Detection of Fatigue Damage in Crankshafts with the Gel Electrode 930409

During fatigue testing of prototype austempered ductile iron crankshafts, cracks formed along crankpin fillets. These cracks were not detected by the conventional magnetic particle method but were readily imaged by a modified version of the gel electrode technique. The crankshaft was coated with a thin (∼0.5 μm) polymer film, either prior to, or after, the fatigue test. When the surface was subsequently inspected with a gel electrode probe, an impressed current from the probe flowed preferentially to the fatigue sites. Information is displayed in two formats:
  1. (i)
    qualitatively as a direct image of the fatigue sites, and
  2. (ii)
    quantitatively as the spatial distribution of charge flow to the surface. Both the primary fatigue cracks and a distribution of secondary sites of less severe fatigue damage were detected. The cracks formed near the edges of a fillet while the root of a fillet developed primarily secondary fatigue damage.


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