Fatigue life estimation of preloaded Aluminium (Al2024-T6) aircraft fasteners using finite element method

Abstract

The fatigue failure of the aircraft fasteners during service conditions are unavoidable. Most of the published research works related to fatigue life estimation of threaded fasteners have neglected the effect of bolt preloading. The present work mainly aims to determine the effect of bolt preload on fatigue life of the aircraft fasteners. High cycle fatigue analysis was carried out using FE based software on aluminium bolts of Al2024-T4 material with same dimensions under two different conditions (with and without the presence of crack). The preload of the bolt was varied based on the limiting stress value of the bolt material. In addition to the bolt preloading, cyclic load was applied to the bolt in order to determine the effect of synergetic loading on fatigue life. 3D finite element model of the bolt under the presence of crack was modelled and the crack region was meshed with singular elements. During meshing, singular nature of stresses and strains at the crack tip was considered and thus 20 node quadratic brick element was used. The static analysis of the bolt was carried out using Abaqus finite element code and the fatigue life of the bolt was determined after applying the cyclic load using Fe-safe software. The residual life of the bolt was determined for various preloads. From the numerical results, it was noted that as the magnitude of the preload increases, fatigue life of the bolt also increases significantly. This is due to the ‘spring action’ provided by the initial preload on the bolt. It is also observed that, the presence of crack at the root region significantly reduces the fatigue life of the bolt.