Modeling mechanical response and texture evolution of a-uranium as a function of strain rate and temperature using polycrystal plasticity Marko Knezevic ⇑ , Rodney J. McCabe, Carlos N. Tomé, Ricardo A. Lebensohn, Shuh Rong Chen, Carl M. Cady, George T. Gray III, Bogdan Mihaila Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA article info Article history: Received 10 August 2012 Received in final revised form 26 October 2012 Available online 15 November 2012 Keywords: A. Anisotropic material A. Microstructures A. Twinning B. Rate-dependent material B. Temperature-dependent material abstract We present a polycrystal plasticity model based on a self-consistent homogenization capa- ble of predicting the macroscopic mechanical response and texture evolution of a-uranium over a wide range of temperatures and strain rates. The hardening of individual crystals is based on the evolution of dislocation densities and includes effects of strain rate and tem- perature through thermally-activated recovery, dislocation substructure formation, and slip-twin interactions. The model is validated on a comprehensive set of compression tests performed on a clock-rolled a-uranium plate at temperatures ranging from 198 to 573 K and strain rates ranging from 10 3 to 3600 s 1 . The model is able to reproduce the stress–strain response and texture for all tests with a unique set of single-crystal hardening parameters. We elucidate the role played by the slip and twinning mechanisms and their interactions in large plastic deformation of a-uranium as a function of strain rate and temperature. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Uranium and uranium alloys are nuclear material systems important for defense-related and energy applications includ- ing metallic nuclear fuels. These materials usually have low-symmetry crystal structures and exhibit complex deformation behavior. During manufacturing and in service, these materials may be subject to high temperature and/or high strain rate conditions. Predicting the material behavior and microstructure evolution during processing and service requires material models that account for temperature and strain rate effects. The accuracy of such models is particularly important for nu- clear materials where operating conditions and material hazards may limit the ability to perform experiments to evaluate the material behavior. The room-temperature allotrope of uranium metal, a-uranium (a-U), is stable up to 940 K and has an orthorhombic crys- tal structure. Due to its low-symmetry crystal structure, the deformation behavior of a-U single crystal exhibits strong anisotropy. Polycrystalline aggregates of a-U are also highly anisotropic due to pronounced texture (non-random distribu- tion of crystallographic orientations) introduced by thermo-mechanical processing. a-U deforms by a wide variety of plastic deformation mechanisms with considerably different activation stresses, and these activation stresses evolve differently with deformation making the evolution of macroscopic hardening also highly anisotropic. Studies of the deformation mech- anisms of single-crystal a-U and the mechanical response of a-U aggregates date back over 50 years (Anderson and Bishop, 1962; Cahn, 1951, 1953; Daniel et al., 1971; Fisher and McSkimin, 1958). The dislocation glide and deformation twinning modes accommodating plastic strains were identified and their relative strengths were measured for single crystals. It 0749-6419/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijplas.2012.10.011 ⇑ Corresponding author. Tel.: +1 505 665 7587; fax: +1 505 667 8021. E-mail address: knezevic@lanl.gov (M. Knezevic). International Journal of Plasticity 43 (2013) 70–84 Contents lists available at SciVerse ScienceDirect International Journal of Plasticity journal homepage: www.elsevier.com/locate/ijplas