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Ett hållbart samhälle behöver ha en klimatvänlig snöröjning. Den traditionella snöröjningen är associerad med en del problem, exempelvis bidrar saltspridning till ökad korrosion av vägar och fordon, förorening av både ytvatten och grundvatten samt ökad mobilitet av tungmetaller. Ett hållbart alternativ är hydronisk markvärme, även kallat Hydronic Asphalt Pavement, HAP. Snösmältning med ett HAP-system sker genom att en varm fluid cirkulerar i rör under ytan som ska hållas snöfri. HAP- systemets energianvändning och snösmältningskapacitet är beroende av hur de värmande rören är placerade samt vilket styrsystem som används. Rapporten syftar till att öka förståelsen för hur styrsystemet och geometrin påverkar HAP-systemets energianvändning och snösmältningstid. En numerisk 2D-modell konstrueras i COMSOL Multiphysics vilken användes för att simulera styrsystemets och geometrins påverkan på HAP-systemet. Snön förenklades som en värmesänka till vilken modellen överförde värme via ett värmeflöde. En avgränsning i rapporten var att det bortsågs från vatten på ytan för att förenkla modellen. Resultatet bekräftar att HAP-systemets styrsystem och geometri har stor påverkan på dess energianvändning och snösmältningstid. Generellt ger en hög energianvändning kortare tid med snö på ytan. Det gör att om det är önskvärt att ha ett energisnålt system behöver en avvägning mellan energianvändning och tid med snö på ytan göras. Ett intermittent styrsystem bedöms vara ett bra alternativ då det ger relativt låg energianvändning och kort tid med snö på ytan. Om det inte finns en begränsning i energianvändning finns det flera styrsystem som kan ge en snöfri yta hela året. Ytans temperatur är den bästa styrparametern att använda för att minska både energianvändning och snösmältningstid. Då värmerören placeras grundare ökar energibehovet och tiden med snö på ytan minskar. Det är möjligt att placera värmerören djupare med bibehållen snöfri tid på ytan om styrsystemet anpassas efter djupet. En viktig anpassning är att styrsystemet ger en förvärmningseffekt, exempelvis att vägen börjar värmas då vägytans temperatur understiger 1°C. En ökning av avståndet mellan värmerören, CCrör, minskar energibehovet och tiden med snö på ytan ökar. Det bedöms vara möjligt att öka CCrör till 350 mm utan att generera för stora skillnader i temperaturprofilen över ytan då rördjupet är 100 mm eller 160 mm. Det styrsystem som gynnas mest av att öka CCrör till 350 mm är ”Grundfall”, vilken värmer vägen under hela vinterhalvåret. Energianvändningen minskar då med 132 kWh/m2 (22,9%) och den längsta ihållande tiden med snö på ytan ökar från 0 h till 4 h. Beroende på vad kraven på ytan är kan det vara möjligt att ha 350 mm som CCrör för de andra styrsystemen. HAP-systemet blir resurseffektivare och billigare vid konstruktion ju större CCrör som används, vilket är önskvärt. Resultatet visar att det är en liten minskning i energianvändning och snösmältningstid då isolering är under värmerören jämfört med ingen isolering. Detbedöms därför vara omotiverat ur både energisynpunkt och snösmältningsmässigt att använda isolering under värmerören på det sätt som undersökts i detta arbete. Det är en markant skillnad i energianvändning mellan ett styrsystem som är enklare och ett som är mer komplext. Om styrsystemet ”Intermittent” används i stället för ”Grundfall” vid Hamngatan i Karlstad skulle det generera en minskad energianvändning av 4,37 GWh fjärrvärme (58,5%), vilket motsvarar 199 ton CO2 per år. Resultatet understryker vikten att ett optimalt styrsystem används. Även en liten skillnad i energianvändning kan ge stora energimässiga besparingar eftersom det ofta är stora ytor som värms med ett HAP-system. För att kunna avgöra vilket styrsystem som är bäst lämpat behöver kraven på ytan bestämmas, vilket inte görs i arbetet, utan resultaten hålls generella. / A sustainable society need to have a climate friendly snow removal system. The traditional snow removal systems generate some problems, for example increased corrosion of roads and vehicles, contamination of both surface- and ground water and increased mobility of heavy metals. A sustainable alternative is Hydronic Asphalt Pavement, HAP. Snow melting with a HAP-system is generated by circulating a warm fluid in pipes underneath the surface that is to be snow free. Both the energy usage and snow melting time is affected by how the heat pipes are placed and which control system that is used. The report aims to increase the knowledge of how both the control system and geometry of the heating pipes affect the energy use and snow melting time of a HAP-system. A numerical 2D-model was constructed in COMSOL Multiphysics which was used to simulate how the control system and geometry of the heating pipes effects the HAP-system. The snow was simplified to a heat sink, to which the model could transfer heat through a convective heat flux. A