Investigation of the material removal mechanism during ultrasonic-assisted grinding of C/SiC composites

Ultrasonic-assisted grinding (UAG) offers significant advantages in machining carbon fiber reinforced silicon carbide (C_f/SiC) composites. These include substantial reduction in grinding force and improvement in surface quality. However, the strong anisotropy of C_f/SiC composites presents challenges. Current research on phase deformation and fracture mechanisms during UAG remains limited. As a result, the material removal mechanism is not well understood, which restricts further advancements in machining quality. In Response, a 3D finite element model of C_f/SiC composites was developed in Abaqus. Using this model, a single-grain abrasive grain UAG simulation was performed. The results demonstrated that grinding force magnitude critically influenced the damage to the carbon fibers and the SiC matrix, while the interfacial layer could impede and redirect crack propagation. Guided by these simulation results, UAG experiments on C_f/SiC composites were then conducted. Experimental verification revealed an average error of 11.8 % between simulated and measured grinding forces, demonstrating that the finite element model could accurately predict the experimental forces. The primary failure modes of C_f/SiC composites include longitudinal, transverse, and normal fiber damage. Ultrasonic vibration promoted brittle fracture of transverse fibers, reduced lateral fiber deflection, mitigated interfacial layer buckling, and suppressed fiber pull-out. Moreover, ultrasonic vibration altered the contact angle between abrasive grains and normal fibers. The high-frequency impacts of the abrasive grains in the normal direction accelerated cracks propagation along the fiber bending path, leading to shear fractures, and resulting in smoother, flatter fractured surfaces. For longitudinal fibers, the multidirectional compressive action of abrasive grains diminished bending fractures but intensified shear fractures, enabling localized fiber removal and inhibiting the formation of lateral cracks.