Institute for Systems Research

Permanent URI for this communityhttp://hdl.handle.net/1903/4375

Browse

Author: search.filters.author.Le, Dung T.Subject: search.filters.subject.Systems Integration Methodology

Search Results

Now showing 1 - 8 of 8
  • Thumbnail Image
    Item
    Optimization of Machining Performance of Dental Ceramic Restorative Materials
    (1997) Le, Dung T.; Zhang, G.; ISR
    Dental ceramics are gaining popularity because of their esthetics, strength, chemical durability, and bio-compatibility. However, the inherent brittleness of ceramics poses a challenge to the manufacturing community as the cracking formed during the material removal leads to premature clinical failures. Consequently, fabrication of excellent-fitting and durable dental prostheses calls for new and innovative processing technologies to minimize the formation of, micro-scale cracking.

    This thesis presents a combined analytical and experimental study with focus on optimizing the machining performance of a type of newly developed dental material. It is called DICOR/MGC, where MGC stands for machinable glass ceramic. The study starts from analyzing their microstructural characteristics to searching for the machining conditions that provide satisfactory performance in terms of surface finish and acceptable flexural strength. To gain a better understanding of the material removal mechanism(s), a dynamometer is designed to perform an on-line recording of the cutting force generated during machining. Method of using an environmental scanning electron microscope is employed to examine the machined surface texture and identify the machining induced cracking. Two major contributions of this thesis study are (1) the fundamental understanding of the relationships among the material microstructures, the machining parameters, and the material preparation on surface integrity of dental ceramics, and (2) the development of an architecture for searching machining conditions that optimize the machining performance of dental ceramics.

  • Thumbnail Image
    Item
    Hardness Assessment of Human Enamel
    (1997) Zhang, G.; Ng, S.J.; Le, Dung T.; Young, D.; ISR
    This paper presents results from investigating indentation impressions on human enamel under micro-hardness tests. The experiments of hardness testing were performed on a microhardness indentation machine under different loading conditions. Images of indentation impressions were obtained using an environmental scanning electron microscope. Geometrical shapes of hardness indentations were visualized in three-dimentional space using computer graphics. Quantitative information was obtained through atomic force measurements to characterize ﲰile-up , ﲳink-in , and elastic recovery of enamel. Special efforts have been made to study the microstructual effect of the calcified rods orientations on the fracture patterns formed during the hardness tests. Significant finding include that the occlusal surface demonstrates much stronger resistance to the indentation force than does the buccal surface and shows 40% elastic recovery after indentation. A new formula to determine hardness value has been proposed. By incorporating the reversible deformation into the evaluation, a normalized hardness measurement can be made to form a basis for comparison and other investigations where hardness has its unique role to play.
  • Thumbnail Image
    Item
    Microstructural Effects on the Machining Performance of Dental Ceramics
    (1997) Le, Dung T.; Qi, L.; Zhang, G.; ISR
    Constraints of mechanical, thermal, and chemical properties are making ceramics the material choice for industrial and dental applications. The quality of a machined surface of ceramics is fundamentally dependent on the response of the material to the machining process. This paper presents a combined analytical and experimental study with focus on optimizing the machining performance of dental ceramics -- DICOR/MGC -- with three distinguished microstructures. The study starts from analyzing the microstructural characteristics to searching for the machining conditions that provide satisfactory performance in terms of acceptable flexural strength. Evidence gained from the cutting force measurements and evaluation of fracture strength degradation indicates that the control of micro-scale fracture formed on the machined surface, with microstructural characteristics being considered, is the key factor which dominates the machining performance.
  • Thumbnail Image
    Item
    Assessment of Non-Linear Dynamics of Material Removal on Surface Integrity
    (1997) Zhang, G.; Ng, S.J.; Le, Dung T.; ISR
    In this chapter, we present our research on the study of non- linear dynamics observed during the machining of ceramic materials. We will focus on both innovation in machining technology and development of non-destructive evaluation methods to assess machining performance. Three aspects of our work are presented in the following sections. They are, 1) Submerged Precision Machining, and 2) Scanning Electron Microscopy Analysis. Aspect 1 relates to an innovative approach to machining, while aspects 2 relates to evaluation methodologies for surface characterization. These methods and techniques have been developed to achieve cost-efficient machining as well as high-quality surface finish in ceramic material.
  • Thumbnail Image
    Item
    Characterization of Indentation Impressions on Human Enamel For Hardness Measurement
    (1997) Zhang, G.; Le, Dung T.; Tucker, S.R.; Ng, S.J.; ISR
    This paper presents results from investigating indentation impressions on human enamel under micro-hardness tests. The experiments of hardness testing were performed on a microhardness indentation machine under different loading conditions. Images of indentation impressions were obtained using an environmental scanning electron microscope. Geometrical shapes of hardness indentations were visualized in three-dimensional space using computer graphics. Quantitative information was obtained through atomic force measurements to characterize "pile-up", "sink-in", and elastic recovery of enamel. Special efforts have been made to study the microstrucutual effect of the calcified rods orientations on the fracture patterns formed during the hardness tests. Significant findings include that the occlusal surface demonstrates much stronger resistance to the indentation force than does the buccal surface and shows 40% elastic recovery after indentation. A new formula to determine hardness value has been proposed. By incorporating the reversible deformation into the evluation, a normalized hardness measurement can be made to form a basis for comparison and other investigations where hardness has its unique role to play.

