The effect of low temperatures on monitoring structural health using acoustic-ultrasonic piezoelectric transducers on composite structures.

Abstract

Composite materials have proven to be one of the ideal choices when it comes to structural applications requiring high performance working at extreme low temperatures, such as hydrogen tanks or space structures. One of the main challenges of using them is that they are susceptible to impact and fatigue, which may lead to different damages. Implementing structural health monitoring (SHM) systems is one strategy to enhancing their reliability, with guided waves (GW) being one of the most promising techniques. For the effective implementation of GW-based SHM in these applications, an in depth comprehension of its behavior up to cryogenic temperatures is required for accurate monitoring. In this regard, the objective of the present work is to preliminary investigate the effect of low temperatures on wave propagation and transducer integration. By progressively removing a composite panel from a liquid nitrogen (LN2) bath with an integrated GW-SHM network based on co-bonded DuraActTM transducers, the GW and temperature are continuously monitored from LN2 CT to room temperature. The results show that the behavior of the GW by decreasing the temperature does not follow a monotonic pattern, having at least local maxima in terms of amplitude, and nonlinear behavior for the time-of-flight. Electromechanical impedance and C-Scans ensured the quality of the bonding of the co-bonded DuraActTM transducers.