STP1343: Description of Crack Growth Using the Strip-Yield Model for Computation of Crack Opening Loads, Crack Tip Stretch, and Strain Rates

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

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

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

    Pages: 16    Published: Jan 1999


    Abstract

    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.

    Keywords:

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


    Paper ID: STP15774S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP15774S


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