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윤해성,Suk Bum Kwon,Aditya Nagaraj,Sangkee Min 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.9
Manufacturability of advanced ceramics has been a challenging issue mainly because of their brittle behaviors and high hardness. One approach to solving this issue is enabling ductile regime cutting, which can also be used to enhance the quality of the surface and accuracy of the final product. There have been many studies investigating how to control and prolong the ductile response regime during cutting; however, it still lacks a straightforward explanation that enables us to predict the transition of the material response from the ductile regime to the brittle regime. In this study, the processing of monocrystalline yttria-stabilized zirconia was investigated to predict material behavior during cutting. Here, it is aimed to confirm that stress intensity factor analysis can be applied with a wide variety of process parameters and investigate the effect of varying the process parameters on the ductile–brittle material response transition. Experimental results showed that negative rake angle and higher cutting speed prolonged the ductile cutting regime. However, the cutting stress at the ductile–brittle transition point remained constant regardless of the process parameters which enabled us to predict the transition point with respect to the stress intensity factor. It is expected that the results of this research can contribute to the development of machining strategies with improved throughput and thus to increasing the utilization of ceramic materials.
Suk Bum Kwon,Aditya Nagaraj,Dalei Xi,Yiyang Du,Dae Nyoung Kim,Woo Kyun Kim,Sangkee Min 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.5
Single-crystal sapphire is used in various fields of industry due to its superior mechanical, optical, and chemical properties, but fabricating sapphire is challenging because of its high hardness and brittleness. Ultra-precision machining (UPM) has been studied as one of the solutions to overcome these issues as it facilitates cutting of brittle ceramics in a ductile manner. However, the material removal mechanisms during UPM of single-crystal sapphire is not yet fully understood. This paper studied the crack initiation mechanism in single-crystal sapphire during UPM with relation to the crystallographic properties of sapphire depending on the cutting direction. By projecting a given stress distribution from molecular dynamics simulation on to different slip and fracture planes, the likelihood of plastic deformation and cleavage fracture was calculated, and respective crack initiation mechanisms were identified. The proposed MD simulation model and analysis were verified through ultra-precision orthogonal plunge cut experiments along the same crystallographic directions as the simulations.