Co-authors​ :

 Linus JACOBSEN (GERMANY) 

Filament-wound CFRP vessels are the state-of-the-art technology for high-pressure hydrogen storage and will become more widely employed as hydrogen takes a larger role in mobility applications. However, the mechanical properties of a manufactured pressure vessel are still affected by uncertainties which can stem from factors such as the employed composite material, winding process, and autoclave variability. Current design methods, based on an idealized model of the tank structure, do not consider these factors. Instead, high safety margins are used, which are meant to account for the combined effects of the uncertainties. By conducting a detailed sensitivity analysis, the presented work contributes to the understanding of the sources of uncertainty in the pressure vessel winding process and their influence on the final mechanical performance.
The study examines a test case of a wet-wound vessel with a nominal working pressure of 700 bar. The uncertainties to be considered are the scattering of the elastic and shear modulus and tensile strength of the composite material, fiber volume content, layer thickness, winding angle, and hoop drop-off location. Imperfections such as voids and gaps are included analytically as variations of the composite properties. For the first time, the statistical distributions used by previous authors for different uncertainties are systematically compared and tabulated, providing a robust data basis for the sensitivity analysis and for future probabilistic investigations. The data are augmented with results of additional material tests.
Employing the Sobol’ method, the study quantifies the relative influence of the uncertainties on the variance of the burst pressure. Each uncertainty is defined by its type, statistical distribution, and the layer it affects. The uncertain parameters are randomly generated for individual tank realizations. They are linked to a commercial tool which performs the winding simulations of the modified tanks and an FEM burst pressure analysis with axisymmetric shell elements. This modelling approach is fast enough to perform the thousands of simulations needed to calculate the Sobol’ indices. The framework is implemented Python and extends the functionality of the open-source tank optimization tool tankoh2.
The influence of uncertainties on the failure of an individual ply, as well as the most influential uncertainties and critical layers on the burst pressure, are found. Findings reveal that, after the material-related variation in tensile strength, winding angle, fiber content, and void content variations have an impact on tank performance, emphasizing the need for more detailed research into the real spatial distributions of these parameters. This study lays the groundwork for a design methodology that can incorporate known manufacturing uncertainties to create a robust and reliable design, as a step towards more efficient high-pressure storage solutions with reduced safety margins.