ABSTRACT The ceramic ball bearing has been used to exact machine for its good properties such as heat-resistant, corrosion-resisting, and wear-resisting. Now, the produced expense of ceramic ball is hundred of steel ball because the grinding process must spend much time and money. This study research the effects of eccentricity (e: the distance is between the center of the ball circulation and the center of the spindle), spindle speed, and load on grinding characteristics of ball by using eccentric ultra-precision ball grinding machine which developed by our lab, under saving cost and time, search the optimum operating conditions of this machine, it¡¦s good for industrial circles in the future. Experimental results show that the converged rate of the saturated value for the sphericity is increased with increasing eccentricity. Saturated value of sphericity is sphericity reduced to a steady state. The saturated value of the sphericity is not fully proportional to eccentricity. The relation between eccentricity and saturated value of sphericity are divided two region by one rb, the first region is that sphericity is proportional to eccentricity when eccentricity is 0~rb, and the second region is that sphericity is inverse proportional to eccentricity when eccentricity is rb~2rb. The converged rate of surface roughness (Ra) are negative with increasing eccentricity and the saturated value of the surface roughness (Ra) is higher. The volume removal rate is increased with increasing eccentricity. The converged rate of the saturated value for the sphericity and surface roughness (Ra) are increased with increasing spindle speed and load, and the saturated value are higher. The volume removal rate is also increased with increasing spindle speed and load.

abstract: Pb-free solder joints are commonly used as interconnects in semiconductor packaging. One of the major defects affecting the mechanical performance of solder joints are reflow pores that form during processing. These pores exhibit significant variability in size and distribution, and understanding the effects of pore geometry on failure is an important reliability concern. In this thesis, the pore microstructures of solder joint samples and the localized plastic deformation around individual pores was characterized in 3D using lab scale X-ray Microtomography. To observe the deformation of a solder joint in 3D, a solder joint was imaged with Microtomography after reflow and then deformed in shear in several loading steps with additional tomography data taken between each. The 3D tomography datasets were then segmented using the 3D Livewire technique into regions corresponding to solder and pores, and used to generate 3D models of the joint at each strain value using Mimics software. The extent of deformation of individual pores in the joint as a function of strain was quantified using sphericity measurements, and correlated with the observed cracking in the joint. In addition, the error inherent in the data acquisition and 3D modeling process was also quantified. The progression of damage observed with X-ray Microtomography was then used to validate the deformation and failure predicted by a Finite Element (FE) simulation. The FE model was based on the as-reflowed tomography data, and incorporated a ductile damage failure model to simulate fracture. Using the measured sphericity change and cracking information obtained from the tomography data, the FE model is shown to correctly capture the broad plastic deformation and strain localization seen in the actual joint, as well as the crack propagation. Lastly, Digital Image Correlation was investigated as a method of obtaining improved local strain measurements in 3D. This technique measures the displacement of the inherent microstructural features of the joint, and can give localized strain measurements that can be directly comparable to that predicted by modeling. The technique is demonstrated in 2D on Pb-Sn solder, and example 3D data is presented for future analysis. / Dissertation/Thesis / M.S. Materials Science and Engineering 2012

No description available.

