Study On Vacuum Infusion Moulding Process And Mechanical Properties Size Effects Of Glass Fibre Reinforce Polymer Composites Thick Laminates

The engineering composite components are developing from miniaturization to maximization recently. For the past few years, the development and production of the typical Glass Fibre Reinforced Polymer (GFRP) engineering composite components–wind turbine blades were booming, which cause the engineering GFRP laminates to be much larger and thicker. In this paper, the particularities of the large size GFRP thick laminates were focused on systematically, including the Vacuum Infusion Moulding Process (VIMP) technique used for the laminates components manufacture, the temperature distribution and the degree of cure distribution in laminates curing process, the size effects in mechanical properties test of laminates and open-hole laminates specimens.Firstly, researches have been made about the resin infusion process of VIMP technique. The mainly controlling parameters of the infusion process are resin infusion temperature and design of flow channel layout. The Huntsman 1564/3486 and the huili LT5078A/5078B-2 epoxy resin systems were chosen as the laminates matrix. Analysis results show that both of them are the modified low viscosity bisphenol A epoxy/ multi-amine reaction systems, the reaction orders are 0.905 and 0.88. The Dual- Arrhenius rheological model and engineering viscosity model were established. These two kinds of models were combined to predict the VIMP processing windows of resin systems. Then the optimum resin infusion temperature was obtained to be 35℃. The permeability of the [0], [0/45/-45] and [0/45/90/-45] multi-axial fabric reinforcement, and the effects of the distribution medium on the resin flow behavior in VIMP had been studied. According to the results, the design principles of the resin flow channel layout were determined and applied to guide the VIMP infusion process of the root and the spar cap of a typical 40m length wind turbine blades.Secondly, the distribution of the temperature and the degree of cure in thick laminates VIMP curing process were studied. The curing characteristic temperatures for the epoxy resin system was gotten by differential scanning calorimeter (DSC) technique at different heating rates. The distribution of the temperature during thick laminates curing process was inspected. The results showed that the temperature gradient at different thickness positions was increasing with the laminate thickness. To avoid the high peak temperature, the thick laminate curing process should be divided into two stages, the pre-curing stage and the curing stage. In order to study the distribution of the degree of cure, the Method of Accumulation by Time Dispersing Steps was proposed to calculate the degree of cure under non-isothermal conditions with the isothermal models-the Kamal kinetic model and the modified Olivier model. The relationship between degree of cure and time under non-isothermal conditions was calculated and verified by the experimental data. It shows that Kamal kinetic model is more accurate in the earlier stage of the curing course, while the modified Olivier model is more accurate in the later stage, especially at the final degree of cure. In the curing process of a typical engineering thick laminates components-the root of a wind turbine blade whose thickness is 85mm, the distribution of the degree of cure was calculated and analyzed. The results showed that the thick laminates could achieve high degree of cure in the pre-cure stage by self-heating, but there were differences of real time degree of cure in thickness direction. The high equivalent degree of cure could be achieved in the cure stage, the time of which could be determined by the calculation results.Thirdly, the size effects were studied and summarized systematically from four aspects: the fibre volume fraction, the tensile test, the short- beam shear test and the flexural test of the multi-axial fabrics reinforced laminates manufactured by VIMP. The fibre volume fraction of the thick laminates uniformly distributes in the thickness direction, and do not change with the thickness when the thickness is higher than 10mm. The fibre volume fractions of [0], [0/45/-45] and [0/45/90/-45] fabric reinforced laminates are 57%, 57% and 54.5% respectively. The mechanical properties experiments show that the modulus doesn’t change with the size of the specimen, while the strength is decreasing with the size grows. Compared with the experimental data, the result shows that the Weibull model is fit for describing the strength size effects. The tensile strength Weibull moduli of [0], [0/45/-45] and [0/45/90/-45] fabrics reinforced laminates are 39.2, 37.6 and 25.3 respectively, while the short-beam shear strength Weibull moduli of them are 39.7, 38.3 and 27.6 respectively, and the flexural strength Weibull moduli of them are 35.4, 28.0 and 21.3 respectively. The Weibull moduli obtained from the experimental data could be useful for design of large size engineering composite components.Fourthly, the size effects of the quasi-static tensile strength of the open-hole laminates specimen were studied by Finite Element Method (FEM) and experiment. The tensile stress fields of [0] and [0/45/-45] fabrics reinforced laminates open-hole specimens with different thicknesses were calculated with the FEM method and the results show that the growth of the number of layers and the thickness has little influence on the stress distribution. The maximum tensile stress SX and the stress concentrate factor K around the hole of the [0] fabric reinforced laminates are of little change with the growth of the number of layers, while the maximum SX and K of the [0/45/-45] fabric reinforced laminates is increasing with the growth of the number of layers and the Boltzmann formula is fit for describing the increasing speed. The experimental results show that when the hole diameter/ width is 30mm/60mm, the tensile strength Weibull modulus of [0] fabric reinforced laminates open-hole specimen is 33.9, of [0/45/-45] fabric reinforced laminates is 31.6; and when the hole diameter/ width is 36mm/60mm, the Weibull moduli are 26.4 and 20.8. The tensile strength Weibull moduli of the open-hole laminates are obviously less than that of the imperforate laminates correspondingly. It’s also found that the ratio of the open-hole laminates strength versus imperforate laminates strength is of little change with the growth of the thickness through the experimental data.