INVESTIGATION OF MOISTURE INGRESS AND MIGRATION MECHANISMS OF AN AIRCRAFT RUDDER COMPOSITES SANDWICH STRUCTURE

摘要

Moisture ingress in honeycomb sandwich structures is an issue that has attracted significant attention from aircraft operators, maintenance, repair and overhaul (MRO) organizations as well as the research community. A particular problem of interest has been rudders on the CF-18, where indications of moisture ingress were found in the composite sandwich structure. Not only does bulk water in honeycomb sandwich components cause weight gain and a change in the dynamic characteristics of components such as the CF-18 rudder, it also affects structural integrity by causing physical and chemical degradation of the matrix and adhesive, and weakened facesheet/core bonds. In this study, an overview of mechanisms for moisture ingress into composite structures and the detrimental effects on structural performance is provided. Based upon nondestructive inspection results, moisture ingress occurrence maps were developed for a large sample size of CF-18 rudders. These maps illustrate a consistent moisture ingress pattern for this structure. Rather than infusing through the honeycomb composite facesheets, moisture ingress mainly occurred via joints where direct water ingress could occur. These maps also provide indications of an important moisture migration path within the sandwich component that was later verified by liquid penetration tests. Based upon this investigation, possible moisture removal strategies including non-invasive and invasive methods are discussed.