The curing characteristics of photopolymer resin determine the relationship between the vat polymerization (VP) process parameters and the layer thickness, geometric accuracy, and surface quality of the 3D printed specimen. Dispersing filler material into the photopolymer resin changes its curing characteristics because the filler scatters and absorbs light, which modifies the curing reaction. However, the ability to cure photopolymer resin with high filler volume fraction is important to 3D print material specimens for specific engineering applications, e.g. structural polymer composite materials, electrical and thermal conductive materials, and ceramic materials for biological and high-temperature environments. We methodically measure the curing characteristics of diacrylate/epoxy photopolymer resin with dispersed glass microspheres. The experiments show that the curing depth, degree-of-cure, and surface roughness depend on both the light exposure dose and the filler fraction. We determine that the degree-of-cure increases with increasing filler fraction for constant exposure dose, and approaches 90% with increasing exposure dose, independent of the filler fraction. The geometric accuracy of the 3D printed specimens decreases with increasing exposure dose and with increasing filler volume fraction due to so-called profile broadening. Finally, we show that the average surface roughness of the 3D printed specimens decreases with increasing exposure dose and filler fraction. This work has implications for VP of photopolymer resins with high filler fraction. / Master of Science / Photopolymer resin is a gel-like liquid material that hardens (cures) into solid after absorbing light energy, and such a material is often used in the field of additive manufacturing (3D printing) to create complex geometry. Certain types of filler materials, such as metal powder or carbon fiber, can be added into the photopolymer resin to tailor the material properties, and thus, affects the curing behavior of photopolymer resin mixed with these filler materials. We conducted an experiment to understand how adding glass microspheres to a consumer grade photopolymer resin affects the process of creating 3D objects. This is important in the context of 3D printing engineered composite materials that derive their function from the organization and orientation of filler material in a matrix. To do this, we created many samples in the shape of a "VT" logo using the composite resin we made and measured their thickness (curing depth), degree-of-cure, surface roughness, and geometric accuracy, as a function of the amount of light energy being exposed to the resin (exposure dose) and the amount of the glass filler being added into the resin (filler fraction). We observed that when we increased the amount of light exposure, it resulted specimens that are thicker and more in degree of cure. Adding the glass filler to the liquid had mixed effects on the hardening process, because glass can scatter light and change how light travels within the resin. As a result, the printed objects became less accurate in shape and have smoother surface with increasing exposure dose and filler fraction, because more light is scattered off the designed curing profile and unintentionally cured the surrounding resin.

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The general trend toward increased use of computer models and simulations during product development has led to a need for accurate and reliable product models. The function of many products relies on contact interfaces between interacting components. To simulate the behavior of such products, accurate models of both components and interfaces are required. Depending on the purpose of the simulation, interface models of different degrees of complexity are needed. In simulation of very large systems with many interfaces, it might be computationally expensive to integrate detailed models of each individual interface. Condensed models, or abstractions, that describe the interface properties with a minimum of degrees of freedom are therefore required. This thesis deals with mechanical interfaces with an emphasis on friction. In the four appended papers friction models are discussed in terms of condensed models, as well as in terms of more detailed contact models. The aim is to study how friction can be modeled in behavioral simulation of products and to discuss the convenience and relevance of using different types of friction models as building blocks of a system model in behavioral simulations. Paper A presents a review of existing condensed friction models for sliding contacts under different running conditions and discusses the models from both simulation and tribological points of view. In papers B and C a simplified contact model, called the elastic foundation model, is used to model friction in a boundary-lubricated rolling and sliding contact. The model is integrated in a dynamic rigid body model of a mechanical system, the system behavior is simulated, and the result is compared with experimental results. Paper D discusses the application of the elastic foundation model to rough surface contact problems and investigates how the error in the elastic foundation results depends on surface roughness. / QC 20101129

