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在室温最大应力为 2 5 0MPa、应力比R =0 .1和频率为 6 0Hz条件下 ,对 3D -C/SiC复合材料进行了拉—拉疲劳试验。用共振法和电阻增量仪分别测试了杨氏模量及电阻的变化。结果表明 :随循环次数增加 ,杨氏模量呈显著下降、缓慢下降和突然下降的变化规律。杨氏模量的下降大部分发生在疲劳循环的前6 0 0次。缓慢降低阶段约占疲劳寿命的 94 %以上 ,此阶段杨氏模量变化率与循环次数的对数近似呈线性关系 ;电阻变化率除首次循环降低外 ,随着循环次数增加一直在增加。增加规律大致可分为缓慢增加、台阶式增加和急剧增加三个阶段。材料的电阻变化率基本反映了纤维的损伤程度和破坏形式 ,可作为表征复合材料纤维损伤的有效参量
The 3D-C / SiC composite was subjected to pull-pull fatigue test at room temperature with a maximum stress of 250 MPa, a stress ratio of R = 0.1 and a frequency of 60 Hz. Resonance method and resistance increment meter were used to test the Young’s modulus and resistance changes. The results showed that the Young’s modulus decreased significantly, slowly decreased and suddenly decreased with the increase of the number of cycles. Most of the decrease in Young’s modulus occurs in the first 600 cycles of the fatigue cycle. The slowly decreasing phase accounts for more than 94% of the fatigue life. The change rate of Young’s modulus at this stage is approximately linear with the logarithm of the number of cycles. The rate of resistance change increases with the increase of the number of cycles except for the decrease of the first cycle. Increase in law can be divided into slowly increasing, step-by-step increase and sharp increase in three stages. The resistance change rate of the material basically reflects the degree of damage and the damage form of the fiber, and can be used as an effective parameter for characterizing the fiber damage of the composite material