A fracture mechanics study of the influence of moisture on the fatigue behaviour of adhesively bonded aluminium-alloy joints

摘要

A fracture mechanics approach has been successfully used to examine the cyclic fatigue behaviour of adhesively bonded joints, which consisted of aluminium-alloy substrates bonded using a toughenedepoxy structural adhesive. The results were plotted in the form of the rate of crack growth per cycle, da/dN, versus the maximum strain-energy release rate, G_(max), applied in the fatigue cycle, using logarithmic axes. The cyclic fatigue tests conducted in a relatively dry environment of 23℃ and 55% r.h. were shown to cause crack propagation at far lower rates of G_(max) compared to the value of the adhesive fracture energy, G_c, which was determined from monotonically loaded fracture tests. Cyclic fatigue tests were also conducted in a 'wet' environment, namely immersion in distilled water at 26℃. The 'wet' fatigue tests clearly revealed the further dramatic effect an aggressive, hostile environment may have upon the mechanical performance of an adhesive joint, and highlighted the important influence that the surface pretreatment, used for the substrates prior to bonding, has upon joint durability. The development and standardization of 'wet' fatigue tests may provide the basis for a very effective accelerated-ageing test.