燃气环境中碳/碳复合材料循环载荷下的损伤机理

Damage Mechanisms of SiC Coated C/C Composites Subjected to Cyclic Loading in Combustion Gas Environment

将覆有SiC涂层的C/C材料置于甲烷燃气风洞中进行了循环载荷试验.应力-应变迟滞回环面积和棘轮应变的变化同时表明材料受到的损伤大部分发生在前50次循环,之后随着循环次数的增加,损伤的积累逐渐趋于稳定状态.材料在风洞环境下受到氧化,呈现出层状氧化形貌,这是由于碳纤维和碳基体之间不同的氧化速率所致.经过循环加载而未断裂的试样的残余强度比原始强度降低了19%,仅遭受氧化而未循环加载的试样强度相对原始值降低了38%.对试样的横截面微结构进行观察发现材料受到循环载荷后纤维/基体界面发生脱粘现象.拉伸实验中的实时声发射信号表明,只有当拉伸应力大于材料遭受的最大历史载荷时,试样才会发生明显的损伤.

A SiC coated C/C composite was subjected to cyclic loading in a combustion wind tunnel at flame temperature of 1300℃. Both the ratchetting strain and hysteresis changes show that the majority of damage is produced in the first 50 cycles, and then the rate of damage accumulation gradually approaches a steady value as the cycles proceeding. Lamellar structure of the C/C composite is observed after oxidation, which is caused by the difference in reactivity between the carbon fiber and carbon matrix. The mean residual strength of survived specimens is lower than that of the as-received ones by 19%, while mean residual strength of the specimens exposed to the combustion gas environment without loading is lower by 38%. Fiber/matrix debonding of the specimen cross section is observed after cyclic loading. Acoustic emission activities throughout the tensile tests of the cycled specimens shows that little damage is produced before the applied tensile load exceeds the maximum history load of the cyclic loading tests.