Although good progress was made by two international benchmark exercises on in-plane permeability, existing methods have not yet been standardized. This paper presents the results of a third benchmark exercise using in-plane permeability measurement, based on systems applying the radial unsaturated injection method. 19 participants using 20 systems characterized a non-crimp and a woven fabric at three different fiber volume contents, using a commercially available silicone oil as impregnating fluid. They followed a detailed characterization procedure and also completed a questionnaire on their setup and analysis methods. Excluding outliers (2 of 20), the average coefficient of variation (c v) between the participant's results was 32% and 44% (non-crimp and woven fabric), while the average c v for individual participants was 8% and 12%, respectively. This indicates statistically significant variations between the measurement systems. Cavity deformation was identified as a major influence, besides fluid pressure/viscosity measurement, textile variations, and data analysis.
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.
This study presents the cure kinetics and the cure modelling of an ambient curing unsaturated polyester (UP) resin system for the simulation of its curing in the vacuum infusion (VI) process. The curing of the thermoset resin system was investigated using the Differential Scanning Calorimetry (DSC) method. The dynamic DSC test measurements were conducted to find out the ultimate heat of reaction and enable experimental conversion determination for the isothermal curing. The empirical autocatalytic cure kinetics model incorporating the Arrhenius law represented the cure behaviour. The results of the cure kinetics study, the cure model, the material properties and the boundary conditions were the inputs in PAM-RTM software to simulate the degree of cure and the temperature during the infusion and the room temperature curing stages. The simulation results were compared with the experimentally measured data. A vacuum infusion experiment involving a non-crimp glass fibre preform was performed in order to identify a typical filling time to aid the simulation, and monitor the curing using thermocouples to validate the temperature simulation. It was shown that the degree of cure and the exothermic temperature of a room temperature curing thermoset resin system in the VI process could be predicted through the steps of this study.
In recent years, a few research studies have been published on the blending of unsaturated polyester and phenolic resins for the purpose of improving the fire properties of unsaturated polyester resins. However, there has been no published study on the cure and strain monitoring of unsaturated polyester/phenolic blends during composite manufacturing. In this study, non-crimp triaxial glass fabric preforms were infused with the unsaturated polyester/phenolic blends, and the strain developments inside the composites were monitored using fibre Bragg grating sensors, as the long and complex curing stages were progressing at different temperatures. Strain-free fibre Bragg grating sensors and also thermocouples were utilised for temperature monitoring and compensation in order to obtain true strain developments and residual strains. The results were associated with a study presenting the cure analyses of unsaturated polyester/phenolic blends. The unsaturated polyester and the phenolics were found to be incompatible and exhibited different curing mechanisms in the blends, which were also observable in the strain development results. This paper has been the first attempt to (i) process these novel resin systems in the vacuum infusion process and (ii) monitor the long, complex and high-temperature cure cycles and the strain developments in the vacuum infusion process using fibre Bragg gratings.
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