Strain and Dislocation Evolution at Crack Tip in Pure Zirconium Under Non-plane Strain Condition

Abstract

Understanding fracture mechanism of Zr alloy has significant importance in preventing abrupt failure and improving fracture reliability in the fuel channel of CANDU power reactors. Mode I fracture testing was conducted on pure Zr foils to investigate the crack growth behavior and dislocation evolution at a crack tip. The plastic deformation of grains near the crack tip was captured by electron backscattered diffraction (EBSD)maps. The result shows that as the loading level increasing, dislocations were initiated at grain boundaries first, then appeared inside the grains at the crack tip. The grains in the fracture process zone have relatively high dislocation density. Strain localization in this process zone leads to new crack surface creation. Digital Image Correlation (DIC) was also used to measure the strain in front of the crack. The strain obtained from DIC shows similar trend with the dislocation density near the crack tip.