SEDL / STP / STP905-EB / STP17408S

Fracture Toughness Testing of Zircaloy-2 Pressure Tube Material with Radial Hydrides Using Direct-Current Potential Drop

Davies, PH
Research Engineer and Technologist, Atomic Energy of Canada Ltd., Chalk River Nuclear Laboratories, TorontoChalk River, OntarioOntario

Stearns, CP
Research Engineer and Technologist, Atomic Energy of Canada Ltd., Chalk River Nuclear Laboratories, TorontoChalk River, OntarioOntario

Pages: 22    Published: Jan 1986

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Abstract

This paper addresses problems involved in measuring fracture toughness of thin pressure tube material which, in the presence of radial-axial hydrides, undergoes a significant brittle to ductile fracture transition. Compact tension specimens (∼5 mm thickness) are machined from flattened tensile strips of Zircaloy-2 in which radial hydrides (30 to 100 ppm hydrogen) are produced by precipitation under stress. Axial fracture toughness is determined for the unirradiated material between room temperature and 300°C using the dc potential drop method. At low and intermediate temperatures crack growth is governed predominantly by the presence of the radial hydrides, and the potential drop is shown to underestimate crack extension due to short-circuiting across tight crack faces. In the upper shelf regime where crack extension is governed mainly by the flow properties of the matrix, the potential drop overestimates crack extension due to through-thickness yielding. It is shown that good, reproducible results can be obtained by careful data analysis using individual specimen calibrations.