demarcation of the study is that water on the surface is ignored to simplify the model. The results confirms that both the control system and geometry of the heat pipes greatly affects the energy usage and snow melting time. In general, a large energy usage generates a shorter total time with snow on the surface. It is therefore needed to do a balancing between energy usage and the total time with snow on the surface if the energy usage is to be restricted. An intermittent control system is considered to be a good alternative as it gives a relative low energy usage and short time with snow on the surface. If there is no limitation on the energy use, there is several control systems that gives a snow free surface throughout the year. The surface temperature is the best parameter for the control system as it minimizes both the energy usage and snow melting time. When the heating pipes is placed shallower the energy usage is increased and the time with snow on the surface decreases. It is possible to place the heating pipes at a greater depth and still have the same functionality of the HAP-system if the control system is adjusted accordingly. One important adjustment for the control system is preheating, for example that the heating is turned on when the air temperature is less than 1°C. An increase of CCrör decrease the energy usage and increase the time with snow on the surface. It is possible to increase CCrör to 350 mm and still have a smooth temperature profile if the heating pipes is placed 100 mm or 160 mm beneath the road surface. The control system that gains the most out of an increase in !!!ö! to 350 mm is “Grundfall”, which reduce its energy usage with 132 kWh/m2 (22,9%) and the longest time with snow on the surface is increased from 0 h to 4 h. Depending on which demands the surface is to meet, it is possible to have 350 mm as CCrör for the other control systems. An increase in CCrör makes the HAP-system more resource efficient and cheaper to build, which is desirable. The results show a small decrease in energy usage and snow melting time when isolation is underneath the heating pipes compared to without isolation. It is therefore deemed to be unmotivated to use isolation as it is used in this paper, in both energy use- and snow melting time-perspective. There is a significant difference in energy use between a simple and more complex control system. If the control system “Intermittent” is used instead of “Grundfall” at Hamngatan in Karlstad the energy usage would decrease with 4,37 GWh heat (58,5%) and 199 ton of CO2. The result underlines the importance of an optimal control system for a HAP-system. Even a small change in energy consumption can generate large energy savings due to the scale of the surfaces that is heated with HAP-systems. To be able to decide which control system that is the best suited, the demand on the surface needs to be set. The demands are not set in this paper in order to keep the results general.

The effect of using high voltage DC and AC on the heat transfer process during the melting of a Phase Change Material (PCM) in a rectangular enclosure was studied experimentally and numerically. The experiments were conducted for two configurations: (a) a horizontal rectangular enclosure in which the initial melting process is governed by heat conduction, (b) a vertical rectangular enclosure in which the initial melting process is governed by heat convection. The level of heat transfer enhancement was quantified by using a novel experimental facility for the horizontal configuration. The experimental methodology was verified first against non-EHD melting cases and then was further expanded to include the EHD effects. The experiments showed that EHD forces can be used to enhance a conduction dominated melting up to a maximum of 8.6-fold locally and that the level of enhancement is directly related to the magnitude of the applied voltage. It was found that the main mechanism of enhancement in these cases can be attributed to the electrophoretic forces and that the role of the dielectrophoretic forces is minimal under the applied voltages. In the vertical configuration, the effect of the magnitude of the applied voltage, the applied voltage wave-form, the gravitational Rayleigh number, Stefan number and the aspect ratio of the enclosure on the heat transfer enhancement were investigated experimentally. A novel shadowgraph experimental measurement system was developed and verified against the analytical correlations of natural convection in rectangular enclosures and the non-EHD melting performance was verified against the bench mark experiments of Ho (1984). The shadowgraph system was used to measure the local heat transfer coefficient across the heat source wall (the heat exchanger surface). The local heat transfer measurements along with the melting temporal profiles were used to explain and visualize the coupling between the Electrohydrodynamics (EHD) forces and the gravitational forces. It was found that the EHD forces could still enhance the melting process even for an initially convection dominated melting process. The mechanism of enhancement was found to be a bifurcation of the initial convection cell into multiple electro-convective cells between the rows of the electrodes. The shadowgraph system was used to assess the interaction between the electrical and the gravitational forces through the visualization of these cells and quantifying their size. The EHD heat transfer enhancement factor was found to increase by the increase of the applied voltage, reaching a 1.7 fold enhancement at the lower gravitational Rayleigh number tested and 1.45 fold for the highest gravitational Rayleigh and Stefan number. The effect of the polarity of the applied voltage was tested for the different cases and it was found that there was no significant difference between the positive and the negative polarities when the magnitude of the applied voltage was below 4 kV. At higher voltages- 6kV- the negative polarities showed better level of enhancement when compared to the positive applied voltage. It was again found that the main mechanism of enhancement is attributed to charge injection from the high voltage electrodes. A scaling analysis was conducted based on the previous conclusions and the dominant mechanism of enhancement to describe the problem in non-dimensional form. An electrical Rayleigh number was introduced and its magnitude was correlated to the magnitude of the injected current. The melt volume fraction was then represented against the non-dimensional parameter (n+1)(H/W)Fo.Ste.RaE^0.25 and the melt fraction temporal profiles for the different voltages collapsed well against this parameter. Finally, a numerical analysis was conducted on the role of the dielectrophoretic forces during the melting of Octadecane and when they would become of significant importance. The results of the numerical model supported the experimental findings and suggested that a minimum of 15 kV is needed in order to realize the effect of the dielectrophoretic forces. The numerical model was used to understand the interaction between the gravitational and the dielectrophoretic forces at different ranges of both gravitational Rayleigh number and electrical Rayleigh number. The model was complemented with scaling analysis to determine the governing scales of the problem and the dielectrophoretic Rayleigh number was deduced from the study. / Thesis / Doctor of Philosophy (PhD)

Industry 4.0 will pave the way to a new age of advanced manufacturing. Additive manufacturing (AM) is one of the leading sectors of the upcoming industrial revolution. The key advantage of AM is its ability to generate lightweight, robust, and complex shapes. AM can also customize the microstructure and mechanical properties of the components according to the selected technique and process parameters. AM of metals using selective laser melting (SLM) could significantly impact a variety of critical applications. SLM is the most common technique of processing high strength Aluminum alloys. SLM of these alloys promises to enhance the performance of lightweight critical components used in various aerospace and automotive applications such as metallic optics and optomechanical components. However, the surface and inside defects of the as-built parts present an obstacle to product quality requirements. Consequently, the post-processing of SLM produced Al alloy parts is an essential step for homogenizing their microstructure and reducing as-built defects. In the current research, various studies assess the optimal process mapping for high-quality SLM parts and the post-processing treatment of Al alloy parts. Ultra-precision machining with single point diamond turning or diamond micro fly-milling is also investigated for the as-built and post-processed Al parts to satisfy the optical mirror’s surface finish requirements. The influence of the SLM process parameters on the quality of the AlSi10Mg and Al6061 alloy parts is investigated. A design of experiment (DOE) is used to analyze relative density, porosity, surface roughness, dimensional accuracy, and mechanical properties according to the interaction effect between SLM process parameters. The microstructure of both materials was also characterized. A developed process map shows the range of energy densities and SLM process parameters for each material needed to achieve optimum quality of the as-built parts. This comprehensive study also strives to reduce the amount of post-processing needed. Thermal post-processing of AlSi10Mg parts is evaluated, using recycled powder, with the aim of improving the microstructure homogeneity of the as-built parts. This work is essential for the cost-effective additive manufacturing (AM) of metal optics and optomechanical systems. To achieve this goal, a full characterization of fresh and