Analytical and numerical approach to determine effective diffusion coefficients for composite pressure vessels

To enable the pressurised hydrogen storage, the leak tightness of the pressure tank has to be assessed. For linerless tanks made of composite material, this assessment has to be conducted for the inhomogeneous composite laminate. In this work, we derive and compare three different homogenisation methods to obtain the effective permeation coefficients for hydrogen permeation through composite laminates: the Wiener bounds, the HASHIN-Shtrikman bounds and a numerical finite element calculation of a representative volume element (RVE). A comparison of the methods shows that the Hashin-Shtrikman bounds give the most satisfactory results. As the leak-tightness of composite tanks is severely reduced by cracks, we further include the effect of inter-fibre cracks through a second homogenisation procedure. Through a combination of the upper and the lower Wiener bounds, it is possible to estimate the influence of the crack volume on the effective permeability. The results shows that matrix cracking should be avoided entirely to ensure the leak-tightness.