弯扭组合载荷作用下复合材料风电叶片承力梁非线性破坏机理研究

Failure phenomenon of wind turbine blades involves interdiscipline of Strength of Mechanical Structures, Mechanics of Composite Materials, and Nonlinear Structural Mechanics, etc., and it brings new research topics to academia. This proposal tries to clarify failure mechanism of load-carrying beams of composite wind turbine blades by investigating nonlinear coupling of mechanics essentially related to different disciplines. Based on theoretical analysis, the research would investigate failure behavior of load-carrying beams primarily through bending, torsion, and combined bending-torsion experiments. Meanwhile, three-dimensional nonlinear numerical simulation would also be performed to complement experimental investigation. The main contents of research consist of four related parts: 1. examining characteristics of nonlinear phenomenon in the failure process of load-carrying beams; 2. analyzing intrinsic relationship among the Brazier effect, local buckling, and material failure; 3. revealing essential rules of failure affected by material, structural, and load parameters; and 4. establishing mathematical and/or mechanical criteria to describe failure of load-carrying beams. In this research, two key issues would be investigated to achieve comprehensive and profound understanding of failure mechanism of load-carrying beams of wind turbine blades and they are: a. interacting mechanism between material and geometric nonlinearities in the failure process, and b. qualitative and quantitative failure rules and their corresponding failure criteria of load-carrying beams. The outcomes of this research are expected to serve as theoretical basis for evaluating ultimate load-carrying capacity and predicting failure modes of composite wind turbine blades, and to provide scientific guides for developing core design methodologies of safer wind turbine blades.

风电叶片的破坏现象衍生出机械结构强度、复合材料力学和非线性结构力学等交叉学科的研究新内涵。本申请项目从突破非线性力学耦合机制这一共性科学问题的角度出发，澄清叶片承力梁的破坏机理。研究工作以承力梁弯扭实验研究为主导，各交叉学科理论分析为支撑，三维非线性数值模拟为补充和完善。研究内容按照：1. 探明非线性现象在承力梁破坏过程中的表现特征，2. 分析承力梁Brazier效应、局部屈曲、材料破坏之间的内在联系，3. 揭示材料、结构、载荷参数对破坏影响的本质规律，4. 建立承力梁破坏的数学、力学判别准则四个有机联系的环节开展。通过解决：a. 材料和几何非线性在破坏过程中的作用机制，b. 关键参数对破坏的定性、定量影响规律与判据两个关键科学问题，获得对叶片承力梁破坏机理的深入认识。研究成果将为评估风电叶片的极限承载性能和预测其破坏模式提供理论依据，为形成风电叶片更加安全的核心设计方法提供科学指导。

随着复合材料叶片向更大更长发展，叶片安全问题已成为制约风电机组向更大功率发展的重要瓶颈之一。风电叶片的结构形式和材料种类多样，所受载荷情况复杂，承力梁结构作为叶片的关键承力部件，探索其非线性破坏机理对研究叶片破坏的普适性规律具有重要意义。同时，材料非线性和扭转载荷这两个被现有研究所普遍忽视的重要因素也在本文中得以考察。本研究通过理论分析，破坏试验和数值模拟相结合的方法深入研究叶片承力梁在弯扭载荷下的非线性破坏机理，澄清了几何、材料和接触非线性在破坏过程中的作用机制和相互联系。研究发现，承力梁在不同方向载荷下呈现出不同的破坏机理。其中，在挥舞载荷下，腹板屈曲引起的压缩溃塌和梁帽屈曲引起的开胶和分层是主要的破坏模式；而在摆振载荷下，材料剪切非线性引起的梁帽非线性变形造成了结构胶开胶，这是影响承力梁极限强度的关键因素。此外，Brazier效应引起的截面扁平化变形也会影响初始破坏，但它与不同载荷下的承力梁横向刚度有关。通过对比试验发现梁帽的初始分层缺陷虽然会降低承力梁的承载能力，但对极限强度和后破坏没有明显影响。叶片弯扭全尺度结构破坏试验与承力梁挥舞加载呈现的破坏模式一致，并发现扭转载荷对叶片极限强度没有明显影响，但会影响后破坏特征。在数值研究方面，承力梁三维实体单元非线性有限元数值模型和叶片二维壳体单元数值模型可精确捕捉到结构的破坏模式和极限强度，能全面补充实验中未获取的应力应变状态和破坏细节特征，并在此基础上开发了叶片局部段参数化三维实体单元非线性有限元数值模型，为叶片从局部到整体的参数分析提供了有利条件。通过该项目研究，探索叶片在子部件尺度上的破坏机理，为叶片子部件结构认证测试基准提供了新的思路，为评估复合材料叶片的极限承载性能和预测其破坏模式提供了理论依据。