Structural health monitoring of bonded composite repairs – A critical comparison between ultrasonic Lamb wave approach and surface mounted crack sensor approach

The effectiveness of the Lamb waves Acoustic-Ultrasound Structural Health Monitoring (SHM) technique for the determination of the adhesive joint failure was evaluated and compared to that of another SHM technique: Surface Mountable Crack Sensor (SMCS). A commercially available Acoustic-Ultrasound system was used. The SMCS consists of a “hot spot” monitoring system based on a three-layer electrically insulating and conductive paint. An electrical signal is used as a boolean operator for the characterization of the passage of damage through the sensor and the underlying material. The coupons consisted of carbon fiber substrates with boron patches bonded to them. The advantages and disadvantages of both techniques are discussed. It has been demonstrated that the Lamb waves Acoustic-Ultrasound technique possesses the capability to identify and quantify damage in a bonded repair. The SMCS proved to be a successful SHM technique for the monitoring of the formation of a disbond at the edges of the patch. All results were validated using the C-Scan ultrasound method.