Laser ultrasonic detection of drilling-induced delamination in composite laminates

The positioning and quantitative testing of drilling-induced delamination in aircraft composite structures is not only one of the main difficulties in the field of non-destructive testing (NDT), but also a security problem need to be solved in aviation industry. Laser ultrasonic testing technique is a possible way to solve the problem. An experiment study concerning the verification of the feasibility of detecting drilling-induced delamination with laser ultrasonic technique is carried out. A composite laminate with drilling holes is made as specimen, the broadband characteristics of ultrasonic waves in composites generated by pulse laser are studied, and the wave signals with good signal-to-noise ratio (SNR), high sensitivity and resolution are extracted. The effects of the interface of drilling-induced delamination on the propagation characteristics of laser ultrasonic waves are studied, and the characterization methods of drilling-induced delamination with laser ultrasonics are acquired. Based on the pulse echo and transmission method, the laser ultrasonic C scan testing of the composite laminate with drilling holes is accomplished, and the morphologies, dimensions and positions of drilling-induced delamination are obtained. The research results show that laser ultrasonic testing is an effective method to detect the drilling-induced delamination in aircraft composite structures.