层间剪切性能及破坏机理
(中南大学 粉末冶金国家重点实验室， 长沙 410083)
摘 要: 以沥青四氢呋喃溶液、 沥青四氢呋喃溶液+20%焦炭粉（质量分数）和酚醛树脂四氢呋喃溶液+60%焦炭（质量分数）为预浸料预浸炭纤维， 模压制成初坯体， 然后再浸渍沥青-炭化， 制备了3种单向纤维增强炭/炭（C/C）复合材料试样。 对试样的密度、 开孔率、 层间剪切强度和显微结构进行了测试和观察，探讨了剪切破坏的机理。 结果表明: C/C复合材料的层间剪切强度随密度的增大和孔隙度的降低而提高，高温处理虽可使致密度得到进一步增大， 但层间剪切强度则由于基体炭的软化， 以及基体炭与纤维（或焦炭粉颗粒）界面的变化而显著降低； 由于微裂纹和孔洞的存在， 剪切裂纹前沿应力集中被释放，可阻止裂纹继续扩展， 载荷的继续增大导致新裂纹的生成并扩展， 所以C/C复合材料的三点弯曲剪切破坏呈多裂纹复合剪切模式。
关键字: 炭/炭复合材料； 浸渍； 层间剪切性能； 显微结构
（State Key Laboratory for Powder Metallurgy，
Central South University， Changsha 410083， China）
Abstract:Three kinds of unidirectional fiber-reinforced C/C composites were fabricated by the liquid pitch impregnation into the mould-preforms. The fibers were firstly pre-impregnated with pitch， pitch plus 20% coke and phenolic resin plus 60% coke， and then moulded into the preforms. Their densities， open porosities， interlaminar shear strengths (ILSS) and microstructures were tested and observed， as well as the destroy mechanism was studied. The microstructures were studied with optical metallograph and SEM. The results show that the interlaminar shear strengths of C/C composites decrease with increasing densities and decreasing open porosities. After high temperature treatment， the ILSS of samples decrease due to the matrix soften and the change of the interface of matrix and carbon fibers as well as coke particles. Due to presence of the microcracks and pores， the stress focus on crack-front in the shear process can be released， and the extension of cracks is prevented. The new cracks will be brought out and extended with increasing load. So the destroy of three-point bending shear in the C/C composites is a model of multi-crack complex shear. The lower the samples density， the more evidently the microcracks and pores， the lower the ILSS， and the more complex the cracks.
Key words: C/C composites； impregnation； interlaminar shear strengths (ILSS)； microstructure
