Studying Crack Generation Mechanism in Single-Crystal Sapphire During Ultra-precision Machining by MD Simulation-Based Slip/Fracture Activation Model

SB Kwon and A Nagaraj and DL Xi and YY Du and DN Kim and WK Kim and SK Min, INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING, 24, 715-727 (2023).

DOI: 10.1007/s12541-023-00776-w

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.

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