recycled powder was performed, in addition to a microstructure assessment of the as-built fabricated samples. Annealing, solution heat treatment (SHT) and T6 heat treatment (T6 HT) were applied under different processing conditions. The results demonstrated an improvement in microstructure homogeneity after thermal post-processing under specific conditions of SHT and T6 HT. A micro-hardness map was developed to help in the selection of optimal post-processing parameters for the part’s design requirements. A study is also presented, which aims to improve the surface characteristics of the as-built AlSi10Mg parts using shot peening (SP). Different SP intensities were applied to various surface textures of the as-built samples. The SP results showed a significant improvement in the as-built surface topography and a higher value of effective depth using 22.9A intensity and Gp165 glass beads. The area near the shot-peened surface showed a significant microstructure refinement up to a specific depth, due to the dynamic precipitation of nanoscale Si particles. Surface hardening and high compressive residual stresses were generated due to severe plastic deformation. Friction stir processing (FSP) was studied as a localized treatment on a large surface area of the as-built and hot isostatic pressed (HIPed) AlSi10Mg parts using multiple FSP tool passes. The influence of FSP on the microstructure, hardness, and residual stresses of parts was investigated. FSP transforms the microstructure of parts into an equiaxed grain structure. A consistent microstructure homogenization was achieved over the processed surface after applying a high ratio of tool pass overlap of ≥60%. A map of microstructure and hardness was prepared to assist in the selection of the optimal FSP parameters for attaining the required quality of the final processed parts. Micromachining to the mirror surface was performed using diamond micro fly-milling and single point diamond turning techniques, and the effect of the material properties on surface roughness after machining was investigated. The machining parameters were also tuned to meet IR mirror optical requirements. A novel mirror structure is developed using the design for additive manufacturing concept additive (DFAM). This design achieved weight reduction of 50% as compared to the typical mirror structure. Moreover, the developed design offers an improvement of the mirror cooling performance due to the embedded cooling channels directed to the mirror surface. A novel mirror structure is developed using the design for additive manufacturing concept additive (DFAM). This design achieved weight reduction of 50% as compared to the typical mirror structure. Moreover, the developed design offers an improvement of the mirror cooling performance due to the embedded cooling channels directed to the mirror surface. / Thesis / Doctor of Philosophy (PhD)

Additive manufacturing (AM) has the ability to fabricate components of high geometric complexity that are difficult or near impossible to be produced by traditional manufacturing technologies. Selective laser melting (SLM) is a commonly used AM technology for metallic fabrications. SLM offers the opportunities to customize the characteristics of the as-build part produced, by adjusting the laser settings. However, high strength aluminum (Al) alloys presents an obstacle for SLM production due to the low alloying content, which increases the alloys’ probabilities to form cracks due to thermal stress induced by the SLM build process. The current study focuses on the study of surface roughness and dimensional accuracy of SLM fabrication of Al6061 and AlSi10Mg. Using design of experiment (DOE), wide ranges SLM process parameters were experimented with, and their individual effect along with their interactive effects on the fabricated parts’ quality were evaluated. The quality characteristics studied are: microstructures, microhardness, tensile strength (ultimate tensile strength, and yield strength), density, surface roughness, and dimensional accuracy. Regression models were created for each quality characteristics, and the combination of density, surface roughness, and dimensional accuracy results was used to create processing window for SLM that ensures the production of high-quality parts. The work aims to not only be used as-is, to help with the selection of SLM process parameters for Al6061 and AlSi10Mg that will reduce the post- processing time, but also to set a foundation for future development for numerical models that could better predict and describe the relations between SLM process parameters and the part’s fundamental qualities. / Thesis / Master of Applied Science (MASc)

