基于静态法和动态热机械分析法的炭/炭复合材料性能的研究

Mechanical properties and oxidation behavior ofcarbon / carbon composites based on static anddynamic mechanical thermal analysis methods

采用静态三点弯曲法和动态热机械分析法的三点弯曲温度扫描模式(DMA)对2D-C/C复合材料进行了测试,探究其在室温和高温下的力学性能和阻尼性能。此外,对C/C复合材料进行了不同时长的低温氧化(350℃),配合扫描电镜分析了氧化时间对材料氧化程度和残余力学性能的影响。在室温下材料的三点弯曲强度和模量为671.6 MPa和44.3 GPa,当三点弯曲测试温度上升到300℃以上时,材料的弯曲强度和模量下降为41.5 MPa和4.7 GPa;使用DMA测试的结果显示了相同的趋势,DMA在室温下测试的弯曲模量为45.9 GPa,在300℃后材料的模量降低到非常低的水平,此外材料在210℃出现了明显的阻尼峰,tanδ约为0.14。实验还发现在72 h氧化后材料的失重率达到7.5%,弯曲强度和模量退化了约为72.1%和27.8%。最后通过扫描电镜对氧化后的试样形貌进行表征后发现复合材料的纤维和基体间隙随着氧化时间的增加越来越大,并且基体炭在72 h氧化后所剩无几,此外纤维在长时间氧化后表面粗糙不平并发现团聚的杂质元素结块。

In this study,three-point bending and dynamic mechanical thermal analysis(three-point bending mode)have been used to test the mechanical and damping properties of C/C composite materials at different temperatures.In addition,the specimens have been oxidized at 350℃for different hours in a furnace,and its morphology after oxidation has been investigated as well.From the results,it was found that the flexural strength and modulus of specimens at room temperature are 671.6 MPa and 44.3 GPa,respectively.When the temperature of testing was raised to above 300℃,the strength and modulus significantly dropped to 41.5 MPa and 4.7 GPa,respective⁃ly.The results of DMA show the same trend to three-point bending.The modulus of specimens is 45.9 GPa at room temperature tested by DMA,and the modulus of specimens has dropped to a very low level as the temperature reaching above 300℃.On the other hand,there is a damping peak found at 210℃,and the tanδwas determined as 0.14 at 210℃.In addition,after 72 hours of oxidation,the weight loss rate of the material reaches about 7.5%,and the bending strength and the modulus degradation are about 72.1%,27.8%,respectively.Finally,the morphology of oxidized specimens showed that the gap between fibre and matrix gets wider as the increase of oxidation time,and the matrix of carbon is severely oxidized,the remaining of matrix carbon keeps a significant low level compared to untreated specimens.Besides,the oxidized fibres show a coarse surface and cross section,and segregations of contaminations also can be found at oxidized fibres.