Browsar Studentarbeten // Student Theses efter Program "Advanced engineering materials, MSc"
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- PostAdditive Manufacturing of Zirconia(2018) Llanos, Gustavo; Chalmers tekniska högskola / Institutionen för industri- och materialvetenskap; Chalmers University of Technology / Department of Industrial and Materials ScienceThe potential of Zirconia for fabrication of components using additive manufacturing technologies extend the application range for this material. There are some limitations with the relatively simple design that can be achieved by conventional manufacturing processes for ceramics. However, there are some challenges to overcome in additive manufacturing of zirconia given the difficulty to obtain fully dense components without defects. In this research, additive manufacturing of Yttria-stabilized zirconia was investigated to increase the overall reliability of a VAT-photopolymerization technique. Powder processing was performed before suspension preparation to study the effect on further steps. An optimum resin composition was developed and printing parameters were adjusted according to the suspension characteristics. Post-processing steps were tested and investigated to analyze the effect on the component and its final properties. Powders with different stabilizing agents using the same resin were tested to evaluate the powder effect on the overall process. The results obtained show that the resin composition developed allows manufacturing of components with Yttria and Magnesia stabilized Zirconia. Powder characteristics such as grain size and surface area showed that they can limit the powders suitable for this technique. Characterization of the components shows uniform microstructure with good dimensional accuracy, allowing to obtain near fully dense components with this technology.
- PostAir gap spinning of cellulose fibers from ionic solvents(2013) Hedlund, Artur; Chalmers tekniska högskola / Institutionen för kemi- och bioteknik; Chalmers University of Technology / Department of Chemical and Biological Engineering
- PostCorrosion of Austenitic Stainless Steel(2018) Turan, Josh; Chalmers tekniska högskola / Institutionen för kemi och kemiteknik; Chalmers University of Technology / Department of Chemistry and Chemical EngineeringThis thesis work focuses on the corrosion behaviour of austenitic stainless steel welds in chloride containing environments. The initial aim was to develop a new method for corrosion testing of welded austenitic stainless steel. The motivation for such work was that previous results indicated that the current accelerated corrosion tests are too harsh for these welds. The specific application is for a stainless steel automotive fuel tank that is being investigated as a possible alternative to the standard plastic fuel tank. For this study, lab-welded samples of 304L and 301 stainless steel were provided by Outokumpu for accelerated corrosion testing. The corrosion mechanisms of most concern were stress corrosion cracking and intergranular corrosion. Three different accelerated corrosion test (ACT) cycles were used. These included two standard Volvo Cars cycles and one new experimental cycle. Chloride environments containing NaCl and a mixture of NaCl and CaCl2 were included. Lastly, an ASTM standard for stress corrosion cracking of stainless steel was utilized. Results showed that the lab-welded samples were corrosion resistant under all conditions due to excellent weld quality. The two different chloride environments did not show significant differences in corrosive attack.
- PostDefining Machine Capability of Metals Additive Manufacturing Machines(2018) DAM, THOMAS CHAN HIEN; Ravirujiphant, Napon; Chalmers tekniska högskola / Institutionen för industri- och materialvetenskap; Chalmers University of Technology / Department of Industrial and Materials Science
- PostDesign of Experiment and Evaluation of Abrasive Waterjet Cutting in Titanium Alloy Sheet(2015) Andersson, Daniel; Ingvarsson, Mikael; Chalmers tekniska högskola / Institutionen för material- och tillverkningsteknik; Chalmers University of Technology / Department of Materials and Manufacturing TechnologyHigh demands on components in the aerospace industry empower the use of advanced manufacturing processes in order to increase quality and reduce costly processing steps. This includes non-conventional machining such as Abrasive Waterjet where the components are cut through abrasive impingement by means of abrasives accelerated by pressurized water. While avoiding effects of heating in the material, the technique entails some considerable characteristics. Thus this master thesis aims to analyze the process and experimentally study the effect of selected process parameters. Titanium alloy sheet samples of different thicknesses were cut by abrasive waterjet while varying cutting speed, water pressure, abrasive feed and grit size with both a standard technique and a finer micromachining technique. Sections of the samples were prepared by polishing followed by etching and then analyzed through visual inspection, optical and scanning electron microscopy and XEDS analysis. The analyses of the samples indicated varying extent of known characteristics and through statistical analysis their relations to process parameters could be assessed. Main factors of the abrasive waterjet process were found to be the material thickness and cutting speed, influencing all responses to some extent. Through the design of experiments approach it was found that some responses could be correlated to models with significance, while other correlations lacked significance due to difficulties in measurements or other error sources. Grit embedment in the kerf was confirmed which might conflict present specifications on contamination. Yet, the consequence and distribution of grit particles needs to be considered.
