Study On Properties Of Micro-Ablation/Bearing Phenolic Matrix Composites

With the development of modern aerospace technology,in order to solve the problem of low thermal enthalpy,low heat flux density and long-time heating of the aerodynamic thermal environment of the aircraft,and considering the requirements of miniaturization and motorization of the aircraft,the material should have higher mechanical properties and Low density.Therefore,materials with a long time near zero ablation and long-term heat insulation have become the focus of modern thermal protection technology research.The development of 2.5D weaving technology makes2.5D fabrics have excellent interlayer performance and structural properties.It can be applied to large-area ablative composite materials to prepare a heat-insulating layer with micro-ablative burning/supporting effect.In this paper,a 2.5D quartz/phenolic composite was prepared as a micro-ablative/support material using 2.5D quartz fiber with good structural properties and high temperature resistance and boron phenolic resin with excellent ablation resistance.The physical properties and thermophysics were studied.Performance,ablation resistance and high temperature mechanical properties.At the same time,a trace amount of nano-Al₂O₃ was used to modify the boron phenolic resin by physical blending.The physical blending method of adding nano-Al₂O₃ did not chemically react with the boron phenolic resin.The addition of nano-Al₂O₃ did not change the boron phenolic resin.During the curing process,the glass transition temperature of the boron phenolic resin is slightly increased,and the nano-Al₂O₃ and the boron phenolic resin cracking product are chemically reacted to form aluminum borate,which improves the carbon residue rate of the boron phenolic resin.The effects of nano-Al₂O₃ on the physical properties,thermophysical properties,ablation resistance and high temperature mechanical properties of 2.5D quartz/phenolic composites were investigated.The main conclusions obtained are as follows:?1?The density of 2.5D quartz/phenolic composite material is 1.45 g/cm³,and the fiber content of 2.5D quartz/phenolic composite material is as high as 56.9%.After the modification by nano-Al₂O₃,the density is increased to 1.56 g/cm3,and the fiber content becomes 55.2%,high fiber content makes 2.5D quartz/phenolic composites have good mechanical properties,overall structural properties and ablation resistance.?2?2.5D quartz/phenolic composite material after high temperature treatment,its thermal deformation rate is very low,no large deformation at high temperatures,can keep the thermal protection structure intact;2.5D quartz/phenolic The weight loss rate of the composite material is 19.3%,and the composite has good ablation resistance.After adding nano-Al₂O₃,the thermal deformation rate and thermal weight loss rate of2.5D quartz/phenolic composites can be effectively reduced,especially the thermal weight loss rate is reduced by 5.1%.?3?2.5D quartz/phenolic composites have a lower thermal conductivity.Before high temperature treatment,the thermal conductivity of 2.5D quartz/phenolic composite was 0.635 W/?m·K?.After high temperature treatment,the thermal conductivity of 2.5D quartz/phenolic composite was 0.524 W/?m·K?,and boron phenolic resin was carbonized.The amorphous carbon formed by cracking has good thermal insulation properties.After the addition of nano-Al₂O₃,the thermal conductivity of the nano-Al₂O₃ is higher,which leads to a slight increase in the thermal conductivity of the 2.5D quartz/phenolic composite before and after high-temperature treatment,but has little effect on the thermal conductivity.?4?2.5D quartz fiber/phenolic composite material has very good mechanical properties,tensile strength reaches 304.62MPa,tensile modulus is 15.18GPa;bending strength is up to 337.57MPa,flexural modulus is 17.22GPa;after heat treatment,2.5D quartz/phenolic composite pyrolysis products still have high mechanical properties,bending strength is 18.9MPa,tensile strength is 20.6MPa;bending strength of 2.5D quartz/phenolic composite pyrolysis products after nano-Al₂O₃ modification At 18.0%,the tensile strength increased by 17.0%.Finally,the Mouritz-Mathys model predicts the variation of the strength of the composite with the increase of heating time.