Research On Acoustic Characteristics And Nondestructive Method For Continuous Fiber-reinforced Ceramic Composites

As the new material favored in all areas, Continuous Fiber Reinforced Silicon Carbide Ceramic Matrix Composites(CFCC-SiC) has high specific strength, high temperature, oxidation and low density, etc, and has been widely utilized in the aerospace field. Among them, the method of phase Chemical Vapor Infiltration(CVI) is the commercial method way to produce large-scale complicated thin-walled components, which makes the material having, the phenomenon of anisotropy, uneven distribution of pore density. Its internal quality becomes difficult to be understood because of these characteristics produced in complicated and long manufacturing process.CFCC-SiC was studied in this paper, aimed at the ultrasonic testing difficulties, and extract the related parameters of the material property to represent internal quality preliminarily.In the first place, the original ultrasonic testing system was updated because of its high attenuation. Sound velocity and acoustic attenuation as typical acoustic parameters represent non-uniformity. This was followed by comparing the result of two kinds of material characteristic. And the characteristic result matched with the result of the metallographic method experiment.Then, characteristic of ultrasonic signal in the frequency domain of CFCC-SiC which might contain porosity content information of the material was analyzed. A further characterization on frequency domain was adopted by using nonlinear coefficient as parameter.In the end, nondestructive testing methods(ultrasonic, X-ray, empty coupling etc.)were used to test CFCC-SiC defective block which contains the graphite layers between Φ3mm and Φ20mm.The results show that the method of the improved penetration testing system can be used to measure the acoustic material parameters. Both acoustic parameters can characterize the internal uniformity of CFCC-SiC. And acoustic attenuation is better than sound velocity in practice and more accurate. Apart from that, the material internal void content can also be characterized by the frequency domain characteristics. The larger the void content, the lower the center frequency and the more narrow the band. Furthermore the nonlinear ultrasonic method is sensitive to material porosity content, which can be effectively applied to the material uniformity pore content measurement and characterization. Meanwhile, the defects of materials whose dimension are between Φ 5mm and Φ 20 mm can also be tested by the nondestructive testing methods. Among these, the size of the defect can be effectively tested by the penetration method, but not in practice. The shape and size of defects can clearly be tested by the ray detection method. There are still certain difficulties applied in practice because of the complexity of the operation. Because the acoustic impedance of artificial graphite layered is closer to the material itself ultrasonic reflection method can’t effectively detect defects, which is best suited to the actual test. Further optimization experimental parameters are needed.