STP927

    Fatigue Life Improvement by Cold Working Fastener Holes in 7050 Aluminum

    Published: Jan 1986


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    Abstract

    The effect of cold working on the fatigue life of 7050-T7451 aluminum that contained fastener holes was investigated. The holes were cold worked using the split sleeve technique. The fatigue life improvement achieved by inserting interference fit fasteners in both cold worked and non-cold worked holes was also determined. Fatigue tests were conducted under constant amplitude loading conditions. Additional evaluations were conducted, including determinations of the effects of precracks emanating from the hole (introduced prior to cold working), specimen orientation, and the amount of material reamed from a hole following cold working. Fractographic and metallographic analyses were undertaken to determine typical crack initiation sites. Cold working of fastener holes in 7050-T7451 increased the fatigue life by a factor of up to five, depending upon the specific cold work and fatigue test parameters employed. The insertion of interference fit fasteners also significantly increased fatigue life. Contributions from interference fit fasteners and cold working of holes were synergistic. The introduction of a precrack prior to cold working the hole reduced fatigue life, though precracked material containing a cold worked hole exhibited a greater fatigue life than if the hole had not been cold worked. The optimum amount of material that should be reamed from a hole after split sleeve cold working to give the maximum fatigue life for given test parameters was determined.

    Keywords:

    7050-T7451 aluminum, split sleeve cold working, fatigue life, interference fit fasteners, reaming, precracks, constant amplitude loading


    Author Information:

    Ozelton, MW
    Engineering specialist and manufacturing technology specialist, Northrop Corp., Hawthorne, CA

    Coyle, TG
    Engineering specialist and manufacturing technology specialist, Northrop Corp., Hawthorne, CA


    Paper ID: STP29054S

    Committee/Subcommittee: E08.04

    DOI: 10.1520/STP29054S


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