Glass fiber reinforced plastics (GFRP) are the predominant materials used for wind turbine rotor blades. To manufacture blades in a vacuum-assisted resin infusion process (VARI), a binder is needed for fiber fixation and preform stability. Moreover, solubility and mechanical compatibility of the binder and the epoxy resin matrix are important parameters for processability and the mechanical properties of the composite. The present study therefore characterized and evaluated five chemically different binders with regard to their solubility in a rotor-blade-proven epoxy resin using microscopy, viscometry, and differential scanning calorimetry (DSC). The solubility tests enabled a binder-classification into critically soluble (KE-60, Epikote 05390), strongly soluble (Grilon MS), partially soluble (D 2433E), and nonsoluble (K-140) binder types. In subsequent mechanical and thermo-mechanical testing of resin-binder plates, the strongly soluble binder Grilon MS showed the best performance, followed by the nonsoluble binder K-140 and the partially soluble binder D 2433E. These results suggest that binders developing no interfaces within the resin should be preferred. Furthermore, interply adhesion for these three binders was investigated in a peeling test using fiber preforms. It was found that differences in peel strength might be controlled predominantly by different kinds of binder layer formations, but also to some extent by the different binder-fiber interaction (binder and fiber sizing correlation). Best performance was shown by D 2433E, followed by Grilon MS and K-140. All in all, the soluble binder Grilon MS exhibited the best results in mechanical testing of resin-binder plates and is therefore expected to also show the best mechanical performance in GFRP laminates. POLYM. COMPOS., 39:708-717, 2018.
The automated manufacturing of wind turbine rotor blades needs binder systems which meet the requirements for online processing, show good preforming properties and do not affect the mechanical performance of the glass fiber reinforced polymer (GFRP) composites. In this study, especially the binder effect on the mechanical performance of corresponding glass fiber reinforced polymer is focused on. Three commercially available thermoplastic binders of different chemical composition and solubility in a rotor blade proven epoxy resin are used: Grilon MS (strongly soluble), D 2433E (partially soluble) and K140 (non-soluble). After manufacturing the binder-modified glass fiber reinforced polymer plates by the vacuum-assisted resin infusion technique, their mechanical performance is investigated with respect to binder solubility and concentration (1–3 wt.%). The mechanical characterization is based on tensile and compression tests – both longitudinal (0°) and transversal (90°) – as well as shearing tests (±45°). It is found that the glass fiber reinforced polymer strength and stiffness is strongly controlled by binder solubility and content. In the case of limited binder solubility and insolubility (D 2433E and K140), the performance of the composites reduces significantly as binder content increases. In contrast, stiffness and strength are not affected by the soluble binder Grilon MS, regardless of its content. These glass fiber reinforced polymer results strongly correspond with the results obtained for binder modified resin plates in a previous study. This correlation highlights the fact that binder ability for the preforming process might be classified by a simple pre-test for solubility and mechanical properties using the modified resin instead of applying the costly and time-intensive manufacturing steps of glass fiber reinforced polymer plates.
Magnetostrictive particles like Terfenol-D are investigated with respect to their ability to detect internal stress, generated in carbon fibre-reinforced polymers (CFRP) in a non-destructive way. The results are presented in two parts. The first part elucidates the ideas for the preparation of dispersions based on these particles with high density in epoxy resins. There is particular focus on the effects of particle size and concentration. Different particle sizes in a range of 0-300 lm are selected by special separation techniques. The particle size distribution is controlled in dry state by laser diffraction method. Changing of the chemical composition, particularly by the oxidation of particles, is analysed by EDX. Use of a magnetic field is identified as a suitable means for the stabilisation of these high-weighted particle fractions dispersed in epoxy resins. The particle size distribution, as well as the alignment of particles, in the cured epoxy resins is investigated by SEM and light microscopy. The second part of the study covers the magnetostrictive properties of the modified epoxy resins which are quantified by the detection of internal stress in CFRP.
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