Mechanical Response Of Si₃N₄ Ceramic Surface In Rotary Ultrasonic Grinding

Hot-pressed Si₃N₄ ceramic material is widely used in aerospace field due to its excellent mechanical properties.Compared with other hard and brittle materials,hot pressed Si₃N₄ ceramic material has high density,high hardness and uneven stress under high frequency impact.Therefore,Si₃N₄ ceramic materials are prone to processing instability,poor surface quality and easy to produce processing cracks and other issues.Aiming at the problem of poor surface quality of Si₃N₄ ceramic materials,the mechanical response characteristics of Si₃N₄ ceramic surface by rotary ultrasonic grinding were studied in this paper.The study provides a theoretical basis for improving the surface quality of hot pressed Si₃N₄ ceramic.Firstly,quasi-static compression and Hopkinson pressure bar tests were carried out to investigate the mechanical properties of diamond grits embedded in Si3N4ceramic materials during rotary ultrasonic grinding.Based on the mechanical properties of Si₃N₄ ceramics under static and dynamic loads,some parameters of JH-2 constitutive model of Si3N4 ceramics were obtained.Then,the JH-2 constitutive model of Si₃N₄ ceramic material is used to define the properties of Si3N4 ceramic material in finite element simulation.Combined with the dynamic simulation software LS-Dyna,the simulation of single abrasive and double abrasive rotary ultrasonic grinding is completed.The material removal and surface crack propagation of single and double abrasive grains in rotary ultrasonic grinding of Si3N4 ceramic were analyzed by crack propagation theory.The variation of local stress and grinding force of Si₃N₄ ceramic material under different ultrasonic amplitude,ultrasonic frequency and grinding depth were compared.Finally,the single abrasive and double abrasive rotary ultrasonic scratch test was carried out,and the scratch depth was detected by the super depth of field microscope.By comparing the scratch depth of the test and the grinding depth of the simulation,the validity of the test data is verified.The grinding force obtained by rotary ultrasonic scratch test and rotary ultrasonic grinding simulation is compared.The error of grinding force obtained by scratch test and rotary ultrasonic grinding simulation is analyzed.Three-grain and four-grain rotary ultrasonic scratch tests were carried out to explore the influence of different abrasive numbers on grinding force during machining.