Estimation of crack control reliability for aircraft structures

Достоверность обнаружения трещин методами неразрушающего контроля (НК) определяется вероятностью обнаружения дефекта с заданным размером а – POD(a). Показано, что этот показатель определяет надежность всей системы НК, включая человеческий фактор. На примере использования вероятностного подхода Бейеса с учетом POD(a) показана возможность некорректного обоснования эмпирического распределения размера дефектов.The realization of the damage tolerance concept for aviation structures is defined appreciably by solution of a problem of the damage detection reliability by nondestructive inspection (NDI) methods. The reliability of cracks detection by NDI methods is defined by probability of detection of the given flow size a – POD (a). The reliability index of the NDI taking into account the reliability of the flow detection or miss POD (a) is the probability of the crack size detection more than a. Another reliability index of the NDI system, which depends on POD (a), is the missing probability of the crack size more than a. It is shown that POD (a) defines reliability of all NDI system, including the human factor. The example of a wing surface control by eddy currents is considered for the plane round rivet holes in knots of skin and stringer fastening. The distribution of the detected crack length is described by a Weibull distribution (a posteriori distribution). However, this distribution cannot be accepted as correct because the part of cracks will be not detect under control (especially small sizes cracks). It is shown that a priori (valid) crack length distribution can be defined by using of the Bayesian probabilistic approach, which essentially differs from initial Weibull distribution. The approach offered in this paper is useful to an estimation of a technical condition of aircraft structures by results of operation defects testing