Study on removal mechanism and surface quality of SiCf/SiC composites by longitudinal torsional ultrasonic vibration-assisted grinding

With properties such as high hardness, low density and high-temperature resistance, SiC_f/SiC composites have been widely used in defense and aerospace. Due to its high brittleness and anisotropic characteristics, traditional machining methods are prone to cause serious material damage and affect the service life of SiC_f/SiC composites. The interference trajectories of neighboring grains in longitudinal torsional ultrasonic vibration-assisted grinding were analysed in this study, and comparative experiments between longitudinal torsional ultrasonic vibration-assisted grinding (LTUAG) and conventional grinding (CG) of SiC_f/SiC composites were conducted. Moreover, the trajectory of the grain and the interference situation were combined to analyse the material removal mechanism of SiC fibres in different directions and the SiC matrix section. The impact of different grinding parameters and ultrasonic amplitudes on surface roughness and grinding force was also studied to analyse LTUAG's mechanism of action on machined surfaces. The experimental results show that the material removal mechanism of SiC_f/SiC composites is primarily brittle fracture, which is manifested by the phenomena of fibre breakage, fibre pull-out and shear fracture. Weft yarn fibre pull-out and fibre debonding phenomenon are obvious. Warp yarn fibres are mainly manifested as fibre breakage and shear fracture. Compared with CG, LTUAG reduces fibre pull-out, inhibits interfibre crack expansion and increases the proportion of ductile removal from the material. The maximum reduction of normal and tangential forces in LTUAG compared to CG is about 40 % and 47.7 %, and the surface roughness reduced by a maximum of 12.8 %.