ABSTRACT
An adhesive is a material (typically polymeric) which forms a structural bond between two materials. Adhesion is when two surfaces are held together. The two surfaces that are held together are called adherends. A discussion on the details of a simple adhesive joint will aid in visualization of the concepts presented in this chapter. Examination of an idealized and a realistic adhesive joint will elucidate the issues required when using adhesives, coatings, matrix materials, and reinforcements for composites. Figure 11.1 shows both the idealized and the realistic adhesive joints. In the idealized case there are three materials, which result in four bonding surfaces and two interfaces that create a simple joint. A generally held view of a surface is that it is a discrete boundary with no associated dimension. However, relative to adhesion, a surface has dimension. The first thing to consider is the surface roughness, or more appropriately, the surface topography. All surfaces, regardless of how smooth they appear, possess topography. Additionally, the material properties near the surface are not necessarily the same as in the bulk material. Thus, the interfacial zone between materials that are adhered cannot realistically be viewed as possessing zero thickness as in the idealized case. In fact, due to the surface roughness effects, varying material properties, and the possible mixing of materials, the interface is referred to as the interphase. The interphase is the zone where the material properties are not the same as the bulk materials. The interphase zone has an associated dimension dependent on the materials and their preparation.
