低密度纤维增强纳米孔树脂基复合材料的断裂机制

纤维增强纳米孔树脂基复合材料(IPC)是一类轻质高效防隔热一体化耐烧蚀材料,具有典型的非均质结构特征。在外加载荷下,内部的纳米孔隙将会衍生出微裂纹。裂纹的萌生、聚合和扩展对复合材料的强度、刚度、变形性等力学性能有着重要的影响。本文分别以石英纤维针刺网胎(NQF)、石英纤维针刺网胎/纤维布(NQCF)为增强体,制备得到不同纤维结构增强的纳米孔酚醛树脂(NPR)基复合材料(NQF/NPR、NQCF/NPR),对比研究了材料拉伸强度、拉伸模量、断裂伸长率及拉伸疲劳性能,并采用CT原位拉伸装置表征了拉伸过程中复合材料的微观结构演变。结果表明：纤维布的引入极大提高了复合材料的力学性能,并且微裂纹首先在针刺区域边缘的树脂基体中出现。在裂纹扩展过程中,纤维结构对树脂基体的损伤起到了不同程度的阻碍作用。最后结合有限元法建立了NPR及纤维布的有限元模型,分析了不同尺度下材料的断裂机制。

Fracture mechanism of low-density fiber reinforced nanoporous resin composites

Fiber reinforced nanoporous resin composites are a kind of lightweight, good insulation and excellent anti-ablation material, which have a typical heterogeneous structure. Under applied load, the internal nanopores will spawn microcracks. Initiation, aggregation and propagation of these microcracks should play a significant role on the strength, deformation and failure properties of the materials. Herein, nanoporous resin composites with different fiber reinforcements have been prepared using needled quartz fiber mesh (NQF) and needled quartz fiber mesh/fiber cloth (NQCF) respectively. Focusing on the mechanical behavior, the present work studied the tensile strength, tensile modulus, elongation at break, crushing strength, bending strength and the tensile fatigue resistance of composites, and the microstructure evolution of composites have been characterized by CT in situ tensile device. The results show that the mechanical properties of composites are greatly improved by introducing the fiber cloth, and the microcracks firstly initiate in the resin matrix around the edge of the needling areas, while the damage of the resin matrix could be effectively hindered by the fiber structure. Finally, finite element models of nano-porous phenolic resin (NPR) and fiber cloth have been established to analyze the fracture mechanism of materials at different scales.