  • Thumbnail Image
    Item
    Control of Machining Induces Edge Chipping on Glass Ceramics
    (1996) Ng, S.J.; Le, Dung T.; Tucker, S.R.; Zhang, G.M.; ISR
    Edge chipping is a phenomenon commonly observed during the machining of ceramic material. Characterization of edge chipping, both in macro and in micro scale, and correlating its formation to machining parameters form a basis for developing new and innovative technologies for controlling in machining induced damage. An experimental-based study using glass ceramic material is performed. Three types of edge chipping are identified. The SEM-sterephotography method and the finite element method are used to evaluate the edge chipping effect under a set of machining conditions. Significant findings are obtained and guidelines for controlling edge chipping during machining are suggested.
  • Thumbnail Image
    Item
    Characterization of the Surface Texture Formed During the Machining of Ceramics
    (1995) Zhang, G.M.; Ng, S.J.; Le, Dung T.; Job, Lenox S.; ISR
    This paper presents the development of a computer-based system to perform characterization of the surface texture formed during the machining of ceramic material. Techniques of image processing and computer graphics are employed to display vivid pictures of micro-scale details of the machined surfaces. Special attention is given to establishing the interrelations between the surface texture formation and the grain facet fracture induced by machining. Results obtained from microscopic analysis of the formed surface texture reveal that grain pullouts and cleavage, as a result of the progressive development of grain boundary micro-cracking, are two mechanisms responsible for the material removal process. The surface texture is an aggregation of macro and micro-scale fractured facets. A new performance index  cavity density is introduced to quantify the combinational effect of material microstructure and the dynamic loading during machining on the micro-mechanisms of the material removal process.
  • Thumbnail Image
    Item
    Characterization of the Surface Cracking Formed during the Machining of Ceramic Material
    (1995) Zhang, G.M.; Ng, S.; Le, Dung T.; ISR
    This paper presents a method to characterize the surface cracking formed during the machining of ceramics material. Ceramic specimens are prepared under two different machining environments, dry and submersion. An environmental scanning electron microscope is used to obtain high-magnification images of machined surfaces. Reconstruction of the surface texture in a three-dimensional space is made by scanning the images and using graphics software to obtain detailed and informative spatial views of the machined surface. The visualized surface cracks provide quantitative information on their size and shape. Two performance indices are proposed to characterize the distribution of surface cracks induced by machining in terms of the density and crack depth with reference to the machined surface. As a case study, the developed nondestructive evaluation method is used to assess the effectiveness of using the submerged machining to process ceramic material. The obtained results present a clear picture illustrating the capability of controlling the crack formation during the submerged machining.