High-Resolution Characterization of Micro-Scale Crack Tip Fields in Zirconium

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Roy, Ronit
In-situ test , Fracture , HR-EBSD , HR-DIC , Crystal plasticity , Zirconium
Zirconium (Zr) alloys are widely used in nuclear reactors as structural core components owing to their low thermal neutron absorption cross-section and adequate mechanical and corrosion properties. To ensure the sustainable design and safe operation of nuclear reactors, understanding the failure mechanisms of these components is essential. In CANDU (CANada Deuterium Uranium) reactors, a few leakages were observed in the 1970s. Since then, the fracture behaviour of Zr has been widely investigated in the nuclear materials community. In the present dissertation, the fracture of Zr and its associated mechanisms are investigated in plane stress conditions in accordance with proton penetration depths, such that the outcome from this research can be used to mimic irradiation effects with proton irradiation in the future. In this dissertation, two high-resolution experimental techniques, high (angular) resolution electron backscatter diffraction (HR-EBSD) and high (spatial) resolution digital image correlation (HR-DIC), are used in combination with crystal plasticity-based finite element (CPFE) analysis for the facture studies. The current dissertation is presented in a manuscript format. Chapters I to III include the Introduction, Literature Review, and Experimental Details. In Chapter IV, localized geometrically necessary dislocation (GND) densities are estimated using HR-EBSD as an indirect measure of plastic deformation ahead of a microscale crack tip. The advantages of HR-EBSD in measuring fine-scale dislocation structures are also described. Chapter V analyzes the elastic field ahead of a microscale crack in Zr with HR-EBSD. The experimental results are compared with CPFE models to identify the effect of a large non-trivial strain floor on the elastic measurements. In Chapter VI, the evolution of the crack tip strain field in Zr is examined with HR-DIC. The experimental results are verified with CPFE models. Next, the slip localization behaviour at the crack tip is analyzed with a Schmid factor analysis. In Chapter VII, a general discussion is presented. The conclusions and recommendations for future works are provided in Chapter VIII.
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