Interlaminar properties and toughening mechanisms of aligned carbon nanotube fiber veil interleaved carbon fiber/epoxy composites
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摘要:
碳纤维增强树脂基复合材料(CFRP)由于比强度高、比模量高等优异性能应用广泛。但受层状结构特性和环氧树脂本征脆性的影响，其沿厚度方面的力学性能较差，在遭受面外冲击和面内压缩等载荷作用下容易发生分层，进而降低复合材料的强度和刚度，影响结构的寿命和使用安全性。因此，提高该复合材料的层间断裂韧性尤为重要。本文通过在复合材料层间区域插层高度取向的碳纳米管纤维纱来提升其层间断裂韧性。相比于其它插层材料，该纤维纱的厚度更薄(约5微米厚)且力学性能更好，对复合材料的厚度、重量及面内力学性能影响相对较小。然而，由于该纤维纱的致密度较高，其树脂浸润问题一直是层间增韧应用的技术难点和关键。本文尝试先将纤维纱浸泡于经丙酮稀释的环氧树脂溶液中，待丙酮挥发后，再将之插层于自制碳纤维预浸料的层间区域，然后热压成型。结果表明，该方法有效地解决了碳纳米管纤维纱的树脂浸润问题。经纳米纤维纱增韧后，复合材料板的I型和II型层间断裂韧性分别提高了37.4%和41.8%。此外，本文结合横截面的光学显微观察和断裂面的扫描电镜分析，再现了裂纹的扩展路径，并进一步揭示了碳纳米管纤维纱的层间增韧机制。 不同裂纹位置的金相抛光图片及其对应开裂面的扫描电镜图片 -
关键词:
- 碳纳米管纤维纱 /
- 层间增韧 /
- 纤维桥接 /
- 裂纹偏转 /
- 碳纤维增强树脂基复合材料
Abstract: Carbon fiber reinforced polymer (CFRP) composites are widely used because of their excellent properties such as high specific strength and high specific modulus, but their mechanical properties along the thickness are poor due to the laminar structure characteristics and the intrinsic brittleness of epoxy resin, and they are prone to delamination under out-of-plane impact and in-plane compression loads, which in turn reduce the strength of the composites. Therefore it is especially important to improve the interlaminar fracture toughness of the composites. In this paper, we attempt to improve the interlaminar fracture toughness of the composite by introducing highly oriented carbon nanotube fiber veils in the interlaminar region. To ensure that the fiber veils are well infiltrated by the resin, they are first immersed in an epoxy resin solution diluted with acetone. After the acetone evaporated, it is inserted into the interlayer region of the homemade carbon fiber prepreg and subsequently cured by a hot pressing process. The Mode I and Mode II interlaminar fracture toughness of the toughened samples are evaluated via ASTM testing standards. Combined with the optical microscopic observation of the cross-section and scanning electron microscopy analysis of the fracture surface, the crack propagation paths are clearly shown and the interlaminar toughening mechanisms of CNT fiber veils are revealed. The results show that the Mode I and Mode II interlaminar fracture toughness of CNT veil toughened samples are improved by 37.4% and 41.8%, respectively. The toughening mechanisms mainly include matrix toughening, strengthening carbon fiber bridging and crack deflection.-
Key words:
- Carbon nanotube veil /
- Interlaminar toughening /
- Fiber bridging /
- Crack deflection /
- CFRP
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图 3 取向碳纳米管纤维纱插层碳纤维/环氧树脂复合材料Ⅰ型断裂韧性测试结果：(a)样品的载荷-裂纹张开位移图；(b)Ⅰ型断裂韧性测试的R曲线；(c)Ⅰ型断裂韧性平均值
Figure 3. Mode Ⅰ fracture toughness test results of aligned carbon nanotube fiber veil interleaved carbon fiber/epoxy composites: (a) Load-crack opening displacement diagram of the sample; (b) R curve of mode Ⅰ fracture toughness test; (c) Mean value of mode Ⅰ fracture toughness
图 4 (a)基准样的I型断裂韧性测试断裂表面; (b)和(c)断裂表面在不同倍率下的电镜图像
Figure 4. (a) DCB test configuration and fracture surface of baseline; (b) and (c) SEM images of fracture surface at different magnifications
图 5 裂纹开裂面中碳纳米管与环氧树脂结合形貌
Figure 5. Morphology of carbon nanotubes and epoxy resin in cracking surface
图 6 (a)DCB测试过程中的碳纤维桥接; (b)~(e)裂纹截面扫描电镜图
Figure 6. (a) Carbon fiber bridging during the DCB test; (b)~(e) SEM images of crack section
图 7 不同裂纹位置的金相抛光图片及其对应开裂面的扫描电镜图片
Figure 7. Metallographic polishing images at different cracking positions and SEM images of corresponding cracking surfaces
图 8 取向碳纳米管纤维纱插层碳纤维/环氧树脂复合材料裂纹偏转之后的Ⅱ型断裂韧性测试结果
Figure 8. The mode Ⅱ fracture toughness test results of aligned carbon nanotube fiber veil interleaved carbon fiber/epoxy composites after crack deflection
图 9 取向碳纳米管纤维纱插层碳纤维/环氧树脂复合材料 裂纹未偏转的Ⅱ型断裂韧性测试结果
Figure 9. The mode Ⅱ fracture toughness test results of aligned carbon nanotube fiber veil interleaved carbon fiber/epoxy composites before crack deflection
图 10 基样II型断裂面的扫描电镜图
Figure 10. SEM images of the Mode II fracture surface of the baseline
图 11 碳纳米管纤维纱增韧样品II型断裂面的扫描电镜图
Figure 11. SEM images of the Mode II fracture surface of the CNT veil toughening sample
表 1 CNT veil参数
Table 1. Parameters of CNT veil
Parameter Thickness
/μmDensity of surface/(g·m−2) Diameter of CNT/nm Value 5±0.5 2.59-3.70 6-15 
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表 2 不同区域的断裂韧性对比
Table 2. Comparison of fracture toughness at different regions
Crack length
/mmGⅠC /(J·m−2) Baseline CNT veil 50-75 730 ± 90 1137 ± 43(+55.8%) 75-100 869 ± 67 1092 ± 62 (+25.7%) 50-100 810 ± 76 1112 ± 50 (+37.4%)
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