Made available in DSpace on 2014-06-11T19:34:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-02Bitstream added on 2014-06-13T18:45:51Z : No. of bitstreams: 1 rodrigues_hl_dr_guara.pdf: 9863359 bytes, checksum: 8b410bae9d6a8516cca10d9c51e2625b (MD5) / Universidade Estadual Paulista (UNESP) / As necessidades do mercado mundial têm motivado a pesquisa de novos materiais para a fabricação de ferramentas e, apesar da evolução no projeto e manufatura de máquinas ferramenta, da otimização constante dos processos de fabricação e da tendência de crescimento da automação industrial, estes materiais continuam como um dos fatores limitantes no processo de usinagem. A deposição de finas camadas de carbetos sobre um substrato de metal duro, ao final da década de 60, resultou em um aumento da velocidade de corte e da vida da ferramenta. Atualmente os revestimentos mais aplicados são o nitreto de titânio (TiN), o óxido de alumínio (Al2O3), o carbeto de titânio (TiC), o carbonitreto de titânio (TiCN) e o nitreto de alumínio titânio (TiNAl). Neste trabalho, com o objetivo de avaliar e relacionar os valores do desgaste de flanco e da rugosidade da peça usinada, foram realizados testes de usinagem em aço ABNT-1050 com ferramentas de metal duro revestido por carbeto de titânio (TiC), óxido de alumínio (Al2O3) e nitreto de titânio (TiN). Sob uma velocidade de corte de 297 m/min, profundidade de usinagem de 0,5 mm e avanço de 0,15 mm/rot, tornearam-se percursos de corte correspondentes aos seguintes tempos: 2,2 min, 4,1 min, 6,14 min, 7,9 min, 14,2 min e 18,6 min. Verificou-se que os mecanismos de desgaste por difusão, adesão e delaminação, atuantes nas superfícies de folga das ferramentas, influenciaram o acabamento superficial das peças usinadas, enquanto que a influência principal no crescimento do desgaste de flanco (VB) resultou da ação do mecanismo de desgaste por difusão. / The needs of the world market have improved the research of new materials for tools production. Besides the design and manufacturing of tool-machines, the constant optimization of production process and the growth tendency of industrial automation, these materials continue being one of the limiters factors in a machining process. The deposition of fine carbide layers on hard metal substrates, at the end of 60 s, resulted in a increase of the cutting speed and tool life. Now, the main coating materials are titanium nitride (TiN), aluminum oxide (Al2O3), titanium carbide (TiC), titanium carbon nitride (TiCN) and titanium aluminum nitride (TiNAl). In this work, several machining tests in a ABNT-1050 steel with hard metal tools coated by TiC, Al2O3 and TiN were been realized in order to evaluate the tool flank wear and the workpiece roughness. Cutting speed of 297 m/min, cutting depth of 0.5 mm and feed of 0.15 mm/rot were applied to machine cutting paths corresponding 2.2 min, 4.1 min, 6.14 min, 7.9 min, 14.2 min and 18.6 min. Diffusion, adhesion and delamination wear mechanisms were verified in the tool flank surface, having influence in the surface roughness of the machined workpieces, while the flank wear growth (VB) were resulted by the action of diffusion wear mechanism.