- PostDesign of Reducing Agent for Sintering of High-Performance Alloyed PM Steels Based on Different Carbon Grades Analysis(2012) Hadhud, Aimn; Chalmers tekniska högskola / Institutionen för material- och tillverkningsteknik; Chalmers University of Technology / Department of Materials and Manufacturing TechnologyCarbon activity in terms of carbon dissolution and reducing ability plays a major role in final performance of structural PM components. Graphite is the most common carbon source for structural PM components and due to the carbon effect on powder compressibility has to be admixed to the metal powder. The role of admixed graphite besides hardening the material by its diffusion into the pure or pre-alloyed iron particles is the reduction of the surface oxides to provide metal-metal contact between adjacent particles and thus allowing the neck formation to take place. According to the latest experimental data, the carbon starts to be active at high temperature (˃900ºC), after which graphite rapidly dissolves in the metallic matrix. This means that there is a lack of reducing agent at low temperature (700-900˚C) as well as in high temperature range (˃ 1100˚C) when there is no any carbon source left in the pores for reduction of the most stable surface oxides. The aim of this work is to evaluate the carbon activity of different carbon sources in order to design carbon source activity of which can cover required temperature range. This can be obtained by mixing of different carbon sources that are active at different temperatures as well as by modification of the existing grades. Astaloy CrM (Höganäs AB, Sweden) was mixed with different carbon sources of various properties, namely PG25, PG10, F25, F10, KS4 and ENSACO 250 (TIMCAL SA, Switzerland). The mixes were then compacted to the density of ~7 g/cc. Interrupted sintering of compacts was performed in the range of temperatures from 700 until 1120˚C and sintering for 30 min at 1120˚C. Metallographic and fractographic analysis were the main methods to evaluate the carbon activity in this study. The investigation shows that the carbon starts to be active at ~ 900˚C in the case of KS4, F10 and PG10 and they are comparable in terms of the carbon dissolution and reducing ability, while PG25 and F25 are the less active, whereas ENSACO 250 is inactive at this temperature. However, the only carbon source that completely dissolves during heating to 1120 ºC throughout the compacts was ENSACO 250. After sufficient time was given, KS4, F10, PG10 and F25 were completely dissolved while some amount of PG25 remained un-dissolve at this temperature even after sintering for 30 min.
- PostDevelopment of a γ’ Precipitation Hardening Ni-Base Superalloy for Additive Manufacturing(2018) Shaikh, Abdul Shaafi; Chalmers tekniska högskola / Institutionen för industri- och materialvetenskap; Chalmers University of Technology / Department of Industrial and Materials ScienceThe performance of superalloy materials at high temperatures is what makes gas turbine technology possible. Continual improvement in superalloy properties and resultant elevation of operating temperatures drives higher efficiency and reduced environmental impact in both aerospace and energy applications. Given the technological and commercial significance of superalloys, their adoption into Additive Manufacturing is of vital importance. The Additive Manufacturing of nickel-base superalloys aims to optimize function through geometric complexity of engineered parts, while reducing product development and marketing times. However, there are challenges to overcome before these materials can be used in serial production. Most superalloys are susceptible to cracking when processed in laser-powder bed fusion processes, and cracking mechanisms must be understood and mitigated in order to produce fully-dense parts. Another challenge is in the postprocessing stage. Additively manufactured microstructures are unlike cast or wrought microstructures, and heat treatment regimens must be re-formulated based on the different starting microstructure. Inconel 939 is a cast Ni-base superalloy for service above 800°C and is widely used in hot-sections of industrial gas turbine engines. This thesis presents a study of the cracking behaviour of IN939, and based on fractographic results, shows solidification cracking to be the primary mechanism responsible. The design of heat-treatment necessitated a comprehensive study of the starting microstructure. This was performed by thermal analysis and metallography and equated to simulation results. Heat treatment trials were conducted and the resulting microstructure and room temperature mechanical properties were characterized. Results showed significant differences in the fractions and morphologies of strengthening phases, compared to the conventionally cast material, while room temperature mechanical properties were better or comparable. The obtained results form a basis for proceeding with high-temperature and creep testing of the material to prove its viability in AM.
