The dependence of the fatigue life of adhesive joints on surface preparation

The fatigue life of epoxy-bonded, single-lap shear joints was investigated as a function of surface preparation both with and without a silane pretreatment, under both dry and wet conditions. The effect of R-ratio was also investigated. The results showed that even in the dry condition, the fatigue life of unsilaned joints was reduced by about an order of magnitude from silaned joints. The fatigue life of the silaned joints was equivalent to that of joints that showed no apparent adhesive failure in the wedge test. Fatiguing the joints while immersed in water had very little effect on both the silaned and unsilaned joints except at low loads where there was an indication that the unsilaned joints performed more poorly than in the dry condition. The unsilaned joints showed very little R-ratio effect, while the silaned joints showed a substantial effect.