Adhesives Technology Handbook (Second Edition)--1 Introduction and Adhesion Theories精选.pdf

1 Introduction and Adhesion Theories 1.1 Defi nition of Adhesives and Adhesive Bonding An adhesive is a material that is applied to the surfaces of articles to join them permanently by an adhesive bonding process. An adhesive is a sub- stance capable of forming bonds to each of the two parts when the fi nal object consists of two sections that are bonded together.[ 1 ] A feature of adhesives is the relatively small quantities that are required compared to the weight of the fi nal objects. Adhesion is diffi cult to defi ne, and an entirely satisfactory defi nition has not been found. The following defi nition has been proposed by Wu.[ 2 ] “Adhesion refers to the state in which two dissimilar bodies are held together by intimate interfacial contact such that mechanical force or work can be transferred across the interface. The interfacial forces holding the two phases together may arise from van der Waals forces, chemical bonding, or electrostatic attraction. Mechanical strength of the system is determined not only by the interfacial forces, but also by the mechanical properties of the interfacial zone and the two bulk phases.” There are two principal types of adhesive bonding: structural and non- structural. Structural adhesive bonding is bonding for applications in which the adherends (the objects being bonded) may experience large stresses up to their yield point. Structural adhesive bonds must be capable of transmitting stress without loss of integrity within design limits.[ 3 ] Bonds must also be durable throughout the useful service life of a part, which may be years. A structural bond has been defi ned as having a shear strength greater than 7 MPa in addition to signifi cant resistance to aging. Nonstruc- tural adhesives are not required to support substantial loads but merely hold ligh