Cryogenic Temperature Effects on Guided Wave Structural Health Monitoring Signals in Unidirectional Carbon Fiber Reinforced Plastics

Structural Health Monitoring (SHM) is a promising technology for enhancing the safety and performance of high-value composite structures operating in extreme environments, such as cryogenic temperatures encountered in aerospace systems, hydrogen storage tanks, and emerging space applications. These structures are subject to significant mechanical and thermal stresses that can degrade material properties, increase brittleness, and threaten structural integrity. In such conditions, traditional inspection methods may be infeasible or insufficient, while SHM enables real-time, insitu damage detection and continuous monitoring throughout a structure's service life. Among SHM techniques, Guided Wave (GW) methods offer significant advantages for fiber-reinforced polymer composites due to their long-range propagation capability and sensitivity to various defect types, including delaminations, matrix cracking, and impact damage. However, GW signals are also influenced by environmental and operational factors such as temperature variations, mechanical loading, and adjacent media (e.g., moisture, frost, or liquid interfaces), which can complicate signal interpretation and potentially mask real damages or produce false positives. This study investigates the effects of cryogenic temperature and surrounding media on GW signal behavior in a unidirectional carbon fiber-reinforced polymer panel equipped with co-bonded DuraAct™ piezoceramic transducers. The specimen is exposed to controlled thermal cycling, including immersion in liquid nitrogen, and guided wave responses are measured across a wide frequency range. Results reveal distinct frequency and temperature-dependent behavior in both S0 and A0 wave modes. Observed changes in amplitude and time-of-flight are linked to transducer performance, material stiffening, and boundary media interactions. These findings highlight the critical need for environmental compensation in guided wave SHM systems and highlight opportunities to monitor both structural health and environmental conditions using wave behavior in applications spanning aeronautics, hydrogen energy systems, and space technologies.