Dynamics and Kinetics of Dislocations in Metals and Alloys Under Dynamic Loading
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Dynamics and Kinetics of Dislocations in Metals and Alloys Under Dynamic Loading Denis Ilnitski1, Vasily Krasnikov2, Alexey Kuksin3,4, Alexander Mayer5, Alexey Yanilkin1,3 1 All-Russia Research Institute of Automatics, Moscow, 22 Sushchevskaya, 127055, Russian Federation 2 South Ural State University, pr. Lenina 76, Chelyabinsk, 454080, Russian Federation 3 Joint Institute for High Temperatures of Russian Academy of Sciences, 13 Izhorskaya, Bld.2, 125412, Russian Federation 4 Moscow Institute of Physics and Technology, 8 Institutski per., Dolgoprudny, 141700, Russian Federation 5 Chelyabinsk State University, 129 Brat’ev Kashirinykh, Chelyabinsk, 454001, Russian Federation
ABSTRACT The work presented is devoted to study the mechanisms and kinetics of plastic deformation of bcc and fcc metals and alloys under shock-wave loading (strain rates > 105 s-1). To study the behavior of metals under conditions described the two scale approach is developed. It comprises molecular dynamics (MD) calculations of dislocation mobility and dislocations nucleation rate and continuum mechanics model with equations for description of elastoplastic deformation, kinetics and dynamics of dislocations. Dislocation velocities as functions of applied shear stress are calculated from MD in a wide temperature range up to the melting point. Velocity-dependent drag coefficient is introduced to approximate the data obtained. The influence of Guinier–Preston (GP) zones on dislocation motion is analyzed. The results obtained are used to evaluate temperature dependence of dynamic flow stress and the evolution of dislocations subsystem under shock loading. Data on the attenuation of the elastic precursor and rare surface velocity profiles calculated for Al are in good agreement with the experiments. Simulation of the free surface velocity profiles during shock-wave loading of AlCu alloys is carried out. INTRODUCTION The behavior of materials under dynamic loading depends strongly on the strain rate. Under low strain rate the dislocation velocity is controlled by the thermal activation of barrier penetration. In single crystals the barriers correspond to the Peierls barriers and dislocation interaction with each other. In alloys additional type of barriers is present: the inclusions of impurities. Under high strain rates the dependence of flow stress on strain rate becomes stronger and its temperature dependence may change as well. It can be attributed to the change of the regime of dislocation motion. Indeed, dislocation velocity is high enough for over-barrier motion of dislocations (without thermal activation) and is limited by a phonon drag. The over-barrier regime can be observed in alloys, when the applied shear stresses are larger than elastic limit observed in quasistatic experiments and correspond to the dynamic loading. The multiscale method, as shown in [1,2], is very useful to describe the plastic deformation under dynamic loading. The different levels of length and time, and different
processes are captured by the different simulation
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