The measurement of creep crack growth rates by a notch region extension method

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Abstract
A simple and accurate method for measuring creep crack growth rates from a starter notch is described. The method consists of measuring the notch region extension at various points along the path of the crack in a ruptured tensile creep specimen. The time dependence of the notch region extension is obtained from the overall specimen extension measured during the test. Collating the two sets of measurements enables the instantaneous crack length and its variation with time to be determined. Experimental determination of creep crack length changes in AISI type 316 stainless steel specimens have been performed by this method and the results compared with those obtained by the DC potential drop technique. The notch region extension method is of particular value in examining the kinetics of crack propagation under conditions where only simple post-test measurements are possible or when specimens are exposed to hazardous or closely controlled reactive environments. Some typical applications would be the determination of crack growth rates for irradiated specimens and specimens exposed to a liquid sodium environment.

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