Damage detection for aerospace composites using matrix resins functionalized with fluorescent probe molecules

Damage detection in aerospace composite parts is difficult because of their opacity and inhomogeneity. Low energy impact damage is especially troublesome because it often leaves no visible surface damage but can cause significant subsurface damage. Ultrasonic C-Scan can detect this damage but requires airplane downtime to conduct. This research proposes a method of damage detection based on fluorescent molecular probes with mechanochromic properties. Several molecules were designed and synthesized to be compatible with aerospace matrix resin and coating chemistry, and to exhibit fluorescent behavior that is dependent on local deformation and damage conditions. In a room temperature cured DGEBA-DETA solid resin, one probe showed strong fluorescent emission color change when samples were compressed. A linear relationship was observed between this change and the strain in the bulk sample. The probe displayed sensitivity to other environmental conditions including temperature and amine-epoxide ratio. The color change of the probe after deformation was not permanent over long periods of time. Probe molecules which are less sensitive to time after deformation and environmental conditions are presently being analyzed. Copyright 2013 by Aurora Flight Sciences.