Structural Precursors to Fracture in Adhesive Joints

Sructure-property relations in adhesive joints are reviewed for the purpose of explaining the general nature of conditions and structural processes leading to fracture. Reference is made to selected homogeneous materials and adhesive joints to illustrate specific features. The adhesive joint is described as a composite structure composed of adherend and adhesive layers and various chemical and structural transition layers. The nature and dimensions of materials structural features are considered. Traditional and modern methods of analysis are summarized with special emphasis placed on the use of materials characteristic curves to indicate the existence of structural precursors to fracture. These features, in relatively small quantities, severely alter the mechanical properties of the adhesive joint. In only a few instances have structural precursors to fracture been directly observed and identified due to their small dimensions, distribution in the system and limited quantity. It is concluded that identifying the presence of structural precursors to fracture by the use of materials characteristic curves may aid the avoidance of adhesive joint failure.