In today’s paper and board production, quality control is made on a single cross direction (CD)sample from each tambour. As several different properties are analysed, only a limited number of measurement results are obtained for one property. Therefore, the measurement results might not be representative for the properties of the entire width of the tambour. The first objective of the project was to investigate variations of thickness, surface roughness and mechanical properties with a much higher resolution and number of measurements. The results of the measurement were compared with the routine quality control of the mill. The second objective of the project was to evaluate the influence of the wire shake unit in the centreply on the properties of the produced board. The measurements were performed on Iggesundpaperboard samples.The high-resolution measurements were performed using the STFI structural thicknessmeasurement device, an OptiTopo topography measurement device and a modified Autolinedevice at RISE Bioeconomy. The statistical evaluation of the results was performed in Matlab.Standard deviation, local variance and a frequency analysis were calculated for the thicknessmeasurements. Only standard deviation was considered for the topography data. For the mechanical properties, the distribution was evaluated using the Weibull distribution, since theresults had a single-sided distribution. In addition, the properties were analysed as a function of their location, for example to identify deterministic deviations in cross direction.The results of the first part of the project showed that the everyday control conducted in Iggesund is sufficient for most of the properties. Greatest difference was found at the edges ofthe samples, where Iggesund standard quality control does not detect a major variation inproperties, as no measurements are performed that close to the edge of the web. For example,at one edge, the high frequent measurements showed a significant drop in thickness which were not detected with the everyday quality control.In the second part of the project, the effect of a shake unit on the paper properties was evaluated. Here it was seen that the thickness variation were reduced, which also can be interpreted as an improvement of formation in the centre ply of the paperboard. As for thesurface roughness a slight improvement was found. Also for the mechanical properties, the shake unit appeared to improve the uniformity of the product / I dagens pappers-och kartongproduktion görs kvalitetskontroll på en enda tvärremsa (CD) från varje tambour. Eftersom flera olika egenskaper analyseras, erhålls endast ett begränsat antal mätresultat för en egenskap. Därför är informationen begränsad och kanske inte representativ för hela bredden av tambours egenskaper. Projektets första mål var att undersöka variationer i tjocklek, ytjämnhet och mekaniska egenskaper med mycket högre upplösning och antal mätningar. Resultaten av mätningen jämfördes med brukets rutinmässiga kvalitetskontroll.Det andra syftet med projektet var att utvärdera effekten av viraskaken på egenskaperna hos den producerade kartongen. Samtliga mätningar utfördes på kartongprover från IggesundsBruk.Mätningarna med hög upplösning utfördes med hjälp av en STFI-mätare för strukturtjocklek,en OptiTopo-enhet och en modifierad L&W Autoline-enhet. Den statistiska utvärderingen avresultaten utfördes i Matlab. Standardavvikelse, lokal variation och en frekvensanalys beräknades för tjockleksmätningarna. Endast standardavvikelse utvärderades för ytråhetsdata.För de mekaniska egenskaperna utvärderades fördelningen med hjälp av Weibullfördelningen,eftersom resultaten visade ett ensidigt beteende. Dessutom analyserades egenskaperna som en funktion av deras placering, till exempel för att identifiera deterministiska avvikelser i tvärriktningen.Resultaten av projektets första del visade att den dagliga kontrollen i Iggesund är tillräcklig för de flesta egenskaperna. Den största skillnaden hittades vid provets kanter, där Iggesundsstandardkvalitetskontroll Missar stora variationer för vissa egenskaper, eftersom inga mätningar utförs i det området på produkten. Vid ena sidan av nätverket visade de högfrekventa mätningarna en betydande minskning av tjockleken.I den andra delen av projektet utvärderades effekten av en skakningsenhet på pappersegenskaperna. Här såg man att variansen i tjockleksmätningarna indikerar en förbättring av formationen i kartongens mittskikt. När det gäller ytråheten konstaterades en liten förbättring. För de mekaniska egenskaperna föreföll viraskaken förbättra produktenslikformighet.

Thermal barrier coatings (TBCs) have been widely used in gas turbine engines to protect the underlying metal from high operating temperature so as to improve the durability of the components and enhance the engine efficiency. However, since the TBCs always operate in a demanding high-temperature environment of aircraft and industrial gas-turbine engines, a better understanding of this complex system is required to improve the durability and reliability. The objective of this study is to investigate the effects of surface modification for the NiCoCrAlY bond coats on the thermal cycling lifetime and failure characteristics of TBCs. Parameters of modification for the bond coats included as-sprayed, barrel-finished, hand-polished and pre-oxidation heat treatment at 1100[degrees]C in P=10O2-8 atm up to 4 hours, carried out prior to the electron beam physical vapor deposition (EB-PVD) of ZrO2-7wt% Y2O3 (7YSZ) ceramic topcoat. The resulting characteristics of the bond coat and the thermally grown oxide (TGO) scale were initially documented by surface roughness, phase constituents of the TGO scale, and residual stress of the TGO scale. The thermal cycling test consisted of 10-minute heat-up to 1121°C, 40-minute hold at 1121°C, and 10-minute forced air-quench. As-coated and thermally-cycled TBCs were characterized by optical profilometry (OPM), photo-stimulated luminescence spectroscopy (PSLS), optical microscopy, scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), and scanning/transmission electron microscopy (TEM/STEM) equipped with high angle annular dark field (HAADF) and X-ray energy dispersive spectroscopy (XEDS). TBC specimens for TEM/STEM analysis were prepared by focused ion beam (FIB) in-situ lift-out (INLO) technique. Superior thermal cycling lifetime was observed for TBCs with as-sprayed bond coats regardless of pre-oxidation heat treatment, and TBCs with hand-polished bond coats only after pre-oxidation heat treatment. With pre-oxidation heat treatment, relative photostimulated luminescence intensity of the equilibrium α-Al2O3 increased. Thus, the improvement in TBC lifetime can be correlated with an increase in the amount of α-Al2O3 in the TGO scale, given a specific surface modification/roughness. The lifetime improvement due to pre-oxidation was particularly significant to TBCs with smooth hand-polished bond coats and negligible for TBCs with rough as-sprayed bond coats. Spallation-fracture paths depended on the lifetime of TBCs. Premature spallation of TBCs occurred at the interface between the YSZ and TGO. Longer durability can be achieved by restricting the fracture paths to the TGO/bond coat interface. Small particulate phase observed through the TGO scale was identified as Y2O3 (cubic) by diffraction analysis on TEM. While small addition of Y in the NiCoCrAlY bond coat helps the adhesion of the TGO scale, excessive alloying can lead to deleterious effects.