Orientador: Sérgio João Crnkovic / Banca: Marcelo dos Santos Pereira / Banca: Marcos Valério Ribeiro / Banca: Olivério Moreira de Macado Silva / Resumo: As necessidades do mercado mundial têm motivado a pesquisa de novos materiais para a fabricação de ferramentas e, apesar da evolução no projeto e manufatura de máquinas ferramenta, da otimização constante dos processos de fabricação e da tendência de crescimento da automação industrial, estes materiais continuam como um dos fatores limitantes no processo de usinagem. A deposição de finas camadas de carbetos sobre um substrato de metal duro, ao final da década de 60, resultou em um aumento da velocidade de corte e da vida da ferramenta. Atualmente os revestimentos mais aplicados são o nitreto de titânio (TiN), o óxido de alumínio (Al2O3), o carbeto de titânio (TiC), o carbonitreto de titânio (TiCN) e o nitreto de alumínio titânio (TiNAl). Neste trabalho, com o objetivo de avaliar e relacionar os valores do desgaste de flanco e da rugosidade da peça usinada, foram realizados testes de usinagem em aço ABNT-1050 com ferramentas de metal duro revestido por carbeto de titânio (TiC), óxido de alumínio (Al2O3) e nitreto de titânio (TiN). Sob uma velocidade de corte de 297 m/min, profundidade de usinagem de 0,5 mm e avanço de 0,15 mm/rot, tornearam-se percursos de corte correspondentes aos seguintes tempos: 2,2 min, 4,1 min, 6,14 min, 7,9 min, 14,2 min e 18,6 min. Verificou-se que os mecanismos de desgaste por difusão, adesão e delaminação, atuantes nas superfícies de folga das ferramentas, influenciaram o acabamento superficial das peças usinadas, enquanto que a influência principal no crescimento do desgaste de flanco (VB) resultou da ação do mecanismo de desgaste por difusão. / Abstract: The needs of the world market have improved the research of new materials for tools production. Besides the design and manufacturing of tool-machines, the constant optimization of production process and the growth tendency of industrial automation, these materials continue being one of the limiters factors in a machining process. The deposition of fine carbide layers on hard metal substrates, at the end of 60’s, resulted in a increase of the cutting speed and tool life. Now, the main coating materials are titanium nitride (TiN), aluminum oxide (Al2O3), titanium carbide (TiC), titanium carbon nitride (TiCN) and titanium aluminum nitride (TiNAl). In this work, several machining tests in a ABNT-1050 steel with hard metal tools coated by TiC, Al2O3 and TiN were been realized in order to evaluate the tool flank wear and the workpiece roughness. Cutting speed of 297 m/min, cutting depth of 0.5 mm and feed of 0.15 mm/rot were applied to machine cutting paths corresponding 2.2 min, 4.1 min, 6.14 min, 7.9 min, 14.2 min and 18.6 min. Diffusion, adhesion and delamination wear mechanisms were verified in the tool flank surface, having influence in the surface roughness of the machined workpieces, while the flank wear growth (VB) were resulted by the action of diffusion wear mechanism. / Doutor

No description available.

A study of heat exchanger tube wear has been completed. A simple theoretical model of elastic/plastic deformation has been developed and used in a new model of wear. Experimental results were used to corroborate the theoretical developments. A literature survey of wear mechanisms and wear models was conducted to provide the author with an opportunity to familiarize himself with current knowledge of the field of tribology. Experiments were conducted to simulate a heat exchanger tube/support wear system. For the first series of experiments, a simple impacting rig was used, while a second set was conducted using a much more accurate rig and facilities of the National Research Council of Canada's Tribology Laboratory. Modifications to the NRC rig were designed by the author to incorporate the specific specimen geometries. The main operating parameters of the test apparatus were varied in an effort to determine their effect on wear rates. Force and displacement data were collected and the normal and shear forces calculated, as was the work input. Comparison between the frictional work input and the measured wear showed that there was an approximately linear correlation between work and wear rates. Inspection of the surfaces of the worn specimens showed that a number of wear mechanisms operate in this wear system but that wear is primarily due to delamination and shear fracture. Also, it was noticed that the micro-surface geometry of the worn specimens has a consistent texture, regardless of magnitude and angle of impact between the tube and ring. A model of plastic contact deformation was developed to allow calculation of the contact parameters between two surfaces, given that the softer surface is repeatedly plastically deformed. This model says that repeated stress cycles lead to the introduction of residual stresses, which combined with work hardening of the material, lead the softer material to an elastic shakedown state. Once the typical asperity contact state is known, the typical stress distribution is calculated using Hertzian line contact stress formulae. A series of computer programs were developed to calculate the stress distribution beneath a sliding contact. The depth of maximum shear stress can then be found. This depth corresponds to the expected wear particle thickness. A wear sheet was assumed to form when the frictional work input is equal to the energy required to cause failure in ductile shear. A wear equation was then developed to predict the wear rate between a heat exchanger tube and its support. The final wear model has seen limited comparison with experimental results. The theoretical work input was found to be about 25% of the correlated bulk work. This indicates that the geometry assumptions of the model are quite reasonable. Unfortunately, the predicted wear rate was found to exceed the measured values by a factor of about 5000. If this empirical value is factored into the the wear model, then the predicted results are found to correspond well with the experimental values. