As superligas à base de cobalto são bem conhecidas por sua excelente resistência ao desgaste. Muitas pesquisas reportadas na literatura abordam o comportamento do desgaste destas ligas, seja no desgaste por deslizamento, erosivo ou abrasivo. Não obstante, o desgaste microabrasivo destas ligas não tem sido muito investigado, apesar dos danos causados por este tipo de solicitação. O comportamento do desgaste microabrasivo de três superligas à base de cobalto: a) 48% Co, 29 %Cr, 19 % Fe; b) uma liga com composição química próxima à da liga comercial Tribaloy T400 (Co 56 %, Cr 8.5%, Mo 29% Si 3.3 %) e c) uma liga com composição próxima à da liga comercial Stellite 6 (Co 64%, Cr 24 %, W 4.2 %, C 2,3%) foram investigadas. Os ensaios de microabrasão foram conduzidos com três abrasivos SiO2, Al2O3, e SiC em suspensão em água destilada, com concentração de 0,1 g/cm3. A carga aplicada foi de 0,3 N, a velocidade angular 20 rpm e a distância total de deslizamento, 48 metros. A análise das superfícies desgastadas por microscopia óptica, eletrônica de varredura e por perfilometria de contato mostraram que o tamanho, forma e dureza dos abrasivos podem influenciar significativamente os coeficientes de desgaste. Os ensaios conduzidos com partículas abrasivas de SiC e Al2O3 apresentaram maiores coeficientes de desgaste que os conduzidos com partículas de SiO2. A Liga Co-Cr-Fe mostrou os maiores coeficientes de desgaste quando comparada com as demais ligas, devido à baixa fração volumétrica de partículas de segunda fase, duras, precipitadas em sua microestrutura. Durante os ensaios, as três ligas, ensaiadas com os três diferentes abrasivos, apresentaram coeficientes de desgaste crescentes com o aumento da dureza do abrasivo; observou-se uma variação linear dos coeficientes de desgaste com a razão entre a dureza do abrasivo (Ha) e a dureza composta da liga (Hs), com R2 = 0.74. O micromecanismo dominante em todos os ensaios foi o desgaste abrasivo a dois corpos (grooving wear). A liga com composição próxima à da liga comercial Tribaloy T400, contendo fases de Laves dispersas em sua microestrutura, apresentou uma transição de micromecanismo de desgaste dúctil para frágil, quando submetida a ensaios com partículas abrasivas de Al2O3. Assim sendo, o volume de material removido nesta liga foi ligeiramente maior que o observado no ensaio com partículas de SiC. Na liga contendo baixa fração volumétrica de partículas de segunda fase, com matriz constituída por Co (CFC), observou-se uma camada subsuperficial nanocristalina de aproximadamente 1 µm de espessura, severamente deformada, imediatamente abaixo da superfície desgastada. Concluiu-se que o desgaste microabrasivo induziu a recristalização a frio do material encruado, com formação de grãos equiaxiais de dimensões nanométricas. / Cobalt alloys are well known for their excellent wear resistance. Many investigations are reported in literature related to the behavior of erosive, abrasive or sliding wear of these alloys. Nevertheless, the micro-abrasive wear of these alloys has not been thoroughly investigated, despite the damage caused by this type of wear. The microabrasive wear behavior of three cobalt alloys: a) 48 wt.% Co, 29 wt.% Cr, 19 wt.% Fe; b) an alloy with chemical composition close to Tribaloy T400 (56 wt.% Co, 8.5 wt.% Cr, 29% wt. Mo, 3.3 wt. %Si) and c) an alloy with chemical composition close to Stellite 6 (64wt.% Co 24 wt.% Cr, 4.2 wt.% W, 2,3 wt.% C were investigated. The tests were carried out using three 0,1 g/cm3 slurries composed by SiO2, Al2O3, and SiC particles, in suspension in distilled water. The applied load was 0.3 N, the rotational speed 20 rpm and the total sliding distance 48 m. Analysis of the worn surfaces of the tested alloys by Optical Microscopy, Scanning Electron Microscopy and Contact Stylus Profilometry showed that abrasive size, shape and hardness could significantly influence the wear coefficients. The tests carried out with SiC and Al2O3 slurries resulted in greater wear rates than those carried out in SiO2 slurry. Stellite 250, showed the greatest wear coefficient, compared to the two other experimental alloys, due to a very low volume fraction of hard second phase particles in the microstructure. Wear coefficients decreased with increasing abrasive particles hardness. An approximate linear correlation with the ratio between the hardness of the abrasives (Ha) and the compound hardness of the alloys (Ha) with a correlation factor R2= 0.74. The dominant wear micromechanism observed in all tests was two-body abrasion (grooving wear). The modified T400 alloy, containing Laves phase showed a transition from ductile to brittle wear mechanisms when testing with alumina slurries. The worn volume was slightly greater than the one observed with SiC. A severely deformed nanocrystalline layer was identified, immediately below the worn surface. It was concluded that cold recrystallization of the work-hardened material occurred, with the formation of nano sized equiaxed grains.

