Unidirectional compression of fibre reinforcements. Part 2: A continuous permeability tensor measurement

Modelling LCM processes, where resin flow and compression of the fibre reinforcements are involved, requires a proper modelling of the fibre reinforcements behaviour in compression and to define how the permeability tensor evolves. The permeability measurement techniques based on fluid injection lead to data scattering. Using a material testing machine, unidirectional compression tests are performed on impregnated fibre reinforcements to induce in-plane and through-thickness fluid flows. With proper viscosities and compression speeds, the expelled-fluid pressure becomes sufficiently high to be measured. Then, using that fluid pressure and following a methodology based on numerical optimizations, the in-plane equivalent permeability and through-thickness permeabilities can be extracted. An additional measurement is needed to know the anisotropy ratio and calculate the two in-plane principal permeabilities. Due to the nature of the compression test, a major advantage of the present method is that it is continuous with respect to fibre volume fraction and that it limits errors involved with injection techniques. Samples can previously be sheared before compression and permeability measurements.