Effect of Cryogenic Thermal Cycling on the Response of a Fiber Bragg Grating Sensor

The manufacturing and use of composites hydrogen tanks for transport applications faces a series of very important challenges among which one of the most critical is the definition of a structural monitoring system that is able to adapt to the conditions present in the tank. Among the different ways of storing H2, two of the most interesting from the point of view of gravimetric and volumetric density are the storage of H2 in liquid form LH2 or in the form of cryo-compressed gas CcH2 in both cases the tank structure (either the liner for class III and IV or the composite structure itself for class V tanks) must be able to withstand very important thermal variations in temperature during the processes of filling and emptying the tank, i.e. able to withstand high thermal cycling requirements. The research work carried out has focused on studying the impact of such thermal cycling on the sensor response. For this purpose, FBG sensors have been integrated in several coupons that have been subjected to multiple thermal cycling (20ºK-80ºK). After each thermal cycling, a reference tensile test has been performed on the coupons, recording the responses of the sensors to see the effect of the accumulation of the cycling, in parallel after each cycling, inspections have been performed by micro computed tomography to try to check if the possible cause of the variation in the response is associated with micro cracking in coupon-sensor interface. The final objective of the research is to ensure the reliability of the response of the FBG sensors for H2 SHM application.