This paper presents information on Navy research and development programs dealing with adhesives and adhesive bonding, with respect to their objectives, approach, findings, and future efforts. Three specific areas are singled out for discussion: stress corrosion failure of bonded aluminum; adhesives for use with difficulty bonded nonmetallic surfaces (polymers) and rocket propellants; and bonding and joining techniques for advanced filamentary graphite composites.
Stress corrosion experimentation demonstrated the accumulation of corrosion products on the exposed aluminum. It is suggested that the diffusion of polyamine from epoxide adhesives contributes to the accelerated corrosion which leads to the formation of weak boundary layers. A proposed mechanism for stress corrosion cracking is presented.
Forty standard adhesives of 26 types were investigated in the study of difficultly bonded surfaces and rocket propellant. The characterization of several of these adhesives is discussed with respect to shear strength, softening temperature, and failure under load.
Epoxy/graphite composite, joined to itself and to other metallic members by adhesive bonding and bolting, was investigated to assess the material aspects with respect to the strength of the joint. Bonded joint strengths found limitation through the interlaminar shear strength of multiangled ply composite. Single lap bolted joints failed in the Carboform composite at the bolt hole at loads equivalent to 30% of the composite strength. Joints using double laps of titanium increased loading to 40% of the composite strength. It is noted that a lack of reliable data, against which bonded joints can be designed and analyzed, presently limits full utilization of adhesive bonding in advanced structures.