We report on a computational study of the fracture properties of polycrystalline graphene (PCG) models upon tensile loading. Starting from an initial model generated with a liquid quench molecular dynamics simulation [1], a series of models was generated by a 25 ns long molecular dynamics simulation at 4000 K during which the structure clearly evolves towards graphene (decrease of energy and hetero-ring fraction, increase of apparent grain sizes, etc...). Simulations of the fracture properties, using the long range, cutoff free, SED-REBO potential [2], at different stages of the annealing process, unravel an unexpected somewhat paradoxical behavior [3]. While the Young's modulus slightly increases with annealing time towards the values characteristic of graphene, fracture strain, stress and energy consistently decrease. A close look at the systems close to fracture (see Fig. 1) reveals the microscopic origin of this paradox, often termed "pseudo Hall-Petch effect"[4-5]. At low annealing time, when the system remains highly disordered, several single-bond cracks can nucleate without fracture propagation. Conversely, in more ordered systems (high annealing time) the load transfer following a bond rupture has a much more local character and quickly activate fracture propagation. [1] Leyssale et al., App. Phys. Lett. 95, 231912 (2009). [2] Perriot et al., Phys. Rev. B 88, 064101 (2013). [3] Gamboa et al. Science Adv. (submitted) [4] Song et al. Nano Lett. 13, 1829 (2013). [5] Sha et al. Sci Rep. 4, 5991 (2014).

Mechanism of strength reduction along the graphenization pathway of polycrystalline graphene

251st National Meeting (2016)

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