抄録
In this paper, a composite material based on epoxy matrix reinforced with glass-fibre non-crimp fabric was evaluated. The multi-axial E-glass reinforcement textile has a mass per unit area of 972±5 % g/m2 and a [0°,+45°, 90°, .45°] stacking sequence. The layers are stitched together with a polyester (PES) multifil binding yarn. Epoxy system chosen was constituted of resin D.E.R331 from Dow Company, which is a liquid resin of low viscosity and high content of epoxy groups. Samples were cut from several laminas having each of the four plies of unidirectional fibers' orientations (0°, ±45°, 90°) parallel to sample length in order to test the effect of the polyester knit yarn on the damage initiation and propagation. To evaluate the mechanical properties of NCF, the three S-S diagrams at different textiles' orientations (0°, 45°and 90°) were compared. Samples at 0°exhibited better mechanical properties, on the other hand, 90°shown higher deformation. Higher Young's modulus and bending strength was shown for 0°composites while results for 45°and 90°were not very dissimilar. For all samples, discontinuities on the curves appeared when a significant crack emerged. Materials at 90°were observed to have more serrations on its curve due to the higher crack density due to the reinforced textile geometry.To evaluate the crack initiation and propagation, Acoustic Emission (AE) Technique was applied during bending tests. Cumulative AE Energy was increased at the decrease point in load on each material. With Projected Wavelet Transform Analysis, the major frequencies of all AE waves were calculated. As the result of frequency analysis, the discriminative frequency was determined with the observation by the optical microscope. Considering with the all of the data suggested that the stress concentration by the outer layer and the PES stitch caused the crack initiation and propagation.
