Finite element simulation and experiment study of residual stress distribution of CVD Nb-C/SiC composites

Residual stresses induced in the cooling process of deposited Nb connection layer on C/SiC composite have significant impact on their mechanical properties. This work aims to characterize the residual stresses and investigate the change rule of the residual stress by the x-ray scattering technique and finite element method (FEM). Nb connection layer was deposited on C/SiC composites by chemical vapor deposition method (CVD). The result shows that temperature of CVD Nb-C/SiC composites is linear over time, the temperature gradient between connection layer and matrix is almost zero. During cooling process, interface residual stress is mainly caused by the large difference of thermal expansion coefficient of both materials. Due to the size effect of the geometrical model, the interface stress gradient is small along the radial direction but large along the axial direction. C/SiC substrate is subjected to compressive stress while Nb layer bears tensile stress. Along the ring direction, equivalent stress from C/SiC substrate to Nb layer presents linearly downward trend. The calculated value is nearly the same with the XRD testing result on the side of Nb layer, which further confirms the correctness of the finite element model. (paper)