Over the years, different lubricants have been used to operate hip simulators. The current applicable ISO standard (ISO 14242-1:2002) recommends the use of 25% calf serum diluted with deionised water. The standard further recommends that the fluid be changed and the acetabular cup be weighed every 500 000 cycles. This procedure results in a loss of both the third body wear particles and the wear pattern. The purpose of this study was to develop a synthetic lubricant that would map the viscosity and lubricity properties of joint fluid (“synovial fluid”) over the whole duration of a simulator test, which is typically five million cycles. The first objective of this study was to find the effect of temperature increase on the viscous and lubricative properties of joint fluid retrieved from both primary and revision patients prior to surgery. The lubricity tests were done on a Linear-Oscillation Test Machine (SRV machine). Three test temperatures were used namely 38ºC, 50ºC and 60ºC. The load at failure and the average coefficient of friction were parameters measured during these tests. A decrease in the load at failure was found for an increase in test temperature, while the coefficient of friction stayed relatively stable. The viscosity tests were done using a Brookfield Viscometer. The three test temperatures mentioned above, were copied. The joint fluid tested showed pseudoplastic flow behaviour. An increase in the viscosity as a function of test temperature increase and a magnitude of shear rate was observed. The second objective of this study was to develop a synthetic lubricant that had the same average properties than that found for the retrieved joint fluid. A mixture of three different chemicals, namely Poloxamer 188, Xanthan Gum and Lube Boosterâ II was used to map the viscous and lubricative properties of the joint fluid. A comparative test using the synthetic lubricant and bovine serum was performed in a custom-built simulator. Wear debris was sampled at 500 000 cycle intervals up to 4 500 000 cycles. During these intervals the bovine serum stations were drained and washed with deionised water, but not stripped and weighed as specified in the ISO standard. This was done intentionally to preserve the wear pattern during the entire test. The synthetic lubricant stations were not stripped or drained during these intervals. This ensured that the wear pattern was maintained and that the effect of accumulative wear could be investigated throughout the duration of the test. The wear debris from the test was then compared to wear debris retrieved from scar tissue of revision patients. The wear debris that was found in the scar tissue retrieved from patients was similar in shape and size to that which was found in the simulator using bovine serum and the synthetic lubricant. It can thus be concluded that an acceptable lubricant had been developed to replace the current test medium in the simulators. / Dissertation (MEd (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted

Structural Health Monitoring (SHM) systems were developed to evaluate the integrity of a system during operation, and to quickly identify the maintenance problems. They will be used in future aerospace vehicles to improve safety, reduce cost and minimize the maintenance time of a system. Many SHM systems were already developed to evaluate the integrity of plates and used in marine structures. Their implementation in manufacturing processes is still expected. The application of SHM methods for complex geometries and welds are two important challenges in this area of research. This research work started by studying the characteristics of piezoelectric actuators, and a small energy harvester was designed. The output voltages at different frequencies of vibration were acquired to determine the nonlinear characteristics of the piezoelectric stripe actuators. The frequency response was evaluated experimentally. AA battery size energy harvesting devices were developed by using these actuators. When the round and square cross section devices were excited at 50 Hz frequency, they generated 16 V and 25 V respectively. The Surface Response to Excitation (SuRE) and Lamb wave methods were used to estimate the condition of parts with complex geometries. Cutting tools and welded plates were considered. Both approaches used piezoelectric elements that were attached to the surfaces of considered parts. The variation of the magnitude of the frequency response was evaluated when the SuRE method was used. The sum of the square of the differences was calculated. The envelope of the received signal was used for the analysis of wave propagation. Bi-orthogonal wavelet (Binlet) analysis was also used for the evaluation of the data obtained during Lamb wave technique. Both the Lamb wave and SuRE approaches along with the three methods for data analysis worked effectively to detect increasing tool wear. Similarly, they detected defects on the plate, on the weld, and on a separate plate without any sensor as long as it was welded to the test plate.

