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    Crack Growth Instability in Piping Systems with Complex Loading

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    The ability of high-energy piping systems in nuclear power plants to tolerate large flaws without unstable crack growth during earthquake conditions is the basis for the leak-before-break concept being used for the safety analyses of new and existing plants. In this work, a stability criterion for a crack in a piping system is developed from simple considerations of the moment-carrying capability of the elastic-plastic cracked pipe cross section without regard to the nature or distribution of applied loads. In particular, the constant load-point displacement assumption used for the development of existing applied tearing modulus stability theories is not required. Although the resulting expression appears to be functionally similar to the traditional applied tearing modulus stability criterion, the physical picture of the crack hinge behavior is more general. As a result, this new view of crack stability is more easily justified for application to piping systems subject to multiple-point or distributed loads. The effects of simplifying assumptions regarding purely plastic or perfectly plastic crack hinge behavior on the conservatism of the stability analysis are investigated. In addition, practical considerations for the evaluation of the stability of real piping systems are discussed.


    elastic-plastic fracture, tearing modulus, J, -integral, cracks in pipes, fracture mechanics, nonlinear fracture mechanics

    Author Information:

    Nestell, JE
    Engineers, MPR Associates, Inc., Washington, DC

    Coward, RN
    Engineers, MPR Associates, Inc., Washington, DC

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP27718S