}, author = {Heckel, Michael and Glielmo, Aldo and Gunkelmann, Nina and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.93.032901}, faupublication = {yes}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Can} we obtain the coefficient of restitution from the sound of a bouncing ball?}, url = {http://link.aps.org/doi/10.1103/PhysRevE.93.032901}, volume = {93}, year = {2016} } @article{faucris.109805124, abstract = {We consider the motion of an aspherical inelastic particle of dumbbell type bouncing repeatedly on a horizontal flat surface. The coefficient of restitution of such a particle depends not only on material properties and impact velocity but also on the angular orientation at the instant of the collision whose variance is considerable, even for small eccentricity. Assuming random angular orientation of the particle at the instant of contact we characterize the measured coefficient of restitution as a fluctuating quantity and obtain a wide probability density function including a finite probability for negative values of the coefficient of restitution. This may be understood from the partial exchange of translational and rotational kinetic energy.}, author = {Glielmo, Aldo and Gunkelmann, Nina and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.90.052204}, faupublication = {yes}, journal = {Physical Review E - Statistical, Nonlinear, and Soft Matter Physics}, peerreviewed = {Yes}, title = {{Coefficient} of restitution of aspherical particles}, volume = {90}, year = {2014} } @article{faucris.122026784, abstract = {A hydrodynamic description of dilute binary gas mixtures comprising smooth inelastic spheres interacting by binary collisions with a random coefficient of restitution is presented. Constitutive relations are derived using the Chapman-Enskog perturbative method, associated with a computer-aided method to allow high-order Sonine polynomial expansions. The transport coefficients obtained are checked against DSMC simulations. The resulting equations are applied to the analysis of a vertically vibrated system. It is shown that differences in the shape of the distributions of the coefficient of restitution are sufficient to produce partial segregation.}, author = {Pöschel, Thorsten and Serero, Dan and Gunkelmann, Nina}, doi = {10.1017/jfm.2015.501}, faupublication = {yes}, journal = {Journal of Fluid Mechanics}, keywords = {granular media; granular mixing; kinetic theory}, pages = {595-621}, peerreviewed = {unknown}, title = {{Hydrodynamics} of binary mixtures of granular gases with stochastic coefficient of restitution}, volume = {781}, year = {2015} } @article{faucris.122031184, abstract = {Strong shock waves create not only plasticity in Fe, but also phase transform the material from its bcc phase to the high-pressure hcp phase. We perform molecular-dynamics simulations of large, 8-million atom nanocrystalline Fe samples to study the interplay between these two mechanisms. We compare results for a potential that describes dislocation generation realistically but excludes phase change with another which in addition faithfully features the bcc -> hcp transformation. With increasing shock strength, we find a transition from a two-wave structure (elastic and plastic wave) to a three-wave structure (an additional phase-transformation wave), in agreement with experiment. Our results demonstrate that the phase transformation is preceded by dislocation generation at the grain boundaries (GBs). Plasticity is mostly given by the formation of dislocation loops, which cross the grains and leave behind screw dislocations. We find that the phase transition occurs for a particle velocity between 0.6 and 0.7 km s(-1). The phase transition takes only about 10 ps, and the transition time decreases with increasing shock pressure.}, author = {Gunkelmann, Nina and Tramontina, Diego R. and Bringa, Eduardo M. and Urbassek, Herbert M.}, doi = {10.1088/1367-2630/16/9/093032}, faupublication = {yes}, journal = {New Journal of Physics}, keywords = {shock wave;iron;molecular dynamics;solid-solid transitions;plasticity;dislocations}, peerreviewed = {Yes}, title = {{Interplay} of plasticity and phase transformation in shock wave propagation in nanocrystalline iron}, volume = {16}, year = {2014} } @article{faucris.218453221, author = {Gunkelmann, Nina and Kataoka, Akimasa and Dullemond, Cornelis P. and Urbassek, Herbert M.}, doi = {10.1051/0004-6361/201630155}, faupublication = {yes}, journal = {Astronomy and Astrophysics}, keywords = {Planets and satellites: formation; Methods: numerical; Protoplanetary disks}, peerreviewed = {Yes}, title = {{Low}-velocity collisions of chondrules: {How} a thin dust cover helps enhance the sticking probability}, volume = {599}, year = {2017} } @article{faucris.119285144, abstract = {Using molecular dynamics simulation, we study the austenitic and the martensitic solid-solid phase transformation in the Fe-C system. Random alloys with C contents up to 1 at% are subjected to a heating/cooling cycle. The martensite and austenite phase transition temperatures can be determined from the hysteresis of the system volume with temperature. The martensite temperature decreases with C content, as in experiment. The influence of the C atom position on the phase transformation and the pathways of the transition are analyzed. The transformed austenite phase shows strong twinning. (C) 2013 Elsevier B.V. All rights reserved.}, author = {Gunkelmann, Nina and Wang, Binjun and Sak-Saracino, Emilia and Urbassek, Herbert M.}, doi = {10.1016/j.commatsci.2013.09.069}, faupublication = {no}, journal = {Computational Materials Science}, keywords = {Solid-solid phase transitions;Molecular dynamics simulation;Martensite;Fe-C alloy;Martensitic transformation}, pages = {399-404}, peerreviewed = {Yes}, title = {{Molecular}-dynamics study of the alpha <-> gamma phase transition in {Fe}-{C}}, volume = {82}, year = {2014} } @article{faucris.218452309, abstract = {

A new approach for characterizing the dislocation microstructure obtained from atomistic simulations is introduced, which relies on converting properties of discrete lines to continuous data. This data is represented by a number of density and density-like field variables containing detailed information about properties of the dislocation microstructure. Applying this methodology to atomistic simulations of nanoscratching in iron reveals a pronounced “length scale effect”:

With increasing scratching length the number of dislocations increases but the density of geometrically necessary dislocations remains constant resulting in decreasing shear stress. During scratching dislocations are mostly generated at the scratch front. The nucleation rate versus scratching length has an approximately antisymmetric shape with respect to the scratch front leading to an almost constant curvature.