ABSTRACT
Epoxy polymers have been widely used as adhesives and as composite matrix materials. In recent years, increasing application of fiber-reinforced organic composites as structural components in weight-critical aerospace and advance marine systems has placed even greater demands on polymeric adhesive systems such as epoxies. This is because structural adhesive bonding is a very versatile and highly desirable method for joining composite structural elements either to themselves or to metallic parts. In many cases, the adhesive resins are also adapted as the composite matrices so as to facilitate the cure and fabrication. In considering the reliability of the designs of adhesive-bonded composite structures, designers have generally recognized that structural adhesives and composites are relatively brittle and stiff materials. Their failure mode is characterized by flaw growth and progressive crack propagation. The flaws that may be anticipated include internal cracks, surface cuts, and microvoids inherently present as a result of the current processing methods employed. The growth of these flaws and the subsequent crack propagation usually lead to catastrophic breakdown of the adhesive-bonded structures.
