Study On Ultrasonic Grinding Of ZTA Nano-Composite Ceramics On Essential Characteristic Of High Efficiency And Ductility Based On Nonlocal Theory

Due to the large brittleness, bad uniformity, low reliability, less malleability and intensity, ultrasonic machining is used as an effective supplementary method for finishing advanced ceramics. In order to better research the ultrasonic machining technology and explain the essential characteristic of high efficiency and ductility. Based on the nonlocal theory, the research pays more attention to the action mechanism of ZTA nano-composite ceramics and ultrasonic vibration to illustrate the effects of ultrasonic vibration on grinding characteristics that from aspects of grinding force, grinding frequency, material removal rate and SEM of grinding surface etc, which discloses the essential characteristic of high efficiency and ductility and establishes the theory base. The main work and achievement of the paper is as follows:The mechanics behavior under the action of ultrasonic vibration is analyzed according to the relationship between the internal character length and the external character length (i.e. ultrasonic wave length) for ZTA composite nano-ceramics. To explain this phenomenon, the nonlocal theory is introduced to establish the constitutive model under the ultrasonic condition. The wave velocity attenuation and the relationship between wave velocity and frequency are obtained through the wave velocity experiment. According to the results, the variation of normalized nonlocal moduli with different frequencies are calculated (the ratio of nonlocal moduli and classical moduli). When the normalized nonlocal moduli are integrated, the nonlocal stress attenuation rule can be obtained. The influence of ultrasonic frequencies on grinding force is researched through the ultrasonic grinding experiment, which also verifies the constitutive model under the action of ultrasonic vibration.As the fatigue and fracture process of grinding crack is difficult to measure during the ultrasonic grinding, the equivalent experiment is designed to study the actual grinding process. Both large (5μm-15μm) and small (2μm-5μm) feeding process are researched with corresponding loading styles. As the large load, the equivalent experiment is designed according to the modified function of Morrow, and the relationship between the crack fracture life and stress amplitude can be obtained. Otherwise, as the small load style is utilized, the relationship between fracture strength and life can be also acquired by specified loading process with step by step. In this way, the conclusion can be acquired that the suppressed grinding cracks and enhanced grinding surface quality can be achieved with higher frequencies.In order to obtain the influence of ultrasonic frequencies on the grinding efficiency, i.e. critical cutting thickness, brittle-ductility transition and material removal rate, the variation of the fracture strength and dynamic fracture toughness with frequencies are researched through the axial tensile experiment. Based on the nonlocal theory, the mechanical behavior and microcosmic characteristic with different frequencies are compared to explain the reduction of fracture strength. Through the experiments of equivalent grinding surface rigidity and grinding material removal rate, the change trend of equivalent rigidity and material removal rate with frequencies are acquired. According to the results, the action of ultrasonic vibration enlarges the critical cutting thickness, increases the transition range and the grinding material removal rate, by which the high efficiency and ductility characteristic is illustrated.Through the ultrasonic single-point scratching test and ultrasonic grinding experiment, the surface quality of ultrasonic grinding using frequencies of 0 kHz, 19.9 kHz, 29.3kHz and 35.6 kHz are researched respectively. It is found that the microcosmic characteristic and material removing style can be influenced by ultrasonic frequencies according to the experiments of grinding surface roughness, phase transition and surface profile,which illustrates the reason of the improvement of surface quality essentially. Finally, through the XRD experiment, the phase transition of ZrO₂ with the action of ultrasonic vibration can be observed, which further shows the relationship between surface quality and grinding frequencies in microscopic views .