In-plane permeability characterization of engineering textiles based on radial flow experiments: a benchmark exercise

Efficient process design for Liquid Composite Moulding requires knowledge of the permeability, which quantifies textile conductance for liquid flow. Yet, existing textile characterization methods have not yet been standardized, although good progress was made by two previous international benchmark exercises on in-plane permeability. The first one was without restrictions on the applied method and the second one focused on systems applying the linear unsaturated injection method. This paper presents the results of a third benchmark exercise on in-plane permeability measurement, based on systems applying the radial unsaturated injection method. In this benchmark study, 19 participants worldwide using 20 different systems participated. The participants were asked to measure the in-plane permeability of a non-crimp (NCF) and a woven fabric (WF) at three different fiber volume contents and at 5 repeats per fiber volume content. A commercially available silicone oil was used by the participants. A detailed characterization procedure was pre-defined, and each participant completed a complementary questionnaire on their measurement system characteristics (geometry, materials etc.), sensors (for pressure, temperature and flow front monitoring) and analysis methods. Excluding the outliers (2 of 20), the average coefficient of variation (cv) between the participant’s results was 32% and 44% (NCF and WF), while the average cv for individual participants was 8% and 12%. This indicates systematic variations between the measurement systems. In this context, cavity deformation was identified as a major influence. If only data from the measurement systems with a cavity deformation < 2% (relative to the target value) are considered, the average cv reduces to 23% and 34% (NCF and WF). Further important sources of variation are fluid pressure / viscosity measurement, textile variations and data analysis. As a result, a strategy to minimise differences in in-plane permeability values from different systems will be drafted