Efficient conditional failure analysis: application to an aircraft engine component

Although many engineering systems and components have a very low probability of failure, the consequences of failures can be catastrophic. The low failure probability precludes the safety certification of such systems or components on the basis of repeated experiments. Therefore the certification must necessarily be done on the basis of adequately validated computational models. Conditional failure analysis (CFA) can be used to provide insight into the failure of a component and the most likely range of values of the input random variables associated with failure. It not only provides valuable information to the engineer for improvement of component design, but also helps to validate the mathematical models and probabilistic input distributions associated with reliability computations. The CFA technique outlined in this paper is based on generation of conditional failure samples obtained during computation of component reliability. It provides a graphical description of the failure region that can be used for failure analysis. The technique is illustrated for a practical design problem involving the fatigue crack growth limit state of a gas turbine engine component. The results can be applied to failure analysis and model validation of general aerospace components.