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Suivant les applications, les composants électroniques passifs dont les connecteurs hyperfréquences évoluent dans des environnements vibratoires importants. Les sollicitations vibratoires induisent des micro déplacements qui se traduisent par l’apparition d’un fretting usure sur les contacts. Ces dégradations modifient les propriétés électriques et HF des connecteurs. Dans cette étude doctorale nous nous intéressons en particulier à l’influence du fretting usure sur le bruit de phase. Pour comprendre l’ensemble des mécanismes mis en jeu, une stratégie multi échelle basée sur le développement de 3 bancs d’essais V1, V2, V3 a été mise en place. Il est donc possible d’étudier les phénomènes macro et micro qui se produisent au sein d’un connecteur HF et d’un système composé de plusieurs connecteurs. Plusieurs phénomènes ont été mis en évidence, notamment la relation entre la résistance électrique de contact et le bruit de phase. En effet, l’expertise des contacts usés révèlent l’apparition d’oxydes au moment de l’augmentation du bruit de phase. Des lois comportementales permettant de prédire la durée de vie en bruit de phase d’un contact HF ont été établies en fonction de l’épaisseur de dépôt appliquée ou de l’amplitude de débattement imposé. De nouveaux axes de recherches ont été définis pour déterminer la durée de vie du contact en fonction de nouveaux paramètres comme la force normale. / In many applications passive electronic components such as microwave connectors operate in severe vibratory environments. Vibratory stresses induce micro displacements which result in surface damage by fretting-wear. Ultimately, this type of damage leads to a change in electric and HF properties of the concerned components. In this doctoral thesis the influence of fretting-wear on phase noise was studied. In order to identify all mechanisms involved in this type of damage, a multi-scale strategy based on the development of three test benches V1, V2 and V3 was established. As a result of this study it is possible to study the macro and micro phenomena that occur within RF connectors and in systems composed of multiple connectors. Several phenomena have been identified, in particular the relation between electrical contact resistance and phase noise. As a matter of fact, the analysis of worn contacts revealed that the presence of oxides coincides with an increase of phase noise. We established a description for the evolution of phase noise in an RF contact as a function of the applied coating thickness and the imposed sliding amplitude. Future areas of research have been proposed in order to determine in how far the lifetime of contacts is influenced by other key parameters such as normal force.

Indiana University-Purdue University Indianapolis (IUPUI) / Background: Increasing prevalence of dental erosion has been observed in many countries, in both children and adults. This condition is often associated with softening of the dental surface by acid exposure, which may lead to severe and irreversible damage. The use of fluoride, pit and fissure sealants, dental adhesives and more recently a resin infiltrant has been suggested to manage dental erosion. Objective: To compare the protective effect of a resin infiltrant and other resin-based materials against dental erosion/toothbrushing abrasion in vitro. Materials and methods: Bovine enamel and dentin slabs were prepared, embedded, flattened and polished. Dental erosion lesions were created using 0.01 M of hydrochloric acid (pH 2.3 for 30 sec) and treated with resin-based materials (HS: Helioseal pit and fissure sealant; SP: Seal and Protect dentin 78 sealant, and IC: Icon resin infiltrant) or fluoride varnish (FV: Duraphat). A no-treatment group represented the negative control (C). The specimens were subjected to an erosion-abrasion cycling model for a total of 10 days. Each cycling day consisted of 2 min immersion in 0.01M HCl, at room temperature, for 4 times; and toothbrushing with either of the abrasive suspensions (low and high, as previously determined by the radioactive dentin abrasivity method). Enamel and dentin surfaces were scanned at baseline, after treatment, at 5 days and at 10 days using an optical profilometer. Surface change (loss/gain) was determined by subtracting the treated area from the reference (protected) areas. Significance level of 5% was adopted for the statistical analysis. Results: No differences were found among groups at baseline, regardless of substrate. After treatment, surface deposition was found for all test groups except for IC, which did not differ from C. For enamel, at day 5, FV, HS and SP had less surface loss than C and IC (p<0.0008), which did not differ from each other (p=1.00). At day 10, similar trend was observed except for FV, which showed surface loss similar to C, when brushed with high abrasive suspension. High abrasive caused more surface loss than low abrasive only for C at day 5 (p=0.0117) and 10 (p=0.0162). For dentin, at day 5, FV, HS and SP had less surface loss than C and IC (p≤0.0001), which did not differ from each other (p=1.00). At day 10, HS and SP had less surface loss than C, IC, and FV (p<0.0001), and FV had less surface loss than C for low abrasive (p=0.0009). Overall, high abrasive had significantly more surface loss than low abrasive at 10 days (p=0.0280). Conclusion: HS was the most effective material protecting enamel and dentin from erosion-abrasion, followed by SP. FV offered limited protection, while no benefit was observed for resin infitrant IC.

