Structural-design, Emulation And Validation Of Broadband Wave-transparent Ceramic Matrix Composite Sandwich

The missile which can be guided with the electromagnetic radiation is called anti-radiation missile (ARM), the main purpose of ARM is to destroys the enemies'radar and its carrier. The frequency of electromagnetic wave emited from different goals lies in broad band. The frequency range usually starts from 2 to 18GHz. The distinct character of ARM is"broadband". Therefore the properties of radome of ARM must be broadband wave-transparent. Radome is at the front of missile. It must be provided with multifunctions such as: wave-transparence, thermal protection, load-bearing and fairing etc. The radome material has its own properties for instance: resistance to high temperature, low dielectric comstant, low loss tangent, high strength, high modulus and easy molding etc. In order to fulfil the requirement of"broadband", a A type interlayer structure like sandwich (called A sandwich)is usually used in the structural design of radome. The dielectric constant and loss tangent of sandwich layer are below those of surface layer. By means of structural design, it is possible to broaden the frequency range of wave-transparence.In the past, the operating temperature of radome is no more than 500℃because of the low speed of anti-radiation missile. A sandwich can be achieved by using polymer matrix composite resisted to high temperature. However, with the continuous growth of the mach number, it is imperative to use ceramic matrix composite. It is hard to get A sandwich prepared by ceramic matrix composite because of the restriction of processing technology. Therefore, in concern with both broadband wave-transparence and the realization of A sandwich prepared by ceramic matrix composite, a A-like sandwich is designed in this paper. The properties of this structure are emulated. According to the theoretical results, the preparation of A-like sandwich is realized by precursor infuse pyrolysis technology. The wave-transparent and mechanical properties of A-like sandwich is certisified by experimental results.The wave-transparent properties of monolayer and symmetrical A sandwich are calculated according to classical theory. After comparison, the broadband wave-transparent properties of symmetrical A sandwich is much better than that of monolayer. In the frequency range from 2 to 18GHz, the average wave-transmittance of symmetrical A sandwich is 6.2～22.1% higher than half-wavelength monolayer, and is 6.4～17.1% higher than thin monolayer.The wave-transparent properties of A-like sandwich are simulated by using CST software. The influence on the wave-transparent properties of the incident angle and the structural parameters of sandwich has been investigated. The wave-transparent properties of sandwich get better while the incident angleθbecomes larger or the ribs of core-layer become narrow or the space width of core-layer decreases. When the incident angleφis equal to 0°andθis large, the mutations of wave-transmittance occur in high frequency. However, when the space width is less than a given value, the mutations of wave-transmittance disappear. The dielectric constant of core-layer of A-like sandwich is simulated in different ways. As the simulant result, volume-method simulation agrees well with the CST results.The mechanical properties of A-like sandwich have been characterized by using material mechanical theories. The results show that: the carrying capacity of I-shaped sample is 83% of ordinary solid sample.The weaving of A-like sandwich is achieved by using 2.5D fabric. A-like sandwich are prepared by using both sol-gel and precursor infuse pyrolysis technology.The test results of wave-transparent properties conform to theoretical ones on the whole. Both two results have similar trends on frequency. There are many factors affecting the test results, including the preparation of materials, the accuracy of materials processing, the choice of test method and the restrictions of material size etc.The test results of mechanical properties are a little lower than the theoretical ones. The bending strength of longitude and latitude I-shaped sample are 74%, 69% of ordinary solid sample. The gap between test and theoretical results is related to that the continuity of fiber is destoried in the processing.After the optimization of the A-like sandwich's properties, the final structural parameters of sandwich have been confirmed: the thickness of surface-layer 1.5mm; the rib width of core-layer 3mm; the space width of core-layer 2mm; the thickness of core-layer to be adjusted to the incident angleθ. When the incident angleθis equal to 0°, wave-transmittance of the sandwich is higher than 90% and the average achieves 94.7% in the frequency range from 2~18GHz.In a word, the properties of A-like sandwich are simulated based on electromagnetic theory. Then the reliability of simulant results and the realization of technology are verified by experiment. The parameters of A-like sandwich are optimized to keep up the wave-transmittance and the mechanical properties to the best value. The investigative results provide theoretical accordance and technology basis to realize A-like sandwich prepared by ceramic matrix composite.