- PostDevelopment of Layup Optimization Toolbox for Predicting and Reducing PCB Warpage(2018) Masinete, Nikhil; Chalmers tekniska högskola / Institutionen för industri- och materialvetenskap; Chalmers University of Technology / Department of Industrial and Materials Science
- PostDevelopment of the Floorball(2015) Fernandez, Sara Mateos; Chalmers tekniska högskola / Institutionen för material- och tillverkningsteknik; Chalmers University of Technology / Department of Materials and Manufacturing TechnologyAs a relatively new sport, the research specifically aimed at developing the game of floorball is limited. The aim of this thesis work was to develop a high performance ball while achieving as much as possible the requirements of International Floorball Federation (IFF). Based on a CAD model of the current design of the ball, some interesting variations of the geometry were introduced as a first approach. The alternative geometries studied were variations of surface dimples and hole geometries. Simulations were reproduced with CFD in order to study the aerodynamic parameters involved in the predictability of the flight. The most promising ball geometry was selected for prototypes made of polyamide and produced with an additive manufacturing technique. The flight performance of the prototypes was then studied by analysing the recorded ball trajectories. In an effort to further evaluate the performance of the prototype, compared with the other precision balls, parameters such as speed and aerodynamic coefficients were experimentally calculated. The major finding in this work was that the modified geometry of the holes of the ball may lead to a more predictable shot. The results suggest new improved ball designs having smaller hole diameter and hole edges with an inside chamfer.
- PostElectrical and thermal properties of high aspect ratio carbon-based polymer nanocomposites(2018) Aliskanovic, Emil; Chalmers tekniska högskola / Institutionen för industri- och materialvetenskap; Chalmers University of Technology / Department of Industrial and Materials ScienceThis project is a part of a collaboration of Borealis AB Stenungsund with Chalmers University of Technology. The objective of this project is to conduct an experimental study on the effect of different carbon based high aspect ratio fillers and different polymer architectures on the resulting thermal, electrical and morphological properties. A literature review was performed on the methods of analytical characterization, results of thermal and electrical properties for similarly used materials in this project. A deeper analysis has been made on the percolation theory which is the quintessential driving factor of the high aspect ratio fillers on the electrical properties. Parameters like filler type, polymer matrix, dispersion method, filler ratios and blend ratios are evaluated with respect to their impact on percolation threshold, degree of crystallinity, thermal stability, melting and crystallization temperature. Regarding the electrical properties of hybrid filler composites, it showed to have a synergetic effect when substituting 10 wt.% with another type of filler with different dimensionality. This was shown to be the case for three different hybrid systems. The degree of crystallinity was observed to have a parabolic trend where when combining certain fillers with each other. It was found that at equal parts of two different fillers, there was a maximum in the degree of crystallinity. Substituting 10 wt.% of a certain filler type showed to improve electrical properties that may be used in commercial applications to lower the cost of certain products. For further studies, a more in-depth analysis of the relationship between the different fillers could perhaps result in a better hybrid composite.
- PostEvaluation of corrosion in different parts of an oil refinery using corrosion coupons(2014) Olsson, Thomas B; Chalmers tekniska högskola / Institutionen för kemi- och bioteknik; Chalmers University of Technology / Department of Chemical and Biological Engineering
- PostExperimental characterization of pearlitic rail steel after thermomechanical straining(2019) Gren, Daniel; Carlsson, David; Chalmers tekniska högskola / Institutionen för industri- och materialvetenskap; Chalmers University of Technology / Department of Industrial and Materials ScienceRails are subjected to very high contact loads during service. The high contact loads cause the surface layer of the rails to be heavily deformed and aligned. The anisotropic nature of the deformed surface layer is prone to crack initiation. The deformed surface layer is also very thin and has a large gradient of accumulated strain. This large gradient makes it difficult to examine the material behavior with conventional testing methods because they requires a fairly uniform microstructure. A predeformation method developed by CHARMEC researchers have proven to be able to produce a material with a fairly uniform microstructure which is consistent with rail field samples with high accumulated shear strain. The aim with the Master Thesis was to expand the knowledge of the material behaviour of pearlitic rail steels (grade R260) under combined thermal and cyclic mechanical loading. The goal was to produce a microstructure with higher accumulated strains compared to previous work. It was achieved by adding a heat treatment to the predeformation method. An axial-torsion test rig with an induction coil has been used to deform and heat treat solid cylindrical test bars. This was done to obtain a microstructure that was similar to the one found in the field. The material was compared with field samples in terms of microstructure and hardness. The results of this thesis describes the mechanical behavior of a pearlitic rail steel during simultaneous axial compression and torsion with different compression loads at elevated temperature. The microstructures have been characterized and accumulated strain and hardness have been measured. The highest amount of accumulated strain was obtained with constant heating at 350 °C with an axial compression of 350 MPa and twist rate of 1.5 °/s. The amount of twisting was 3.5 times higher compared to previous work. Heating in between the twisting cycles resulted in the least amount of accumulated strain.
