Zhaoguo Mi

Silicon carbide fiber-reinforced silicon carbide matrix ceramic composites (SiC_f/SiC) are extensively utilized in high-temperature resistant materials in the aerospace industry. This study investigated the influence of stacking structure on the performance of SiC_f/SiC laminated composite plates with film cooling. Initially, the thermal conductivity of cross-piled SiC_f/SiC composites was determined using the laser flash analysis (LFA) method and differential scanning calorimetry (DSC) method. Subsequently, a representative volume element (RVE) model that reflected the stacking structure was established. The anisotropic thermal conductivity of the unidirectional SiC_f/SiC layer was calculated using numerical methods and experimental results. Finally, numerical simulations were carried out to assess the film cooling effectiveness of various stacking sequences and layers. The results showed that the thermal conductivity values predicted by the RVE model for the laminated composite aligned well with the experimental results, and the unidirectional SiC_f/SiC composite thermal conductivities at different temperatures were obtained. The stacking sequence impacted the temperature distribution near the film hole, with the [0-90-0] structure exhibiting a more pronounced effect on film cooling performance compared with the [0-90] and [0-90-90-0] structures. The performance of the film cooling in the laminated SiC_f/SiC composites was consistent across all stacking layers [0-90]₁, [0-90]₂, and [0-90]₃. The maximum difference in overall cooling efficiency was 1.7% between [0-90-0]₁ and [0-90]₁ and [0-90-90-0]₁

The silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC), ceramic matrix composite (CMC) and nickel-based superalloy GH4169 can be utilized in high-temperature applications due to their high-temperature performance. The SiC/SiC composites are commonly used in turbine outer rings, where they encounter friction and wear against the turbine blades. This high-speed rubbing occurs frequently in aircraft engines and steam turbines. To investigate the tribological behavior of these materials, rubbing experiments were conducted between the SiC/SiC and the GH4169 superalloy. The experiments involved varying the blade tip speeds ranging from 100 m/s to 350 m/s and incursion rates from 5 μm/s to 50 μm/s at room temperature. Additionally, experiments were conducted at high temperatures to compare the tribological behavior under ambient conditions. The results indicated that the GH4169 superalloy exhibited abrasive furrow wear during rubbing at both room temperature and high temperature. Furthermore, at elevated temperatures, some of the GH4169 superalloy adhered to the surface of the SiC/SiC. The analysis of the experiments conducted at ambient temperatures revealed that the friction coefficient increased with higher blade tip velocities (100~350 m/s). However, the coefficient was lower at high temperatures compared to room temperature. Furthermore, significant temperature increases were observed during rubbing at room temperature, whereas minimal temperature changes were detected on the rubbing surface at high temperatures.

SiC fiber-reinforced silicon matrix (SiC_f/SiC) composites are of significant interest for the aircraft engine. The thermal conductive behaviors of [0-90-0]s SiC_f/SiC composites along in-plane and out-of-plane (thickness) directions were reported in this paper. The thermal conductivity of the SiC_f/SiC composite was tested by using the steady-state measuring apparatus. Then, the thermal conductivity of the SiC matrix was predicted by finite element analysis (FEA). The representative volume element (RVE) models of SiC_f/SiC composites were built, and FEA was used to investigate thermal conductive behaviors. It was found that the thermal conductivity along the fiber radial direction was greater than it was in the axial direction in the SiC_f/SiC composite and that the thermal conductivity of the out-of-plane direction is lower than that of the in-plane one. The thermal conductivity of the SiC_f/SiC composite in the in-plane direction at room temperature was 31.1Wm⁻¹K⁻¹ and 28.5Wm⁻¹K⁻¹, and the thermal conductivity in the thickness direction was 24.9Wm⁻¹K⁻¹. The experimental thermal conductivity showed a good agreement with the thermal conductivity of FEA.

Radial cracks appear in the labyrinth seal fins of the shrouded turbine blade of an aero-engine during service. To clarify the influence rule of rubbing force on crack initiation, a high-speed rubbing test bench and a numerical calculation model are established, and the research is carried out through experiment and numerical calculation. It is found that cracks can be initiated when the rubbing force is greater than 20 N with a high rubbing temperature at high speed. It is verified by numerical calculation and shows that pure mechanical load will not cause crack initiation, while the thermal load is the main reason for the radial crack initiation of fins. With the increase of rubbing force, the time of crack initiation increases, and the number and length of cracks decrease. At high rubbing temperatures, rubbing force will lead to radial crack initiation, which mainly affects the position of crack initiation.

The labyrinth-honeycomb seals have been widely used in aero-engine. However, radial cracks appear on labyrinth seal fins of shrouded turbine blade in use. To clarify the rubbing mode of radial crack initiation, a high-speed rubbing test bench was designed. The effects of five rubbing modes on crack initiation were studied. Through the test, it is found that cracks would be formed at the junction of the fin tip and side of the labyrinth seal fins under all five modes. When two successive rubbing modes are different, the temperature of the last rubbing can be lower than that of it alone rubbing, and simultaneous radial and axial rubbing can inhibit each other. Radial rubbing mainly affects the initiation of cracks on fin tip, while axial rubbing mainly affects the initiation of cracks on the side. Moreover, the rubbing temperature is mainly affected by radial force.