.
A multiscale modeling approach is being developed to capture the size
effect phenomenon and to achieve predictive capabilities. Atomistic
simulations of bi-crystals and nanowires are pursued to quantify
dislocation nucleation and dislocation-grain boundary interactions. 3D
Discrete Dislocation Dynamics simulations are carried out to understand
the effects of dislocation source distributions and their interactions.
FEM calculations based on crystal plasticity are used to account for
texture and grain boundary types.
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