Non-destructive characterisation and evaluation of manufacturing defects in SiCf/SiC composites using the relative energy attenuation behaviour of X-rays

Silicon carbide fibre/silicon carbide (SiCf/SiC) composites are important for manufacturing the hot-section components of aero engines and supersonic vehicles. Hence, quality control, as well as qualitative and quantitative non-destructive testing and evaluation (NDT&E) are critical. A grey (G) value method for the characterisation and NDT&E of manufacturing defects in SiCf/SiC composites based on the attenuation behaviour of low-energy X-rays was proposed, and a digital X-ray imaging detection system was developed. Specimens with artificial and manufacturing defects were evaluated, thereby revealing that imperfections were induced when the SiCf/SiC composites were formed at the high-temperatures; microcracks (100-mu m-wide) and rectangular defects (0.1-mm-deep) were detected with a sensitivity exceeding 100 mu m. Our results demonstrated that 'voids', 'microcracks', 'porosity', 'polymer impregnation inhomogeneity', 'fibre-lack', and 'gap-delamination' were the typical manufacturing defects caused during formation of SiCf/SiC composites at high temperatures; the minimum deviation between the detected and designed length of a 10-mm-long microcrack in the 3.0-mm-thick SiCf/SiC composite specimen was similar to 3%; the manufacturing defects were effectively characterised and evaluated using the distribution behaviours of G values and digital radiographic imaging features.