Fatigue crack-growth reliability

A method is shown for estimating the reliability of structural components subject to fatigue crack growth. The method is general in that it can be used in conjunction with any crack-growth law and either first- or second-order reliability techniques. The initial crack length, final crack length, and crack-growth parameters are taken as uncertain with known probability distributions, and the reliability is calculated by determining the probability that the component will survive to some desired service life. The method accounts for the effect of structural configuration on crack growth and can be adapted to take advantage of finite element methodologies. Two examples demonstrate the method. In the first example, the component is inspected and taken out of service when the crack length reaches a predetermined value. In the second example, the component is kept in service until the fracture toughness of the material is exceeded. In both examples the Weibull distribution is used to show the relation between the method and standard timedependent reliability techniques.