Experimental characterization and testing of adhesive bonding for space structure applications

The high toughness, strength, particularly shear and peel strength, and resistance to moisture absorption of EA9309.3NA epoxy adhesives make them an ideal choice for bonded joint applications in spacecraft and other structures. This paper presents a detailed experimental investigation on the bulk adhesive response and shear strength of Hysol EA9309.3NA adhesives under room and high temperature conditions. First, a flash thermography technique is used to nondestructively evaluate and characterize the manufacturing-induced defects and morphology in bulk adhesive specimens. This is followed by uniaxial testing under quasi-static load conditions, using a mechanical load frame equipped with an environmental chamber and hydraulic gripping system, to obtain the mechanical properties at room (24^o C) and high (57^oC) temperatures. The effects of manufacturing-induced defects and temperature on the thermomechanical properties and damage mechanisms of the adhesive are investigated. Furthermore, in-situ experimental techniques are used to test double lap shear joints with EA9309.3NA adhesive layers to obtain the shear strength and identify the failure modes under these environmental conditions. The defects in the bulk adhesives were relatively large and spherical in shape and post fracture surfaces showed that these flaws act as hotspots for damage initiation and failure. In conjunction with degradation in mechanical properties at high temperatures, the material also exhibited drastically different response under different temperatures.