The test evaluates wear resistance of quenched and tempered steels of 8 grade materials. The steels are low alloyed carbon steels within a hardness range of 120HV to 600HV. The carbon content in the range of 0.3-0.6%. The wear tests were undertaken in a laboratory at SSAB in Oxelösund with a newly designed wear test machine. The wear performance was evaluated by abrasive material clinkers and slag in Room temperature as well as High temperature at 400°C. Eight samples are used for each test, the samples are placed inside the drum with sample holders. The wear test performed by 217mm diameter drum rotate over the two-horizontal bar at 37 RPM, thus creating sliding, rolling and some impact over the surface of the materials. Investigations were performed by weight measurements of the samples, hardness measurements at room temperature, after the 400°C test, and at high temperatures up to 400°C, and light optical microscopy examinations. The results show that wear rate at Room temperature depends on hardness of material and hardness of abrasive material. The wear rate at high temperature 400°C show that wear rate depends on alloying element and the tempering temperature of the material.

Since the beginning of the last century, many studies have been performed in order to improve our understanding on the milling process. Recently, Mishra and Rajamani (1992) applied the Discrete Element Method (DEM) to solve the milling problem. Since then, this method gained considerable success due to its ability to predict load motion and power draw by tumbling mills as affected by operating conditions. The application of this method at an industrial stage requires a more rigorous validation in order to produce realistic output. Lifter profiles play a key role in the performance of tumbling mills since they influence the motion of mill charge. Since lifters change profiles during their useful life due to wear, the performance of tumbling mills will correspondingly vary as a function of time. There is therefore a need to predict forces and wear on mill lifters in order not only to chose or design an initial lifter profile which optimizes tumbling mills performance over the lifters’ useful life but also to evaluate lifter replacement time and type and also modifications which can be performed on lifters and/or operating mill conditions in order to extend the lifters’ useful life. Despite the importance related to this subject, few works has been done in this field. In this thesis, we firstly assess the ability of the Discrete Element Method to model the tangential and normal forces exerted by the mill charge on lifters. Data from an experimental two-dimensional mill designed in order to record the normal and tangential forces exerted on an instrumented lifter were available. The measured results obtained at different speeds and percentages of filling have been compared to the Discrete Element Method simulated results in the same conditions. A good agreement has been found between the experimental and the simulated results in terms of toe, shoulder positions and amplitude of forces. After this validation of the DEM, we secondly assess the ability of this method to predict the wear of lifters in dry milling conditions. We derived a mathematical wear equation describing the removal of materials from lifters which takes into account all types of wear occurring in dry milling environment. We introduce a new approach to implement this equation in the DEM code in order to produce realistic simulated profiles. Our new method developed has been tested against laboratory and industrial data of evolving lifter profiles due to wear. Good agreement has been found between the simulated and the measured profiles. The variation of the load behaviour as a function of lifter wear in industrial tumbling mills studied was also investigated in this thesis. The objectives were to improve the understanding of the grinding process and quantify the variation of load behaviour as a function of lifter wear. Lifter modifications were also explored in order to extend lifters useful life. An attempt was also made in this thesis to derive, from the description of the load behaviour, equations in order to predict the wear of lifters without using the Discrete Element Method. Equations derived show the difficulty to use this approach. Success in this case was achieved only in a particular case where no significant changes occur in the load behaviour as a function of lifters wear. This finding confirms the DEM as the adequate tool to model forces and wear of tumbling mill lifters. The results obtained are of great economical significance since they can improve the profitability of mineral processing plants. A step forward in the use of the DEM not only to design milling equipments but also to improve the understanding, optimise and quantify the change occurring as a function of lifters wear was achieved.

