FEM based fatigue crack growth predictions for spar of light aircraft under variable amplitude loading

In the last decades, the assessment of the service durability of aerospace components and assemblies has become an important segment of design, mostly because of the growing needs for the light-weight structures which will be safe and reliable, and at the same time, not too expensive. It is especially true for the main structural elements such as wing spar, fuselage bulkheads and fittings, whose sudden failure could lead to the catastrophic consequences. In order to meet the strict safety requirements, as well as to check structural components before usage, a number of expensive and long experiments are carried out. Taking into account ever-present manufacturers´ tendencies to shorten time-to-market periods, the use of finite element method (FEM) for the estimation of fatigue life has been proved as a good alternative to the experimental methods. The purpose of this article is to show that it is possible, by using finite element analysis (FEA), to obtain not only the good estimation of the fatigue life of the assembly such as the spar of the light aircraft, but also a good prediction of a number of load cycles which will propagate a crack on the spar to a certain length. On the basis of these results, it is possible to determine the proper inspections intervals which could prevent the catastrophic failure of the aircraft structure under variable amplitude loading.

► In this paper, finite element based simulation of fatigue crack growth in spar of light aircraft is presented.
► Crack growth was simulated in FRANC2D/L software and obtained values were compared to experimental results.
► Mini-FALSTAFF and mini-TWIST spectra were used in order to determine approximate crack fatigue life in service.
► Developed numerical model proved to be reliable and fairly accurate.