Extrusion is a metal forming process used extensively in industry to produce different structural, mechanical, electrical, architectural, automotive and aerospace application parts. Currently after extrusion, the rod is subjected to environmental wear due to long storage time and hence requires an additional cleaning process before further use. This cleaning process can be eliminated by extruding a polymer coated metal rod workpiece such that the polymer coating is sustained on the final product after the extrusion process. In the present research study a new upper bound analytical model is developed to predict the forces required to conduct extrusion of a polymer coated metal rod successfully. The search for the lower upper bound power functional is modeled as a non linear optimization problem. Optimizing the functional also determines the set of constraints defining the shape of rigid plastic deformation boundaries and the final coating thickness. Also an upper bound analytical model was developed to predict forces for failure of the polymer coating during the extrusion. Both the analytical models for successful and failed extrusion are compared to obtain critical die angle which can provide tooling and process design guidelines. Finite element analysis simulations were modeled using commercially available software package, ABAQUS. Predictions of FEA simulations were in good agreement with published results and with the predictions of analytical model developed in this study.

Recently, with the escalating demands for optical communication, the need to use broadband laser light sources in optical communication network system has increased. Henceforward, the broadband characteristes of Cr4+:YAG crystal fiber possess signifies its indispensability. Furthermore, Yb3+:YAG-silica also has its advantages in high power laser domain. In this thesis, the crystal fiber grown by the laser heated pedestal growth method is used as the laser gain medium with fused silica packaging technique. Cr4+:YAG double-clad crystal fiber with a core diameter as small as 11 £gm was achieved. Moreover, a Yb3+:YAG-silica layer was formed due to the strong inter-diffusion between silica capillary and Yb3+:YAG crystal. When the silica all diffused into the Yb3+:YAG, a Yb3+:YAG-silica fiber with 125-£gm core was obtained with waveguide structure. By directly coating the optical thin films onto the end faces of the two types of fibers, the laser configuration is compact and cost effective. Besides, heat dissipation is also improved. By Cu-Al alloy packaging, a record-low Cr4+:YAG double-clad crystal fiber laser was achieved with threshold of 0.75 mW and a record-high slope efficiency of 6.9% at room temperature. And we also successfully fabricate the Yb3+:YAG-silica fiber laser with low threshold (100 mW) and high efficiency (67.2%) at room temperature. In fiber laser development, we have successfully fabricated the coating of high-reflective thin films which match the faces of fiber heterostructure (single cladding and double cladding structures). It forms a cavity with anti-reflectivity for pumping wavelength and high-reflectivity for lasing wavelength. For these reasons, low threshold, high slope efficiency, and stable laser output have been achieved. Finally, through different thin-film designs, the strain effect between thin film and heterosubstrate is significantly reduced, which facilitates the realization of high performance fiber lasers.

This study aims to experimentally explore the possibility to join the two pieces of low-carbon steel and Cu-Ni alloy as the cladding material into a thick clad steel plate during a Friction Stir Lap Welding¡]FSLW¡^process without a probe. Two methods are employed to enhance the welding strength. Firstly, a layer of nickel is coated on the low-carbon steel to prevent it from oxidizing during the welding process. Secondly, the surface of the low-carbon steel is knurled to increase the contact area between the welding surfaces. Experimental results show that Ni-coating can effectively prevent the generation of oxidation and improve the welding strength. According to the tensile test using a plate of Cu-Ni alloy with a thickness of 4 mm, the welding strength of the clad steel plate with Ni-coating is about 2.3 times greater than that without Ni-coating. Moreover, according to the impact test, the clad steel plate with Ni-coating can absorb more impact energy than that without Ni-coating. This difference increases with increasing thickness of the plate. It is also found that the welding strength at the center of joints using the Ni-coating is greater than that at the substrate of copper-nickel alloy. For the clad steel plate with knurling, since it is difficult to fill the gap between the patterns of knurling, the increase in the contact area between the welding surfaces has been offset. Hence, the welding strength of the clad steel plate with knurling is less than that with Ni-coating.

