纤维混编CMC-SiC的残余热应力计算

摘要

将SiC纤维引入到C/PyC/SiC中,有望减少因C纤维与SiC基体热膨胀系数不匹配而导致的基体残余热应力.研究了C纤维和SiC纤维混编方式和混编比例对复合材料残余热应力的影响规律.采用有限元法建模、计算了纤维混编接触分布和相间分布复合材料的残余热应力,结果表明:(1)与C/PyC/SiC比,C纤维和SiC纤维混编增强SiC基复合材料可减少SiC基体的残余拉应力;(2)相同混编比例时,纤维混编接触分布((xC-ySiC)/PyC/SiC)复合材料的基体轴向残余应力比纤维混编相间分布((xC×ySiC)/PyC/SiC)复合材料基体的小;(3)以纤维混编接触分布为例,SiC基体的轴向残余应力随混编复合材料中SiC纤维的增加而减小,但当C纤维和SiC纤维的混编比例由1∶2变为1∶4时,基体的轴向残余热应力仅从174 MPa 下降到170 MPa.%It was anticipated that the residual thermal stress in C/PyC/SiC composite,which was due to the coefficients of thermal expansion mismatch between carbon fiber and SiC matrix,would be decreased by introducing the silicon carbide fiber to the composites.The effects of hybrid styles and hybrid ratio between the carbon fiber and silicon carbide fiber on the residual thermal stress in the composites were studied by constructing the finite element models and calculation.The results show that:(1) the residual thermal stresses in carbon fiber and silicon carbide fiber hybrid reinforced SiC matrix composites are lower than those in C/PyC/SiC composites;(2) the axial residual thermal stresses of SiC matrix in hybrid composites with contacted distribution of carbon fiber and silicon carbide fiber ((xC-ySiC)/PyC/SiC) are lower than those in hybrid composites with alternative distribution of carbon fiber and silicon carbide fiber ((xC×ySiC)/PyC/SiC) at the same ratio of carbon fiber to silicon carbide fiber.(3) Taking an example of contacted distribution of carbon fiber and silicon carbide fiber in ((xC-ySiC)/PyC/SiC) composites,the axial residual thermal stresses of SiC matrix are reduced with the silicon carbide fiber volume percent increases in the ((xC-ySiC)/PyC/SiC) composites.However,the axial residual thermal stresses in SiC matrix decreases from 174 MPa to 170 MPa only when the hybrid fiber volume percent ratio of carbon fiber to silicon carbide fiber change from 1∶2 to 1∶4.