Evaluation And Manufacture Of Grading Bamboo And Chinese Fir Laminated Lumber Of Wind Turbine Blades Materials

Over the centuries, energy has been supplied by wood, coke, coal, oil and natural gas, as well as by uranium (nuclear energy). All these energy sources are limited and at the same time these energy sources create pollution problems. This has led to the focus on a sustainable energy supply, which implies optimized use of energy, minimized pollution. That is why wind energy is prominent and it is the solution to the global energy problem. The wind energy is generated by using wind turbines. The turbine blades plays very important role in the wind turbines. The efficiency of the wind turbine depends on the material of the blade, shape of the blade and angle of the blade. So, the material of the turbine blade plays a vital role in the wind turbines. The material of the blade should possess the high stiffness, low density and long fatigue life.Currently, the materials used for wind turbine blades are mainly glass fiber reinforced plastic (GFRP), carbon fiber reinforced plastic (CFRP), and wood-based composites (Wood/Epoxy), etc. However, these materials have their own merits and defects. It is commonly known that turbine blades work by rotation in service, which demands uniformity and low variability in the properties of the materials used. More importantly, the strength and stiffness of the materials must be high with a low density. The fatigue properties of materials must be superior as well. It is also important that the materials used must be widely available with a low cost. Because of the high cost of CFRP materials, the manufacture of the wind turbine blades products is subsequently expensive. Furthermore, the GFRP products and CFRP products are difficult to be disposed of when out of service. On the other hand, the raw materials used for Wood / epoxy laminated composites, which are made from the large diameter natural forest wood ( such as Douglas Fir,) are difficult to be available. In this dissertation, Moso bamboo (Phyllostachys pubescens) and Chinese fir (Cunninghamia lanceolata) were selected as raw material to manufacture wood and bamboo laminated composites from their grading elements used for wind turbine blades, since they are abundant in China with low cost and excellent properties, and are easily to be decomposed of.Compared with engineering materials such as glass fiber reinforced plastic, the physical and mechanical properties of Chinese fir sapwood showed great variability, which is largely dependent on various factors such as the growing environment, site conditions and silviculture treatments. In order to produce wind turbine blades composite material with excellent physical and mechanical properties, all quartersawn boards made from the Chinese fir sapwood must be tested and then graded based on the wood properties determined. Only in this way may the wind turbine blades composite material with excellent physical and mechanical properties be produced.The conventional wood grading method is the machine grading which is based on the modulus of elasticity in static bending of wood. This grading method is characterized by higher accuracy, but it is time-expensive and is difficult to be applied in industrial production. Compared with the machine grading, visual grading has higher accuracy, and may take only 1/10 time used for machine grading, greatly reducing working time and labor intensity. It can be expected that, with the visual grading skills being increasingly improved, the accuracy of visual grading will also be further improved, and the visual grading time needed will also be further reduced, which appear to make the massive production of wind turbine blades composite material in industrial scale possible.For the process of reconstituted wood composites, the optimum adhesive spread is 170 g/m2 (single surface), the optimum slip joint angle is 3.81°(slope 1/15). In the manufacture process of the wood and bamboo laminated composites from their grading elements, there was a positive relationship between the solid content of the epoxy resin and the resin content impregnated. With the impregnation time and resin solid content being constant, impregnation under pressure resulted in more impregnated resin within the wood and bamboo laminas compared with the situation with no pressure applied.On the other hand, based on the classical lamination theory, the modulus of elasticity (MOE) of the wood and bamboo laminated composites was computed and predicted, Comparison between the predicted and measured MOE1 and MOE2 indicated that the prediction model had fairly high accuracy. According to the Serial model of composite material theory, the prediction model of tensile strength parallel to grain and compressive strength parallel to grain of the wood and bamboo laminated composites were established, respectively. Comparison between the predicted and measured values indicated again that the prediction model have relatively high accuracy in predicting the tensile and compressive strength of the laminated composites.The bamboo samples of various ages were tested by a Q800 dynamic mechanical thermal analysis (DMA) instrument. The results showed that storage modulus of the outer layer of bamboo under air-temperature conditions increased with aging of bamboo. In other words, the stiffness of bamboo increased with the increasing age of bamboo. However, up to a certain age, the stiffness of the outer layer of bamboo gradually remains constant, or even shows a decrease trend. General speaking, the outer layer of bamboo of 5-6 year old has a storage modulus on the order of 1010Pa(10GPa)under air- temperature conditions, which is definitely qualified as the reinforcement material for the wind turbine blades composites, with the loss modulus under air temperature conditions on the order of 108Pa. Therefore, the out layers of bamboo of 5-6 year old showed great potential to be used as the reinforcement materials of the wind turbine blades composite.For the wood laminated composites made from the grading Chinese fir wood lamellas, tensile strength parallel to grain exceeded 132 MPa,compressive strength parallel to grain exceeded 82 MPa,tensile modulus of elasticity parallel to grain exceeded 17.9 GPa,tensile modulus of elasticity perpendicular to grain exceeded 5.3 GPa,and shear strength exceeded 15.67 MPa. Besides, the specific gravity of this composite ranged from 0.75 to 0.85g/cm3. In other word, the manufactured wood laminated composites in this study have a relatively low density and high physical and mechanical properties, with the compression strength/density ratio being 104 Mpa.cm3/g,the modulus/density ratio being 22.8 GPa,and the modulus/ (compression strength)2 ratio being 2.68(1/ Mpa). It is concluded that the physical and mechanical properties of the wood laminated composites were superior compared with those of wood / epoxy laminated composites currently used abroad.For the bamboo laminated composites made from the grading outer layer portion of bamboo culms, tensile strength parallel to grain exceeded 254 MPa,compressive strength parallel to grain exceeded 180 MPa,tensile modulus of elasticity parallel to grain exceeded 26 GPa,tensile modulus of elasticity perpendicular to grain exceeded 5.5 GPa,and shear strength exceeded 21.65 Mpa. Besides, the specific gravity of this composite ranged from 1.00 g/cm3 to 1.10g/cm3. In other word, the bamboo laminated composites in this study have a relatively low density and high physical and mechanical properties, with the compression strength/density ratio being 174 MPa.cm3/g,and the modulus/density ratio being 25.2 GPa. It is concluded that the physical and mechanical properties of the bamboo laminated composites were superior compared with those of wood / epoxy laminated composites currently used abroad.Finally, for the wood and bamboo laminated composites developed for wind turbine blades products, the fatigue property is another important indicator of the material. Following the static loading experiments, the fatigue properties of the wood laminated composites were tested. The results showed that 60% of maximum loading strength of this material remained after 106 times of fatigue test, which is superior to the corresponding value of 55% for the high-quality wood/epoxy laminated, and 40% for GFRP under the same testing conditions. The fatigue properties of the bamboo laminated composites were tested as well. The results showed that 50% of maximum loading strength of this material remained after 106 times of fatigue test, which was comparable to the corresponding value of 55% for the high-quality wood/epoxy laminated remained, and was superior to 40% for GFRP under the same testing conditions.