The main aim of this thesis is to investigate the manufacturability of different gyroid designs using Selective laser melting (SLM) process . This study paves the way for a better understanding of design aspects, process optimization, and characterization of titanium alloy (Ti6Al4V) gyroid lattice structures for bone implant applications. First, A MATLAB® code was developed to create various gyroid designs and understand the relationship between the implicit equation parameters and the measurable outputs of gyroid unit cells. A novel gyroid lattice structure is proposed, where the porosity is graded in a radial direction. Second, gyroid designs were investigated by developing a permissible design map to help choose the right gyroid parameters for bone implants. Third, response surface methodology was used to study the process-structure-property relationship and understand the effect of SLM process parameters on the manufacturability of Ti6Al4V gyroid lattice structures. Laser power was found to be the most significant factor affecting the errors in relative density and strut size of gyroid structures. A volumetric energy density between 85 and 103 J/mm3 induces the least errors in the gyroid’s relative density. Fourth, the quasi-static properties of the novel designs were compared to uniform gyroids. The proposed novel gyroids had the highest compressive strength reaching 160 MPa. Numerical simulations were studied to give insight into how manufacturing irregularities can affect the mechanical properties of gyroids. Last, an in-depth defect analysis was conducted to understand how SLM defects may influence the fatigue properties of different Ti6Al4V gyroids. Thin struts have less internal defects than thick ones; thus, they show less crack propagation rate and higher normalized fatigue life. These favorable findings contributed to scientific knowledge of manufacturability of Ti6Al4V porosity graded gyroids and determined the influence of SLM defects on the mechanical properties of gyroid designs for bone implants. / Thesis / Doctor of Philosophy (PhD) / This thesis studies the integration of design aspects, SLM manufacturability, and mechanical characterization of Ti6Al4V gyroid lattice structures used for bone implants. A MATLAB® code was developed to design novel porosity graded gyroids, and develop permissible design map to aid the choice of different gyroid designs for bone implants.. Process maps were also developed to investigate the relationship among laser power, scan speed, and the errors in the relative density of lattice structures. Moreover, the normalized fatigue strength of thin struts gyoid was found to be higher than that of thicker struts.Analytical models and finite element analysis (FEA) models were compared to experimental results. The variation of the results gives a better understanding of the effect of manufacturing defects. An improved insight of gyroids manufacturability has been obtained by integrating the permissible design space with the process-structure-property relationship, and the defect analysis of porosity graded gyroids.

A slit die has been constructed to use both flow birefringence and direct pressure measurements to study the extrapolated exit pressure (Px) and the exit pressure theory used to evaluate the magnitude of the primary normal stress difference (N1) from the value of the exit pressure. Flow birefringence is used to directly assess the principal assumptions in the exit pressure theory and to evaluate the magnitude of Px from an expression derived from the macroscopic momentum balance equation. The effect of stress field rearrangement upstream of the die exit plane on the value of the exit pressure was then evaluated using flow birefringence data. The effect of stress field rearrangement was also shown to affect the pressure drop ΔP/ΔL in the exit region of the die and the pressure distribution from the centerline of the slit to the die wall. To complement the experimental investigation, a mixed penalty method finite element simulation of the die swell problem was performed using the White-Metzner and upper-convected Maxwell constitutive equations. The flow birefringence experiments were performed for a polystyrene (Styron 678), LDPE (NPE 952), and HDPE (LY600-00) melts for the following shear rate (γ̇) and wall shear stress (σw) 0.05 ≤ γ̇w ≤ 3.2 s⁻¹ and 4.84 ≤ σw ≤ 16.4 KPa. It was found that the flow in the die exit region is not a unidirectional shear flow, which is direct violation of the assumptions in the exit pressure theory. Normal stresses generated by an elongational flow field were observed along the slit centerline and in the region adjacent to the die walls. Also, shear stress contributions due to stress field rearrangement evaluated using an expression obtained from a macroscopic momentum balance, comprise over 50% of the magnitude of the calculated exit pressure. The numerically calculated stress field was in good agreement with the results of the flow birefringence results. Convergence for the numerical technique was limited to Deborah numbers of 0.61 for the White-Metzner model and 0.75 for the upper-convected Maxwell constitutive equation. / Ph. D.

