| The radome must possess multifunctions of thermal protection, electromagnetic transparence and load bearing to meet the requirements of the homing guidance systems of the missile. As the precision guided werpon aiming at radars, broadband wave-transparent radome is especially required for the anti-radiation missile. In this dissertation, based on the anti-radiation missile and aiming at the broadband wave-transparent radome, the 2D SiO2f/SiO2 and 2D SiO2f/Nitride composites were prepared after composites selection and structural design. The mechanical properites, dielectrical properites and thermal physical properties of the composites were characterized systematically, and the relationship between preparation process, microstructure and properties of the composites were studied.The 2D SiO2f/SiO2 composites were formed and prepared successfully via sol-gel process with the help of silica sol concentration, hand lay-up and molding process. The effects of sintering temperatures and fiber volume fraction on the microscopic structure and properties of the composites were investigated. The results show that composites prepared at 800℃show good toughness and high fracture energy, with the flexural strength and elastic modulus at 97.0MPa and 11.6GPa, respectively. Composites prepared at 900℃also show certain toughness, and the flexural strength and elastic modulus reach 72.3MPa and 10.2GPa, respectively. But composites prepared at 1000℃show poor mechanical properites, with the flexural strength and elastic modulus are 46.2MPa and 9.8GPa, respectively. The better mechanical properties are attributed to microcrystallization of the silica fiber. The composites exhibit better mechanical properties as the fiber volume fraction increases, and the better mechanical properties are attributed to the higher fiber volume fraction and strengthening of the fiber/matrix interfacial bonding, respectively. But fiber volume fraction are raised via elevating molding pressure, when the molding pressure are too high the fibers will be damaged seriously, the composites will become brittler and show poor mechanical properties as a result. The composites exhibit best mechanical properties when the molding pressure is 1.5MPa and the fiber volume fraction is 45%. When the fiber volume fraction increases from 34% to 45%, the flexural strength, interlaminar shear strength and elastic modulus of the composites increase from 50.2MPa, 3.1MPa and 8.3GPa to 97.0MPa, 9.1MPa and 11.6GPa, respectively. When the fiber volume fraction increases to 48%, bending strength, interlaminar shear strength and elastic modulus decreased to 57.3MPa, 5.7MPa and 9.3GPa. For composites with fiber volume fraction of 40% and 45%, the dielectric constant are 2.64 and 2.59, the loss tangent are 1.9×10-3 and 1.6×10-3, the theoretic power transmission coefficient are above 75% in the frequency range from 2 to 18 GHz, the thermal conductivity are 0.57 and 0.55W×m-1×K-1, while the coefficient of thermal expansion are 0.30×10-6 and 0.33×10-6K-1, respectively.The 2D SiO2f/Nitride composites were prepared via precursor infiltration and pyrolysis process with the introduction of molding process. The relationship between pyrolysis temperature, fiber volume fraction, structure and mechanical properties of the composites were studied. The results show that the mechanical properties of the composites decrease significantly as the pyrolysis temperature increases. As the pyrolysis temperature increases from 800℃to 1000℃, the flexural strength and elastic modulus of the composites decrease from 180.7MPa and 20.3GPa to 90.5MPa and 14.5GPa, respectively. With the increase of fiber volume fraction, the flexural strength and elastic modulus of the composites increase gradually, while the interlaminar shear strength remains stable. When the fiber volume fraction increases from 45% to 55%, the flexural strength and elastic modulus of the composites increase from 119.1MPa and 17.4GPa to 180.7MPa and 20.3GPa, respectively, while the interlaminar shear strength remains stable at around 13.0GPa. The dielectric properties and thermophysical properties of 2D SiO2f/Nitride composites exhibited similar results with 2D SiO2f/SiO2 composites with the change of fiber volume fraction. For composites with fiber volume fraction between 45% and 55%, the dielectric constant are between 2.92 and 2.82, while the loss tangent are between 3.5×10-3 and 2.9×10-3, the theoretic power transmission coefficient are above 70% in the frequency range from 2 to 18 GHz, the thermal conductivity are between 0.82 and 0.80W×m-1×K-1, while the coefficient of thermal expansion are between 1.11×10-6 and 1.05×10-6K-1. |
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