C/SiC Composites X-ray Nondestructive Testing

C/SiC is a kind of new promising structural material. NOT techniques can raise the reliability of C/SiC in its manufacturing and service, deepen the understanding of its structure and performance and guide its design. X-ray radiography, X-ray radioscopy and X-ray computed tomography (X-ray CT) were performed to the C preforms and C/SiC composites made by chemical vapor infiltration(CVI) method. Elementary research of the simulation of X-ray nondestructive testing of C preforms and C/SiC composites was conducted. The main contents and conclusions are summarized as follows:(1) The equivalent absorption coefficients of graphite and SiC to Al (KAl/sic, KAI/C) were measured. It was found that in 35-45KV, KAl/sic=1.1~1.2 and KAl/c=0.08~0.12. That means X-ray radiography was much less sensitive to fiber defects than to SiC matrix. It was suggested that Al Image Quality Indicator(IQI) would be used to evaluate the quality of X-ray radiographs of C/SiC.(2) The radiographic sensitivity was sensitive to the SiC or C/SiC defects' parameters of the shape and orientation. The radiographic sensitivity of the linear matrix defects vertical to the braiding orientation was up to 3.2% and that of the grooves vertical to the braiding orientation was 2.7%, while that of the linear matrix defects parallel to the braiding orientation was 5.2%. This phenomenon was explained by the principle of signal-to-noise ratio obtained from the radiographs' energy density spectrum.(3) Braiding defects were detected in the C preforms by X-ray radiography. The holes in C/SiC caused by the braiding faults, the braiding pattern and the density variation in relatively large region were also detected.(4) X-ray CT (BT-400) was applied to inspect the sections of C/SiC components. Density distribution in sections was detected precisely. Although the details of abundant micro-pores would not be revealed, the figure, location and size of the holes between the fiber tows were clearly shown. The holes caused by the fabrication faults were detected distinctly, which corresponded well to the X-ray radiography results.(5) Simulated radiographs of X-ray radiography of C preforms and C/SiC composites, the defects and the change of braiding patterns were obtained by image superimposition, masking and image direct generation. CAD models of plain weave and 4-step braiding structures were built. A new method that applying the CAD models of the composites' microstructure and macrostructure to X-ray nondestructive testing was developed and was performed to create the simulated radiograph of plain weave C preform and plain weave C/SiC composites.