ADHESIVES IN ENGINEERING

When considering methods for joining materials, there are many advanta ges that engineering adhesives can offer, compared to the more traditi onal methods of joining such as bolting, brazing, welding, mechanical fasteners, etc. The advantages and disadvantages of using engineering adhesives are discussed and it is shown that it is possible to identif y three distinct stages in the formation of an adhesive joint. Firstly , the adhesive initially has to be in a 'liquid' form so that it can r eadily spread over and make intimate molecular contact with the substr ates. Secondly, in order for the joint to bear the loads that will be applied to it during its service life, the 'liquid' adhesive must now harden. In the case of adhesives used in engineering applications, the adhesive is often initially in the form of a 'liquid' monomer which p olymerizes to give a high molecular weight polymeric adhesive. Thirdly , it must be appreciated that the load-carrying ability of the joint, and how long it will actually last, are affected by: (a) the design of the joint, (b) the manner in which loads are applied to it and (c) th e environment that the joint encounters during its service life. Thus, to understand the science involved and to succeed in further developi ng the technology, the skills and knowledge from many different discip lines are required. Indeed, the input from surface chemists, polymer c hemists and physicists, materials engineers and mechanical engineers a n needed. Hence, the science and technology of adhesion and adhesives is a truly multidisciplined subject. These different disciplines have been brought together by developing a fracture mechanics approach to t he failure of adhesive joints. The advances that have been made in app lying the concepts of fracture mechanics to adhesive joints have enabl ed a better understanding of the fundamental aspects of adhesion and t he more rapid extension of adhesives technology into advanced engineer ing applications.