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    Volume 1, Issue 2 (February 2004)

    Probabilistic Life Prediction Isn't as Easy as It Looks

    (Received 29 August 2002; accepted 11 August 2003)

    Published Online: 18 February 2004


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    Many engineers effect “probabilistic life prediction” by replacing constants with probability distributions and carefully modeling the physical relationships among the parameters. Surprisingly, the statistical relationships among the “constants” are often given short shrift, if not ignored altogether. Few recognize that while this simple substitution of distributions for constants will indeed produce a nondeterministic result, the corresponding “probabilities” are often woefully inaccurate. In fact, even the “trend” can be wrong, so these results can't even be used for sensitivity studies. This paper explores the familiar Paris equation relating crack growth rate and applied stress intensity to illustrate many statistical realities that are often ignored by otherwise careful engineers. Although the examples are Monte Carlo, the lessons also apply to other methods of probabilistic life prediction, including FORM/SORM (First/Second Order Reliability Method) and related “fast probability integration” methods.

    Author Information:

    Annis, C
    Principal, Charles Annis, P.E., Statistical Engineering, Palm Beach Gardens, FL

    Stock #: JAI11557


    DOI: 10.1520/JAI11557

    Title Probabilistic Life Prediction Isn't as Easy as It Looks
    Symposium ,
    Committee E08