复合材料因其材料性能的优越性、使用范围的广泛性，尤其是航空航天等领域应用需求成为当前研究的热点。为实现复合材料件单件、小批量快速制造，近年来复合材料增材制造成为研究新热点，特别是连续纤维复合材料增材制造技术。本文针对连续纤维复合材料增材制造过程中存在的成形工艺参数匹配难、界面和层间结合差等亟需解决关键问题，采用理论研究、仿真分析和工艺实验方法，研究了连续纤维复合材料层间增强增材制造技术的相关工艺方法、成形机理和成形设备。为实现层间增强的目标，分析了树脂的熔融流动过程、熔融沉积过程中的热学分布和粘结颈的形成机理，研究了连续纤维复合材料的增材制造和丝材成形工艺过程，揭示成形机理、影响因素和调控原理，改善成形件的性能，有效的提升了层间力学性能，为后续的推广应用提供性能保障。本文提出了一种层间交织结构与热力耦合压实的增材制造方法，研发了包含热压实机构的增材制造成形设备和成形工艺，设计了层间交织结构的填充路径，减少了成形构件的层间孔隙缺陷，改善层间粘结质量，制备了层间正交交织结构的成形构件，有效的解决了构件层间性能差的问题，分析了构件在低速载荷下的损伤机理和失效形式，成形构件的层间剪切强度可提升约20%。本文创建了连续纤维复合材料层间的粘结颈形成和翘曲变形的数学模型，通过力学性能测试和CT表征，分析了基于粘结颈理论的增材制造构件的断裂机理，揭示了纤维含量、温度和层数等成形参数对复合材料构件层间粘合质量和翘曲变形量的影响规律，获得了减少翘曲变形量的工艺控制策略。本文提出了一种应用于增材制造技术的层间铺放短纤维的增强方法，将短纤维随机分散铺放在打印单层间，研究了层间短纤维在外界应力作用下的应力传递，建立了层间随机取向短纤维的传递力学模型，揭示了铺放纤维含量、纤维长度等铺放工艺参数对成形性能的影响规律。将短纤维铺放在连续纤维复合材料层间实现复合增强，有效的抑制裂纹在复合材料层间的失稳扩展，提高了打印成形件的强度和性能。本文所取得的创新型研究成果推动了连续纤维复合材料增材技术的发展，有效的解决了成形件浸渍程度差、层间性能差等关键技术问题，具有重要的理论意义和工程应用价值。
Composite materials have attracted increasing attention from research institutions because of their superior mechanical properties, wide range of usage and potential applications in aerospace. Additive Manufacturing (AM) is used to rapid prototyping single and small batch of composite components, is becoming a research hotspot in recent years, especially the AM technology of continuous fiber composite. Concerning the AM process of continuous fiber composites, there are still some key problems need to be solved urgently, such as inappropriate manufacturing parameters, poor interfacial and interlayer bonding. In this study, theoretical research, simulation analysis and experimental investigations are combined to explore the relevant manufacturing processes, mechanism and equipment in AM. In order to realize the enhancement of interlayered performance, the melt flow process of resin flow and subsequent impregnation, the thermal distribution in forming process and the formation mechanism of the bonding neck were mainly analyzed. In addition, the AM process of continuous fiber composite materials and the forming process of filament are studied. The related formation mechanism, influencing factors and control principle are revealed to improve the mechanical performance of printed parts and the interlaminar bonding performance effectively, which can guarantee the subsequent applications.An method of thermal-mechanical coupled compaction and interlaminar reinforcing structure are proposed. The AM equipment and forming processes including hot compaction mechanism are developed to reduce pore defects and improve the interlayer bonding performance of the formed components. Moreover, the filling path of interlaminar interlaced structure is designed. The forming components of interlaminar orthogonal structure are prepared and further tested for the analysis of damage mechanism and failure mode under low-speed loading. It was concluded that interlaminar shear strength of the formed components can be increased by ~20%. The mathematical model of the formation of bonding neck and warpage deformation of continuous fiber reinforced composites are established. Based on mechanical testing and CT characterization, the fracture mechanism of AM component is analyzed. The influence of fiber content, temperature and layer number on interlaminar bonding performance and warpage deformation of composite components is revealed, and the processing control strategy of reducing warpage deformation is obtained. A reinforcing method by adding short fibers during additive manufacturing is proposed. The short fibers are randomly distributed on the printing layer, and the reinforcement model of the short fiber interlaminar placement is established. The influence of several processing parameters including fiber content and fiber length on formability are revealed. The short fibers are placed between the continuous fiber composite layers to realize interlaminar reinforcement, which can effectively restrain the unstable crack propagation in the composites, and further improve the strength and performance of the printed components.The innovative results obtained in this study promote the development of AM technology of continuous fiber reinforced composite. Several key problems including poor impregnation and weak interlaminar performance are effectively solved, which provides great value in theoretical investigation and engineering application.
