挖补修理复合材料层合结构湿热性能研究

This project focuses on the hygrothermal effects on the properties of scarf-repaired composite laminates during the service period. The properties of the selected adhesive materials and the interface between adhesive and composite materials under hygrothermal environments are studied experimentally. The mechanical behavior under hot/wet environments of the scarf-repaired laminates subjected to different loads, including tension, compression, low velocity impact, and tension and compression after impact are studied experimentally. Based on these studies, theoretical models are established to analyze the hygrothermal inner stress and the mechanical properties under tension, compression, low velocity impact, tension and compression after impact of the scarf-repaired laminates under hygrothermal environments. The deterioration mechanism of the selected adhesives and the interface between adhesive and composite materials will be revealed. The influences of non-uniform stress distribution along the bond line on the failure mechanism and fracture behavior will also be studied. The effects of the non-uniform properties under hygrothermal environments on the properties of scarf-repaired composite laminates will be studied, and an effective analytical method will be developed to analyze the mechanical properties of the scarf-repaired composite laminates subjected to tensile and compressive loads before and after low velocity impact, as well as the mechanical behavior under low velocity impact. In this research, all the materials are domestic and the composite laminates are common structures used in flight vehicle. The research results can be meaningful in practical engineering application, such as providing useful experimental data for the engineering database of repaired materials for composite laminates and typical structures, providing detailed analytical methods and design references for composite structure repair，giving evaluation method for adhesive meterial properties and giving the direction of the future research on the adhesive materials used in composite scarf repair.

针对挖补修理复合材料结构服役中的湿热问题，试验研究挖补用胶粘剂、胶粘剂与复合材料胶接界面的湿热性能，湿热条件下挖补层合板的拉伸、压缩、低速冲击、冲击后拉伸与压缩行为。在此基础上，建立理论分析模型，对挖补层合板的湿热内应力及其拉伸、压缩、低速冲击、冲击后力学性能进行分析。揭示常用挖补胶粘剂、胶粘剂与复合材料胶接界面湿热性能退化机理，以及挖补中斜接面应力分布不均匀对胶粘剂损伤机理与破坏行为的作用，研究挖补胶层湿热性能不均匀性对挖补复合材料结构性能的影响，建立湿热条件下挖补复合材料结构拉伸、压缩、低速冲击以及冲击后力学性能有效的分析方法。所有试件全部采用国产材料和航空飞行器结构常用层合结构，研究结果可为复合材料挖补修理材料与典型结构工程数据库提供可用的数据，为复合材料挖补修理提供具体的分析方法与设计参考，并可为复合材料挖补胶粘剂材料的评定与研制方向提供指导。

随着复合材料在飞机上大量使用，挖补修理作为复合材料修理中修理效率最高的修理方法也得到了广泛应用。与完好板相比，挖补结构多了胶层这部分，胶层比复合材料更容易受到湿热环境的影响，而飞机在服役期间又不得不在复杂湿热天气下工作，所以挖补修理复合材料的湿热性能值得被研究。.本项目研究四种湿热环境，即常温干态（RD），常温湿态（RW），高温干态（ED），高温湿态（EW），高温指95℃，湿态指水中吸湿平衡。采用试验和有限元法首先研究了两种常用复合材料修理用胶黏剂在湿热环境下的力学性能，探索胶黏剂湿热损伤机理，然后采用这两种方法分别研究了湿热环境下挖补修理层合板结构的拉伸、压缩、冲击、冲击后拉伸以及冲击后压缩等性能，探索湿热效应对挖补板力学性能和损伤机理的影响。.结果表明，湿热环境会明显降低胶黏剂和挖补层合板的力学性能，湿热环境对结构力学性能的影响主要体现在湿热内应力和材料性能衰减两个方面，最大湿应力位于胶层两侧自由端部，最大热应力位于层合板90°层，高温环境下胶黏剂表现出明显塑性，湿态环境下更容易发生复合材料/胶层胶接界面破坏。综合考虑湿热下拉压性能和工艺因素，建议修理角度为4~6°，胶层厚度为0.15~0.2mm。冲击能量和冲击位置对冲击响应和损伤形貌有很大影响。冲击后拉伸载荷下，损伤以基体破坏和纤维断裂为主；压缩载荷下，损伤以纤维基体剪切破坏和纤维断裂为主。