Comparison of Methods for Calculating <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>B</mi></mrow></math></inline-formula>-Basis Crack Growth Life Using Limited Tests

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Comparison of Methods for Calculating $B$ -Basis Crack Growth Life Using Limited Tests

Bhachu, K. S. / Haftka, R. T. / Kim, N. H.

Large sampling uncertainty is generally introduced in the calculation of a low percentile of fatigue crack growth life due to a small number of coupon tests. It is often desirable to estimate a low percentile (for example, 10th percentile) with a certain coverage probability (for example, 95%) using the confidence bound approach. An equally competing objective is not to have overly conservative bounds.The performance of two bootstrap-based methods are investigated for calculating a one-sided 95% confidence bound on a low percentile of lognormal and gamma fatigue crack growth life distributions. A comparison is also made with the classical tolerance interval method and nonparametric (Hanson–Koopmans) method. These confidence bounds methods are tested to estimate $B$ -basis fatigue crack growth design life using material properties estimated from coupon test samples ranging from 8 to 64.