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This thesis presents the research results of a correlation and model based on nano and macroindentation hardness measurements. The materials used to develop and test the correlation include bulk tantalum and O1 tool steel. Following the literature review and a detailed description of the experimental techniques, the results of the nanoindentation hardness measurements are presented. After applying the methods and correlation recommended here, the results should give an accurate value of hardness in the Vickers scale for microstructural features that are too small to be precisely and exclusively measured using the traditional macroindentation hardness technique. The phenomena and influential factors in nanoindentation hardness testing are also discussed. These phenomena and theories are consistent with the microstructural behavior predicted in the Nix and Gao model for mechanism-based strain gradients. Implementing the correlation factors and/or correlation curve, accurate results can be found for metals over a broad hardness range. Initially, this research may impact the pipeline division of the petroleum industry by providing a correlation to the Vickers scale for nanoindentation testing of microstructural features. This thesis may also provide a research methodology to develop hardness correlations for materials other than metals. This thesis consists of eight chapters. Following an introduction in Chapter I, the research motivations and objectives are highlighted in Chapter II. Chapter III explains the multi-scale indentation techniques used in this thesis and Chapter IV presents the materials preparation techniques used. Then, the results are presented in Chapter V, followed by the factors affecting nanoindentation hardness in Chapter VI. Finally, Chapters VII and VIII reveal the indentation contact analysis, correlation, and conclusions of this research, respectively.

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A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Doctor of Philosophy.‘ Johannesburg, August 2017 / Fe-B-C composites were produced, from boron carbide and iron powders, using spark plasma sintering. This provided information on the effects of rapid sintering on densification, composition and the microstructure of the materials produced. The composition range included a selection high Fe contents (69.3, 78 and 80.9 vol. % Fe-B4C) and high B4C concentrations (1, 3, 5 vol. % Fe-B4C). The properties of the materials were investigated to determine the potential for using relatively cheap Fe and B4C powders to produce hard, wear resistant materials. High Fe-B4C composites were sintered at 900, 1000 and 1100°C at 60 MPa. Densification increased with increasing temperature and at 1100° each composition achieved ≥ 97 % densification. The materials reacted during sintering with the main phases observed being Fe2B and Fe3(B,C) whilst additional phases formed were FeB, C and Fe23(B,C)6.Comparing the phases that were produced to Fe-B-C phase diagrams showed deviations from expected compositions, indicating the non-equilibrium nature of producing the composites using SPS. Although the composites were not at equilibrium, all the B4C reacted and could not be maintained, even with fast heating and cooling rates. The properties of the materials were dependent on both densification and the phases that were present after sintering. Materials containing higher amounts of the Fe2B phase showed higher hardness and fracture toughness results, up to 13.7 GPa and 3.5 MPa.m0.5 respectively for the 69.3 vol. % Fe-B4C. The materials were sensitive to grain and pore growth which negatively affected properties at 1100°C. The transverse rupture strength of 388.3 MPa for 80.9 vol. % Fe-B4C composite was the greatest, and showed evidence of both intergranular and transgranular fracture. The strength was affected by a fine dispersion of porosity at the grain boundaries, throughout the material, and free carbon in the structure was detrimental to the strength of the 69.3 % Fe-B4C. The wear rates were lower using Si3N4 wear balls compared to stainless steel balls, where 69.3 vol. % Fe-B4C showed the best wear rates, 8.9×10-6 mm3/Nm (stainless steel ball) and 1.77×10-6 mm3/Nm (Si3N4 ball), due to the higher Fe2B composition and free carbon acting as a lubricant during sliding. 1, 3 and 5 vol. % Fe-B4C composites were sintered to densities above 97 % of theoretical at 2000°C and 30 MPa. The formation of a transient FeB liquid phase assisted densification. 