Relationship of Interfacial Compatibility to Durability of Adhesive - Bonded Joints

Abstract

Previous investigations reported reduced lap-shear strength or stress durability of some 350 F curing adhesive systems on phosphoric acid anodize (PAA) compared to Forest Products Laboratory (FPL) etch. When certain elastomer- modified primers were utilized, the reported reductions in mechanical properties were more severe. These investigations employed 0.0625 in. thick adherend machined lap-shear specimens. Various mechanisms were hypothesized to explain an apparent primer/PAA compatibility problem. This investigation determined the structure and chemistry of the PAA and FPL oxides; and investigated the mechanical properties and component interactions of bonded joints containing 350 F curing adhesive systems combined with PAA and FPL. On .0625 in. thick adherend machined lap-shear specimens. FPL had greater strength. However the significant reduction in strength, reported earlier, were not substantiated. Because of the significant normal stress gradients present in this specimen other investigators have recommended that it not be employed to measure shear strength. On .125 in. thick adherend machined lap-shear specimens, PAA had greater shear strength. Stress durability on PAA was superior to or equal to that of FPL.