Experimental Simultaneous Measurement of Ultrasonic Properties and Thickness for Defect Detection in Curved Polymer Samples

In the context of alternative energies, the French Alternative Energies and Atomic Energy Commission (CEA) is developing hyperbaric tanks for onboard hydrogen storage applications. The aim of these tanks is to increase the operating life of vehicles using hydrogen as primary energy source. These tanks are made of a polymer layer surrounded by a composite shell. The composite shell is the structure that allows the storage of hydrogen in hyperbaric mode, while the polymer layer acts as a barrier to hydrogen. The capacity of polymer to enclose hydrogen depends on the layer thickness and its physicochemical and mechanical properties. Therefore, the manufacturing process of these tanks could be advantageously optimized by using proper measurement techniques that allow estimating the characteristics of the polymer layer. The method hereby presented aims to study the feasibility of ultrasonic nondestructive evaluation of polymer liner properties. A measurement campaign was thus conducted using 3.5 MHz transducers in order to realize the mapping of ultrasonic properties and thickness of a polymer reservoir sample. The measurements are achieved using the analysis of transmitted and reflected echoes in normal incidence. The study was done in a sample with an artificial defect. Resolution was enhanced through proper experimental configuration and signal processing. Results are in agreement compared to literature values and the defect detection is discussed.