15 - Use of Acoustic Emission for inspection of various composite pressure vessels subjected to mechanical impact

Motivated by the emerging hydrogen mobility uses, especially the need for storing a high amount of energy in a small and lightweight volume, type IV composite pressure vessels have become a state-of-the-art technology for high pressure hydrogen. They comprise a non load-bearing liner, generally made of plastic and assembled with metallic bosses, around which a carbon fibre-epoxy composite is wound. Though such vessels can already be operated safely, there is a lack of knowledge concerning their residual performance after a mechanical impact. There is a need for associated nondestructive examination (NDE) methods, able to assess whether a cylinder is still fit for service after impact. The FCH-JU funded pre-normative research project HYPACTOR was set up to investigate the damage created in type IV pressure vessels by mechanical impacts, and then the use of Acoustic Emission to build rejection criteria during inspection. The methodology was to combine several AE tests on healthy and impacted vessels and correlate the results with residual performances. The developed criteria were applied to a wide database of Type IV composite vessels with different sizes, design specifications and working pressures. The validation was carried out on 114 hydraulic tests on healthy and impacted vessels. Results have demonstrated a capacity to differentiate damaged cylinders from healthy ones, with some small influence of the number of pressure cycles between impact and inspection.