制孔缺陷耦合对碳纤维复合材料承力构件连接力学性能的影响与评估

Recent trends in the aircraft industry have been to increase the use of Carbon Fiber Reinforced Plastic (CFRP) in both primary and secondary structures, in which bolted joints are widely used to fasten components together. Although bolted joints can transfer high loads, they are still the weakest regions in composite structures. That CFRP is anisotropic and sensitive to force and heat always results in unremedied defects including delamination, burr and tear during drilling. These defects have become a huge challenge to correctly assess the reliabilities of bolted joints. The objective of this work is to study the relationship between drilling defects of CFRP and bolted joints behavior. On the basis of theoritical analysis and experiments a three dimentional characterization method of drilling defects is presented and a way to evaluate the bolted machining quality is proposed first in this research. Then the effects of drilling defects on bearing strength of CFRP with bolted joints is studied by using experiments and finite element analysis. An assessment method of damage tolerant of CFRP under the influence of drilling defects is finally introduced and varified by tests. The importance of this research lies in not only revealing and evaluating the effects of drilling defects on bearing strength of CFRP using bolted joints in learning, but also providing a theory evidence for assessing the residual life of CFRP structures containing drilling defects.

被广泛应用于碳纤维复合材料承力结构中的螺栓连接虽能传递较高的载荷但却是结构中最薄弱的环节，其可靠与否是关系结构服役寿命的关键所在。碳纤维复合材料各向异性及对力、热敏感等特点致使在制孔作业中极易产生分层、撕裂和毛刺等无法修补的缺陷，是对连接部位可靠性正确评估所面临的重要挑战。本课题以制孔缺陷对碳纤维复合材料厚板连接力学性能的影响规律为研究对象，在理论分析和实验观测的基础上，提出制孔缺陷的三维表征方法，建立制孔加工质量评价体系，在此基础上采用试验和有限元仿真相结合的方法研究制孔缺陷耦合机理及其对碳纤维复合材料承力构件连接力学性能影响的作用机制及规律，提出含制孔缺陷的碳纤维复合材料构件损伤容限评估方法并试验验证。本项目的重要意义不仅体现在学术上系统地对制孔加工缺陷影响碳纤维复合材料连接力学性能的揭示与评估，而且在于研究成果能够为我国碳纤维复合材料承力构件服役寿命的精确评估提供理论依据。

碳纤维复合材料所具有的优异性能使其在航空航天领域承力结构中的应用越来越广泛。然而，受碳纤维复合材料各向异性及其对力、热敏感等特点的影响，连接孔加工中极易出现如尺寸偏差、垂直度误差、分层缺陷等制孔缺陷，对连接的可靠性构成潜在威胁。本课题以揭示制孔缺陷对碳纤维复合材料厚板连接力学性能的影响规律为研究目标，在理论分析和实验观测的基础上依据制孔缺陷对连接拉伸性能影响的大小甄选垂直度误差和分层缺陷作为重点研究对象，提出了基于双参数的三维表征方法；采用实验与仿真相结合的方法揭示了连接孔倾斜角度、倾斜方向、螺栓预紧力、孔轴配合间隙等参数变化对单钉单剪、双钉单剪连接拉伸性能的影响规律；针对碳纤维复合材料连接结构损伤模式多样的特点，基于渐进损伤理论提出了适用于碳纤维复合材料多模式损伤的预测模型，并以此对分层缺陷在碳纤维复合材料连接结构中的演化过程进行了深入解析，阐明了分层缺陷尺度、沿构件厚度方向分布及其与制孔几何缺陷共同影响连接结构力学性能的规律；研究发现孔轴配合间隙有助于缓解连接孔垂直度误差所带来的不利影响，而当分层缺陷出现在不同的装配组件中时引起分层缺陷扩展的载荷阈值亦不尽相同，据此提出在损伤容陷评估时对于不同的缺陷要考虑制孔缺陷的相容性特点，而对于同种缺陷要重点关注其在连接结构中最大影响区的主体思想。研究成果不仅阐明了制孔加工缺陷影响碳纤维复合材料连接力学性能的规律，而且为碳纤维复合材料承力构件服役寿命的精确评估提供了数据支撑。