O objetivo deste estudo foi avaliar a prevalência de lesões cervicais não cariosas (LCNC), além de observar possíveis fatores de risco relacionados ao seu desenvolvimento. Pacientes de ambos os gêneros e com idade a partir de 18 anos, da Clínica Integrada da Faculdade de Odontologia do Recife, foram examinados, totalizando 1110 dentes, onde se buscou a presença de LCNC, facetas de desgaste e prematuridades oclusais. Os pacientes também foram investigados quanto a presença de problemas gastrintestinais, hipersensibilidade dentinária, hábitos parafuncionais e a dieta utilizada. A presença de LCNC foi observada com auxílio de sonda periodontal posicionada paralela ao longo eixo do dente, e a severidade, medida pelo índice de desgaste dental (IDD) de Smith e Knight, utilizando a mesma sonda, porém, perpendicular ao longo eixo do dente. Posteriormente foi observada a presença de contatos prematuros em RC ou interferência nos movimentos de lateralidade e protrusão. A presença de LCNC foi encontrada em 72,5% dos indivíduos, com maior freqüência no primeiro pré-molar, seguido do segundo prémolar e primeiro molar. Foi observada relação entre LCNC e a presença de facetas de desgaste, de contatos prematuros e interferências. Nos dados referentes ao questionário, não foram encontradas diferenças significantes, entre os grupos com e sem lesão, quanto a idade, gênero, dieta, problemas gastrintestinais, hábito parafuncional ou hipersensibilidade dentinária. Concluiu-se que as LCNC estão associadas à facetas de desgaste e contatos oclusais parafuncionais, embora, novos estudos sejam necessários para esclarecer seu complexo desenvolvimento. / The aim of this study was to observe the prevalence of noncarious cervical lesions (NCL),and the risk factors involved in this development. Patients of both genders and over eighteen years old, were examined, with 1110 teeth where the presence of NCL, wear facets and oclusal prematuritiess were sought. The patients also given a questionnaire about age, gender, gastrointestinal problems, diet, dentin hipersensitivity and parafunctional habits. The NCL was detected by a periodontal probing located parallel to the long axis of the tooth, and its severity was evaluated by the Smith and Knight tooth wear index (TWI) by using the same periodontal probe, but perpendicular to the long axis. Later, the presence of premature contacts at centric relation (CR) or interference in lateral and protrusive movements was observed. NCL was found in 72,5% of the individuals, with greater frequency in the first premolars, followed by seconds premolars and then first molars. It was observed relationship between NCL and wear facets and between NCL and premature or interferents contacts. In the data gotten fron the questionnaire, no significant diference for age, gender, diet, gatrointestinals problems, parafunctional habits or dentin hipersensitiveness, between the groups with and without lesions. We conclude that NCL are associate with wear facet and parafunctional oclusal contacts, inspite of new studies must to be necessary to explain their complex development.

