@article {609, title = {A time-dependent atomistic reconstruction of severe irradiation damage and associated property changes in nuclear graphite}, journal = {Carbon}, volume = {120}, year = {2017}, month = {Aug-2017}, pages = {111 - 120}, abstract = {

Wheat grains can be considered as a natural cemented granular material. They are milled under high forces to produce food products such as flour. The major part of the grain is the so-called starchy endosperm. It contains stiff starch granules, which show a multi-modal size distribution, and a softer protein matrix that surrounds the granules. Experimental milling studies and numerical simulations are going hand in hand to better understand the fragmentation behavior of this biological material and to improve milling performance. We present a numerical study of the effect of granule size distribution on the strength of such a cemented granular material. Samples of bi-modal starch granule size distribution were created and submitted to uniaxial tension, using a peridynamics method. We show that, when compared to the effects of starch-protein interface adhesion and voids, the granule size distribution has a limited effect on the samples\’ yield stress.

}, keywords = {TRANSMISSION ELECTRON-MICROSCOPY; MOLECULAR-DYNAMICS SIMULATIONS; HIGHLY ANISOTROPIC PYROCARBONS; THERMAL-CONDUCTIVITY; NEUTRON-IRRADIATION; CARBON; GRAPHENE; DEFECTS; ENERGY; NANOSTRUCTURE}, issn = {00086223}, doi = {10.1016/j.carbon.2017.05.009}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0008622317304542}, author = {Baptiste Farbos and Freeman, Helen and Hardcastle, Trevor and Da Costa, Jean-Pierre and Brydson, Rik and Scott, Andrew J. and Weisbecker, Patrick and Germain Christian and G{\'e}rard L. Vignoles and Jean-Marc Leyssale} } @article {146, title = {Investigating carbon materials nanostructure using image orientation statistics}, journal = {Carbon}, volume = {84}, year = {2015}, month = {Apr-2015}, pages = {160 - 173}, abstract = {

A new characterization method of the lattice fringe images of turbostratic carbons is proposed. This method is based on the computation of their orientation field without explicit detection of fringes. It allows meaningful insights into the material nanostructure and nanotexture at several scales, either qualitatively or quantitatively. The calculation of pairwise spatial statistics of the orientation field at short distance provides measurements of the coherence lengths along any direction, in particular along and orthogonally to the layers. These statistics also allow representing orientation coherence patterns typical of the observed nanostructure. At larger distances, the mean disorientation of the fringes is computed and information about the homogeneity of the sample is obtained. An experimental validation is carried out on various artificial images and an application to the characterization of four bulk turbostratic carbons is provided.

}, issn = {00086223}, doi = {10.1016/j.carbon.2014.11.048}, author = {J. Philippe Da-Costa and Weisbecker, P. and Baptiste Farbos and Jean-Marc Leyssale and G{\'e}rard L. Vignoles and Germain, C.} } @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 {143, title = {Nanoscale elasticity of highly anisotropic pyrocarbons}, journal = {Carbon}, volume = {94}, year = {2015}, month = {Nov-2015}, pages = {285 - 294}, abstract = {

We report on the elastic properties of high-textured laminar pyrocarbons (PyCs) as obtained at the nanoscale using atomistic simulations on realistic models of the rough laminar (RL) PyC, the regenerative laminar (ReL) PyC, and the ReL PyC heat treated at temperatures up to 1700 \°C. The purely longitudinal ( and ) and transverse ( and ) elastic properties of such materials have values of around 50\–75\% of those found for graphite. Conversely, cross longitudinal-transverse properties ( and ) are much larger in PyCs than in graphite (up to around one order of magnitude for ). Our results also show that stiffness decreases with the hydrogen content, that longitudinal properties increase with the extent of graphene domains and decrease with the misorientation of the layers, and that transverse and cross properties significantly increase with the amount of interlayer cross-links present in the materials. Comparison to known experimental data indicates that texture effect at superior scales play an important role in the effective macroscopic elasticity constants. Finally, from a materials perspective and in agreement with the structural evolution, the elastic properties of the ReL PyC evolve with heat treatment towards those of the RL PyC.

}, issn = {00086223}, doi = {10.1016/j.carbon.2015.06.060}, author = {Baptiste Farbos and J. Philippe Da-Costa 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} }