The goal of this research is developing a computational framework to study mechanical fatigue and fracture at different length scales for a broad range of materials. The developed multiscale framework is utilized to study the details of fracture and fatigue for the rolling contact in rails, additively manufactured alloys, and bio-inspired hierarchical materials. Rolling contact fatigue (RCF) is a major source of failure and a dominant cause of maintenance and replacements in many railways around the world. The highly-localized stress in a relatively small contact area at the wheel-rail interface promotes micro-crack initiation and propagation near the surface of the rail. 2D and 3D microstructural-based computational frameworks are developed for studying the rolling contact fatigue in rail materials. The method can predict RCF life and simulate crack initiation sites under various conditions. The results obtained from studying RCF behavior in different conditions will help better maintenance of the railways and increase the safety of trains. The developed framework is employed to study the fracture and fatigue behavior in 3D printed metallic alloys fabricated by selective laser melting (SLM) method. SLM method as a part of metal additive manufacturing (AM) technologies is revolutionizing the manufacturing sector and is being utilized across a diverse array of industries, including biomedical, automotive, aerospace, energy, consumer goods, and many others. Since experiments on 3D printed alloys are considerably time-consuming and expensive, computational analysis is a proper alternative to reduce cost and time. In this research, a computational framework is developed to study fracture and fatigue in different scales in 3D printed alloys fabricated by the SLM method. Our method for studying the fatigue at the microstructural level of 3D printed alloys is pioneering with no similar work being available in the literature. Our studies can be used as a first step toward establishing comprehensive numerical frameworks to investigate fracture and fatigue behavior of 3D metallic devices with complex geometries, fabricated by 3D printing. Composite materials are fabricated by combining the attractive mechanical properties of materials into one system. A combination of materials with different mechanical properties, size, geometry, and order of different phases can lead to fabricating a new material with a wide range of properties. A fundamental problem in engineering is how to find the design that exhibits the best combination of these properties. Biological composites like bone, nacre, and teeth attracted much attention among the researchers. These materials are constructed from simple building blocks and show an uncommon combination of high strength and toughness. By inspiring from simple building blocks in bio-inspired materials, we have simulated fracture behavior of a pre-designed composite material consisting of soft and stiff building blocks. The results show a better performance of bio-inspired composites compared to their building blocks. Furthermore, an optimization methodology is implemented into the designing the bio-inspired composites for the first time, which enables us to perform the bio-inspired material design with the target of finding the most efficient geometries that can resist defects in their structure. This study can be used as an effective reference for creating damage-tolerant structures with improved mechanical behavior. / Doctor of Philosophy / The goal of this research is developing a multiscale framework to study the details of fracture and fatigue for the rolling contact in rails, additively manufactured alloys, and bio-inspired hierarchical materials. Rolling contact fatigue (RCF) is a major source of failure and a dominant cause of maintenance and replacements in many railways around the world. Different computational models are developed for studying rolling contact fatigue in rail materials. The method can predict RCF life and simulate crack initiation sites under various conditions and the results will help better maintenance of the railways and increase the safety of trains. The developed model is employed to study the fracture and fatigue behavior in 3D printed metals created by the selective laser melting (SLM) method. SLM method as a part of metal additive manufacturing (AM) technologies is revolutionizing industries including biomedical, automotive, aerospace, energy, and many others. Since experiments on 3D printed metals are considerably time-consuming and expensive, computational analysis is a proper alternative to reduce cost and time. Our method for studying the fatigue at the microstructural level of 3D printed alloys can help to create more fatigue and fracture resistant materials. In the last section, we have studied fracture behavior in bio-inspired materials. A fundamental problem in engineering is how to find the design that exhibits the best combination of mechanical properties. Biological materials like bone, nacre, and teeth are constructed from simple building blocks and show a surprising combination of high strength and toughness. By inspiring from these materials, we have simulated fracture behavior of a pre-designed composite material consisting of soft and stiff building blocks. The results show a better performance of bio-inspired structure compared to its building blocks. Furthermore, an optimization method is implemented into the designing the bio-inspired structures for the first time, which enables us to perform the bio-inspired material design with the target of finding the most efficient geometries that can resist defects in their structure.

A one-dimensional model of a heterogeneous material consisting of a matrix with embedded separated particles is considered, and the melting or solidification of the particles is investigated. The matrix is in imperfect contact with the particles, and the lumped capacity approximation applies to each individual particle. Heat is generated inside the particles or is transferred from the matrix to the particles coupled through a contact conductance. The matrix is not allowed to change phase and energy is either generated inside the matrix or transferred from the boundaries, which is initially conducted through the matrix material. The physical model of this coupled, two-step heat transfer process is solved using the energy method. The investigation is conducted in several phases using a building block approach. First, a lumped capacity system during phase transition is studied, then a one-dimensional homogeneous material during phase change is investigated, and finally the one-dimensional heterogeneous material is analyzed. A numerical solution based on the finite difference method is used to solve the model equations. This method allows for any kind of boundary conditions, any combination of material properties, particle sizes and contact conductance. In addition, computer programs, using Mathematica, are developed for the lumped capacity system, homogeneous material, and heterogeneous material. Results show the effects of control volume thickness, time step, contact conductance, material properties, internal sources, and external sources. / Master of Science