风力机叶片原生缺陷转捩的能量释放机理研究

针对风力机叶片原生缺陷演化为裂纹进而扩展导致断裂的问题,分析细观缺陷在外载荷作用下转捩为宏观裂纹的能量释放定量关系明晰裂纹萌生机理。首先根据风力机叶片的载荷特点构造一个新的应力函数,基于正交异性复合材料基本公式求解原生缺陷层间开裂的应力强度因子、应力应变和位移分量,由此获得细观缺陷变形过程释放的塑性应变能;使用红外热像仪采集原生缺陷转捩过程的温度场并计算热能耗散量,基于不可逆热力学定律获得内储能随着疲劳周期的变化规律;最后,在万能试验机上对含有气泡和纤维断裂的叶片试件进行疲劳试验。结果表明,应用提出的应力函数的计算结果与试验结果误差较小,可作为细观缺陷变形时塑性应变能的计算依据。原生缺陷转捩为微小裂纹时,内储能的变化规律可作为判断缺陷类型和程度的依据。这项研究探索复合多层材料跨尺度的疲劳能量理论,有助于实现风电机组关键部件的全寿命周期监测。

Study on energy release mechanism of native defects transition for wind turbine blade

In order to solve the problem of fracture caused by the failure of the native defects of wind turbine blades, the mechanism of crack initiation is defined by analyzing the quantitative relation of energy release during the transition from mesoscopic defects to macroscopic cracks under external loading. Firstly, a new stress function is constructed according to the load characteristics of wind turbine blade. Based on the basic formula of the orthotropic composite, the stress intensity factor, the stress strain and the displacement of the native defect are calculated, and the plastic strain energy of the mesoscopic defects can be obtained. Using the infrared thermal imager, the temperature field of transition process of native defects is collected and the thermal energy dissipation is calculated. Then, based on the irreversible thermodynamics, the variation law of the internal storage energy with the fatigue cycles is obtained. Finally, the blade specimen with bubble and fiber fracture is selected for the fatigue test. The results show that the error between the calculated displacement using the new stress function and the test value is smaller. This indicates that the proposed stress function can be applied to calculate the plastic strain energy for the mesoscopic defects. When the native defects are transitioned into a small crack, the change of the internal energy storage can be used as to determine the type and extent of the defects. The fatigue energy theory of multilayer composites is explored in this study, which helps to realize the life cycle monitoring of key components of wind turbine.