Investigation on static and fatigue performance of CFRP/Al-alloy interference bolted joint considering the influence of hole-axis error

Hole-axis error is one of the normal manufacturing errors during aircraft assembly due to non-uniform deformation caused by drilling, assembly force, and post-assembly positioning. This paper investigated the influence of hole-axis error on the static and fatigue performance of CFRP/Al-alloy bolted joints. Experimental investigations were carried out to evaluate the impact of hole-axis error (0.00 mm, 0.05 mm, 0.10 mm, and 0.15 mm) on static and fatigue performance of CFRP/Al-alloy interference bolted joints. The variation of hole-axis error within a certain range has a slight influence on the ultimate tensile strength of the joint. At the same time, the fatigue life increases at first and then decreases with the increase in the value of the hole-axis error. The hole-axis error introduces a pre-loading state of the bolted joint, which makes the material damaged in advance and decreases the structure stiffness. A scanning electron microscope (SEM) was used to observe the damage of holes. A modified fatigue life model was proposed to predict the fatigue life of CFRP/Al-alloy bolted joints with different hole-axis errors. A rational threshold for hole-axis error can be established, which is less than 0.15 mm (3 %). The results of this paper can provide corresponding guidance for the tolerance design of bolted joints with hole-axis error.