Unsaturated out-of-plane permeability measured with three-dimensional flow monitoring by etched optical fiber sensors

Abstract

In our work, the three-dimensional flow in stacks of biaxial E-glass fiber non-crimp fabrics (NCF) and unidirectional carbon fiber layers was monitored by the etched optical fiber sensors embedded inside the fabric stack. The influence of embedding sensors with a diameter of 200 µm on the flow was experimentally illustrated and discussed. The out-of-plane permeability of the two fabric materials was estimated with a radial infusion model using the in-plane permeability values as the prior knowledge. The assumed radius of the semi-ellipsoidal flow was derived and showed a good agreement with the results obtained by the best fit of the exact solution, which provides an approximate solution that simplifies the calculation process. The asymptotic form and the modified semi-ellipsoidal inlet radius method for the case of a non-negligible radius of injection tube compared to the fabric sample thickness were verified. The uncertainties related to the unknown flow pattern near the inlet were also demonstrated. The presented results facilitate the further development and standardization of out-of-plane permeability measurement methods with embedded sensors.