“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)