<p>The influence of particle shape of coating pigments on theirpacking ability and on the flow properties of coating colourshas been investigated. The particle shapes considered werespherical, flaky and acicular (needle-shaped). In the case ofsuspensions containing monodisperse spherical polystyreneparticles, a concentration gradient appeared in the filter cakeforming during filtration under static conditions. Such agradient, monitoredby non-destructive magnetic resonanceimaging (MRI), is not accounted for in the traditionalfiltration theory used in coating technology. Good agreementwas found between a literature model describing filtrationthrough a compressible filter cake and the concentrationgradients measured by MRI. According to this model, the scaledconcentration gradient was the same at all times.</p><p>For flaky (mainly kaolin) and acicular (aragonite)particles, a rapid method was evaluated to estimate a shapefactor of the pigment particle. Generalised mathematical modelsof oblate and prolate spheroids were applied to reduce thethree geometrical dimensions of the particle to two, the majoraxis and the minor axis. The shape factor, which is mass-based,was derived from a comparison between the results obtained bytwo different size-assessment instruments, viz. the Sedigraphand an instrument using light scattering. This yields a shapefactor distribution as a function of equivalent sphericalparticle size, but the results are uncertain for small particlediameters, below 0.2 µm. Good agreement was obtainedbetween the shape factor and a mass-based aspect ratio obtainedby image analysis, but the rapid method is generally moreaccurate for flaky than for acicular particles.</p><p>Results obtained by capillary viscometry showed that therewas a relationship between the viscosity at high shear rates(>10⁵s^-1) and the shape factor, but that it was notsufficient to use the median value of the shape factor toachieve proper information. A more complete evaluation requiresknowledge of the shape factor distribution, which is also givenin part by the method mentioned above. However, a large medianshape factor was related to a high high-shear viscosity.Non-Newtonian entrance pressure losses were sometimessignificant in capillary viscometry, indicating that it wasinappropriate to measure the shear viscosity with only onecapillary. Such effects were however relatively much morepronounced in slit die viscometry, especially in the case ofacicular particles, where the aspect ratio was a crucialparameter. The influence of the shape factor of kaolinparticles on the non-Newtonian entrance pressure losses over aslit die was surprisingly small. The high-shear viscosity ofcoating suspensions based on different pigments correlated withthe median pore size of the corresponding coating layer ratherthan with the porosity.</p><p><b>Keywords</b>: Aspect ratio, capillary viscometry, coatingcolour, filtration, particle packing, pigment, pore structure,rheology, shape factor, slit die viscometry, spheroid.</p>

<p>This study focuses on the wear of piston rings in a hydraulic radial piston motor. The piston ring has to satisfy increasing demands for reliability and longer service life. It has two contacting surfaces, the face and the flank, and operates under a boundary lubrication state.</p><p>This first part of the project aimed to detect and characterise piston ring wear. Measurement by weighing gives an overall value for wear defined as loss of mass. Two-dimensional form and surface roughness measurements show the distribution of wear on the piston ring face in contact with the cylinder bore and the piston ring flank in contact with the piston groove. Three-dimensional analyses, both quantitative and qualitative, allow the wear mechanisms to be identified.</p><p>The wear of piston rings from an actual hydraulic motor was characterised. As well, rig testing was performed in two different test rig set-ups, one simulating the sliding movement of the piston ring and the other the tilting movement at the end of the strokes. Wear during the running-in period was investigated, and the findings indicate that the period when this takes place is of short duration. In the long term, mild wear makes the surfaces smoother than they were when new, resulting in a very low wear coefficient. Significant levels of wear were measured on both contacting surfaces of the piston ring. In cases in which the flank exhibits more wear than the face, the wear on the flank can be reduced by proper design of the piston groove.</p><p>The second part of the project aimed to evaluate use of a textured surface for the cylinder bore counter surface and a coated surface for the piston ring. Three modelling experiments were performed to characterise the friction and wear properties under lean boundary lubrication conditions. Under such conditions, textured surfaces have the advantage of retaining more lubricant and supplying it over a longer time. Stable friction was also a distinctive feature of the textured surface. Use of a coating could also possibly reduce the amount of wear. Though a smooth surface, like a polished one, is hard to beat for a working texture, a coated surface is far ahead of a smooth uncoated one. Different manufactured and commonly used cylinder bore surfaces, including textured ones, were evaluated in the sliding movement test rig. That allowed favourable wear properties, such as lowest wear coefficient, to be determined with the use of a roller burnished surface.</p><p>A final part of the research involved simulating wear on the piston ring face throughout the entire service life of a hydraulic motor. This allowed us to determine the roles of surface roughness and coating in prolonging service life and achieving acceptable and secure piston ring operation. The model is simple and realistic, but still needs to be refined so as to correspond even better to reality.</p>

Thesis (doctoral)--Göteborg University, 2003. / Includes bibliographical references (p. 137-157).

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xiv, 137 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 106-109).

Flexographic printing is a process that employs a flexible printing form and low viscous ink, often water-based. The flexible printing form is favourable for printing on rough surfaces, but the high surface tension of the ink may cause printability problems. This work has focused on the interaction between paper/paperboard coating and water-based flexographic ink, aimed at increasing the knowledge about the printing process in form of physical/chemical parameters that are important for ink setting. The effects of printing conditions on print quality, such as printing pressure and temperature, have also been in focus. The work has shown that fluids of different polarities, i.e. different dipole moments, behave differently when being absorbed by a coating layer. Due to their chemical compatibility to the coating layer, fluids with large dipole moment fill the pore matrix of the coating to a lesser extent but penetrate further into the coating than fluids with small dipole moments. On the other hand, polarity of the coating layer also affects the print. When printing on coatings with different polarities, higher print densities was obtained on the more polar substrates. As a tentative explanation, it is proposed that the ink builds different layer structures during drying depending on the coating polarity. Print gloss is related to the ink setting which, in turn, is affected by the solvent retaining capacity of the ink. Large water holding capacity allows the ink components to smoothen out before the structure is set, resulting in a higher print gloss. The rheology of inks is affected by temperature; at a higher temperature the viscosity is reduced. The reduction in ink viscosity at higher temperature has been shown to affect the print quality, e.g., print density and dot gain. It is suggested that a thicker layer is immobilised during impression due to the lower viscosity and that it is an explanation of the higher print density at a higher printing temperature. The influence of impression pressure on dot gain has been experimentally evaluated and mathematically modelled with good agreement. The dot gain is shown to respond non-linearly to the applied printing pressure. Studies based on pilot coated and printed paperboards is also reported, and it is shown that the print quality, e.g. print density, print gloss and dot gain, is largely dependent on the type of ink chosen and on the coating characteristics. Higher clay content in the coating resulted in increased dot gain and a decreased mottling.

