挠度修正法评价碳/碳复合材料的高温弹性模量

Evaluation of Elastic Modulus of C/C Composites at High Temperature by Relative Deflection Method

作为理想的高温结构材料,碳/碳(C/C)复合材料的高温弹性模量对其高温热应力分析及结构设计至关重要。三点弯曲试验可以采用电感量仪准确测得陶瓷试样的挠度,从而计算得陶瓷室温弹性模量,但三点弯曲试验在高温下的应用由于挠度变形难以准确测量而鲜有报道。本研究基于相对法理论,提出了挠度修正法,可以方便准确地获得其高温弹性模量。采用电感量仪与挠度修正法测试了2D与3D C/C复合材料室温弹性模量,结果表明2种方法的测试结果相近。测试了C/C复合材料在室温至1700℃间的弹性模量,结果表明2D与3D C/C复合材料的弹性模量均在1200℃时达到最大值82.22 GPa、66.73 GPa;而后在1200~1700℃,随着温度的升高,其弹性模量逐渐降低,且2D C/C复合材料的降低幅度更大。本研究显示挠度修正法可以准确、可靠地评价碳/碳复合材料的高温弹性模量,有望推广应用于其它高温结构材料弹性模量测量领域。

C/C composites are a kind of ideal structural materials used at high temperatures. Their high temperature elastic modulus are very important for the thermal stress analysis and composite structure design. The inductance micrometer can be used to determin the deflection accurately in the three-point bending tests, and the tested results can be used to calculate the elastic modulus at room temperature(RT). However, the application of three-point bending method at high temperature is scarcely reported due to the difficulty of the deformation measurement. In this study, the relative deflection method based on the relative method was used to evaluate the elastic modulus at various temperatures. The measured results of elastic modulus of 2 D and 3 D C/C composites at RT by inductance micrometer and relative deflection method are similar. The elastic modulus of C/C composites at RT^1700 ℃ was measured by the relative deflection method, and the results show that the maximum of the 2 D and 3 D C/C composites which appear at 1200 ℃ are 82.22 GPa and 66.73 GPa, respectively. The elastic modulus decreases gradually with the increasing temperature from 1200 ℃ to 1700 ℃, and the modulus of 2 D C/C composites decreases more quickly. These results demonstrate that the C/C composites measurement by the relative deflection method for determining high-temperature elastic modulus is accurate and reliable, which could be used to evaluate the modulus of other high-temperature structural materials.