基于纳米纤维网络的复合材料层间增韧及损伤和裂纹原位检测研究

The investigation about enhancing the fracture toughness and simultaneously detecting the internal damage and crack propagation of the carbon fiber (CF)/epoxy composite is important in both the theoretical study and application. In this project, epoxy functionalized carbon nanotubes (E-CNTs) are decorated onto the surface of polyvinylidene fluoride (PVDF)/ polyamides66 (PA66) nanofiber possessing a core-shell structure. The obtained nanofiber composite is then used as an interleaf in the laminate composite. E-CNTs can improve the compatability between the nanofiber and epoxy, thereby enhancing the interfacial interaction. The role of nanofiber bridging, CNT debonding or pull out as well as the reflection of crack induced by the hierarchical nanofiber network on the fracture toughness will be investigated, in order to reveal the multi-level toughening mechanism. We will also study the influence of the hierarchical nanofiber network and fatigue load on the electrical signal generated from the core of the nanofibers, i.e., the piezoelectrical PVDF layer, uncover the relationship between the signal and residual modulus, strength and fatigue life of the laminate composite, and finally clarify the mechanism for the detection of internal damage and crack propagation. The project will open a new way for the interlaminar toughening and in-situ detection of damage and crack propagation of the CF/epoxy composite, and provide both theoretic and experimental basis for developing the CF based laminated composite with high performance and multi-functionality.

如何提高碳纤维/环氧复合材料的层间断裂韧性，并能同时原位检测复合材料内部损伤及裂纹扩展具有非常重要的理论研究和实际应用价值。本项目将利用超声将环氧官能化的碳纳米管（CNTs）均匀负载于具有核壳结构的聚偏氟乙烯/尼龙66（PVDF/PA66）纳米纤维表面，将获得的多层级纤维膜用于碳纤维/环氧的层间材料，CNTs可以改善纳米纤维和环氧的相容性，增加界面相互作用。本课题将分析纳米纤维的桥连、CNTs的脱粘或拔出及多层级纤维网络对裂纹的阻挡和偏转作用等因素对复合材料断裂韧性的影响，揭示其层间多层次增韧机理。通过研究多层级纤维网络结构及疲劳载荷对纳米纤维核层PVDF压电信号的影响规律，建立复合材料剩余刚度、剩余强度及疲劳寿命与压电信号的关系，阐明损伤和裂纹的检测机制。本项目的重要意义在于为碳纤维/环氧复合材料层间增韧及损伤和裂纹的原位检测提供新的思路和方法。

如何提高碳纤维/环氧复合材料的层间断裂韧性，并能同时原位检测复合材料内部损伤及裂纹扩展具有非常重要的理论研究和实际应用价值。本项目利用纳米纤维及其复合膜作为层间增韧材料，研究了材料的制备、微观形貌及裂纹扩展路径与复合材料断裂韧性之间的关系。探究了聚偏氟乙烯纤维膜（PVDF）用于层间增韧时断裂扩展模式及长度对压电信号的影响。研究发现低熔点的聚己内酯可以改善尼龙纤维与环氧基体的相互作用，从而提高增韧效果。从断裂面的形貌揭示了复合材料I型及II型层间多层次增韧机理，即：CNTs的“拔出”和“销钉”及纤维的桥连。此外，对于I型断裂，在同一个裂纹长度下，PVDF纤维膜的输出电压与位移成正比；在II型断裂过程中，输出电压首先随着施加力线性增加直至一稳定值，当裂纹开始扩展后，电压急剧提升。本项目为碳纤维/环氧复合材料层间增韧及损伤和裂纹的原位检测提供新的思路和方法。