STP677: Prediction of Fatigue Crack Growth Under Spectrum Loads

    Gemma, AE
    Senior assistant project engineer and analytical engineer, United Technologies Corp., Pratt and Whitney Aircraft Group, East Hartford, Conn.

    Snow, DW
    Senior assistant project engineer and analytical engineer, United Technologies Corp., Pratt and Whitney Aircraft Group, East Hartford, Conn.

    Pages: 19    Published: Jan 1979


    Abstract

    The reduced crack growth rate caused by each high-low load sequence of a complex load spectrum is modeled by a modified empirical constant-amplitude crack propagation relationship. The modification consists of the replacement of the crack rate term by a fractional derivative. The order of the derivative is a nondimensional parameter which is defined in terms of each high-low load sequence occurring in the spectrum. A cycle-by-cycle solution of the fractional differential equation yields the crack growth behavior for the spectrum. The approach is evaluated by comparing predictions with available experimental results for three aluminum alloys (7075-T6, 7050-T73, 2024-T3), two titanium alloys (Ti-6A1-4V, Ti-6Al-2Sn-4Zr-6Mo) and a nickel base superalloy IN-100. In all cases the method accurately predicted the general trends and estimates were well within a factor of two for 39 out of 40 tests analyzed.

    Keywords:

    crack propagation, fatigue (materials), delay cycles, overload, retarding, aluminum alloys, titanium alloys, predictions


    Paper ID: STP34921S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP34921S


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