Papers by Author: S.Y. Yu

Abstract: Ceramic is prone to engender surface/subsurface crack damage layer because of great grinding force and high brittle. Prediction of crack damage of ground ceramic is important for design and assessment of grinding process. In this paper, an investigation for surface/subsurface crack damage of ground ceramic is introduced. Depth of crack damage layer can predicted by calculating crack propagation balance size and a predicting model of crack damage layer depth is obtained.

Abstract: A new method is proposed for machinability comprehensive evaluation of engineering ceramic materials based on digraph theory. Machinability attributes of the materials are taken as the nodes and the correlations between attributes are taken as the edges. The digraph model for machinability evaluation of ceramics is set up. According to the diagraph model, the machinability attribute matrix was constituted. Then machinability indexes of ceramic materials were calculated with permanent function and machinabilities of the ceramics were evaluated. In this paper, mechanical property parameters of ceramic materials, including hardness, fracture toughness and elastic modulus, were selected as machinability attributes. Machinability of four typical engineering ceramics were evaluated and ranked with machinability indexes. The grinding experiments give further proof of evaluation results.

Abstract: Molecular dynamics (MD) simulation can play a significant role in addressing a number of machining problems at the atomic scale. This simulation, unlike other simulation techniques, can provide new data and insights on nanometric machining; which cannot be obtained readily in any other theory or experiment. In this paper, some fundamental problems of mechanism are investigated in the nanometric cutting with the aid of molecular dynamics simulation, and the single-crystal silicon is chosen as the material. The study showed that the purely elastic deformation took place in a very narrow range in the initial stage of process of nanometric cutting. Shortly after that, dislocation appeared. And then, amorphous silicon came into being under high hydrostatic pressure. Significant change of volume of silicon specimen is observed, and it is considered that the change occur attribute to phase transition from a diamond silicon to a body-centered tetragonal silicon. The study also indicated that the temperature distributing of silicon in nanometric machining exhibited similarity to conventional machining.

Abstract: While be ground, ceramic is prone to engender surface/subsurface crack damage layer because of great grinding force and high brittle of the material. The crack damage layer was investigated in this research. In experiment, it is observed that the surface/subsurface crack damage layer consists of three kinds of cracks: surface micro-cracks, surface macro-cracks and subsurface crack system. To evaluate expediently the degree of damage to the machined components, the index of surface/subsurface crack damage - Dc, is defined.