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    Description of Crack Growth Using the Strip-Yield Model for Computation of Crack Opening Loads, Crack Tip Stretch, and Strain Rates

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    Nowadays, application of the strip-yield model for computation of crack opening load levels is well known. In this paper the incremental formulation of a fatigue crack growth law is used to demonstrate the role of the crack opening load level in time-independent fatigue crack growth. Less known is the ability of the strip-yield model to define the strain rate at the crack tip. A threshold level εth of this strain rate is introduced and used to formulate a criterion for initiation of time-dependent accelerated fatigue crack growth. This process is called corrosion fatigue. To account for effects of environment and frequency on the crack growth rate a time-dependent part is added to the incremental fatigue crack growth law. The resulting incremental crack growth equation is integrated to obtain the crack growth rate for a load cycle.

    The model discussed in this paper is a mechanical model. Physical aspects other than strain rate, loading frequency and load wave shape are not modeled in an explicit way. Hence, the model is valid for specific environment/base metal combinations. However, in consideration of the effects of small variations of environment, temperature, and other variables on the crack growth rates, it can be used as a reference solution.

    The fatigue crack growth model has been implemented in the NASGRO (ESACRACK) software. The time-dependent part is still subject to further evaluation.


    crack opening loads, crack tip stretch, strain rates, crack growth, fatigue crack growth

    Author Information:

    de Koning, AU
    National Aerospace Laboratory (NLR), NOP,

    ten Hoeve, HJ
    National Aerospace Laboratory (NLR), NOP,

    Henriksen, TK
    European Space Agency (ESA), ESTEC, Noordwijk,

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP15774S