Wear is an important phenomenon that occurs in all the polymer applications in one form or the other. However, important links between materials properties and wear remain illusive. Thus optimization of material properties requires proper understanding of polymer properties. Studies to date have typically lacked systematic approach to all polymers and wear test developed are specific to some polymer classes. In this thesis, different classes of polymers are selected and an attempt is made to use multiple scratch test to define wear and to create a universal test procedure that can be employed to most of the polymers. In each of the materials studied, the scratch penetration depth s reaches a constant value after certain number of scratches depending upon the polymer and its properties. Variations in test parameters like load and speed are also studied in detail to understand the behavior of polymers and under different conditions. Apart from polystyrene, all the other polymers studied under multiple scratch test reached asymptotes at different scratch numbers.

This licentiate thesis has the main focus on evaluation of the wear of coated and uncoated polycrystalline cubic boron nitride cutting tool used in cutting operations against hardened steel. And to exam the surface finish and integrity of the work material used. Harder work material, higher cutting speed and cost reductions result in the development of harder and more wear resistance cutting tools. Although PCBN cutting tools have been used in over 30 years, little work have been done on PVD coated PCBN cutting tools. Therefore hard turning and hard milling experiments with PVD coated and uncoated cutting tools have been performed and evaluated. The coatings used in the present study are TiSiN and TiAlN. The wear scar and surface integrity have been examined with help of several different characterization techniques, for example scanning electron microscopy and Auger electron spectroscopy.   The results showed that the PCBN cutting tools used displayed crater wear, flank wear and edge micro chipping. While the influence of the coating on the crater and flank wear was very small and the coating showed a high tendency to spalling. Scratch testing of coated PCBN showed that, the TiAlN coating resulted in major adhesive fractures. This displays the importance of understanding the effect of different types of lapping/grinding processes in the pre-treatment of hard and super hard substrate materials and the amount and type of damage that they can create. For the cutting tools used in turning, patches of a adhered layer, mainly consisting of FexOy were shown at both the crater and flank. And for the cutting tools used in milling a tribofilm consisting of SixOy covered the crater. A combination of tribochemical reactions, adhesive wear and mild abrasive wear is believed to control the flank and crater wear of the PCBN cutting tools. On a microscopic scale the difference phases of the PCBN cutting tool used in turning showed different wear characteristics. The machined surface of the work material showed a smooth surface with a Ra-value in the range of 100-200 nm for the turned surface and 100-150 nm for the milled surface. With increasing crater and flank wear in combination with edge chipping the machined surface becomes rougher and showed a higher Ra-value. For the cutting tools used in milling the tendency to micro edge chipping was significant higher when milling the tools steels showing a higher hard phase content and a lower heat conductivity resulting in higher mechanical and thermal stresses at the cutting edge.

When operating hydraulic mining excavators the loading equipment is exposed to harsh conditions which lead to extensive wear of the equipment, especially the bucket and bucket teeth. Simulations are used to better understand the wear development and to evaluate new methods to operate excavators more efficiently. At the Aitik mine, operated by the high-tech metal company Boliden Mines, hydraulic excavators are used when loading the mined ore. One of the hydraulic excavators used at Aitik is the Komatsu PC7000. In this master thesis, a simulation model for the hydraulic excavator Komatsu PC7000 was developed with the simulation software LS-DYNA. This model consists of multi rigid body dynamics to describe the motion of the excavator and a granular material model to describe the rocks loaded into the bucket of the excavator. Simulations with two different types of granular material models have been utilized to study the wear development of the bucket. One of the models (bonded DE model) uses bonded discrete elements to describe the large rocks and single discrete elements are used to describe smaller rocks. This model is compared to the current FE-DE model which is being used today at Boliden. This model uses finite elements (FE) to model the larger rocks and discrete element spheres (DES) for smaller rocks. By using the bonded DE method a 71\% reduction in simulation time could be achieved. This can be partly explained by the reduction of the number of elements included in the rock pile.  