Research on structure health monitoring for composite fuel tank : PZT ultrasonic attenuation and acoustic emission localization

Abstract

As the hydrogen energy industry grows, its applications expand across various sectors, including aerospace engineering. Hydrogen fuel storage systems use composite overwrapped pressure vessels to store hydrogen fuel. Type IV composite pressure vessels comprise a plastic liner and filament-wounded composite materials like CFRP and GFRP. Pressure vessels undergo repeated expansion and contraction during fuel charging and discharging, accumulating damage over time. Therefore, proper structural health monitoring methods are essential for safely operating hydrogen fuel storage systems. In this study, the PZT active sensor network is based on the PZT pitch-catch method to monitor the structure health of the composite pressure vessels. The PZT active sensor network measures the change of attenuation of the ultrasonic wave propagation through the pressure vessel depending on the hydraulic test cycles. Also, the crack density was calculated using the micro-CT imaging method of the hydraulically tested pressure vessels. A correlation was derived from these two hydraulic test cycle-dependent parameters. This correlation allows the PZT active sensor mounted on the operating pressure vessel to monitor the state of the pressure vessel by measuring the ultrasonic signal attenuation. Another structural health monitoring method, acoustic emission based on laser ultrasonic signal modulation, was also proposed. With frequency domain information of the acoustic emission and laser ultrasonic signal, a neural network-based frequency modulation algorithm was proposed. This algorithm modulates the laser ultrasonic signal's frequency components to resemble the emission signal. With this modulated laser ultrasonic signal, a localization of the acoustic emission on the composite pressure vessels was conducted.