Calculation on residual thermal stress for hybrid fiber reinforced CMC-SiC

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.