低密度纤维增强酚醛气凝胶复合材料的力学特性及断裂机制

Mechanical properties and fracture mechanisms of low-density fiber preforms reinforced phenolic aerogel composites

  • 摘要: 分别以低密度玻璃纤维、石英纤维、碳纤维针刺预制体为增强体,制备出不同的纤维针刺预制体增强酚醛气凝胶复合材料(NF/PA),研究了纤维种类对材料力学性能及断裂行为的影响。结果表明:酚醛气凝胶与纤维预制体形成良好的界面结构,微观上呈现“珠串”状三维开孔网络结构特征,因而复合材料具有较低的密度(0.45 g/cm3)和室温热导率(0.046~0.067 W/(m·K))。在拉伸与压缩过程中,基于NF/PA明显的塑性形变现象,分析了裂纹扩展过程中材料所吸收的能量,发现纤维种类会显著影响界面特性进而影响材料断裂和失效机制。其中,碳纤维的界面结合强度小于酚醛气凝胶极限剪切应力,在断裂过程中纤维先与酚醛气凝胶脱粘,表现为“滑脱界面”;玻璃纤维与石英纤维界面结合强度大于酚醛气凝胶极限剪切应力,在断裂过程中酚醛气凝胶先被破坏,表现为“粘性界面”。相较于玻璃纤维、石英纤维,碳纤维对NF/PA增韧、补强效果较优。

     

    Abstract: Three kinds of needled fiber preforms reinforced phenolic aerogel composites (NF/PA) were prepared using lightweight needled preforms of glass fibers, carbon fibers and quartz fibers as reinforcements, respectively. The resultant fiber-dependent mechanical properties and fracture behavior were studied systematically. It is found that the NF/PA has a low density of ~0.45 g/cm3 and good insulation with room-temperature thermal conductivity as low as 0.046-0.067 W/(m·K). The phenolic aerogel has typical 3D porous structure with the overlapped and interconnected phenolic aerogel nanoparticles filling in fiber preforms, which has excellent interface structure with fiber. The NF/PA have obvious plastic deformation in the process of tension and compression. Furthermore, this work analyze the energy absorption of NF/PA during the crack propagate, and conclude that the type of fiber significantly affects the interface characteristics and thereby the fracture and failure mechanisms of composites. The interfacial bonding strength of carbon fiber is less than the ultimate shear stress of phenolic aerogel, and thereafter fibers are initially deboned with phenolic nanoparticles during the fracture process, responding to a “slip interface” feature. On the other hand, the bonding strengths of glass fiber and quartz fiber are both greater than the limit of shear stress of phenolic aerogel. Therefore, the phenolic aerogel is destroyed initially during the fracture process, which manifests as a “sticky interface” feature. Compared with glass fiber and quartz fiber, the carbon fiber shows more toughening and reinforcing effect on NF/PA.

     

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