Damage Mechanisms and Non-Destructive Testing in the Case of Water Ingress in CF-18 Flight Control Surfaces

Most service failures of adhesive bonded aircraft structures have been attributed to environmental degradation of bonded joints exposed to moist conditions. High humidity normally leads to plasticisation of the adhesive and an associated reduction of mechanical properties recoverable upon drying. Conversely, direct water ingress causes permanent adhesive bond degradation. Very little is known of the degradation mechanisms experienced with direct water ingress; however, this knowledge is required to establish the inspection requirements and for fielding nondestructive testing (NDT) techniques. This technical memorandum details the possible damage mechanisms and the results obtained with various nondestructive testing techniques tested during the course of the project.