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With increasing demand for bonded structures in industrial applications, there is a need for accurate characterization of adhesives. Adhesives have been observed to behave differently in tension and shear. Their properties also vary between bulk resins and thin films in a bonded structure. An important aspect of structural adhesives is the ability to demonstrate toughness beyond their yield point. This makes the study of adhesive yield criteria important for design. Usually, the yield surface of materials is studied by loading in biaxial stress space. However, adhesives in a bonded structure can only be loaded perpendicular to the bond surface and in shear. A circular tension-shear mixed mode Arcan fixture has been used to study yielding of thin film metals, polymers and composites. This article describes the design of an Arcan fixture and test specimen to achieve reduced stress concentrations, increased stress uniformity, a higher shear to peel stress ratio and the ability to test a bond in compression-shear. Adhesive strain measurements using a noncontact Digital Image Correlation technique are also discussed. [ABSTRACT FROM AUTHOR]

Cohesive failure is preferred over adhesive failure in bonded joints. Cohesive failure can be defined in terms of mechanical properties of adhesive, while adhesive failure is a property of adhesion strength between two bonding surfaces. Although the benefits of bonding apply to both metallic and non-metallic materials, the use of bonding has proven particularly attractive for fiber reinforced composites due to the complications involved with bolted attachment of composites. Bonding of composite parts is challenging since the interface (adhesive) failure or adherend failure should be avoided. The present work considers cohesive, adhesive and adherend failure in shear, so that the effect of bond quality on mode II crack growth can be better understood. Failure modes for weak bonds were observed to be adhesive failure in static and fatigue loading. Strong bonds showed cohesive failure for fatigue loading. However, in static loading, strong bonds with a tough adhesive had a cohesive-adherend mixed failure mode and strong bonds with the standard adhesive had a cohesive-adhesive mixed failure. The fracture toughness for strong bonds in comparison to weak bonds, increased by 100 % for a tough adhesive and 50% for a standard adhesive. The fatigue crack growth rate for weak bonds increased with a decrease in adhesive toughness. [ABSTRACT FROM AUTHOR]