Study On Mechanical Properties Of Carbon/glass Hybridized Fabric Reinforced Composites And Applications For Wind Turbine Blades

Lightweight and robust design have become key points for advanced fiber reinforced polymer composites,especially in wind energy field.Wind turbine blades are one of the largest composite components in the world.Since the blade length has a significant impact on the power generation,wind turbine blades are continuously growing bigger and bigger.Limitation of stiffness and weight of wind turbine blades are bottlenecks of material-designing,thus,high stiffness and high fatigue properties become the critical properties of spar caps.Extensive researches of various hybrid materials were carried out by worldwide researchers;they not only included different fibers with different compositions,such as woven fabrics,knitted fabrics,prepregs and so on,but also related interlayer and intralayer structures.However,significantly different even opposite behaviors were found,bringing difficulties to get a reasonable conclusion.The content of this thesis includes following two parts:Firstly,four uni-directional carbon/glass hybrid fabrics with inter-layer structure,pure glass and pure carbon were used to prepare various composites,the static properties,tension-tension and tension-compression fatigue behaviors as well as inter-laminar properties at high and low temperatures were intensively studied.Results demonstrate that tension,compression and flexure properties at 0° are mainly dependent on the properties of fibers.Moduli on fiber direction follows the linear rule of mixtures(ROM),but the ultimate strength doesn't obey the rule,instead,a bi-linear rule of upper and lower limits can be used to predict the tolerant of strength.Tension at 90°,compression at 90°,in-plane shear and inter-laminar shear are matrix-domain properties,the "bucket effect" that depends on the weakest part of the material was observed.Composites based on hybridized fabrics or pure glass fabrics have different properties at different temperatures.Compared with properties at room temperature,property of all composites rises at 50? while drops at other temperatures.However,the hybridized fabric reinforced composites(HF1)has a better property retention rate than glass fabric reinforced composites at all temperatures.The high-cycle fatigue of both tension-tension and tension-compression obey the linear rule of mixtures,but low-cycle fatigue is more similar to static strength.A fatigue life model based on static upper and lower bounds as well as a linear rule of mixtures have been developed,and the prediction of fatigue properties on carbon/glass hybridized fabric reinforced composites with all carbon-glass ratios has been achieved.Secondly,optimization and cost analyses for wind blade model were carried out.Based on the Upwind 5 MW blade model,carbon/glass hybrid reinforced composites have a significant advantage on the weight reduction compared with glass fiber reinforced composites and a cost reduction compared with carbon fiber reinforced composites.There is an optimism carbon-glass ratio for each blade,which depends on the price and properties of carbon and glass fabrics.