STRUCTURAL ADHESIVES: STILL SEARCHING FOR THE 'HOLY GRAIL'

摘要

One of the most important requirements of an adhesive joint is the ability to retain a significant proportion of its load-bearing capability for long periods under the wide variety of environmental conditions which are likely to be encountered during its service-life. Unfortunately, one of the most hostile environments for joints involving high surface-energy substrates, e.g. metals, glasses and ceramics, is water and this is, of course, one of the most commonly encountered. Indeed, empirical laboratory investigations established [1-7] many years ago that water, either in the liquid or the vapour form, is the most hostile environment that is commonly encountered; and in natural outdoor climatic trials it is invariably the presence of moisture which is responsible for environmental attack rather than, say, oxygen or ozone. Thus, the lack of joint immortality is basically due to water permeating into the joint which may lead to a loss of strength and premature failure. This effect is accelerated by relatively high applied loads, especially cyclic fatigue loads, and by elevated temperatures. And a very common observation is that the locus of joint failure changes from being cohesive in the adhesive to apparently interfacial.