Mode I Fracture Testing on Zirconium Foils Under Plane-stress Condition
Zirconium alloys are commonly used in nuclear reactor in-core components due to their good mechanical properties and low neutron-absorption cross-section. Especially for CANada Deuterium Uranium (CANDU) reactors, zirconium alloys serve as the main structural material for fuel channels. In order to ensure such Zr components operate safely, fracture analysis of Zr alloys has been widely studied. Considering the high cost and difficulties associated with using neutron-irradiated Zr specimens for fracture analysis, proton irradiated testing has been proposed to reduce the cost and maintain a good control of experimental conditions during irradiation. However, limited by the proton penetration depth, fracture testing on proton-irradiated samples needs to be conducted on thin foils which brings increased plastic deformation due to the low constraint. This dissertation mainly focuses on conducting fracture testing with Zr foils. Combined with finite element modeling, scanning electron microscopy analysis, and digital image correlation analysis, the fracture behavior at a crack tip from both macroscopic strain analysis and microscopic dislocation motion analysis was achieved. The current study is comprised of three manuscript chapters. The Mode I fracture testing of Zr foils under plane-stress conditions is discussed in Chapter 3. Using conventional fracture testing combined with digital image correlation analysis, the J-integral, J-resistance curves and the singular strain field in front of a crack were all obtained. In Chapter 4, the dislocation evolution at the crack-tip field was analyzed during the crack initiation and propagation stages from a microscopic perspective. Both fracture toughness J-integral analysis and geometrically necessary dislocation determination indicate a single J-integral characterized crack-tip field may exist in Zr foils regardless of the large scale yielding condition. The crack propagation behavior was investigated from a crystallographic view in Chapter 5. Schmid factor analysis were compared with the geometrically necessary dislocation determination and relatively good agreement was observed. It was found that the crack is more likely to propagate along grains with c-axis close to the loading axis. A general discussion is given in Chapter 6, followed by a summary in Chapter 7.