In-Situ Characterization of Laser Shock Dismantling Process Using Ultrasonic Guided Waves Sensed by Bonded Piezoelectric Transducers

Abstract

Laser shock dismantling allows to selectively separate the various plies of a composite material in order to sort aged or damaged ones from virgin or healthier ones and to build new composite materials from these recycled plies. However, following in situ the laser shock process is in practice hard to achieve due to the very short laser pulse duration (around 10 ns) and to the large associated energy density (around 10 GW/cm²). Piezoelectric elements are low cost transducers that can be easily bonded to composite structures and that are able to sense ultrasonic guided waves propagating in such structures in the frequency range below 500 kHz. Consequently, if a composite coupon enduring laser shock dismantling is equipped with piezoelectric elements, those sensors should potentially be able to collect dynamical signals directly following laser shock. In order to validate this approach, an experimental campaign has been carried out where a composite coupon has been impacted by laser shocks of increasing intensity in order to achieve delamination damages. Dynamical signals resulting from those consecutive laser shocks have been measured by the piezoelectric transducers. The signal collected by the piezoelectric transducers during a laser shock are shown to be exploitable despite the short laser shock duration in comparison with sensor bandwidth and can be reliably used to locate laser shock position and to estimate its intensity. Such an in-situ process monitoring approach could thus allow to ease the deployment and practical use of laser shock technology for composite materials dismantling and recycling purposes.