Machining-induced damage in milling of Cf/SiC composites: mechanisms and evaluation methods

Carbon fiber-reinforced silicon carbide (C_f/SiC) composites have been widely utilized in the aerospace industry due to their high specific strength and ablation resistance. However, owing to their high hardness, brittleness, and anisotropy, machining-induced damages are prone to occur. In this study, the formation mechanisms of milling-induced damage in C_f/SiC composites were investigated. The results demonstrated that pit damage, as the most prominent form of milling-induced damage, exhibits three primary formation mechanisms: crushing damage caused by axial machining loads compressing subsurface inherent defects, extrusion cracking damage resulting from radial-load-induced crack propagation along fiber bundles, and fragment spalling damage occurring when the tool’s compressive and scraping actions on fragments within inherent defects cause damage expansion. A novel damage evaluation model for milling C_f/SiC composites was established by weighting the maximum damage depth with the ratio of newly generated damage area to the total machined area. A response prediction model for the damage index was developed with respect to three parameters: cutting speed, feed pre tooth, and radial depth of cut. Verification tests conducted with the optimized parameters yielded results with a deviation of 2.26% from the predicted model, confirming the reliability of the prediction model.