Silicon carbide (SiC) is utilized in the automotive, semiconductor, and aerospace industries because of its desirable characteristics. Nevertheless, the traditional machining method induces surface microcracks, low geometrical precision, and severe tool wear due to the intrinsic high brittleness and hardness of SiC. Femtosecond laser processing as a high-precision machining method offers a new approach to SiC processing. However, during the process of femtosecond laser ablation, temperature redistribution and changes in geometrical morphology features are caused by alterations in carrier density. Therefore, the current study presented a multi-physics model that took carrier density alterations into account to more accurately predict the geometrical morphology for femtosecond laser ablating SiC. The transient nonlinear evolutions of the optical and physical characteristics of SiC irradiated by femtosecond laser were analyzed and the influence of laser parameters on the ablation morphology was studied. The femtosecond laser ablation experiments were performed, and the ablated surfaces were subsequently analyzed. The experimental results demonstrate that the proposed model can effectively predict the geometrical morphology. The predicted error of the ablation diameter is within the range from 0.15% to 7.44%. The predicted error of the ablation depth is within the range from 1.72% to 6.94%. This work can offer a new way to control the desired geometrical morphology of SiC in the automotive, semiconductor, and aerospace industries.

In order to improve the stability of the wave power generation device, the mechanism of variable displacement control mechanism of hydraulic motor is proposed and the control strategy of motor speed is built. The detailed mathematical representation and dynamic characteristics of motor control are analyzed; the adaptive sliding mode control method and a back-stepping control strategy are designed for the proposed controller to overcome the influence of the parameter uncertainty in the nonlinear system. The adaptive law is designed by Lyapunov criterion to ensure the stability and convergence of the whole closed-loop system. In order to verify the feasibility of the proposed control strategy, a wave power generation land experimental platform is designed, the experimental platform is mainly consists of the test bench bracket, the hydraulic transmission system and the electric power processing system. Through comparative analysis with PID control method, the advantages of this control method are described and the speed of motor can be controlled accurately.

The prediction of micro milling forces in difficult-to-machine materials such as titanium alloys, which have small dimensions and arc-thin-walled features, has become a major challenge due to the coupling effect of multi-physics fields. This problem has become a key bottleneck in the development of aerospace, space, biomedical and other fields. To address this issue, this study focuses on titanium alloy arc-thin-walled parts and develops a micro milling force prediction model that considers the dual flexible coupling deformation and geometric features of arc-thin-walled parts in the process of micro milling. Firstly, a micro milling force theoretical model is established based on the instantaneous cutter position angle and the actual instantaneous uncut thickness. Secondly, detailed geometric analysis is conducted to calculate the entry and exit angles and instantaneous uncut thickness considering the characteristics of arc micro milling paths. Subsequently, the Euler beam and Timoshenko beam are assumed based on the characteristics of the cutter and workpiece structure, as well as the force situations. The unit stiffness matrix is then solved to calculate the deflection deformation value. An iterative algorithm is used to introduce the coupling deflection deformation into the micro milling force prediction model, thereby improving the instantaneous uncut thickness model. Finally, the micro milling force data is obtained through arc micro milling experiments and the coefficient of micro milling force is identified. The micro milling force is predicted using a theoretical model and its rationality and accuracy is verified through experiments. The proposed model and methodology have practical significance and provide a basis for optimizing micro milling processes and promoting the development of related fields.