O dimensionamento de sistemas de transporte hidráulico de polpas minerais exige especial atenção à medida que partículas grossas apresentam um comportamento de sedimentação no interior dos tubos. Dentro desta situação, a velocidade de transporte da polpa mineral deve ter magnitude suficiente para suspender e transportar os sólidos, evitando que os mesmos se depositem na base da tubulação. O bombeamento de polpas minerais em tubos horizontais contendo partículas grossas constituiu o objeto desta tese. Um levantamento sobre a literatura corrente foi realizado e, através de procedimentos experimentais, obteve-se um banco de dados para o modelamento da velocidade crítica (VC), isto é, a velocidade mínima em que ocorre a formação de um leito móvel na base do tubo, apresentando magnitude ligeiramente superior à velocidade de deposição VD, caracterizada pelo início da deposição das partículas na base dos dutos. Para a realização dos ensaios, foram construídas duas unidades experimentais de bombeamento de polpa mineral, onde foram estudadas as seguintes variáveis: i) gradiente de pressão por metro de tubo horizontal (\'delta\'P/L), ii) velocidade média do fluxo (V), iii) perfil de concentração de sólidos ao longo da seção transversal, iv) fator de forma através da função de esfericidade das partículas (\'psi\'), v) densidade do sólido e do líquido, vi) concentração volumétrica dapolpa mineral, vii) granulometria dos sólidos e viii) diâmetro da tubulação. A primeira unidade experimental foi montada com tubulação em PVC transparente de diâmetro interno de 25,4mm e a segunda unidade foi construída em PVC branco com um trecho de 2m em acrílico transparente, apresentando diâmetro interno de 50,8mm. A velocidade critica (VC) para cada condição estudada foi determinada visualmente, através das seções transparentes da tubulação. As amostras utilizadas neste trabalho foram: concentrados de apatita e hematita e o mineral quartzo. As frações granulométricas estudadas foram inseridas em duas classes de tamanho, sendo a primeira classe passante em 297µm e retida em 249µm e a segunda classe passante em 149µm e retida em 105µm. Os resultados permitiram determinar um novo modelo semiempírico para VC, alcançando desvios menores que 10% para as velocidades preditas em relação aos valores de velocidades observadas experimentalmente. / The design of hydraulic systems of slurry transport demands a special attention due to coarse particles present a settling behavior inside the pipes. In this situation, the transport velocity should have order of magnitude sufficient to promote the suspension and the transport of particles, avoiding the solids deposition at the bottom of pipe. The transport of mineral slurries containing coarse particles was the primary goal of the thesis. A survey of the available literature was done and through the experimental tests could be possible to raise a data bank in order to develop a new best fit correlation for the critical velocity (VC) which included the particle shape effect, through the sphericity function. VC could be defined as the minimum velocity where a moving bed of particles takes place at the bottom of the horizontal pipe and it is slightly above the deposition velocity VD, which could be characterized by a bed of stationary particles at the bottom of pipe. The research was conducted using two recirculating pipe test rigs with transparent PVC pipe of 25.4mm and 50.8mm internal diameter with slurry concentrations from 8% up to 27% by volume. The material used was apatite and hematite concentrates and quartz mineral, clustered in two classes of size range (-0.297+0.210mm; -0.149+0.105mm), where the variables were: i) Head losses per meter of horizontal pipe (\'delta\'P/L), ii) Mean transport velocity (V), iii) solids distribution profile, iv) particle shape effect, through the sphericity function (\'psi\'), v) density of particles and liquid, vi) Volumetric concentration of slurries, vii) particles size and viii) pipe diameter. The critical velocity (VC), for each studied condition, was visually determined through the transparent sections of the pipes. The results have yielded a new semi empirical model to predict the critical velocity, yielding a deviation of less than 10% from the observed values of experimental data for VC.

Atmosphärisches Aerosol kann den Strahlungstransport signifikant beeinflussen. Mineralstaub, der über der Sahara und anderen Wüsten in die Atmosphäre gelangt, ist das hinsichtlich der in letzterer dauerhaft verbleibenden Masse bedeutendste Aerosol. Darüber hinaus sind Saharamineralstaubpartikel nichtkugelförmig, und die Wirkungen dieser Partikeleigenschaft auf den Strahlungstransport in der Erdatmosphäre sind bislang nur ungenügend untersucht worden. Es werden die optischen Eigenschaften, Strahlungs- und Erwärmungseffekte von Saharamineralstaub unter Berücksichtigung der Nichtkugelförmigkeit seiner Partikel quantitativ untersucht, wobei der gesamte, im Hinblick auf den Strahlungshaushalt energetisch relevante Spektralbereich zugrunde gelegt wird. Zunächst werden auf Basis in-situ-gemessener Experimentaldaten die atmosphärischen Umgebungsbedingungen, Größenverteilungen, Brechungsindizes, Bodenalbedo und Partikelgestalt festgelegt, die in einem zweiten Schritt in ein Strahlungstransportmodell einfließen. Mit dessen Hilfe wird in umfangreichen numerischen Simulationen des Strahlungstransports in einer realistischen mineralstaubhaltigen Modellatmosphäre im Vergleich zu Messdaten beispielsweise geklärt, welche Partikelform und Größenäquivalenz angenommener sphäroidaler Modellpartikel am meisten realistisch sind. Des Weiteren werden im Zusammenhang mit der Partikelnichtkugelförmigkeit Sensitivitätsstudien zur Beantwortung der Fragen durchgeführt, inwieweit diese das Strahlungsfeld beeinflusst und zu veränderten Strahlungserwärmungswirkungen führt.

