Effect of film cooling holes on the mechanical properties of 3D braided SiC_f/SiC composites at 1350 °C in air

3D braided SiC_f/SiC composites are the preferred material for turbine blades of advanced aero engines, but film cooling holes (FCHs) severely destroy the structural integrity and affect the mechanical properties. There are few studies concerning the mechanical performance of composites with FCHs. This paper presents the effect of FCHs on the mechanical properties of 3D braided SiC_f/SiC composites at 1350 °C in air. The number of drilled holes were 1, 5, 10 (rectangular) and 11 (triangular), and the average diameter was 0.5 mm. Monotonic tensile tests, microstructure characterization and finite element method were performed to investigate the initiation and evolution of local damage around the FCHs. The results indicated that the coating effectively prevents oxygen penetration in short-term tests and composites with FCHs still maintain excellent ultimate tensile strength (UTS). The UTS of the composites seriously decrease due to stress concentration and unbridged cracking propagation around the FCHs in long-term tests. A triangular arrangement should be avoided in FCHs design of 3D braided composites because specimens with 11-H present low UTS. The failure mechanism of the composites with FCHs was discussed in detail according to the FEM calculation results. The research results of this paper provide a reference for the design of SiC composite turbine blades.