OFDR Distributed Strain Measurements for SHM of Hydrostatic Stressed Structures: An Application to High Pressure Hydrogen Storage Type IV Composite Vessels - H2E Project
Résumé
This paper deals with SHM of Composite Overwrapped Pressure Vessels (COPV) for high pressure hydrogen storage, based on embedded optical fibres and Rayleigh OFDR. Fibre Bragg Gratings in situ strain measurements on flat samples are first presented to assess the mechanical state of such anisotropic structures, and define a preliminary SHM criterion. Comparative fatigue tests were also performed on NOL rings to evaluate optical fibres mechanical impact, but their analysis in terms of energy revealed the difficulty to provide reliable results if the first cycles energy is not accurately controlled.
Therefore, with no detrimental effect of the optical fibre embedment within the composite architecture, several instrumented pressure vessels were manufactured and tested. Accordingly, a mechanical criterion based on OFDR differential strain profiles analysis was defined to bring out internal defects, demonstrating the ability to early detect and locate internal flaws without requirements to inflate vessels at high pressures. Additionally, their sensitivity vs. pressure, analysed during a first burst test, provided additional valuable data about structure integrity. Finally, we define four complementary criteria based on in situ strain measurements to control pressure vessels for damage assessment, or any hydrostatic stressed structure since the underlying principles rely on strains proportionality vs. uniformly applied stresses.
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