1. “Hard to Deform” Grain Interior
Strain Rate Sensitivity of Nanostructured Materials
M. Dao, N. Chollacoop, Y.-N. Kwon and S. Suresh, MIT r
Motivation
Experimental Observations
To explore the dominating mechanism of strain-rate dependent mechanical behavior in NsM
To capture the trend in experimental results using continuum FEM modeling
nCu: Lu et al, Scripta Mat. (45), 2001, 1163
nNi experiment results
Computational Model
Grain Boundary
Model Assumptions (from TEM, MD simulations):
Grain Boundary: almost atomic sharp
Grain Boundary Affected Zone:
Low sy, rate-sensitive (Coble creep, GB Sliding)
Grain Interior:
nNi: High sy ( stheo) , hard to deform
nCu: Much higher sy than conventional sy
Failure/Damage Criterion:
A strain-based criterion if eeff > 100%, sy0
Parameter Studies Performed
based on the above assumptions
Unit Cell
Grain Boundary
Affected Zone
Grain Boundary
Affected Zone
Grain Boundary
“Hard to Deform” Grain Interior
Grain Interior
Computational Results
Possible Mechanism
Parameter Studies show that the
predicted trends in both rate-dependent
stress-strain behavior and strain-to-failure agree with experimental observations
A Proposed Possible Mechanism:
With a strain based damage criterion, localized deformation in Grain Boundary Weakened Zone would trigger the macroscopic failure.
Due to the rate-sensitivity, higher strain rate should strengthen the Grain Boundary Weakened Zone syGBWZsyxtl
This strengthening effect can reduce
the intensity of localized deformation,
and delay the macroscopic failure.
nNi: 25% GB vol (D,n) = (300,4)
nCu: 25% GB vol (D,n) = (30,2.7)
Publications
“Computational Modeling of the Deformation of
Nanostructured Materials,” M. Dao, N. Chollacoop and
S. Suresh, in 2001 MRS Fall Meeting, Boston, Massachusetts,
November, 2001.
nNi: 15% GB vol (D,n) = (300,4)
nCu: 15% GB vol (D,n) = (30,2.7)