1 % Fe-B4C attained hardness and fracture toughness up to 33.1 GPa and 5.3 MPa.m0.5 with a strength of 370.5 MPa. Thermal mismatch between the FeB phase and B4C caused high residual stresses at the interface which led to cracking and pull-out of the FeB phase. Residual carbon at the grain boundary interface exacerbated the pull-out effect. Increasing Fe and the subsequent FeB phase had an embrittling effect. The materials suffered severe wear of up to 36.92×10-6 mm3/Nm as a result of the pull-out with the remaining porosity acting as a stress raiser. 20 vol. % of the Fe in each system was substituted with Ti to reduce the presence of residual carbon. Although in some case the properties of the respective compositions improved, residual carbon was still present in the composites. / MT2018

Synthesis of high molar mass polycarbonate polyurethanes using a novel polyol is described. The resulting elastomers demonstrate excellent mechanical properties as well as the capability to re-heal after rupture without the addition of additives or imbedded healing agents. The self-healing functionality is shown to greatly improve with the addition of up to 1% single and multi-walled carbon nanotubes. The interface of the carbon nanotubes and self-healing polymer are probed using Raman techniques and provide an insight into how the self-healing actions are improved with the addition of carbon nanotubes. Synthesis of polycarbonate polyurethanes and carbon nanotube composites using a novel casting method is described and compared to the more traditional solution casting method. The dispersion of the carbon nanotubes is evaluated as well as the effect of effective dispersion on the composites through tensile testing, rheometry and hardness testing. Although complete agglomeration avoidance could not be achieved, significant size decrease was observed. Over 200% improvement in tensile strength is shown with conventional solution casting method which is further improved by the described novel solution casting method. Contact angle measurements on our novel self-healing poly (carbonate urethane) and CNTs composites show that surface energies are drastically changed when CNTs are used. The most revealing finding is that f×svp increases in CNT composite materials from ~30% of the surface energy on average for the samples tested, to ~80%. We have shown that surface free energies increase most likely as a result of exposing hydrogen bonding sites typically found within the bulk in polyurethanes. Our polyurethane differs from traditional polyurethanes in that it has both novel soft segments made from a novel polycarbonate polyol discussed in chapter 2 and relatively soft ¡§hard¡¦ segments resulting from the use of H12MDI, all leading to increased ability to hydrogen bond within the material. The availability of the hydrogen bonding sites is demonstrated by FTIR absorbance bands for associated and unassociated hydrogen bonding sites, which do not seem to be accessible to a large until the PCPU¡¦s surface is disrupted. Once disrupted, the exposed hydrogen bonding sites are able to bond with other bonding sites of adjacent ruptured surfaces. This would explain why our material is non-blocking, e.g. won¡¦t stick to itself, until the surface is ruptured. It would also explain why any two ruptured surfaces of our material will reheal, even if they were not attached previously.

Made available in DSpace on 2014-06-11T19:33:01Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-07-27Bitstream added on 2014-06-13T20:04:53Z : No. of bitstreams: 1 oliveira_albm_dr_arafo.pdf: 1363942 bytes, checksum: 31b5ccd566c55e1abf5a60c112fc13be (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O objetivo deste estudo foi avaliar a influência de soluções fluoretadas sobre a estabilidade de cor, a rugosidade e a dureza superficiais de diferentes resinas compostas, em curto e em longo prazo. Para isso, foram realizadas pesquisas científicas, apresentadas em três capítulos. Setenta e cinco espécimes de 10 mm de diâmetro e 2 mm de espessura foram confeccionados e polidos com discos de óxido de alumínio (Super-Snap®, Shofu Dental Corp. Kyoto, Japão) em ordem decrescente de granulação. Os grupos experimentais foram divididos de acordo com o tipo de resina composta (nanoparticulada - Filtek Z350 XT, microhíbrida - Filtek Z250 e microparticulada - Durafill VS) e diferentes meios de imersão (saliva artificial, solução de fluoreto de sódio a 0,05%- manipulado, Fluordent Reach, Oral B, Fluorgard). Os espécimes permaneceram imersos