Tension-tension fatigue behaviour of 3D braided SiC_f/SiC composite with film cooling holes at 1350 °C in air

The tension-tension fatigue behaviour of SiC_f/SiC composites with film cooling holes (FCHs) was investigated at 1350 °C in air. The number of drilled holes were 1, 5, 10 (rectangular arrangement) and 11 (triangular arrangement), and the average diameter was 0.5 mm. The fatigue stresses were 80 MPa and 120 MPa at a frequency of 3.0 Hz, and the R ratio of minimum stress to maximum stress was 0.1. The stress-strain hysteresis curve, strain accumulation and modulus decrease were investigated, and characterization of the fracture morphology and microstructure was performed to reveal the initiation and evolution of damage during fatigue cycles. The results indicated that the FCHs exhibit little effect on the ultimate tensile strength of the composites. The fatigue life decreases with an increasing number of FCHs, and the effect of the FCHs on the fatigue life gradually decreases as stress levels increase. Specimens with triangular arrangement 11-H exhibit the worst fatigue life, and the damage mechanism is significant relative to large-area of fibre oxidation on the fracture surface. The weakening effect of FCHs on the fatigue performance of the composites is mainly due to the oxidation and embrittlement of fibres around the hole, and it is significant relative to initial crack nucleation and propagation in the coating and matrix.