Flaw-Governed Failure in Nanocrystalline Pt Nanostructures
X Gu (Caltech), Zhaoxuan Wu (Institute of High Performance Computing, Singapore), Yong-Wei Zhang (IHCP Singapore), David Srolovitz (University of Pennsylvania), Julia Greer (Caltech)
From Atomistics to Reality: Spanning Scales in Simulations and Experiments Symposium A
Tue 10:45 - 12:15
CIT 165
Understanding nanoscale fracture is critical for the design of structural materials that incorporate nano length scales and mechanically robust nanoscale devices. There is not yet a consensus on the effect of flaws in nanoscale samples on fracture behavior, but theories include flaw-tolerance at the nanoscale, and the existence of macroscopic fracture relationships at the nanoscale. We explore existing theories of nanoscale fracture by testing nanoscale samples with pre-fabricated flaws in experiment and simulation. Nanocrystalline Pt nanopillars, ~120 nm diameter, with surface flaws are created using a template-assisted electroplating method, and subjected to uniaxial tension in an in-situ SEM. 8 out of 12 nanopillars failed at the pre-existing flaws, and tensile failure strengths were on the order of 1.8 GPa regardless of whether failure occurred at or away from the flaw. This implies that nanocrystalline nanoscale materials are flaw-insensitive in strength but flaw-sensitive in fracture location. Molecular dynamics simulations support these observations and reveal the competing effects of microstructural and structural flaws. Limited dislocation activity ahead of the notch serves to reduce the stress concentration at the structural flaw such that the stress at this flaw is comparable to the stress at the microstructural features such as grain boundary triple junctions. Failure strength and location is governed by the “weakest link”, the microstructural or structural feature with the highest local stress.