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John Binner - Week 6 - Coggle Diagram

- - - - Weak interface composites - a low cohesion coating is applied to the fibres before the matrix is formed yielding toughening mechanisms such as crack deflection, crack bridging and fibre pullout. The approach is used in dense matrix CMCs, such as SiC/SiC, however, the coating (often C or BN) is subject to oxidation at high temperatures.
      - Weak matrix composites - The matrix is engineered to be porous - its reduced stiffness allows damage tolerant behaviour. It is generally used when it is not possible to obtain weak interface composites, since it leads to inherent permeability combined with low strength, low wear resistance and low thermal conductivity.
- - - - Energy absorption during polymer pyrolysis (burning) - endothermic reaction.
      - Gas flow in the boundary layer
      - Formation of char layer and re-radiation of thermal energy (re-radiation as a result of charring)
  - - - When exposed to re-entry, surface material heats up and rejects energy via the following mechanisms
        
        Re-radiation from the surface and internal storage due to high heating conditions.
        
        Re-radiation and convective cooling under post flight conditions
  - - - Lightweight
      - Dimensionally stable up to surface temperatures of up to 1650 C
      - High total hemispherical emittance
      - Low catalytic efficiency
      - Thermal response similar to Shuttle-type fibrous insulation
    - - Silicon oxycarbide phase slows oxidation.
      - HETC treatment near surface slows oxidation and keeps emissivity. Coated with borosilicate reaction cured glass for oxidation resistance.
        
        Solved thermo-structural issues by adding boron oxide (B2O3) and alumino-borosilicate fibres, which also improved mechanical strength. Increased temp capability to 1370 C by adding alumina Al2O3 fibre