Thermal effects on the properties of epoxy and polyimide adhesives bonded graphite/bismaleimide composites

In this paper, high temperature bonding properties of adhesive bonded composite systems and thermal aging effects on the bonding properties were studied. The adhesives used for the study were epoxy based FM300 and FM400 as well as BMI based Metlbond2550. The composite adherends used were IM7/5250-4 laminates. Single-lap-shear testing was performed under various temperatures and SEM was used to observe the fracture surfaces to determine the failure mode. The results indicated that FM300 bonded systems showed significant drop in lap shear strength at elevated temperature. When the two high temperature adhesives, FM400 and Metlbond2550, were compared, the latter showed better high temperature performance and more resistant to thermal aging. The mechanical properties and failure mode of adhesive bonded composites also depended on lay-up configuration of the adherend. The bonded systems with unidirectional laminated adherents showed higher single-lap shear strength than those with ±45 laminated adherends.