Archard's wear law was used to numerically describe the wear development of the bucket. When simulating the wear a total of 30 bucket fillings were performed with the excavator. This was done with both the bonded DE method and the FE-DE method. In this wear study, the inside of the bucket was of interest. The resulting simulated wear map was compared to experimental measurements from which the plate thickness of the bucket had been measured two times to obtain the wear depth of some points inside the bucket. The experimental measurements and two 3D scanned point clouds were used to determine the wear depth inside the bucket. Results from the simulation showed that the wear is concentrated to the center of the bucket while less wear is concentrated to the sides of the bucket. With the bonded DE method the wear appeared to be more evenly distributed inside the bucket while the wear from the FE-DE method appeared in spots inside the bucket. The experimental results also showed that the wear was more extensive in the center of the bucket and also in the back of the bucket. Both simulation methods also showed that the wear was concentrated to the back of the bucket. From the simulations, it was also seen that the behavior of the material flow differed between the two methods. In the bonded DE method the material flow had more sliding behavior while the material flow in the FE-DE method had more rolling behavior. This could also be the reason why the bonded DE method captures the wear more evenly. The rolling behavior seen in the FE-DE method leads to more impact wear which is not captured by Archard's wear law. Overall, the bonded DE method leads to a big reduction in simulation time which is favorable when it comes to simulation. The larger rocks will have simpler shapes without sharp corners. However, the method allows for a more complex shape than just an ordinary sphere which is the simplest and most common shape to describe granular material. The bonded DE method also allows for easier configuration of contact definition since fewer contact interfaces must be added to the model. Furthermore, the post-processing of wear in LS-DYNA was facilitated since the wear does not have to be divided into two wear collectors for FE elements and DE elements.

In sheet metal forming (SMF) of materials such as stainless steels there is a major problem with transfer and accumulation of sheet material to the metal forming tool surface. The problem is known as galling; a kind of severe adhesive wear, which results in severe scratching of produced parts. In this thesis, galling observed in contacts between tool steels and stainless steel sheets under lubricated sliding conditions was studied, focusing on the early stage of galling. It was found that changes in friction cannot be used as galling indicator in the early stage of galling because transfer and accumulation of sheet material happens even though friction is low and stable. The progression of galling is influenced by tool steel damage occurring around the tool steel hard phases caused by sheet material flow, which results in formation of wear-induced galling initiation sites. A correlation between the critical contact pressure to galling and sheet material proof stress was found. Galling happened at lower pressures for sheet material with lower proof stress possibly due to easier sheet material flow, resulting in quicker tool damage. Material transfer and tool steel damage were delayed for tool steels comprising homogenously distributed, small and high hard phases. Additionally, the galling resistance was higher for tool steels with higher hardness due to decreased tool steel damage. In a comparison between observations of the worn tool surfaces after wear tests and calculations in FEM it was found that material transfer did not take place at regions with highest contact pressures but at regions with highest plastic strains. The results obtained in this thesis indicate that tool steel damage and sheet material flow occurring in the contact during sliding are important factors influencing galling.

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Syftet med detta arbete är att undersöka om det är möjligt att upptäcka om ett barn fallit i vattnet. För att undersöka det har ett system har utvecklats för att upptäcka ett fall i vatten har skett, med hjälp av en smartklocka och smarttelefon. Systemet består av en algoritm för att upptäcka fall i vatten och två applikationer, en på smartklockan och en på smarttelefon. Applikationen på smartklockan implementerar algoritmen som utvecklats under arbetet för att upptäcka om ett fall i vatten har skett och skickar det vidare till den uppkopplade smarttelefonen. Vid detektion av ett fall i vattnet varnas föräldern via sin smarttelefon. Arbetet resulterade i att algoritmen tillförlitligt kunde upptäcka om ett fall i vatten har skett. / The purpose of this paper is to investigate the possibility of detecting if a child has fallen into a pool. To investigate this a system has been developed, using a smartwatch and smartphone. The system contains an algorithm to detect falls in water and two applications has been developed, one on the smartwatch and the other on the smartphone. The application on the smartwatch implements the algorithm to detect if a fall in water has occurred and communicates this with the smartphone. When a fall in the water is detected the parents gets an alert on their smartphone. The work resulted in an algorithm which can reliably detect a fall in water.