Reducing the effects of rivet holes on fatigue life by adhesive bonding

Rivet holes are potential sites for fatigue crack initiation in aircraft structures. Several methods for improving the life of such details were investigated including coating the surface of the hole with adhesive, cold-expansion of the holes, the insertion of close-fit rivets and the use of adhesively-bonded rivets. Of the various techniques examined, only that involving adhesively-bonded rivets provided any significant improvements in fatigue life. It resulted in a reduction in fatigue crack propagation rate of about 50% compared with that for specimens incorporating open holes.A finite element analysis indicated that adhesive bonding significantly reduces both the local stress concentration at the hole and the stress intensities at the crack tips, thus retarding crack initiation and reducing fatigue crack propagation rates. However, the effective reduction in stress intensity resulting from bonding (about 17%) is much less than the 50% predicted by the finite element analysis. This discrepancy is attributed mainly to shortcomings in the model for defining the characteristics and behaviour of the adhesive.