# Damage assessment of hydrogen-exposed PA11 liners via structural and mechanical analysis

Barthélémy Gros, Hervé Mathis, Jean-François Gérard, Xavier P Morelle, Paul Sotta

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Barthélémy Gros, Hervé Mathis, Jean-François Gérard, Xavier P Morelle, Paul Sotta. Damage assessment of hydrogen-exposed PA11 liners via structural and mechanical analysis. FRH2 - 5èmes Réunions Plénières de la Fédération Hydrogène, Fédération Hydrogène, Nov 2025, Annecy, France. hal-05405360

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Submitted on 8 Dec 2025

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# Damage assessment of hydrogen-exposed PA11 liners
via structural and mechanical analysis

Barthélémy Gros<fnref n="1" />, Hervé Mathis<fnref n="2" />, Jean-François Gérard<fnref n="1" />, Xavier P. Morelle<fnref n="1" />, Paul Sotta<fnref n="1" />

PA11 is a semi-crystalline polymer currently used as a promising liner material in hyperbaric hydrogen storage vessels for transport applications [1]. This study focuses on trying to detect early microstructural damage (for instance in the form of nano-cavities) in PA11 liners that were exposed to rapid decompression from different high H₂ saturation pressures and at different decompression rates. The primary goal is to determine in which critical operating conditions damage can occur in such liners.

For that purpose, PA11 specimens were exposed to high pressure compression-fast decompression cycles and then were structurally characterized by Ultra-Small-Angle X-ray Scattering (USAXS) to monitor potential residual damage. Indeed, USAXS is a powerful technique to detect early damage by nano-cavitation in polymer materials [2] and polyamides have been shown to exhibit cavitation-type of damage under other loading conditions, such as fatigue [3].

In parallel, virgin and exposed specimens were also studied through in-situ USAXS monitoring during tensile deformation to investigate whether their exposition history would modify their mechanical response and associated deformation scenario.

Indeed, another interesting specificity of PA11 is that, under tensile loading at room temperature, it exhibits a sequential plasticity activation phenomenon with two consecutive stress thresholds, called double yielding (DY) [4]. The first yield point is intimately connected to the plasticization of the amorphous phase, while the stress increment up to the second yield point is associated to the crystalline phase. A secondary goal is thus to determine whether DY can be used as a sensitive probe for microstructural damage assessment in semi-crystalline polymers used under extreme and complex mechanical loading conditions that do not always enable in-situ monitoring. Ideally, compared to the use of synchrotron based structural analysis such as USAXS, this simple characterization, would enable determining if damage occurs in the amorphous or crystalline phase (or both), based on the amplitudes and positions of the two yield points.

## Acknowledgements:

The authors acknowledge support from the French ANR under France 2030 program (project PEPRH2-HYPERSTOCK-004) as well as the support from ESRF synchrotron facility (ID02 beamline operated by T. Narayanan and M. Sztucki). The authors express their gratitude to Hyperstock consortium partners, namely Pprime Institute, IFPen and Femto-ST, for their help in exposing PA11 specimens to various H₂ compression-decompression cycles.

## References:

[1] C. Le Talludec et al. "Consequences of repeated hyperbaric hydrogen exposures on mechanical properties and microstructure of polyamide 11". *Polym. Test.* **2024**, 140, 108581.

[1] A. Charvet, C. Vergelati, P. Sotta, D.R. Long, "Damage Mechanisms of Plasticized Cellulose Acetate under Tensile Deformation Studied by Ultrasmall-Angle X-ray Scattering". *Macromolecules* **2019**, 52, 6613-6632.

[3] E. Mourglia-Seignobos, D.R. Long, L. Odoni, L. Vanel, P. Sotta, C. Rochas, "Physical Mechanisms of Fatigue in Neat Polyamide 6,6". *Macromolecules* **2014**, 47, 3880-3894.

[4] Gros, B., Gérard J.-F., Sotta, P., Morelle, X. "Double yielding in PA11: discriminating the mechanical contributions of the amorphous and crystalline fractions." *Polymer* **2025**, 128844.

<footnote n="1">¹Laboratoire Ingénierie des Matériaux Polymères (IMP), UMR CNRS 5223 – INSA de Lyon, 17 Avenue Jean Capelle, 69621 Villeurbanne, France.</footnote>

<footnote n="2">²CEA Le Ripault, Centre d'Etudes du Ripault, 37260 Monts, France.</footnote>