Thesis (M. Arch.)--University of Michigan, 1967.

Thesis (M. Arch.)--University of Michigan, 1967.

Thesis (Ph. D.)--University of Rhode Island, 2003. / Typescript. Includes bibliographical references (leaves 228-239).

Thesis (M. S.)--Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, 2009. / Committee Co-Chair: Beckham, Haskell; Committee Co-Chair: Cook, Fred; Committee Member: Collard, David; Committee Member: France, Stefan; Committee Member: Griffin, Anselm

Submitted in fulfillment of requirements of the degree of Master in Health Sciences: Dental Technology, Durban University of Technology, Durban, South Africa, 2016. / Pumice is used in the polishing of dental appliances to remove surface irregularities. It is usually used in a slurry form that is pumice powder mixed with water. In Nigeria, the increased cost of pumice as a result of its limited supply into the country has encouraged dental technicians to re-use pumice slurry for longer periods than advocated when polishing acrylic dentures, whether new or old dentures which have been worn in the mouth. Consequently, this is likely to increase cross-infection of communicable diseases in the dental technology laboratory. Although materials such as white sand, black sand and porcelnite can be used, literature documents that these materials are less effective in the polishing of acrylic dentures (Areeg 2011). The focus of this study was to use eggshells, a natural waste product, to develop and test the quality of an alternative material to reduce the surface roughness of heat-cured acrylic resins. A quantitative research paradigm and an experimental research strategy were adopted. The research design included two phases. In phase one of this study, different characterisation techniques such as Brunnae-Emmer Teller (BET); Fourier Transform Infrared Spectroscopy (FTIR); X-ray Diffraction (XRD); Energy Dispersive X-ray Spectroscopy (EDX) and Scanning Electron Microscope (SEM); Transmission Electron Microscopy (TEM); Laser Scattering Particle Size Distribution Analyser (PSA); Thermo-Gravimetric Analysis (TGA); and Induction-Coupling-Optical Emission Spectroscopy (ICP-OES) were used to assess the suitability of the new abrasive material (NAM). In addition, the level of microbial contamination of the NAM was assessed in line with the specified microbial limits for cosmetic products. In contrast, phase two investigated the product-based quality of the NAM as an abrasive material for removable dental appliances. There were two sample groups, that is, the NAM (test group) and Pumice (control), and each sample group had 50 PMMA acrylic specimens. The surface roughness (Ra) was measured using a Talysurf profilometer. An Independent Tukey test was used to analyse the Ra values (p=0.05). A Scanning Electron Microscope (SEM) and Optical Microscope (OEM) were further used to support the results of the profilometer in terms of the quality of surface finish and polish. Validity of the study was achieved following the ISO 20795-1 (2013) methods of preparation and fabrication of the acrylic specimens. The reliability was determined via reproducibility and repeatability of tests. The BET analysis showed that the NAM is predominantly a mesoporous powder. The FTIR and XRD analyses confirmed that the NAM is pure calcite with unique water absorbing characteristics, and is free of bacteria. The EDX and ICP-OES analyses revealed calcium, oxygen and carbon as the major elemental composition of the NAM. The SEM and TEM images revealed irregular shaped particles in the NAM. The PSA analysis of the particle distribution showed the NAM to be superfine (50nm to 0.3µm) and medium (44µm powder), respectively. The TGA analysis revealed a high-grade carbonate product in the NAM (>66.0 mass% of calcium carbonates). In addition, and in terms of in the qualities of the NAM in reducing the surface roughness of PMMA resins, the test group and the control group produced Ra values that were significant different (p<0.0001). The SEM and OEM analyses further confirmed the differences in the surfaces between the polished sample groups at different magnifications. Overall, the control showed the highest mean average (0.1056±0.03688µm), whereas the test group had the lowest Ra values (0.0476±0.01379). The lowest Ra values measured with the test group indicated that the NAM improves the surface smoothness of PMMA acrylic specimens. Notably, this study conclusively showed that the NAM effectively reduces the surface roughness to below the threshold limit value of 0.2µm. Significantly, and in associating the Ra values to the threshold limit value of 0.2µm, the NAM produced better results than pumice. Hence the use of the NAM as a polishing material for acrylic dentures is highly recommended. Finally and in line the NAM being a suitable alternative to pumice as it effectively reduces the surface roughness of PMMA specimens, future investigation into the use of eggshell nanoparticles to develop dental prophylaxes will be encouraged. / M

This is a study of the facilities and processes used in finishing wood and metal projects used in industry as compared with facilities available and the processes used in industrial arts programs in one hundred Texas schools.

Brittle materials such as silicon, germanium, glass and ceramics are widely used in semiconductor, optical, micro-electronics and various other fields. Traditionally, grinding, polishing and lapping have been employed to achieve high tolerance in surface texture of silicon wafers in semiconductor applications, lenses for optical instruments etc. The conventional machining processes such as single point turning and milling are not conducive to brittle materials as they produce discontinuous chips owing to brittle failure at the shear plane before any tangible plastic flow occurs. In order to improve surface finish on machined brittle materials, ductile regime machining is being extensively studied lately. The process of machining brittle materials where the material is removed by plastic flow, thus leaving a crack free surface is known as ductile-regime machining. Ductile machining of brittle materials can produce surfaces of very high quality comparable with processes such as polishing, lapping etc. The objective of this project is to develop a comprehensive predictive model for ductile machining of brittle materials. The model would predict the critical undeformed chip thickness required to achieve ductile-regime machining. The input to the model includes tool geometry, workpiece material properties and machining process parameters. The fact that the scale of ductile regime machining is very small leads to a number of factors assuming significance which would otherwise be neglected. The effects of tool edge radius, grain size, grain boundaries, crystal orientation etc. are studied so as to make better predictions of forces and hence the critical undeformed chip thickness. The model is validated using a series of experiments with varying materials and cutting conditions. This research would aid in predicting forces and undeformed chip thickness values for micro-machining brittle materials given their material properties and process conditions. The output could be used to machine brittle materials without fracture and hence preserve their surface texture quality. The need for resorting to experimental trial and error is greatly reduced as the critical parameter, namely undeformed chip thickness, is predicted using this approach. This can in turn pave way for brittle materials to be utilized in a variety of applications.

