【作者】 张洋；

【导师】 王宇；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2025， 硕士

【摘要】 碳纤维复合材料作为航空航天结构件的主承力材料,在平行纤维方向会受到不容忽视的压缩应力,但碳纤维及其复合材料的拉伸强度和压缩强度严重失衡,且前人研究存在多种不同的理论与见解,严重制约其实际应用中的结构设计,也限制了材料的进一步减重。因此,为开发出更高品质的碳纤维、提高碳纤维复合材料的压缩强度,探究碳纤维的压缩破坏影响因素及机理至关重要。本文借助XRD、SEM、TEM、Raman等表征方法,针对碳纤维本征及复丝压缩强度的影响因素及破坏机理展开了研究,探究了碳纤维微观结构尺寸及碳结构分布与压缩强度的关联性,分析了不同因素影响权重,揭示了不同结构碳纤维的压缩破坏机理,为开发高压缩强度的碳纤维提供了理论支撑。研究结果表明:(1)通过调控工艺制备不同拉伸模量的碳纤维,受聚集态结构差异的影响,随着碳纤维拉伸模量的升高,其压缩强度呈现先升高后降低的趋势,拐点在碳纤维拉伸模量为310 GPa左右。当碳纤维拉伸模量≤310 GPa时(中模范围内),碳纤维的压缩强度随着微晶结构的完善而提高,且复丝压缩强度从3.21 GPa增加到了4.15 GPa,提高了29.28%,单丝压缩强度从1.48 GPa增加到了1.83 GPa,提高了23.65%,压缩破坏模式为屈曲扭结破坏;当碳纤维拉伸模量>310 GPa时(高模范围内),碳纤维的微晶结构进一步完善,而微晶相互之间缠结结构变少,微晶间的牵制作用逐渐减弱使其更易发生相对滑移运动,导致压缩强度下降,压缩破坏模式为滑移剪切破坏。碳纤维本征及复丝两种方法测得的压缩强度与微晶结构的相关性规律相同。(2)通过调控工艺制备内部平均晶粒尺寸相同,宏观直径不同的高强中模型碳纤维,探究其内部碳结构分布对其压缩强度的影响,发现碳纤维本征压缩强度随着纤维直径的增大而增大。当直径从5.05μm增加到6.66μm时,其本征压缩强度从1.560 GPa增加到1.876GPa,增加了20.26%。直径较大的碳纤维皮芯结构差异大,皮部微晶尺寸大且结构更加完善,抵抗压缩变形的能力更加优异,压缩强度更高,压缩破坏模式均表现出屈曲扭结破坏。(3)在前两节研究的基础上,设计直径更大且晶粒尺寸亦有差别的高强中模型碳纤维,并与东丽T800碳纤维进行对比,探究碳纤维本征及复丝压缩强度的影响权重,研究得出的影响因素占比大小排序如下:微晶尺寸、表面性能、宏观直径。更多还原

【Abstract】 Carbon fiber composites,as primary load-bearing materials for aerospace structural components,are subjected to non-negligible compressive stresses along the fiber direction.However,the tensile and compressive strength of carbon fiber and its composites are severely imbalanced.Previous studies have proposed diverse theories and opinions,which significantly restrict structural design in practical applications and limit further weight reduction.Therefore,to develop higher-quality carbon fibers and enhance the compressive strength of carbon fiber composites,it is critical to investigate the influencing factors and mechanisms of carbon fiber compressive failure.In this study,we used characterization methods such us XRD,SEM,TEM,Raman etc.to study the influencing factors and failure mechanisms of the intrinsic and multifilament compressive strength of carbon fibers.The correlation between microstructure,carbon structure distribution,and compressive strength was investigated.The weighting of different influencing factors was analyzed,and the compressive failure mechanisms of carbon fibers with varying structures were elucidated.This work provides theoretical support for developing high-compressive-strength carbon fibers.The main research results of this paper are as follows:(1)CFs with different tensile moduli were prepared by controlling the processing technology,the compressive strength of carbon fibers showed a trend of first increasing and then decreasing with the increase of tensile modulus due to the influence of differences in aggregate structure,and the inflection point is around 310 GPa for the tensile modulus of carbon fibers.When the tensile modulus of carbon fiber is≤310 GPa(within the medium modulus range),the compressive strength of carbon fiber improves with the increase of microcrystalline structure,and the compressive strength of multifilament increases from 3.21 GPa to 4.15 GPa,an increase of 29.28%,while monofilament compressive strength increases from 1.48 GPa to 1.83GPa,an increase of 23.65%.The compressive failure mode is buckling and twisting failure;When the tensile modulus of carbon fiber is>310GPa(within the high modulus range),although the microcrystalline structure becomes more complete,the entangled structures between crystallites decrease,weakening the mutual containment effects between crystallites and making it more prone to relative slippage,consequently reducing compressive strength.The compressive failure mode transitions to slip-shear failure.The correlation between compressive strength and microcrystalline structure measured by monofilament and multifilament methods of carbon fiber is the same.(2)CFs with the same average grain size but different macroscopic diameters were prepared by adjusting the process,and the influence of internal carbon structure distribution on compressive strength was investigated.It was found that the intrinsic compressive strength of carbon fibers increases with the increase of diameter.When the diameter increases from 5.05μm to 6.66μm,the intrinsic compressive strength increases from1.560 GPa to 1.876 GPa,representing a 20.26%improvement.Carbon fibers with larger diameters exhibit greater differences in their skin-core structures,where the skin region features larger microcrystals and a more complete structure.They have better resistance to compressive deformation,higher compressive strength,and exhibit buckling and twisting failure modes.(3)Based on the previous two sections,high-strength medium-modulus carbon fiber with larger diameters and different grain sizes were designed,and compared with Toray T800 carbon fibers to investigate the influence weight of intrinsic and multifilament compressive strength of carbon fiber.The ranking of influencing factors obtained from the study is as follows:microstructure size,surface properties,and diameter size.更多还原