Effect of environment conditions on adhesive properties and material selection in composite bonded joints

Adhesives have been widely used in aircraft composite bonded structures, which are required to stand severe environment conditions involving high temperature and moisture during the service. Current relevant investigations focus on the environment effects on adhesive specific properties with little attention to adhesive material selection in different environment conditions. In this paper, the properties of two types of adhesives from the same material system, SY14M (an elevated temperature curing epoxy adhesive) and SY24C (a medium temperature curing epoxy adhesive), were studied in different environment conditions. An adhesive selection method based on property matching between adhesive tensile and shear strength in different environment conditions was proposed. Results show that hydrolysis reaction can cause adhesive color variation, moisture absorption acceleration and plasticity decrease. Thermal effect on tensile properties of the adhesives is greater than that on shear properties, while moisture effect is opposite. High temperature can extremely increase adhesive plasticity, especially for tough adhesive. For the two adhesives, the matching consistency between tensile and shear strength is different in different environment conditions, so environment conditions must be considered in the adhesive selection.