Overload Fracture Resistance of Flaw-Tip δ-hydrides in Zr-2.5Nb Pressure Tubes by High-Resolution Digital Image Correlation

Abstract

The pressure tubes of Canada Deuterium Uranium (CANDU) reactors are made of Zr-2.5Nb alloy, which is susceptible to hydrogen embrittlement by delayed hydride cracking (DHC). The present work investigates the fracture initiation of the Zr-2.5Nb alloy when hydrides precipitate under stress (in the radial-axial plane) in a simulated flaw-tip. In-situ high-resolution digital image correlation (HR-DIC) was used to understand the hydride and the matrix deformation during overload conditions (when the hydride is stressed past its formation stress). A key observation was the distinction between the flaw-tip hydride and Zr-2.5Nb matrix strain at 225 °C. Also, the localized plasticity in the Zr-2.5Nb matrix at 225 °C prevented the hydride fracture up to 380% overload.