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We present 3D-nonequilibrium molecular dynamics results for the velocity dependence of the frictional force at smooth sliding interfaces for Ta and Al single crystals. For Ta/Al we consider Al(100)/Ta(100) and Al(111)/Ta(110) interfaces sliding along [001] and [110]fcc /[001]bcc respectively. These are compared with Al(111)/Al(100) interfaces at the same loads, corresponding to a pressure of 15 GPa. Both interfacial pairs show similar behavior in the velocity dependence of the frictional force: a low velocity regime with an increasing frictional force followed by a strain induced transformation regime at velocities above approximately 1/10 the transverse sound speed, followed by a fluidized interface at high velocities. For both interfacial pairs, the high velocity dependence of the frictional force exhibits power law behavior, Ft ∝ v-β with β=3/4. We discuss the structural changes that influence dissipation in each of these regimes. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

This research focuses on analyzing shock wave propagation in <100>, <110>, and <111> oriented single crystalline Al, <0001> oriented single crystalline Fe2O3, and an interface of {100} surface of Al with {0001} surface of Fe2O3. For this purpose, an interatomic potential is developed to describe atomic interactions in the Fe+Al+Fe2O3+Al2O3 material system. The analyses in single crystalline systems focus on the relationships between the shock wave velocity (US) and the particle velocity (UP) as a function of the single crystalline orientation. Calculations also focus on the formation and propagation of defects. The interfacial shock wave propagation analyses focus on the change in atomic structure near the interface as a function of UP. Calculations show that there is a threshold UP value above which the atomic structure on both sides of the interface undergoes significant changes which are accompanied by enhanced increase in temperature and pressure relative to what is seen in both phases when they are deformed alone. This observation suggests a possibility that this threshold may represent the onset of a shock-induced reactive structural change. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]