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    Development of a Numerical Model for Predicting Fatigue Lives of Tubular Threaded Connections

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    Tubular threaded connections are used in the off-shore oil industry for applications such as tension leg platforms and drill string components. The design of these components requires full-scale fatigue testing to ensure their reliability. This is an extremely expensive undertaking (actual connectors may be as large as 1.2 m in diameter). Therefore, an analytical method is needed to provide preliminary estimates of how various parameters will affect the fatigue lives of the connections. This model must have the ability to estimate fatigue life under variable amplitude cyclic loading conditions. The key to such a model is relating the applied variable amplitude loading history to the local elasto-plastic stress-strain response at the roots of the threads. The load dependent nature of the stress concentration factor in preloaded threaded connections requires the use of a numerical solution to determine the local stresses. The development of this model is described starting with a discussion of the type of loading and fatigue failure that must be modeled, the assumptions that are made in developing the model, and the synthesis of the numerical solution and its application to predicting the fatigue life of a real connector geometry. The fatigue crack initiation life is calculated using the strain-life approach. The model is then used to demonstrate the effects on fatigue life that result from changing various aspects of the connector design, such as geometry and load configuration.


    threads, fatigue, stress concentration factor, load distribution, finite element analysis (FEA)

    Author Information:

    Liebster, TD
    Graduate student and professor, University of Waterloo, Waterloo, Ontario

    Glinka, G
    Graduate student and professor, University of Waterloo, Waterloo, Ontario

    Committee/Subcommittee: E08.01

    DOI: 10.1520/STP13991S