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The out-of-plane permeability of two glass fibre fabrics was measured by 26 institutions using silicone oil as a test fluid. Participants in this study were free to select the test procedure, specimen dimensions and data analysis method, provided that testing was carried out at three target fibre volume fractions, 46%, 50% and 54%. While results showed a variability of two orders of magnitude between participants, most values were within a significantly narrower band. A majority of participants used 1D saturated test method. A few selected 1D unsaturated and 3D unsaturated flow method which gave very similar results. Focusing on analysis of data and results of 1D saturated flow measurements, results are not conclusive, but they are consistent with number of layers in a specimen, fibre volume fraction, injection pressure and sealing of specimen edges all having an effect on the measured permeability. Specifying limits for these parameters is expected to result in reduced scatter in measured permeability.

This paper reports the results of an international benchmark exercise on the measurement of fibre bed compaction behaviour. The aim was to identify aspects of the test method critical to obtain reliable results and to arrive at a recommended test procedure for fibre bed compaction measurements. A glass fibre 2/2 twill weave and a biaxial (±45°) glass fibre non-crimp fabric (NCF) were tested in dry and wet conditions. All participants used the same testing procedure but were allowed to use the testing frame, the fixture and sample geometry of their choice. The results showed a large scatter in the maximum compaction stress between participants at the given target thickness, with coefficients of variation ranging from 38% to 58%. Statistical analysis of data indicated that wetting of the specimen significantly affected the scatter in results for the woven fabric, but not for the NCF. This is related to the fibre mobility in the architectures in both fabrics. As isolating the effect of other test parameters on the results was not possible, no statistically significant effect of other test parameters could be proven. The high sensitivity of the recorded compaction pressure near the minimum specimen thickness to changes in specimen thickness suggests that small uncertainties in thickness can result in large variations in the maximum value of the compaction stress. Hence, it is suspected that the thickness measurement technique used may have an effect on the scatter.

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.