Guided-wave Health Monitoring of Aircraft Composite Panels under Changing Temperature

This study deals with the health monitoring of fiber-reinforced composite panels using ultrasonic guided waves and flexible piezocomposite transducer patches in a changing temperature environment corresponding to normal aircraft operations (-40 degrees C to +60 degrees C). The wave propagation problem is first studied analytically by a model that accounts for temperature effects on the transducer piezo-mechanical properties, the transducer-panel interaction, and the panel wave dispersion properties. Experiments are also conducted on a Carbon-fiber Reinforced Plastic (CFRP) [0/+/- 45/0](S) laminate subjected to the -40 degrees C to +60 degrees C temperature excursion. Both model and experiment indicate substantial changes in the detected guided wave amplitude solely due to the temperature excursion. The second part of the study presents an application to bond defect detection in a simulated CFRP skin-to-spar joint of Unmanned Aerial Vehicle wings. It is shown that a statistical outlier analysis based on multiple guided-wave amplitude features and on a baseline partition is effective in detecting bond defects (poorly cured adhesive and two sizes of disbonds) despite the -40 degrees C to +60 degrees C temperature change. The results encourage the development of a continuous health monitoring system for composite aircraft wings during their normal operations.