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A critical examination of fatigue crack closure concepts indicates that (a) procedures commonly followed in estimating crack closure are in error, (b) complete premature crack closure occurs only when cracks are completely filled with oxides or corrosion products, (d) such closure manifests as an infinite slope in the load-displacement (crack mouth opening) curves; rarely observed in experiments, (e) asperities cause only local closure, (f) their contribution is less significant than is assumed and (g) plasticity does not contribute to closure. New concepts are developed to explain fatigue phenomena hitherto attributed to crack closure. Implications of these concepts to understand fatigue crack growth are discussed.
fatigue, crack closure, fatigue thresholds, crack growth, load ratio, dislocation model, asperity, plasticity
Section Head, Naval Research Laboratory, Code 6323, Naval Research Laboratory, Washington D.C.,
Program Manager, Office of Naval Research, Arlington, V.A.