Surface Generation Characteristics of SiC f /SiC Composite Machined by Brazed Diamond Core Drill

ABSTRACT SiC f /SiC composites are key aerospace structural materials, yet their susceptibility to fiber fracture, matrix spalling, and microcracks during drilling severely limits component integrity. This paper establishes single‐grit kinematic models and derives calculation formulas for maximum undeformed chip thickness ( a gmax ) under both conventional drilling and ultrasonic vibration‐assisted abrasive drilling, and uses them to conduct systematic single‐grit machining tests on 2D woven SiC f /SiC. The results reveal that the critical a gmax values governing the transition from microfracture to macrofracture removal are orientation‐dependent, 0.7–0.9 µm for 0° fibers and 0.8 µm for 90° fibers. Under the tested ultrasonic vibration condition ( A = 5 µm, f = 25 kHz), trajectory elongation reduces the single‐grit chip thickness and alters the stress state at the grit‐workpiece contact zone, redirecting crack propagation from downward penetration toward lateral spreading and promoting microfracture as the dominant removal mode. These effects yield a reduction in average chip length, smaller stepped‐fracture spacing on 0° ≤ θ ≤ 90° fiber surfaces, enlarged extrusion zones for 90° ≤ θ ≤ 180° fibers, and significantly less fiber fragmentation for 90° fibers. Cross‐sectional SEM quantification further confirms that ultrasonic vibration‐assisted machining reduces the maximum subsurface damage layer depth by 12%–50% for the SiC matrix, 13%–38% for 0° fibers, and 12%–55% for 90° fibers within the tested a gmax range of 0.4–1.2 µm. These findings provide a mechanistic foundation for understanding how ultrasonic vibration modulates surface generation and subsurface damage at the single‐grit scale in SiC f /SiC machining.