Made available in DSpace on 2016-06-02T19:56:54Z (GMT). No. of bitstreams: 1 5890.pdf: 8136490 bytes, checksum: f4dc359468928494ebdd96e3f1c64ebe (MD5) Previous issue date: 2014-02-28 / Universidade Federal de Sao Carlos / The drying of seeds of the pioneer species Cecropia glaziovii Snethlage is motivated due to its restoration characteristics of heterogeneous degraded forests. In this work the main goal is the physical and drying characterization of Cecropia glaziovii seeds in batch fluidized bed, as well as the physiological quality. The dimensions and shapes of seeds were obtained by image analysis, assessing the reproducibility of these measures for in natura samples and those classified by sieving. The drying characterization in fluidized bed drying was performed, with initial fixed bed heights of 3 and 5 cm, with air temperature (40 ± 2)°C and drying air velocity (1.0 ± 0.3) m/s. It was noted that the dimensions and shapes of seeds classified by sieving have higher reproducibility than the in natura ones. Therefore, the seeds retained on the 20 mesh sieve were used for the drying characterization. By using the moisture ratio as a function of time, it could be seen that the mixture in the fluidized bed was homogeneous, as the variation between the bed heights of 3 and 5 cm was negligible. Based on the dimensionless drying rate as a function of moisture ratio, only the decreasing rate period was observed. It was also found that the seeds constitute a porous and hygroscopic particulate system in the conditions used in this study. Therefore, samples with statistical reproduction of sizes and shapes were obtained by physical characterization, and for these seeds, drying characterization was carried out, obtaining the classification of the particulate system as porous and hygroscopic medium without reporting constant drying rate period. The germination index of Cecropia glaziovii seeds was 77%, this value is consistent with government reforestation programs. / A secagem de sementes da espécie pioneira Cecropia glaziovii Snethlage é motivada devido às suas características de recuperação de florestas heterogêneas degradadas. Neste trabalho o principal objetivo é a caracterização física e de secagem de sementes de Cecropia glaziovii em leito fluidizado em batelada, bem como a qualidade fisiológica. As dimensões e formas das sementes foram obtidas através de análise de imagens, avaliando a reprodutibilidade destas medidas para amostras in natura e classificadas por peneiramento. Foi realizada a caracterização de secagem em leito fluidizado com alturas de leitos fixos iniciais de 3 e 5 cm, com temperatura do ar de (40±2)°C e velocidade do ar de secagem de (1,0±0,3) m/s. Foi observado que as dimensões e formas das sementes classificadas por peneiramento apresentam maior reprodutibilidade que as in natura. Portanto, foram utilizadas as sementes retidas na peneira de 20 mesh para a caracterização de secagem. Através do adimensional de umidade em função do tempo pode-se constatar que a mistura no leito fluidizado foi homogênea, pois a variação foi desprezível entre as alturas de leito de 3 e 5 cm. Com base no adimensional de taxa de secagem em função do adimensional de umidade observou-se apenas o período de taxa de secagem decrescente, também se constatou que as sementes de embaúba constituem um sistema de partículas poroso e higroscópico nas condições utilizadas neste trabalho. Portanto, através da caracterização física obtiveram-se amostras com reprodução estatística das medidas de dimensões e formas, e para estas sementes foi realizada a caracterização de secagem, obtendo-se a classificação deste sistema de partícula como meio poroso e higroscópico e sem apresentação de período de taxa constante. O índice de germinação das sementes de embaúba foi de 77%, valores adequados para programas governamentais de reflorestamento.

O dimensionamento de sistemas de transporte hidráulico de polpas minerais exige especial atenção à medida que partículas grossas apresentam um comportamento de sedimentação no interior dos tubos. Dentro desta situação, a velocidade de transporte da polpa mineral deve ter magnitude suficiente para suspender e transportar os sólidos, evitando que os mesmos se depositem na base da tubulação. O bombeamento de polpas minerais em tubos horizontais contendo partículas grossas constituiu o objeto desta tese. Um levantamento sobre a literatura corrente foi realizado e, através de procedimentos experimentais, obteve-se um banco de dados para o modelamento da velocidade crítica (VC), isto é, a velocidade mínima em que ocorre a formação de um leito móvel na base do tubo, apresentando magnitude ligeiramente superior à velocidade de deposição VD, caracterizada pelo início da deposição das partículas na base dos dutos. Para a realização dos ensaios, foram construídas duas unidades experimentais de bombeamento de polpa mineral, onde foram estudadas as seguintes variáveis: i) gradiente de pressão por metro de tubo horizontal (\'delta\'P/L), ii) velocidade média do fluxo (V), iii) perfil de concentração de sólidos ao longo da seção transversal, iv) fator de forma através da função de esfericidade das partículas (\'psi\'), v) densidade do sólido e do líquido, vi) concentração volumétrica dapolpa mineral, vii) granulometria dos sólidos e viii) diâmetro da tubulação. A primeira unidade experimental foi montada com tubulação em PVC transparente de diâmetro interno de 25,4mm e a segunda unidade foi construída em PVC branco com um trecho de 2m em acrílico transparente, apresentando diâmetro interno de 50,8mm. A velocidade critica (VC) para cada condição estudada foi determinada visualmente, através das seções transparentes da tubulação. As amostras utilizadas neste trabalho foram: concentrados de apatita e hematita e o mineral quartzo. As frações granulométricas estudadas foram inseridas em duas classes de tamanho, sendo a primeira classe passante em 297µm e retida em 249µm e a segunda classe passante em 149µm e retida em 105µm. Os resultados permitiram determinar um novo modelo semiempírico para VC, alcançando desvios menores que 10% para as velocidades preditas em relação aos valores de velocidades observadas experimentalmente. / The design of hydraulic systems of slurry transport demands a special attention due to coarse particles present a settling behavior inside the pipes. In this situation, the transport velocity should have order of magnitude sufficient to promote the suspension and the transport of particles, avoiding the solids deposition at the bottom of pipe. The transport of mineral slurries containing coarse particles was the primary goal of the thesis. A survey of the available literature was done and through the experimental tests could be possible to raise a data bank in order to develop a new best fit correlation for the critical velocity (VC) which included the particle shape effect, through the sphericity function. VC could be defined as the minimum velocity where a moving bed of particles takes place at the bottom of the horizontal pipe and it is slightly above the deposition velocity VD, which could be characterized by a bed of stationary particles at the bottom of pipe. The research was conducted using two recirculating pipe test rigs with transparent PVC pipe of 25.4mm and 50.8mm internal diameter with slurry concentrations from 8% up to 27% by volume. The material used was apatite and hematite concentrates and quartz mineral, clustered in two classes of size range (-0.297+0.210mm; -0.149+0.105mm), where the variables were: i) Head losses per meter of horizontal pipe (\'delta\'P/L), ii) Mean transport velocity (V), iii) solids distribution profile, iv) particle shape effect, through the sphericity function (\'psi\'), v) density of particles and liquid, vi) Volumetric concentration of slurries, vii) particles size and viii) pipe diameter. The critical velocity (VC), for each studied condition, was visually determined through the transparent sections of the pipes. The results have yielded a new semi empirical model to predict the critical velocity, yielding a deviation of less than 10% from the observed values of experimental data for VC.

