Title: Atomistic simulation of high strain rate plasticity, spall damage, and fracture of crystalline and polycrystalline metals: Nanocrystalline Cu; single crystal Al; nano-precipitates influence Speaker: Prof. Henry Norman, Alexey Yanilkin, Alexey Kuksin, Vladimir Stegailov, Joint Institute for High Tempertures of the Russian Academy of Sciences, Moscow, Russia Date/Time: Monday, July 2, 2007, 10:00 am – 11:00 am Location: CSRI Building/Room 95 (sandia NM) Brief Abstract: Modeling and simulation of dynamic atomistic phenomena and processes accompanying intensive shock compression and release, and uniaxial and hydrostatic stretching in condensed matter are discussed. Employing standards for molecular dynamics (MD) modeling and simulation of relaxation processes [A.Y. Kuksin et al., “Standards for molecular dynamics modelling and simulation of relaxation,” Molecular Simulation 31 (2005) 1005-1017] we summarize our investigations of high strain rate deformation of Al, Cu, and Al or Cu with nanoprecipitates of the other metal. Microscopic mechanisms of plasticity and fracture in nanocrystalline copper are considered using the EAM potential model [Y. Mishin et al // PRB 63 (2001) 224106] to describe interatomic potential. Three ways of the high strain rate (10^8/s -- 10^10/s) plastic deformation and fracture processes modeling are compared: hydrostatic, uniaxial strain, and shock wave loading in the impactor-target model. The dependence of the results on the average grain size, orientation and shape is studied. We then present the kinetic model of fracture of single crystal Al under high-rate strain based on the results of molecular dynamic (MD) simulations. At temperatures close to the melting point, void formation is shown to be a process of crystal homogeneous melting with cavitation occuring in the melt. With the help of the developed model, the dynamic spall strength of ideal single crystal Al is calculated. The results obtained are compared with the experimental data [G.I. Kanel et al. // J. Phys.: Cond. Mat. 16 (2004) S1007]. While good agreement is observed in the high-temperature region, it becomes worse when temperature decreases. This fact could manifest the increasing role of defects. The dependence of the spall strength on loading duration and on strain rate is governed mostly by nucleation rate of voids and not by their growth rate. Last, we discuss simulations motivated by recent experimental results [G.I.Kanel et al., 2006] that show the essential influence of the nanoprecipitates on spall strength of copper single crystals. We consider the EAM systems of Al nanoclusters in the Cu matrix and Cu clusters in the Al matrix as the representative examples of nanocluster-matrix difference in shear strength. Interaction of preexisting edge dislocations with the precipitate under shear deformation is addressed. The effect of the precipitate size is considered. CSRI POC: John Aidun, (505) 844-1209 |