em saliva artificial por 24 horas e foram submetidos à análise da cor, rugosidade e dureza iniciais. A partir disso, foram imersos nas diferentes soluções por 1 minuto ao dia durante 60 dias. Nos intervalos entre as imersões foram mantidos em saliva artificial a 370C  1 0C. Após esse período, foram submetidos às novas avaliações de cor, rugosidade e dureza superficiais. Em sequência, foram realizados os procedimentos de envelhecimento artificial utilizando-se 20.000 ciclos de termociclagem, 1.200.000 ciclos de simulação de forças mastigatórias e imersão contínua nas soluções por 1825 minutos. Após estes processos, foram realizadas leituras finais para todas as propriedades avaliadas. Os dados obtidos, nos diferentes tempos, foram avaliados estatisticamente pela Análise de Variância. Para a estabilidade de cor, utilizou-se o teste de Tukey e para a rugosidade e a dureza superficiais, os testes de Tukey e de Sidak... / The aim of this study was to evaluate the influence of fluoride solutions on color stability, surface roughness and hardness of different composite resins, in short and long term. Seventy-five specimens of 10mm diameter and 2mm thickness were made with composite resins and polished with aluminum oxide discs (Super-Snap®, Shofu Dental Corp. Kyoto, Japan) in a decreasing order of granulation. Experimental groups were divided according to (1) composite resin (nanofilled- Filtek Z350 XT, mycrohybrid Filtek Z250 and microfilled - Durafill VS) and (2) different immersion media (artificial saliva, a manipulated 0.05% sodium fluoride solution, Fluordent Reach, Oral B, Fluorgard). Specimens were kept in artificial saliva for 24 hours and submitted to color, roughness and hardness tests. From this period, specimens were immersed in the different solutions for 1 minute per day, during 60 days. In periods between immersions, specimens were kept in artificial saliva at 370C  10C. After that, the specimens were submitted to color, roughness and hardness analysis again. Then the artificial aging was carried out using 20,000 thermal cycles, 1,200,000 mechanical loading cycles and continuous immersion in the solutions for 1825 minutes. After the artificial aging, specimens were submitted to color stability, roughness and hardness tests. The obtained data for different periods were submitted to ANOVA. The color change data were evaluated by Tukey test. Surface roughness and hardness data were submitted to Tukey and Sidak tests, both at 5% significance. The highest color change and surface roughness were observed with the microfilled composite resin, followed by the nanofilled and microhybrid resin. Besides that, the lowest hardness also was obtained with the microfilled resin. The artificial aging promoted an increase of roughness and... (Complete abstract click electronic access below)

Orientador: Elisa Maria Aparecida Giro / Co-orientador: Patricia Petromilli Nordi Sasso Garcia / Banca: Patricia Aleixo dos Santos Domingos / Banca: Jacqueline Braga Barbosa Cerqueira-Leite / Banca: Victor Humberto Orbegoso Flores / Banca: Edson Alves Campos / Resumo: O objetivo deste estudo foi avaliar a influência de soluções fluoretadas sobre a estabilidade de cor, a rugosidade e a dureza superficiais de diferentes resinas compostas, em curto e em longo prazo. Para isso, foram realizadas pesquisas científicas, apresentadas em três capítulos. Setenta e cinco espécimes de 10 mm de diâmetro e 2 mm de espessura foram confeccionados e polidos com discos de óxido de alumínio (Super-Snap®, Shofu Dental Corp. Kyoto, Japão) em ordem decrescente de granulação. Os grupos experimentais foram divididos de acordo com o tipo de resina composta (nanoparticulada - Filtek Z350 XT, microhíbrida - Filtek Z250 e microparticulada - Durafill VS) e diferentes meios de imersão (saliva artificial, solução de fluoreto de sódio a 0,05%- manipulado, Fluordent Reach, Oral B, Fluorgard). Os espécimes permaneceram imersos em saliva artificial por 24 horas e foram submetidos à análise da cor, rugosidade e dureza iniciais. A partir disso, foram imersos nas diferentes soluções por 1 minuto ao dia durante 60 dias. Nos intervalos entre as imersões foram mantidos em saliva artificial a 370C  1 0C. Após esse período, foram submetidos às novas avaliações de cor, rugosidade e dureza superficiais. Em sequência, foram realizados os procedimentos de envelhecimento artificial utilizando-se 20.000 ciclos de termociclagem, 1.200.000 ciclos de simulação de forças mastigatórias e imersão contínua nas soluções por 1825 minutos. Após estes processos, foram realizadas leituras finais para todas as propriedades avaliadas. Os dados obtidos, nos diferentes tempos, foram avaliados estatisticamente pela Análise de Variância. Para a estabilidade de cor, utilizou-se o teste de Tukey e para a rugosidade e a dureza superficiais, os testes de Tukey e de Sidak... