To facilitate the transition to liquid hydrogen (LH2) as an alternative aircraft fuel, the stor age tanks need to be closely monitored to allow for safe operation. This research explores the feasibility of using an acoustic emission-based structural health monitoring method to detect and localise simulated damage on a metal double-walled vacuum insulated tank. The complicated inner and outer tank geometry makes it a novel application of an established method.
To be able to perform experiments, a metal double-walled vacuum insulated tank with a fixed and flexible support was cut in half to make the inner tank accessible. Pencil lead break tests were performed on the inner and outer tank and recorded by lead zirconate titanate (PZT) sensors to assess localisation accuracy. It was found that a pencil lead break (PLB) performed on the inner tank could be detected by a sensor placed on the outer tank. Subsequently, an accuracy of 80% was achieved in making the distinction whether the PLB was located on the inner or outer tank. For the PLBs placed on the inner tank a 1D localisation accuracy of 17 [mm] and 21 [mm] was achievable for the flexible and fixed support respectively. For the outer tank a 1D localisation accuracy of 46 [mm] was achievable, while for 2D localisation this was 41 [mm].
It is concluded that with sensors placed solely on the outer tank, both the inner and outer tank can be monitored. Additionally, simulated damage on the inner and outer tank could be localised with an accuracy below 10% of the tank’s dimension. Therefore, based on the feasibility study performed, acoustic emission-based structural health monitoring is deemed a viable method to enhance the reliability and safety of metal double-walled vacuum insulated LH2 tanks. ... Read more