<p>Wear of hardmetals is a complicated topic because the wear resistance and the wear mechanisms are influenced by microstructural factors. Although edge wear resistance has a vital importance, most of the researches made in laboratories are related to flat wear resistance using coarse abrasive paper. This situation produces problems with the prediction of abrasive wear behaviour and with the estimation of the lifetime of cutting edges of different kinds of tooling.</p><p>Several studies have been done in order to clarify edge wear behaviour. It has been published correlations of the edge toughness to the load and to the bulk fracture toughness. In those publications coarse abrasive or Vickers indenter were used.</p><p>In the present research, edge shaped specimens of WC-6wt%Co grades were investigated. In order to compare the obtained results for flat sliding and edge wear behaviour two test arrangements, pin on flat disc and edge on flat disc were employed. The specimens were tested using 120, 320, 800 and 2400 mesh SiC abrasive paper and the worn surfaces were investigated using SEM instrument to evaluate wear mechanisms. The edge wear was observed was discussed in relation to wear mechanisms investigated and correlated to the flat wear behaviour.</p><p>The obtained results showed limited applicability of the results obtained with the pin on the flat disc test arrangement for prediction of the edge wear resistance, especially in the case when size of the abrasive particles is close to the WC grain size. However, both edge and flat wear results were similar in; 1) large WC grain sized hard metals wore more than fine grain sized against coarse abrasive paper whereas the reverse occurred against fine abrasives, and 2) wear mechanisms were mainly ploughing (or grooving) for fine grain sized hardmetals in all cases, whereas wear mechanisms changed from ploughing to binder removal and carbide pull-out going from coarse to fine abrasive paper.</p>

Wear of hardmetals is a complicated topic because the wear resistance and the wear mechanisms are influenced by microstructural factors. Although edge wear resistance has a vital importance, most of the researches made in laboratories are related to flat wear resistance using coarse abrasive paper. This situation produces problems with the prediction of abrasive wear behaviour and with the estimation of the lifetime of cutting edges of different kinds of tooling. Several studies have been done in order to clarify edge wear behaviour. It has been published correlations of the edge toughness to the load and to the bulk fracture toughness. In those publications coarse abrasive or Vickers indenter were used. In the present research, edge shaped specimens of WC-6wt%Co grades were investigated. In order to compare the obtained results for flat sliding and edge wear behaviour two test arrangements, pin on flat disc and edge on flat disc were employed. The specimens were tested using 120, 320, 800 and 2400 mesh SiC abrasive paper and the worn surfaces were investigated using SEM instrument to evaluate wear mechanisms. The edge wear was observed was discussed in relation to wear mechanisms investigated and correlated to the flat wear behaviour. The obtained results showed limited applicability of the results obtained with the pin on the flat disc test arrangement for prediction of the edge wear resistance, especially in the case when size of the abrasive particles is close to the WC grain size. However, both edge and flat wear results were similar in; 1) large WC grain sized hard metals wore more than fine grain sized against coarse abrasive paper whereas the reverse occurred against fine abrasives, and 2) wear mechanisms were mainly ploughing (or grooving) for fine grain sized hardmetals in all cases, whereas wear mechanisms changed from ploughing to binder removal and carbide pull-out going from coarse to fine abrasive paper.