Multiaxial fatigue failure is the most common problem in engineering structures. It is worth noting that short crack growth accounts for most of the fatigue life. Hence, it is necessary to study the short crack growth models for multiaxial fatigue life assessment. The primary focus of this study is to develop a hierarchical Bayesian linear regression method to estimate parameters in multiaxial fatigue crack growth model. The Bayesian method is used to estimate the intercept and slope of the regression equation for each loading path and ensemble test datasets. The method of this work was demonstrated on three multiaxial fatigue crack growth datasets. The main results obtained in this paper were that the parameters of the multiaxial fatigue crack growth model changed significantly with different loading paths, and the parameters of the model depended on the multiaxial loading path.

The prediction of aircraft structure service life is of great importance to safety of aircraft structure and human beings. The relation between aircraft structure service life and reliability can be found by utilizing the fatigue scatter factor of whole life. Only when the service life satisfies the requirements of reliability, can the safety of airplane be ensured. The fatigue scatter factors of the service life accords with lognormal distribution and Weibull distribution were studied to provide important reference for predicting the safe service life of aircraft structure.

Two multiaxial damage parameters are proposed in this paper. The proposed fatigue damage parameters do not include any weight constants, which can be used under either multiaxial proportional loading or non-proportional loading. On the basis of the research on the critical plane approach for the tension-torsion thin tubular multiaxial fatigue specimens, two multiaxial fatigue damage models are proposed by combining the maximum shear strain and the normal strain excursion between adjacent turning points of the maximum shear strain on the critical plane. The proposed multiaxial fatigue damage models are used to predict the fatigue lives of the tension-torsion thin tube, and the results show that a good agreement is demonstrated with experimental data.

The project presents the theory of active reliability-based design for predetermined life targeted at their economic life. The structural reliability is designed from the view point of economic efficiency and maintainability requirements, so that the destruction of products led by fatigue and fracture is eliminated to the highest possible degree to provide the longest life, the highest reliability and the lowest cost. The reliability assessment of conventionally finished product is developed into an active reliability design at preset life, which is implemented before the design of products is finalized, to improve the safety and reliability of structures.

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