Direct Methanol Fuel Cells (DMFC) provide an exciting alternative to current energy storage technologies for powering small portable electronic devices. For applications with sufficiently long durations of continuous operation, DMFC’s offer higher energy density, the ability to be refueled instead of recharged, and easier fuel handling and storage than devices that operate with hydrogen. At present, materials and manufacturing challenges impede performance and have prevented the entry of these devices to the marketplace. Higher-performing, cost-effective materials and efficient manufacturing processes are needed to enable the commercialization of DMFC. In a DMFC, the methanol-rich fuel stream and the oxidant are isolated from one another by a proton-conducting and electrically insulating membrane. Catalysts in the electrodes on either side of the Membrane Electrode Assembly (MEA) promote the two simultaneous half-reactions which allow the chemical energy carried in the fuel and oxidant to be converted directly into electricity. The goal of this research effort is to develop a continuous manufacturing process for the fabrication of effective DMFC MEAs. Based on the geometry of the electrode and materials used in the MEA, we propose a roll-to-roll process in which electrodes are coated onto a suitable substrate and subsequently assembled to form a MEA. Appropriate coating methods for electrode fabrication were identified by evaluating the requirements of continuous manufacturing processes; an appropriate set of these processes was then reduced to practice on a custom-designed flexible test bed designed explicitly for this project. After establishing baseline capabilities for several candidate methods, a spraying process was selected and a continuous manufacturing process concept was proposed. Finally, key control parameters of the spraying process were identified and their influence tested on actual MEAs to define optimal operating conditions. / text

The attachment and detachment of circulating tumor cells in a functionalized microchannel under hydrodynamic loading have been studied. For the cell attachment experiments, EpCAM antibodies are immobilized on the microchannel surface to capture either PC3N prostate or MDA-MB-231 breast cancer cells from homogeneous cell suspensions. Using the same protocol, N-Cadherin antibodies are immoblilzed and used to study the detachment of target cancer cells captured in the microchannels.A critical flow rate Qc has been identified to characterize the kinetics of cell capture in a functionalized microchannel. Approaching one limit, when the receptor-ligand interaction dominates, more than 90% of moving cells can be captured and a sharp peak is observed in the spatial distribution of the captured cells. Approaching another limit, when hydrodynamic loading dominates, almost all cells cannot be captured in the channel. Between these two limits, there is a transition region in which both capture efficiency and cell distribution are sensitive to the flow parameters. Proper characteristic time and length scales have been identified to describe the cell spatial distribution using a log-normal statistical model. The kinetic details of cell capture are determined by the competition between the flow rate and the ligand-receptor association/dissociation rates.Additionally, the attachment dynamics of circulating tumor cells in a bio-functionalized microchannel under hydrodynamic loading has been explored. The target cells initially role along the microchannel with fluctuating velocity prior to firm adhesion. When a successful bond is established, the cancer cells require a certain length to come to a complete stop; this stopping length is found to depend linearly on the applied hydrodynamic flow rate. The force balance in the vertical cross stream direction is dominated by the gravitational force; as a result, all cells loaded into a microchannel intimately contact the functionalized channel bottom surface within a short time. The streamwise horizontal motion of the cells on the surface is dominated by the balance between the shear flow hydrodynamic loading and the receptor-ligand binding interaction. A linear spring element is incorporated in the physical model to represent the dynamics of a cancer cell captured by immobilized antibodies. Featuring a mobility matrix, a proposed theoretical model is utilized to estimate the binding and hydrodynamic forces acting on the cell in a microchannel. Inserting certain fitting parameters, the time evolution of a stopping cell is successfully predicted by a simplified exponential function.The mechanical response of a captured cancer cell to a hydrodynamic flow field is investigated and, in particular, the effect of flow acceleration is examined. The observed cell deformation is dramatic under low acceleration, but is negligible under high acceleration. Consequently, the detachment of captured cells depends on both flow rate and flow acceleration. The flow rate required for cell detachment is a random variable that can be described by a log-normal distribution. Two flow acceleration limits have been identified for proper scaling of the flow rate required to detach captured cells. A time constant on the order of 1min for the mechanical response of a captured cell has been identified for scaling the flow acceleration. Based on these acceleration limits and the time constant, an exponential-like empirical model is proposed to predict the flow rate required for cell detachment as a function of flow acceleration.