Fuzzy Probabilistic Assessment of the Impact of Corrosion on Fatigue of Aircraft Structures

Abstract

A strategy for fuzzy-probabilistic assessment of the impact of corrosion on fatigue of aging aircraft structures is developed. Depending on the level of subjectivity and degree of belief with which they are known, corrosion-assisted fatigue crack growth parameters may be represented as either purely random variables or fuzzy random variables. The membership functions of the probabilistic characteristics of fuzzy random variables, namely mean values and coefficients of variation are developed. Probabilistic models for corrosion-assisted fatigue crack growth are also presented. First order reliability method (FORM) is employed to compute the discrete values of reliability indices and probabilities of failure for components subjected to corrosion-assisted fatigue cracking. A fuzzy modeling strategy is then used to compute the possibility distributions of the probabilistic response quantities, namely reliability index and probability of failure. Rather than providing a crisp value for the reliability of aging aircraft, as is conventionally done, the merit of the present formulation lies in its ability to combine experimental data with expert knowledge to provide confidence bounds on aging aircraft structural integrity. The predicted bounds are dependent on the level of knowledge regarding the input parameters, with a high degree of knowledge resulting in narrow bounds. An example problem is used to demonstrate the proposed methodology.