Fatigue resistance of composite joints with countersunk composite and metal fasteners

Composite bolted joints were tested in cyclic loading to obtain results of the joint resistance to fatigue. Specimen plates manufactured from a carbon fibre/epoxy material system were joined by fasteners of three different types: composite, titanium torque-set, and titanium Huck-comp. Strain gauge measurements were carried out to analyse strain distribution and the load transfer between the bolt rows. An extensometer was used to measure relative displacement between two composite plates. Joints bolted by Huck-comp fasteners showed the highest fatigue resistance followed by the joints with torque-set bolts. The specimens with composite fasteners displayed the lowest fatigue durability. The fatigue analysis has determined that the dominant joint failure mode was generally due to bolt fractures. The load-transfer calculations showed that asymmetry of the joints with countersunk fasteners affected the load transfer in the outer plates. Extensometer measurements displayed a steady increase in the relative displacement between the specimen plates due to fatigue degradation of the bolt holes and the composite plates.