STP668

    An Elastic-Plastic R-Curve Description of Fracture in Zr-2.5Nb Pressure Tube Alloy

    Published: Jan 1979


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    Abstract

    An R-curve approach was investigated with the aim of establishing a means of predicting critical crack lengths in Zr-2.5Nb pressure tubes using small fracture-mechanics specimens. Because of the elastic-plastic nature of the fracture process and limitations on the maximum specimen size, conventional R-curve methods were not applicable. The crack growth resistance was therefore expressed in terms of the crack opening displacement (COD) and R-curves were plotted for several sizes of specimens and crack lengths at 20°C and at 300°C. The effect of hydrogen on R-curve behavior at these two temperatures was investigated as well.

    Conventional clip-gage methods were not suitable for this work. Crack length was determined from electrical resistance, and COD, at the actual crack front, was determined from photographs of the specimens taken during testing. Crack length and specimen size had little, if any, effect on the R-curve shape. A method for expressing crack growth resistance in terms of the J-integral was also investigated and appears to be consistent with the COD approach. The effects of hydrogen and temperature on R-curve shape are consistent with their known effects on the mechanical behavior of Zr-2.5Nb. Finally, predictions of critical crack length in pressure tubes obtained by matching R-curves to crack driving force curves are consistent with published burst-testing data.

    Keywords:

    crack propagation, fracture, R-curves, metals, zirconium, pressure tubes, potential drop


    Author Information:

    Simpson, LA
    Research officer and research technician, Atomic Energy of Canada Ltd., Whiteshell Nuclear Research Establishment, Pinawa, Man.

    Clarke, CF
    Research officer and research technician, Atomic Energy of Canada Ltd., Whiteshell Nuclear Research Establishment, Pinawa, Man.


    Paper ID: STP35852S

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP35852S


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