Molecular dynamics simulations of shock-induced plasticity in tantalum Diego Tramontina a, b , Paul Erhart c, k , Timothy Germann d , James Hawreliak c , Andrew Higginbotham e , Nigel Park f , Ramón Ravelo d, g , Alexander Stukowski h , Mathew Suggit e , Yizhe Tang i , Justin Wark e , Eduardo Bringa b, j, * a Agencia Nacional de Promoción Científica y Tecnológica, CABA, C1054AAH, Argentina b Instituto de Ciencias Básicas, Universidad Nacional de Cuyo, Mendoza M5502JMA, Argentina c Lawrence Livermore National Laboratory, Livermore, CA 94550, USA d Los Alamos National Laboratory, Los Alamos, NM 87545, USA e Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, UK f Materials Modeling Group, AWE, Aldermaston, Reading, Berkshire RG7 4PR, UK g Physics Department and Materials Research Institute, University of Texas, El Paso, TX 79968, USA h Darmstadt University of Technology, Darmstadt 64289, Germany i Johns Hopkins University, Baltimore, MD 21218, USA j Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina k Chalmer University of Technology, Department of Applied Physics, Gothenburg 41296, Sweden article info Article history: Received 10 October 2013 Accepted 16 October 2013 Available online 31 October 2013 Keywords: Tantalum Molecular dynamics Shocks abstract We present Non-Equilibrium Molecular Dynamics (NEMD) simulations of shock wave compression along the [001] direction in monocrystalline Tantalum, including pre-existing defects which act as dislocation sources. We use a new Embedded Atom Model (EAM) potential and study the nucleation and evolution of dislocations as a function of shock pressure and loading rise time. We find that the flow stress and dislocation density behind the shock front depend on strain rate. We find excellent agreement with recent experimental results on strength and recovered microstructure, which goes from dislocations to a mixture of dislocations and twins, to twinning dominated response, as the shock pressure increases. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Shock compression of condensed matter allows the study of materials under extreme conditions [1]. Improving experimental and simulation techniques allow detailed studies of the shock- induced microstructure, which can lead to large changes in me- chanical properties. A large amount of work has been recently carried out for Face-Centered Cubic Metals (FCC) [2e13], and Body- Centered Cubic metals (BCC) [2,14e20]. However, most of the work on BCC metals has focused on Fe, due to the large number of technological applications for Fe, for instance as part of structural materials, and also due to the role of Fe properties in Earth’s interior mechanics. Fe displays a solidesolid phase transformation near 15 GPa, which makes dislocation plasticity difficult to identify in simulations [21e23]. Atomistic simulations of high strain rate loading of BCC metals [3,24e26] are sparse, mostly due to the lack of interatomic poten- tials which are reliable at high pressures. In particular, it has been shown for Nb [18] and Ta [27], that many potentials display an artificial phase transition from BCC to Hexagonal Close-Packed (HCP). Among BCC metals, Ta has several technological applications, and no phase transitions are thermodynamically present up to fairly high pressures and temperatures [28]. Shock-loaded Ta has been studied using both gas-gun [29] and laser-driven shocks [30e32]. These experiments show a rich behavior, including high strength [32,33], dislocations [29e31], twinning above a critical pressure around 40 GPa [30,31,34,35], and the presence of u- phase [30,31] in some recovered samples shocked above w70 GPa. Recent Non-Equilibrium Molecular Dynamics (NEMD) simula- tions from Cuesta-Lopez and Perlado [36] subjected Ta, W and Fe monocrystals to particle velocities U p ranging from 0.1 to 2.5 km s 1 , spanning the elastic to shock-melting response. They did not observe dislocation activity, but instead found nucleation * Corresponding author. Instituto de Ciencias Básicas, Universidad Nacional de Cuyo, Mendoza M5502JMA, Argentina. E-mail address: ebringa@yahoo.com (E. Bringa). URL: http://sites.google.com/site/simafweb/ Contents lists available at ScienceDirect High Energy Density Physics journal homepage: www.elsevier.com/locate/hedp 1574-1818/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.hedp.2013.10.007 High Energy Density Physics 10 (2014) 9e15