考虑界面层和孔隙的SiCf/SiCm复合材料热膨胀性能研究

Investigation on thermal expansion properties of a braidedSiCf/SiCm composite considering fiber-matrix interface and porosity

以三维四向编织SiCf/SiCm复合材料为对象,建立基于周期性边界条件、包含界面层和孔隙的复合材料单胞有限元模型,模型细观结构与工业CT扫描结果一致。计算了材料各个方向的热膨胀系数,发现界面层对纤维束热膨胀系数的影响不可忽略,基体孔隙位置的随机分布对热膨胀系数计算结果没有影响,孔隙率的增加会引起系数的显著减小,对胞元的热应力分析表明纤维束上的热应力水平大于基体。通过自由膨胀加温试验对材料纵向热膨胀系数进行了测定,在室温至1100℃区间内热膨胀性能稳定,试验结果与预测值符合较好。可为含界面层和基体孔隙的三维编织复合材料及其他多孔复合材料热膨胀性能研究提供理论基础。

A three-dimensional four-step braided SiCf/SiCm composite was taken as the object.The finite element unit cell model of the composite was present based on periodic boundary condition,including fiber-matrix interface and porosity.The thermal expansion coefficient of the composite in each direction was predicted.The result indicated that the influence of the interface should be taken into consideration.On one hand,the randomness of pore location distribution contributed less to the thermal expansion coefficient.On the other hand,the increasing of porosity induced an obviously thermal expansion coefficient diminution.The thermal stress analysis illustrated a discrepancy of stress level in the yarn and matrix,and the former was much higher.The longitudinal free expansion test showed stability of the thermal expansion property in the range of room temperature to 1100℃.Meanwhile,the test results performed well agreement with the simulation.The methodology might provide theoretical basis for the thermal expansion property investigation of three-dimensional four-step braided composites and other pored materials.