Fiber-reinforced ceramic matrix composite (FRCMC) have been widely used in aerospace and other high-technology fields due to their excellent mechanical and physical properties. However, FRCMC is a kind of typical material with anisotropic and inhomogeneous structure; thus, it is difficult to guarantee the precision and surface quality using traditional machining. The present paper employed ultrasonic vibration-assisted grinding (UAG) to machine 2.5D woven SiO_2f/SiO₂ composites. By comparing the grinding force, surface microstructure, chip formation, surface topography and surface roughness with and without ultrasonic vibration for the machining of SiO_2f/SiO₂ composites, the feasibility of UAG on FRCMC was investigated experimentally. In addition, the effects of the process parameters (including spindle speed, feed rate, grinding depth, grain mesh size and ultrasonic power) on grinding force and surface roughness were studied through an orthogonal experiment. The research obtained can be a useful technical support for the development of UAG in the machining of FRCMC.

Polyether-ether-ketone (PEEK) and polyimide (PI) are two kinds of engineering polymer materials widely used as roller bearing cages and rings under extreme environment because of their noise reduction and corrosion resistance properties. The Si₃N₄ ceramic is the most common ball bearing material. Many current engineering applications of ball bearings require aqueous lubrication. Therefore, this study presents the aqueous lubrication of tribopairs formed by PEEK and PI material sliding against Si₃N₄ ceramic. Experimental results show that two tribopairs exhibited the similar tribological properties under the dry condition. Water as a lubricant for the PI–Si₃N₄ tribopair pairs effectively reduces both friction coefficients by 35.5% and wear rates by 32%. The water absorption of PI induces better tribological properties by changing the tribopair surface properties. In addition, the dimples appearing on the PI tribopair surface under water generate additional hydrodynamic lubrication and further improve the friction properties of surface. The PEEK–Si₃N₄ tribopair shows similar friction coefficients under two kinds of environments. The wear rates under water are approximately more than two times of that under dry sliding. However, water inhibits the appearance of the crush phenomenon and enhances the carrying capacity of the tribopair. Energy dispersive spectroscopy and X-ray diffraction spectra demonstrate no chemical corrosion. The 3D profiler and SEM morphologies illustrate that the transfer film would be formed from the surface of PEEK under water but hindered under dry friction. Overall, the PI–Si₃N₄ tribopair exhibits better properties than PEEK under water and is promising for future applications in the bearing industry.

A new rotary ultrasonic machining (RUM) spindle is proposed. It adopts contactless rotary transformer replacing the well‐established slip ring technology to supply power for the transducer. Owing to the large leakage inductances, the capacitive piezoelectric transducer and the variable mechanical load, the circuit compensation is crucial for efficient and reliable power transfer. In this study, the mathematical models are presented to identify the power transfer efficiency and capability of the rotary transformer used in RUM. A general optimisation method of compensation for maximum transfer efficiency is proposed. The mechanical load dependencies of the transfer efficiency, transfer capability and power factor are researched and discussed. The efficiency has been found to be dependent of the secondary compensation elements. The series‐series (SS) topology is applicable to a wide range of mechanical load variations, followed by parallel‐series (PS) topology. For a varying load in RUM, the contactless energy transfer is possible to achieve high efficiency, high power factor and appropriate output power that adapts to load variations.