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The aim of this study was to evaluate the influence of fluoride solutions on color stability, surface roughness and hardness of different composite resins, in short and long term. Seventy-five specimens of 10mm diameter and 2mm thickness were made with composite resins and polished with aluminum oxide discs (Super-Snap®, Shofu Dental Corp. Kyoto, Japan) in a decreasing order of granulation. Experimental groups were divided according to (1) composite resin (nanofilled- Filtek Z350 XT, mycrohybrid Filtek Z250 and microfilled - Durafill VS) and (2) different immersion media (artificial saliva, a manipulated 0.05% sodium fluoride solution, Fluordent Reach, Oral B, Fluorgard). Specimens were kept in artificial saliva for 24 hours and submitted to color, roughness and hardness tests. From this period, specimens were immersed in the different solutions for 1 minute per day, during 60 days. In periods between immersions, specimens were kept in artificial saliva at 370C  10C. After that, the specimens were submitted to color, roughness and hardness analysis again. Then the artificial aging was carried out using 20,000 thermal cycles, 1,200,000 mechanical loading cycles and continuous immersion in the solutions for 1825 minutes. After the artificial aging, specimens were submitted to color stability, roughness and hardness tests. The obtained data for different periods were submitted to ANOVA. The color change data were evaluated by Tukey test. Surface roughness and hardness data were submitted to Tukey and Sidak tests, both at 5% significance. The highest color change and surface roughness were observed with the microfilled composite resin, followed by the nanofilled and microhybrid resin. Besides that, the lowest hardness also was obtained with the microfilled resin. The artificial aging promoted an increase of roughness and... (Complete abstract click electronic access below) / Doutor

Studies of mechanics and deformation in metal cutting operations have been largely limited to steady-state processes assuming constant forces and shear strain of cutting. However, ‘transient’ or varying deformation conditions are frequently encountered in manufacturing processes, when one or more processing parameters vary during the progress of the cut. Such conditions impose a lower overall strain on the resulting chip and affect the cutting forces and energies. In this study, the transient deformation characteristics are studied through the analysis of chip attributes (hardness and shape change) in a periodic cutting technique, Modulation Assisted Machining (MAM). In MAM, a sinusoidal modulation is superimposed on the tool feed, resulting in periodic engagement between the tool and workpiece. Deformation is confined to a specific volume of material and is also transient due to varying local conditions, manifesting an inhomogeneous and lower shear strain compared to steady-state cutting. A wide variety of deformation conditions from near steady-state to completely transient was achieved through the control of modulation frequency, which determines the contact length in each cutting cycle. Particles produced at lower frequencies exhibit increased hardness, consistent with the deformation more approaching steady state. Micro-indentation tests performed on each particle tracked the local variations in hardness along the length of cut, which agreed well with the non-uniform shape change observed on the cross-section of the particles. Microstructural examination of the chips made with and without modulation helped further describe the different deformation modes acting under periodic and continuous cutting conditions. MAM is also a valuable technique for metal powder processing. Individual chip particles are produced during each modulation cycle with controllable shape and size, and composition identical to that of the workpiece. Advantages of the process include a significant reduction in the specific energy of production, zero compositional variance and a tight distribution of particle sizes compared to atomization. Implications of scaling up the process for large-scale production and the possible applications of the metal particles made with MAM are highlighted.