Experimental characterisation of textile compaction response: A benchmark exercise

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

SIMULATION OF THE COMPLETE RESIN INFUSION PROCESS

International audienceResin Infusion (a.k.a. VARTM) is one of the Liquid Composite Moulding processes, for which liquid resin is drawn into dry fibre reinforcement. Resin Infusion is a closed mould process in which half of the mould is formed by a flexible vacuum bag. Significant cavity thickness changes occur during processing, due to the flexibility of the vacuum bag and the complex stress balance within the laminate. While the magnitude of thickness change is often small, the influence is significant on reinforcement fibre volume fraction. Dynamic changes in permeability during mould filling and post-filling have the potential to significantly affect the process. To simulate this behaviour, it is important to accurately model the compaction and relaxation of reinforcement in the dry and wet state. A series of tests have been completed to determine the compaction behaviour of an isotropic glass fibre mat. From these tests several non-linear elastic compaction models have been determined, and applied within a new Resin Infusion simulation. The process simulation, which addresses the pre-filling, filling and post-filling stages, is compared to an experiment employing a full field cavity thickness measurement apparatus, as well as measurement of resin pressure at three discrete points within the laminate

OBSERVATIONS FROM THE FILLING AND POST-FILLING STAGES OF AXISYMMETRIC LIQUID COMPOSITE MOULDING WITH FLEXIBLE TOOLING

International audienceThis paper presents experimental observations from the filling and post-filling stages of 1D axisymmetric Resin Infusion (VARTM) and RTM Light. A series of experiments have been performed to investigate the influence of mould flexural stiffness and fill mode on fluid pressure, cavity thickness, filling stage time, and post-filling stage time. Observations are also made on the effect of those parameters on the repeatability of nominally identical experiments

Processing and characterization of 100% hemp-based biocomposites obtained by vacuum infusion

Novel biocomposites made of an acrylated epoxidized hemp oil based bioresin reinforced with random hemp fiber mat were manufactured by the vacuum infusion technique. Mechanical properties (tensile, flexural, Charpy impact and interlaminar shear), dynamic mechanical properties (glass transition temperature, storage modulus and crosslink density) and moisture absorption properties (saturation moisture level and diffusion coefficient) were investigated and compared with samples manufactured under the same conditions but using a commercial synthetic vinylester resin as the polymeric matrix. Results showed that the 100% biocomposites mechanical performance is comparable to that of the hybrid composites made with the synthetic resin. Moisture absorption tests showed that acrylated epoxidized hemp oil based samples displayed both higher diffusion coefficient and saturation moisture content; however, fiber reinforcement was the dominant transfer mechanism. Vinyl ester based samples were found to have higher storage modulus, glass transition temperature and crosslink density than acrylated epoxidized hemp oil samples