Atomistic to Continuum Constitutive Modeling of Radiation Damage on FCC Metals and its Adaptation for the Generation of
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Atomistic to Continuum Constitutive Modeling of Radiation Damage on FCC Metals and its Adaptation for the Generation of New Materials Shree Krishna1 and Suvranu De1* 1 Department of Mechanical, Aerospace, and Nuclear Engineering Rensselaer Polytechnic Institute 110 8th St., Troy, NY 12180, USA Email: [email protected]; [email protected] ABSTRACT The paper presents a rate-independent dislocation growth and defect annihilation mechanism to capture the pre- and post-yield material behavior of FCC metals subjected to different doses of neutron radiation. Based on observation from molecular dynamics simulation and TEM experiments, the developed model is capable of capturing the salient features of irradiation induced hardening including increase in yield stress followed by yield drop and non-zero stress offset from the unirradiated stress-strain curve. The key contribution is a model for the critical resolved slip resistance that depends on both dislocation and defect densities which are governed by evolution equations based on physical observations. The result is an orientation-dependent nonhomogeneous deformation model which accounts for defect annihilation on active slip planes. Results for both single and polycrystalline simulations of OFHC copper are presented and are observed to be in reasonably good agreement with experimental data. Extension of the model to other FCC metals is straightforward and is currently being developed for BCC metals giving its way for generation of new materials. INTRODUCTION In this paper we present a micromechanics-based model for the nonlinear mechanical response of FCC metals subjected to neutron radiation. It is well-known that the macroscopic response of irradiated materials is a manifestation of mechanisms occurring at disparate temporal and spatial scales that results from the evolution and interaction of microstructural features including dislocations, defects and grain boundaries [1-2]. In this paper we focus on low to intermediate homologous temperatures (T/ Tm 0.5) where irradiation causes increase in yield strength followed by reduction in ductility. With increase in dose, a yield drop is observed followed by reduction in strain hardening [1-3] It is believed that the increase in yield strength is primarily due to the increase in the number density of defect clusters including stacking fault tetrahedra (SFT) and prismatic dislocation loops that obstruct dislocation motion. These defects are annihilated due to the passage of the dislocations leading to softening and, therefore, yield drop. Defect free channels resulting from the passage of dislocations during plastic loading, observed in in-situ TEM experiments [4] provide indirect evidence in favor of this hypothesis. Various efforts including molecular dynamics simulations [4-6 and several others] and macroscale phenomenological plasticity modeling [3, 6] have been undertaken to predict the post yield stress-strain behavior of FCC metals. Our model is inspired by various in-situ experimental works, particularly Singh et al., [7], R
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