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    Investigation of Cyclic Crack Growth Transitional Behavior

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    Observations of tensile to shear transition behavior of fatigue crack fronts have been recorded numerous times during tension-tension cycling of sheet materials. Based on recent crack growth data, correlation of shear lip development and associated crack tip stress intensities has been obtained for a variety of aluminum, steel, and titanium alloys. Assumption of a crack growth transition zone region allows for direct application to deviations in crack growth rate versus stress-intensity relationships at low crack tip intensities. A stress-controlled specimen of 7075-T6 aluminum sheet was fatigue cycled from tensile to shear and back to tensile within the transition zone; crack front behavior was microscopically observed. Macroscopic and microscopic correlations were established with discontinuities in stress intensity versus crack growth semilog relationships. The beginning of shear lip development in 2024-T3 aluminum appears to be independent of thickness and dependent only on the stress-intensity factor at transition.


    fatigue (materials), crack popagation, aluminum alloys, steels, titanium alloys, crack growth rate, fracture, transitional behavior, microstructure, stress intensity

    Author Information:

    Wilhem, D. P.
    Senior engineer, Northrop Corp., Hawthorne, Calif.

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP47236S