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Pseudo Hall-Petch strength reduction in polycrystalline graphene
Zhigong Song1, Vasilii I Artyukhov, Boris I Yakobson
1Department of Engineering Mechanics and Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China.
Nano Letters
|March 27, 2013
Summary
Molecular dynamics simulations show polycrystalline graphene fractures at grain boundaries, with cracks initiating at junctions. Larger grain sizes surprisingly reduce strength, explained by a dislocation-pileup model.
Area of Science:
- Materials Science
- Nanotechnology
- Solid Mechanics
Background:
- Polycrystalline graphene's mechanical properties are crucial for advanced applications.
- Understanding fracture mechanisms in polycrystalline materials is essential for predicting performance.
- Grain boundaries significantly influence material strength and failure modes.
Purpose of the Study:
- To investigate the fracture behavior of polycrystalline graphene using molecular dynamics simulations.
- To elucidate the role of grain boundary ends and junctions in graphene's mechanical failure.
- To explore the relationship between grain size and the tensile strength, failure strain, and elastic modulus of graphene.
Main Methods:
- Performing molecular dynamics (MD) simulations.
- Utilizing realistic finite-grain-size models of polycrystalline graphene.
- Analyzing crack initiation, propagation, and localization at grain boundaries and junctions.
Main Results:
- A strength reduction of approximately 50% or more was observed due to grain boundaries.
- Cracks preferentially initiated at grain boundary junctions.
- Increasing grain size led to a systematic decrease in tensile strength and failure strain.
- Elastic modulus increased with larger grain sizes.
- Observed phenomena were explained by a dislocation-pileup model.
Conclusions:
- Grain boundaries, particularly junctions, significantly weaken polycrystalline graphene.
- The Hall-Petch-like relationship observed is driven by distinct physics related to dislocation pile-ups.
- The findings provide critical insights for designing stronger graphene-based materials.
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