STP982: Effects of Closure on the Fatigue Crack Growth of Small Surface Cracks in a High-Strength Titanium Alloy

    Jira, JR
    Materials engineer, materials research engineer, and materials research engineer, Materials Laboratory, Air Force Wright Aeronautical Laboratories, AFWAL/MLLN, Wright-Patterson Air Force Base, OH

    Weerasooriya, T
    Research scientist, University of Dayton Research Institute, Dayton, OH

    Nicholas, T
    Materials engineer, materials research engineer, and materials research engineer, Materials Laboratory, Air Force Wright Aeronautical Laboratories, AFWAL/MLLN, Wright-Patterson Air Force Base, OH

    Larsen, JM
    Materials engineer, materials research engineer, and materials research engineer, Materials Laboratory, Air Force Wright Aeronautical Laboratories, AFWAL/MLLN, Wright-Patterson Air Force Base, OH

    Pages: 19    Published: Jan 1988


    Abstract

    Fatigue crack growth experiments were conducted on surface flaws in a high-strength titanium alloy. Surface crack lengths in the range 50-μm to 8 mm were investigated under both increasing and decreasing ΔK conditions. Crack length and closure loads were determined from load-displacement data obtained with the aid of a laser interferometric displacement gage, which has resolution capability at 0.01 μm. Stress ratios of 0.1, 0.5, and −1.0 and net-section stress levels from 0.2 to 0.9 of yield stress were utilized. The applied stress intensity factor range, ΔK, correlated crack-growth-rate data for R = 0.1 and R = −1, but all R = 0.5 data fell along a separate band. The effective stress intensity factor range ΔKeff determined from closure data, consolidated most of the data into a single band, but some small-crack data fell outside the band. Fracture surface roughness and plasticity were concluded to be the primary features contributing to crack closure.

    Keywords:

    crack closure, crack propagation, fatigue (materials), fracture mechanics, mechanical properties, minicomputers, microcracks, short cracks, small cracks, surface cracks, test methods, titanium alloys


    Paper ID: STP27236S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP27236S


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