Fatigue Crack Growth Simulation of Aluminium Alloy under Cyclic Sequence Effects

Abstract

During service time machine and component failures may occur, that cause the structure breakdown. This generally yields enormous economical costs and sometimes in worst-case scenarios evens the death of human beings. Frequently such damage events originate from misconstructions, manufacturing and material failures, inappropriate fatigue strength calculations, overloads or other problems during service time or maintenance. Beginning from already existing or newly originating flaws, often extended fatigue crack growth (FCG) occurs due to service loads. Finally, the functional capability of structures and components is lost with the already mentioned consequences. In case of existing damage events, it is of major importance to fundamentally analyse them in order to obtain valuable information on structural improvements. Therefore, the knowledge about the real global and local loadings, the relevant material parameters and the initiation and growth of cracks under various general loading situations is essential. By fracture mechanics the development of FCG processes than can be reconstructed. So it is possible to improve the strength optimised and fracture safe design of structures and components. This goal can ideally be achieved by a composition of numerical and experimental simulations. FCG in structure components, which is subjected to variable amplitude (VA) loading, is a complex subject. Studying of FCG rate and fatigue life calculation under the spectrum loading is vital in life prediction of engineering structures at higher reliability. The ability to understand and predict fatigue life remains a key technical factor in maintaining aircraft fleets, which are required to safely operate up to their design lives, and sometimes beyond. The load spectra applied to this aircraft are complex and highly variable, and experience has shown that traditional fatigue prediction tools do not always perform well in calculating the lives of modern, highly optimised airframes. The main aim of this chapter is to address how two characterise the load sequence effects in fatigue crack propagation under VA loading and to select appropriate model from the large number of FCG models with validation of it. Thus, a fatigue life under various load spectra, which was predicted, based on the Austen, modified Forman and NASGRO models. This article analyses FCG under random loading using experimental results taken from literature on the subject and from growth simulations carried out based on different FCG models. These models are validated with the literature-based FCG test data in 2024-T3 aluminium alloys under spectrum loadings. This work summarises recent FCG models that appear to