Thesis (Ph. D.)--University of Wisconsin, 1967. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Made available in DSpace on 2014-06-11T19:22:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-03-20Bitstream added on 2014-06-13T20:49:16Z : No. of bitstreams: 1 martins_chr_me_bauru.pdf: 3300032 bytes, checksum: c6be05b5fe4d2831ce67d7e7ddc84b4d (MD5) / A retificação é um processo de acabamento de peças, que objetiva produtos e superfícies avançadas. Porém, como o constante atrito entre a peça e rebolo, este perde a agressividade, de modo que o resultado da retificação fica prejudicado. Quando isso ocorre é imprescindível à realização do processo de dressagem, que consiste em reavivar os grãos gastos do rebolo. Como as condições de dressagem provocam uma grande influência no desempenho da operação de retificação, monitorá-las durante todo o processo pode aumentar a sua eficiência. Assim, no presente trabalho foi realizado um estudo do desgaste de três tipos de diamantes para dressadores e, posteriormente, foram desenvolvidos modelos neurais, baseados em redes MLP e de Kohonen, capazes de classificar o nível de desgaste dos dressadores. Para se atingir esse objetivo foram ensaiados três tipos de dressadores de ponta única, um com diamante sintético CVD e dois com diamantes naturais, Mato Grosso e Brasil Extra. Serviram de entradas para os modelos neurais as estatísticas RMS e ROP obtidas após o estudo do conteúdo harmônico do sinal da emissão acústica. Para cada diamante foi obtido um modelo neural mais apto para as características do diamante. Os resultados mostraram um bom desempenho das redes neurais empregadas, atingindo-se taxas de acerto de 100% em alguns modelos neurais / Grinding is a part finishing process for advanced products and surfaces. However, continuous friction between the work piece and the grinding wheel causes the latter to lose its sharpness, thus impariring the grinding results. This is when the dressing process is required, which consist of sharpening the worn grains of the grinding wheel. The dressing conditions strongly affect the performance of the grinding operation; hence, monitoring them thoughout the process can increase its efficiency. The main objective of this study was to classify the levels of wear of a single-point dresser during the operation; hence monitoring them throughout the process can increase its efficiency. The main objective of this study was to classify the levels of wear of a single-point dresser during the operation using neural models. A digital signal processing of acoustiv emission was used to obtain the network inputs. In the experiments three types of single-point dresser were used, one with CVD synthetic diamond and two with natural diamonds, Mato Grosso and Brasil Extra. The harmonic content of the acoustic emission signal was found to be influenced by the condition of the dresser, and when used to feed the neural model it is possible to classify the wear level. The results showed a good performance of the neural networks employed, reaching a hit rate of 100% for some models

Orientador: Paulo Roberto de Aguiar / Banca: Rogério Andrade Flauzino / Banca: José Alfredo Covolan Ulson / Resumo: A retificação é um processo de acabamento de peças, que objetiva produtos e superfícies avançadas. Porém, como o constante atrito entre a peça e rebolo, este perde a agressividade, de modo que o resultado da retificação fica prejudicado. Quando isso ocorre é imprescindível à realização do processo de dressagem, que consiste em reavivar os grãos gastos do rebolo. Como as condições de dressagem provocam uma grande influência no desempenho da operação de retificação, monitorá-las durante todo o processo pode aumentar a sua eficiência. Assim, no presente trabalho foi realizado um estudo do desgaste de três tipos de diamantes para dressadores e, posteriormente, foram desenvolvidos modelos neurais, baseados em redes MLP e de Kohonen, capazes de classificar o nível de desgaste dos dressadores. Para se atingir esse objetivo foram ensaiados três tipos de dressadores de ponta única, um com diamante sintético CVD e dois com diamantes naturais, Mato Grosso e Brasil Extra. Serviram de entradas para os modelos neurais as estatísticas RMS e ROP obtidas após o estudo do conteúdo harmônico do sinal da emissão acústica. Para cada diamante foi obtido um modelo neural mais apto para as características do diamante. Os resultados mostraram um bom desempenho das redes neurais empregadas, atingindo-se taxas de acerto de 100% em alguns modelos neurais / Abstract: Grinding is a part finishing process for advanced products and surfaces. However, continuous friction between the work piece and the grinding wheel causes the latter to lose its sharpness, thus impariring the grinding results. This is when the dressing process is required, which consist of sharpening the worn grains of the grinding wheel. The dressing conditions strongly affect the performance of the grinding operation; hence, monitoring them thoughout the process can increase its efficiency. The main objective of this study was to classify the levels of wear of a single-point dresser during the operation; hence monitoring them throughout the process can increase its efficiency. The main objective of this study was to classify the levels of wear of a single-point dresser during the operation using neural models. A digital signal processing of acoustiv emission was used to obtain the network inputs. In the experiments three types of single-point dresser were used, one with CVD synthetic diamond and two with natural diamonds, Mato Grosso and Brasil Extra. The harmonic content of the acoustic emission signal was found to be influenced by the condition of the dresser, and when used to feed the neural model it is possible to classify the wear level. The results showed a good performance of the neural networks employed, reaching a hit rate of 100% for some models / Mestre