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Through machinable ceramic turning tests, the crack propagation at the machined surface and subsurface is explored, and the mechanism of unstable propagation is studied. The arrangement of the grains affects the direction of crack propagation, and the instability deflection angle (IDA) has a positive correlation with the instability deflection length (IDL). Crack propagation occurs in four stages: initial crack formation stage, metastable propagation stage, unstable propagation stage, and upward propagation stage. Based on the energy conversion principle and the fracture mechanics theory, a binary model of unstable crack propagation is developed. The IDA and IDL are quantified together with their positive correlation and accuracy. The experimental validation results reveal that the theoretical values of the IDA and IDL approach the experimental values, indicating that the model is accurate and may be utilized as a theoretical basis for forecasting the unstable crack propagation behavior in brittle material cutting. [ABSTRACT FROM AUTHOR]

The influence of tool wear on cutting force in turning glass–ceramics was studied, and a theoretical model of turning force considering tool wear was established in this paper. Firstly, the crack propagation behavior and the form of energy dissipation were analyzed during chip formation, and the model of the force due to chip formation was established based on the fracture mechanics of brittle solids and the principle of energy transfer. Secondly, the mechanical model caused by the flank wear was established by analyzing the microscopic wear mechanism of the tool and the source of friction. Finally, the theoretical model of turning force considering the tool wear was established. The model is only applicable to brittle removal mode. Two different cutting tools were selected to carry out the experiment of turning fluorophlogopite glass–ceramics. The relationship between cutting force and tool wear was discussed, and the accuracy of the model was verified. The results showed that the tool wear has a direct impact on the cutting force, and the theoretical model of cutting force established is in good agreement with the experimental data in this paper. [ABSTRACT FROM AUTHOR]