Temperature effects on failure mode of double lap glass-aluminum and glass-GFRP joints with epoxy and acrylic adhesive

In this experimental study, a series of mechanical tests were conducted on double-lap joint specimens, where glass sheets were adhesively bonded on two different supports, namely aluminum and glass fiber reinforced polymer (GFRP). Five different types of adhesives (three epoxy and two acrylic) were compared and three temperature conditions (room temperature, work temperature and maximum service temperature) were investigated. The main aim is to verify the applicability of this type of junction on civil applications, such as windows, glass façades, and so on. The first part of this study describes the results of tensile tests conducted in order to verify the compatibility of the bonding system at room temperature; the second part illustrates the degradation of the adhesive bonding due to high temperatures; in fact, if used in civil applications, these junctions are generally exposed to severe temperatures that could reach the glass transition temperature of the used adhesive, this leads to the necessity to verify the correct functionality of the adhesive joint. The results evidenced that the mechanical performance of adhesive junctions is considerably reduced as the temperature increases. This phenomenon is more evident in acrylic adhesives rather than epoxy ones. The epoxy adhesives in all tests exhibited the highest load carrying, while the acrylic ones showed the highest joint elongations. Different failure modes, classified as “Adhesive Failure”, “Cohesive Failure”, ‘‘Light-Fiber-Tear Failure” or “Mixed Failure”, were observed at room temperature while, at high temperatures, only “adhesive failure” was observed. The study demonstrates that high temperatures have a remarkable impact on the mechanical properties of adhesive junctions. Such effect should be suitably taken into account in the design and verification phase of components. The research results can be appropriately used in practical applications.