碳纤维轴向导热性能表征及其影响因素

对比分析了采用碳纤维集束和基于单向复合材料的碳纤维轴向导热性能测试方法的差异性,研究了纤维体积分数、试样厚度等对导热测试的影响,分析了聚丙烯腈基高强型、高模型碳纤维和中间相沥青基碳纤维对该测试方法的适用性,考察了碳纤维轴向导热性能与其结构关联规律。结果表明,由于纤维向树脂的传热作用,单向复合材料试样比碳纤维集束试样具有更低的热扩散系数,采用碳纤维集束试样可获得准确的纤维导热系数,而基于单向复合材料计算得到的纤维导热系数偏高。纤维体积分数越高、试样厚度越大,基于单向复合材料计算得到的碳碳纤维导热系数越大;采用碳纤维集束试样测试碳纤维导热系数时,碳纤维体积分数变化对碳纤维热扩散系数、导热系数测试结果影响不大。中间相沥青基碳纤维、高模型碳纤维、高强型碳纤维导热系数依次降低,晶面间距越小、晶粒尺寸越大,碳纤维导热系数越高。研究结果对准确表征碳纤维导热性能、设计高导热复合材料具有重要指导意义。

Characterization on axial thermal conductivity of carbon fiber and its influence factors

Two measurement methods for carbon fiber's axial thermal conductivity are compared,which use fiber bundle and unidirectional fiber reinforced composite samples,respectively.The influence of fiber volume fraction and sample thickness on the measurement was discussed.The applicability of the method based on fiber bundle was investigated by testing polyacrylonitrile-based high-strength and high-modulus carbon fibers,and mesophase pitch-based carbon fiber.The relationship between thermal conductivity and microstructure was further discussed.The results indicate that unidirectional composite shows lower axial thermal diffusivity than fiber bundle sample due to the thermal conduction between fiber and polymer matrix in composite.Accurate thermal conductivity can be obtained by using fiber bundle sample,while unidirectional composite sample yields bigger thermal conductivity.For the measurement with unidirectional composite,the calculated thermal conductivity increases with the increase of fiber volume fraction and sample thickness.On the contrary,fiber bundle samples result in stable thermal conductivity which is not affected by fiber volume fraction.Moreover,the thermal conductivity increases in the order of mesophase pitch-based carbon fiber,high-modulus and high-strength carbon fiber.Lower lattice spacing and larger crystallite size leads to bigger thermal conductivity.These results may contribute to the accurate characterization on axial thermal conductivity of carbon fiber and the structural design of highly thermal conductive fiber composite.