Fatigue crack growth is a key contributor to a decline in reliability of aging aircraft. Knowledge of the distribution of crack sizes is essential to properly evaluate the ability of aging aircraft to continue to perform safely in future missions. The primary tool for determining the crack size distribution is nondestructive inspection. However, not all cracks will be detected, so interpreting the information in the sizes of detected cracks is difficult. This paper will discuss a Bayesian approach to using the results of in-service inspections to quantify the POD function for the inspection system and the distribution of the sizes of the cracks present in aging aircraft. The potential for using Bayesian methods to estimate parameters for both the crack size distribution and the POD function has been demonstrated through a simulation sensitivity study. The use of an informative prior provided the best parameter estimates with a slight degradation when using finite uniform priors centered at the true parameter values. Improper infinite uniform priors produced estimates with considerably more sampling variation than the informative and finite uniform priors. Larger sample sizes generally produce less sampling variation as would be expected. The amount of scatter in the crack size distribution relative to the steepness of the POD curve has an impact on the sampling variation as well. There are clearly better estimates of the crack size distribution parameters when the logarithm of the initial crack size is small compared to sigma and there appears to be some improvement in estimates of the POD function as well although it is not as pronounced as for the crack size distribution parameters.


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    Title :

    Using the information in field service inspections to assess the damage state of the aircraft and the detection capability of the inspection system


    Additional title:

    Nutzung der Information bei Außendienstprüfungen zur Bewertung des Schadenszustandes von Flugzeugen und der Nachweisfähigkeit des Prüfsystems


    Contributors:


    Publication date :

    2008


    Size :

    7 Seiten, 1 Bild, 1 Tabelle, 4 Quellen




    Type of media :

    Conference paper


    Type of material :

    Storage medium


    Language :

    English





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