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An experimental method, developed to monitor the formation and subcritical propagation of small surface cracks, was evaluated and confirmed by comparisons with conventional “large” crack data. Analytical procedure were developed to produce quantitative crack growth rate—stress-intensity data from measured electrical potential values. Accurate and reproducible results were obtained for surface-defected specimens of 10Ni steel, machined from the heat of material investigated in an ASTM interlaboratory exchange program. Specifically, crack growth rates between 10−6 and 10−3 mm/cycle were correlated uniquely with the stress-intensity range, independent of crack depth (0.10 to 0.80 mm) and applied stress (30 to 90 percent of σys). Data obtained for small surface cracks were in excellent agreement with the growth rate—stress-intensity relationship developed based on conventional tests with compact tension and center crack panel specimens. Accelerated cracking, associated with “short” crack effects, was not observed. The electrical potential monitoring technique for small surface cracks was qualified for investigations of “short” crack effects, and for screening studies requiring timely data acquisition.
fatigue (materials), crack propagation, fracture mechanics, steel, defects
Metallurgist, Corporate Research—Science Laboratory, Exxon Research and Engineering Company, Linden, N.J.