@article {145, title = {Mechanism of strength reduction along the graphenization pathway}, journal = {Science Advances}, volume = {1}, year = {2015}, month = {Nov-20-2015}, pages = {e1501009 - e1501009}, abstract = {

Even though polycrystalline graphene has shown a surprisingly high tensile strength, the influence of inherent grain boundaries on such property remains unclear. We study the fracture properties of a series of polycrystalline graphene models of increasing thermodynamic stability, as obtained from a long molecular dynamics simulation at an elevated temperature. All of the models show the typical and well-documented brittle fracture behavior of polycrystalline graphene; however, a clear decrease in all fracture properties is observed with increasing annealing time. The remarkably high fracture properties obtained for the most disordered (less annealed) structures arise from the formation of many nonpropagating prefracture cracks, significantly retarding failure. The stability of these reversible cracks is due to the nonlocal character of load transfer after a bond rupture in very disordered systems. It results in an insufficient strain level on neighboring bonds to promote fracture propagation. Although polycrystallinity seems to be an unavoidable feature of chemically synthesized graphenes, these results suggest that targeting highly disordered states might be a convenient way to obtain improved mechanical properties.

}, doi = {10.1126/sciadv.1501009}, author = {Antonio Gamboa and Baptiste Farbos and Aurel, P. and G{\'e}rard L. Vignoles and Jean-Marc Leyssale} } @article {144, title = {On the prediction of graphene{\textquoteright}s elastic properties with reactive empirical bond order potentials}, journal = {Carbon}, volume = {89}, year = {2015}, month = {Aug-2015}, pages = {176 - 187}, abstract = {

The elastic properties of graphene as described by the reactive empirical bond order potential are studied through uniaxial tensile tests calculations at both zero temperature, with a conjugate gradient approach, and room temperature, with molecular dynamics simulations. A perfect linear elastic behavior is observed at 0\ K up to \≈0.1\% strain. The Young\’s modulus and Poisson\’s ratio obtained with this potential are of \≈730\ GPa and 0.39, respectively, with little chirality effects. These values differ significantly from former estimations, much closer to experimental values. We show that these former values have certainly been obtained by neglecting the effect of atomic relaxation, leading to a severe inaccuracy. At larger strains, an extended apparent linear domain is observed in the stress\–strain curves, which is relevant to Young\’s modulus calculations at finite temperature. Our molecular dynamics simulations at 300\ K have allowed obtaining the following, chirality dependent, apparent Young\’s moduli, 860 and 761\ GPa, and Poisson\’s ratios, 0.12 and 0.23, for armchair and zigzag loadings, respectively.

}, issn = {00086223}, doi = {10.1016/j.carbon.2015.03.035}, author = {Antonio Gamboa and G{\'e}rard L. Vignoles and Jean-Marc Leyssale} }