Role of the interphase in the environmental failure of adhesive joints

Abstract

The cyclic-fatigue behaviour of adhesive joints, which consisted of an aerospace-grade epoxy-adhesive bonding aluminum-alloy substrates, has been investigated. Fracture-mechanics tests were used to obtain the relationship between the rate of fatigue crack growth per cycle, da/dN, and the maximum strain-energy release rate, Gmax, applied during the fatigue cycle. These cyclic-fatigue tests were conducted in both a `dry' environment of 23±1 °C and 55% relative humidity and a `wet' environment of immersion in distilled water at 28±1 °C. In particular, the effect of using various surface pretreatments for the aluminum-alloy substrates, prior to forming the adhesive joint, has been investigated. X-ray photoelectron spectroscopy and electron microscopy techniques have been used to identify the locus of joint failure and the mechanisms of environmental attack.