Study On Modification And Ablation Mechanism Of Fiber Reinforced Phenolic Heat-proof Material

The thermal insulation material is the key to maintain the structural strength and normal operation of high-speed aircraft under the aerothermal action.The ablative insulation material is irreplaceable under the condition of heat flow exceeding 10MW/m².The superior thermal insulation material has occupied a dominant position for many years.However,with the flight distance and speed of the aircraft greatly increased,the ablation resistance of the ablative heat-proof materials is put forward a new requirement.Traditional fiber reinforced phenolic heat-proof materials have caught the elbow in several use environments.By modifying the ablative material and improving its ablative resistance,the application of fiber reinforced ablative heat-proof material can be expanded.In this thesis,the phenolic-based ablative and heat-proof materials were studied,focusing on the different ceramic phases of the introduced system.Different ceramic systems were screened not only for quartz phenolic materials and carbon phenolic materials,but also for the change of ablation mechanism after the introduction of ceramic phases.The effect of metal dissipation on the ablation properties of phenolic heat-resistant materials was also investigated.In the quartz fiber reinforced phenolic heat-proof material system,both Zr B₂ and B₄C can significantly improve the ablation resistance of the heat-proof material.It is shown from the results of oxygen-acetylene ablation test that the highest linear ablation rate reduced the mass ablation rate by 72.5%and 44.2%respectively.B₂O₃ was formed by the oxidation of B₄C during ablation,reducing the surface energy of molten silicon.Accordingly the wettability of molten silicon and carbide layer were improved,promoting the spreading of ceramic layer on the surface of carbon layer.Therefore,the carbide layer was effectively protected,significantly reducing the ablation rate;Zr O₂ oxidation of Zr B₂ with quartz phenolic system can produce Zr O₂ in Si O₂.The particles,like nails,played a role in the melting layer,avoiding the Si O₂ melt being blown away by the airflow,thus reducing the ablation rate.In the quartz phenolic system,the introduction of Zr B₂ and B₄C was optimized,and excessive introduction of Zr B₂ and B₄C may degrade the protection of pyrolysis layer and carbide layer to improve the ablation resistance of materials.Si C was introduced into the carbon fiber reinforced phenolic system.Si O₂ was formed during ablation in order to protect carbon fibers and resin pyrolytic carbon layer from rapid oxidation.Antioxidant ceramics were introduced to protect carbon fibers.The linear ablation rate can be reduced by 39.6%and the mass ablation rate can be reduced by 5.4%.Based on the above consideration,Al₂O₃ coating was coated on the surface of carbon fibers reinforced by liquid plasma treatment.The linear ablation rate and mass ablation rate decreased by16.9%and 5.4%respectively.The aluminum alloy open cell foam was used as oxygen dissipation phase to be introduced in the phenolic system.The aluminum foam was filled with high density phenolic resin and low density phenolic resin respectively.The ablation rate was verified by oxy acetylene ablation test,and the line ablation rate was between ceramic phase modified quartz phenolic resin and carbon phenolic resin.The aluminum foam introduced in ablative thermal protection material can realize phase change heat blocking and ablation process oxygen consumption,and oxidation reaction product penetrated into the carbon layer contacted to further protect the original layer of ablative material.The introduction of oxygen dissipator has a significant effect on improving the ablation resistance of phenolic heat-proof materials.The introduction of oxygen dissipation phase into phenolic heat-proof materials is an exploratory attempt,and there is still much work to be done in the near future.