Laser cutting using the controlled fracture technique has great potential to be used for the machining of brittle materials. In this technique, the applied laser energy produces a mechanical stress that causes the material to separate along the moving path of the laser beam. The material separation is similar to a crack extension and the fracture growth is controllable. The fracture mechanism of laser cutting with controlled fracture is studied in this paper. The temperature and stress distributions are obtained by using the finite element software ANSYS. The laser heat first induces compressive stress around the laser spot. After the passage of the laser beam, the compressive stress is relaxed, and then a residual tensile stress is induced, which makes the fracture grow from upper surface to lower surface of the substrate. The stable separation of the brittle material is due to the local residual tensile stress. However, if the tensile stress is distributed throughout the thickness around the crack tip, the crack will extend unstably. The experimental materials in this study are alumina ceramic and the laser source is $CO2$ laser. It is found that the crack propagation is non-uniform and the speed is variable during the cutting process. The relationships between laser power, cutting speed, diameter of laser spot, and specimen geometry are obtained from the experimental analysis, and the phenomena are also explained from the results of stress analysis.

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