Abstract
Abstract —An experimental method was developed to quantify the formation and subcritical propagation of small cracks emanating from artificial surface defects. Continuous crack depth information was obtained from dc electrical potential measurements employing an analytical model. Fatigue experiments were conducted to evaluate the crack monitoring procedures for conditions relevant to the elevated temperature defect tolerance of superalloys. Cracking progressed uniformly and predictably from small surface defects (0.1 mm deep and 1.4 mm long) in A286, 304 and 10Ni steels and in René 95 and MP–159 superalloys. Crack depths, computed based on analytical calibration of measured electrical potentials, agreed to within ±18% of corresponding values measured optically. Similar results were obtained for a penny‐shaped defect, 75 μm deep. Applications of the technique were investigated, including characterizations of fatigue crack formation and growth in René 95.
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