Hierarchical computational approaches of the effects of interstitial and vacancy loops on plastic deformation
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Hierarchical computational approaches of the effects of interstitial and vacancy loops on plastic deformation Tomohito Tsuru 1, Yoshiteru Aoyagi 1 and Yoshiyuki Kaji 1 1 Nuclear Science and Engineering Directorate, Japan Atomic Energy Agency, 2-4 ShirakataShirane, Tokai-mura, Ibaraki, Japan ABSTRACT Hierarchical modeling based on atomistic and continuum simulations were established to describe the fundamental characteristics of plastic deformation in irradiated materials. Typical irradiation defects of a self-interstitial atom (SIA) loop and vacancy loop are considered. At first atomic models, including a SIA loop and a vacancy as well as a straight dislocation loop in single crystals were constructed. Constant strain is applied to each model and the equilibrium configuration under deformation is calculated by a molecular statics simulation. Maximum shear stresses in various radii of irradiated defects are stored in a database for the continuum mechanics analysis. Then local interaction events between glide dislocation and irradiation defects were introduced through crystal plasticity finite element analysis. In this model the effect of radiation hardening was considered by referring to the experiment. We found that softening after the first yield event is caused by annihilation of irradiation defects resulting from unfaulting of the radiation defects. INTRODUCTION In recent years, cracks in the internal components of operating boiling water reactors have been observed, which is due to the material properties being changed by accumulating irradiation. Neutron irradiation-induced embrittlement caused by irradiation fluence is one of the central issues in recent ageing management and maintenance of nuclear power plants. Among various problems on irradiation, irradiation-assisted stress corrosion cracking (IASCC) which is induced from the combined influence of material properties, tensile stress, being in a corrosive environment and neutron irradiation, is a quite complicated and high-priority problem [1-3]. In general failure of the core components, cracks propagate along the grain boundaries, so-called intergranular SCC. Although intergranular failures have so far been thought to be caused by thermal sensitization around the grain boundary, recent studies indicate that another undiscovered mechanism could cause IASCC since no chromium-depleted-layer is observed along the grain boundary. Thus, a renewed recognition of the IASCC mechanism is required. Dislocation channeling observed in irradiated metals is generated as the result of strain localization and is thought to be the one of the potential dominant stress factors in IASCC [4]. The stress concentration is produced by a number of plied-up dislocations at grain boundaries due to the localized accumulation of dislocation. Although the conclusive mechanism of IASCC is still not fully understood due to the number of complicated factors contributing to crack propagation, the role of irradiation defect-generated cascade damage on plastic deformation is one of the key i
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