As the semiconductor industry grapples with escalating scaling challenges associated with the floating gate MOSFET, alternative memory technologies like Resistive Random Access Memory (ReRAM) are gaining prominence in the scientific community. Boasting a straightforward device structure, ease of fabrication, and compatibility with CMOS (Complementary Metal-oxide Semiconductor) Back-end of Line (BEOL), ReRAM stands as a leading candi- date for the next generation of non-volatile memory (NVM). ReRAM devices feature nanoionics-based filamentary switching, outperforming flash memory in terms of power consumption, scalability, retention, ON/OFF ratio, and endurance. Furthermore, integrating ReRAMs within the CMOS BEOL/low-k Cu interconnect system not only reduces latency between the connectivity constraints of logic and memory modules but also minimizes the chip footprint. However, investigations have revealed a significant concern surrounding ReRAMs—specifically, their electro-thermal reliability. This research provides evidence highlighting the critical influence of material properties, deposition effects, and thermal transport on the device's performance and reliability. Various material systems have undergone in this work scrutiny to comprehend the impact of intrinsic material properties such as thermal conductivity, specific heat capacity, thermal diffusivity, and deposition effects like surface roughness on the electroforming voltages of ReRAM devices. The reference device structure considered in this work is Cu/TaOx/Pt, which has been compared with alternative configurations involving metals like Ru and Co as potential substitutes for Pt. Additionally, a new vehicle has been introduced to quantify cell degradation resulting from thermal cross-talk in crossbar Resistive Random Access Memory (ReRAM) arrays. Furthermore, a novel methodology has been presented to predict cell degradation due to remote heating, taking into account the cell's location, the material properties of the device, and geometry of its electrodes. The experimental results presented in this study showcase filament rupture caused by remote heating, along with spontaneous filament restoration ensuing from the subsequent cooling of the ReRAM cell. / Doctor of Philosophy / As the demand for compact, high-speed logic-memory modules continues to surge, the diminishing silicon real estate in our gadgets poses a challenge in extending Moore's law to meet the scaling needs of the semiconductor device industry. To tackle this challenge, emerging memory technologies like Resistive Random Access Memory (ReRAM) are positioned as promising successors to flash memory. ReRAM devices offer distinct advantages over flash memory, showcasing superior power consumption, scalability, long retention, a high ON/OFF ratio, and good endurance. Their compatibility with current CMOS (Complementary Metal-oxide Semiconductor) technology facilitates seamless integration. However, a significant concern associated with ReRAMs is their electro-thermal reliability. This research delves into how material properties comprising a ReRAM device and fabrication factors, such as the surface roughness of the material, can impact the electrical and thermal reliability of a ReRAM cell. In this context, a novel methodology has been introduced to predict cell degradation within ReRAM crossbar arrays induced by thermal cross-talk, considering material properties and the geometry of the device. The new methodology has been thoroughly verified on manufactured ReRAM arrays with various composite electrodes. The study also presents experimental results demonstrating the rupture of cell filaments due to remote heating, along with instances of spontaneous filament restoration due to subsequent cooling.

Measurements were made in two-dimensional zero pressure gradient turbulent boundary layers over 5 geometries of three-dimensional densely distributed surface roughness. A 3-velocity component laser Doppler velocimeter was used to measure instantaneous velocities. These measurements permitted an independent estimate of skin friction on the surfaces using a momentum balance approach, and the validity of the von Karman constant for rough walls was tested. Five roughness fetches were evaluated: three sandpaper roughness fetches of varying grit size and two cases of uniformly distributed hemispheres of different spacing. Optical surface profilometry was used to characterize the geometry of the sandgrain surfaces. It was found that the smooth wall von Karman constant can not be assumed for densely distributed rough wall flows in order to determine the skin friction for these flows. This requires an independent measure of skin friction using more than a single boundary layer profile. Near wall flow structure measurements found that the hemispherical elements do not have high TKE or Reynolds shearing stress regions at the trailing edge of elements as had been shown for sparsely spaced cylindrical elements. This is likely due to the sharp trailing corner of the cylindrical elements, as opposed to an effect of spacing. Rather, hemispherical roughness has a periodically occurring high stress and TKE region located between two element centers in the stream-wise direction at a height of approximately 1.5 times the roughness element height. The periodic nature of the near wall flow extends to approximately 4 roughness element heights. The traditional roughness function f(λ) did not correlate well with λ or the modified Λ for the experimental data. However, it was found that the friction coefficient for the current dense roughness cases is a constant 0.004, within the experimental uncertainty. Traditional inner wall scalings, outer wall scalings, and roughness scalings were not able to collapse surface pressure fluctuation spectra for the various rough wall surfaces tested. However, the data do collapse for individual geometries based on Reynolds number. This gives rise to the ability to predict pressure fluctuation spectra at other Reynolds numbers. / Ph. D.