Adhesives in engineering

When considering methods for joining materials, there are many advantages that engineering adhesives can offer, compared to the more traditional 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 identify 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 readily spread over and make intimate molecular contact with the substrates. 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 polymerizes 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) the environment that the joint encounters during its service life. Thus, to understand the science involved and to succeed in further developing the technology, the skills and knowledge from many different disciplines are required. Indeed, the input from surface chemists, polymer chemists and physicists, materials engineers and mechanical engineers an 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 the failure of adhesive joints. The advances that have been made in applying the concepts of fracture mechanics to adhesive joints have enabled a better understanding of the fundamental aspects of adhesion and the more rapid extension of adhesives technology into advanced engineering applications.