3D-C/SiC复合材料拉—拉疲劳模量和电阻的变化

Variation of Youngs Modulus and Electric Resistance of 3D-C/SiC Composite During Tension-tension Fatigue at Room Temperature

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 。

Tension tension fatigue tests of 3D C/SiC composite are conducted at room temperature under a maximum stress of 250 MPa, a sinusoidal loading frequency of 60 Hz and stress ratio of 0.1.Variation of electrical resistance and Young′s modulus is measured by dynamic resonance method and electrical resistance appearance respectively. As fatigue cycles increase,experimental data curve of normalized modulus shows three parts: normalized modulus decrease significantly at first,then decrease slowly and decrease abruptly at last. Most of normalized modulus reduction occurres in first 600 cycles.Fatigue cycles in the second part are more than 94% of fatigue life,which can be approximated by logarithmic correlation.Except variation rate of electrical resistance decreases in first cycle,it increases continuously as cycles increase,which mainly consists of steady increment, spurting and abrupt increment. The variation rate of electric resistance basically reflectes damage degree and type of the fibres, and can be used to characterize the fiber damage of the 3D C/SiC composite.