Integral bridges are designed without expansion joints or bearings to eliminate the maintenance and repair costs associated with them. Thus, the expansion and contraction due to daily and seasonal temperature variations of the deck of the bridge are restricted by the abutments, causing the abutments to move cyclically towards and away from the granular material used as backfill. This movement results in a stress accumulation in the backfill retained by the abutments. The Discrete Element Method (DEM) was used was used to perform a numerical sensitivity analysis, investigating the effect of granular particle shape on the response of backfill material retained by integral bridge abutments.   Two DEM software suites were used to perform the simulations, namely STAR-CCM+, a commercial code, and Blaze-DEM, a research code under development at the University of Pretoria. Blaze-DEM makes use of Graphics Processing Unit (GPU) computing as opposed to traditional Central Processing Unit (CPU) computing. Blaze-DEM delivered computational times over 150 times faster than the equivalent simulation in STAR-CCM+. The results from the numerical sensitivity analysis showed that the particles with lower sphericities (higher angularities) experienced larger accumulations of stresses on the abutment as opposed to the more spherical particles. This was suggested to be a result of particle interlocking and reorientation. / Dissertation (MEng)--University of Pretoria, 2018. / Civil Engineering / MEng / Unrestricted

No description available.

<p>In an effort to better understand the physical mechanisms responsible for pool boiling heat transfer, an analytical model is developed that better describes the changing shape and size of a growing bubble. Indeed, any analysis of thermal transport due to nucleate pool boiling requires bubble frequency predictions which are intimately linked to bubble volume. The model is developed and validated for quasi-static bubble growth due to gas injection and for bubble growth due to vaporization within the heat-transfer controlled growth regime; it highlights the need to include the asymmetric nature of growing bubbles when modeling bubble growth.</p> <p>In addition, a numerical study of quasi-static bubble shape for both adiabatic bubble growth and vapour bubble growth provides insight into the dependence the bubble shape evolution has on the Bond number. In so doing, bubble profiles generated from a numerical treatment of the Capillary equation are benchmarked to quasi-static gas injected bubble formations and to heat-transfer controlled vapour bubble formations.</p> <p>The numerical treatment of bubble shape evolution leads to a simplifying bubble geometry for low Bond number applications. The geometric model accounts for bubble shape transformation throughout the bubble growth cycle including the necking phenomenon. An analytical model of quasi-static adiabatic bubble growth is accordingly developed based on the proposed low Bond number geometric model; it is coupled with a geometric detachment relation and a force balance detachment criterion that are dependent on the Bond number. The resulting predicted bubble growth characteristics, such as profile, volume, centre of gravity and aspect ratio, are validated with the benchmarked numerical treatment of the problem.</p> <p>Furthermore, the low Bond number geometric model is applied to bubble growth due to vaporization. In order to solve the mass-energy balance at the vapour bubble interface, a spherical surface area is commonly assumed. This leads to the need for correction factors and provides little insight into the physical mechanism responsible for bubble shape. In this study, the transitioning shape of a vapour bubble is considered in the integral analysis of the interfacial mass-energy balance. The model predicts the following bubble growth characteristics: profile, volume, centre of gravity, and aspect ratio.</p> / Doctor of Philosophy (PhD)