- PostFEM the Wood Revolution In-depth FE-analysis of a wood-glue-steel joint in a wind turbine tower(2019) Borglund Aspler, Emil; Jern, Linnéa; Chalmers tekniska högskola / Institutionen för industri- och materialvetenskap; Chalmers University of Technology / Department of Industrial and Materials ScienceModvion is a company that develop 150m tall wind turbine towers made out of modules of Engineered Wood Products (EWP), specifically Laminated Veneer Lumber (LVL). One of the big challenges in their design is the joining of the modules, which is the focus of this thesis. The joint design was given from the beginning along with physical test data from tensile tests performed at Research Institutes of Sweden (RISE). In this thesis a Finite Element (FE)-model of the joint was created, with the aim to replicate the response obtained from the physical tensile tests using simulations. The main goal was to use the FE-model in order to describe the inner mechanics of the joint. The joining of two LVL panels is made with Loctite CR 421 Purbond and a perforated steel plate. The joint and its materials are studied using physical testing and the commercial softwares ANSA as pre-processor, Abaqus Unified FEA as solver, and META as postprocessor. The material parameters for the wood given by data sheets provided by the manufacturer are compared to physical test data. Remaining material parameters and simulation parameters are calibrated through material validation and parameter studies. Finally a small study was performed on whether the joint can be improved by making modifications to the perforated steel plate. The effects of these modifications were studied in order to find the critical areas of the joint. The obtained results show that the number of holes in the steel plate are critical for the performance of the joint when it comes to its tensile strength. This is because the holes enables the glue to create adhesive anchors that facilitates the stress transfer from the glue to the steel. Since the steel plate is the component of the joint that can withstand the highest amount of loading, the efficiency of the stress transfer is crucial in order to prevent the glue from breaking entirely at relatively small loads, which would result in a lower ultimate tensile strength of the joint. Although, some insecurities remains in the implementation of the FE-model, the results in this thesis can be used as a foundation for future research on this topic.
- PostFinite element simulations of intergranular fracture of forged Haynes 282(2014) Isakson, Simon; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
- PostHeat treatment optimization of through-hardening bearing steels(2019) Larsson, Anton; Chalmers tekniska högskola / Institutionen för industri- och materialvetenskap; Chalmers University of Technology / Department of Industrial and Materials ScienceNon-contact infrared thermometers, such as pyrometers, are excellent for monitoring surface temperatures of objects that are moving, difficult to reach or extremely hot without damaging the object. Pyrometers are also easy to handle and often less expensive than contact temperature sensors. If pyrometers are to be used in a greater extent at SKF when evaluating or creating new heat treatment recipes for large bearings, more data is needed. The purpose of the study was to evaluate the current heat treatment recipes with the help of a hand held pyrometer. Twelve inner rings and ten outer rings of a large spherical roller bearing made from the through hardening bearing steel 100CrMnMoSi8-4-6 were measured and the results were verified using thermocouples. The pyrometer measurements showed consistent heat-up and soaking times for inner and outer rings, respectively, and relatively small time differences compared to the thermocouple measurements. Soaking time between the inner and outer rings as well as between the different furnaces did, however, differ quite a lot. The author concludes that pyrometers can be used effectively to monitor the heat treatment and that the inner ring’s recipe should be changed to assure a more consistent heat treatment.
- PostHigh Temperature Corrosion of Coated and Uncoated Nickel Based Alloys in a H2O/CO2 Combustion Gas Environment(2013) Berndtsson, Markus; Chalmers tekniska högskola / Institutionen för kemi- och bioteknik; Chalmers University of Technology / Department of Chemical and Biological Engineering
- PostInfluence of Repeated Recycling and Aging Effects on Mechanical Performance of WEEEBR(2014) Yu, Ze; Chalmers tekniska högskola / Institutionen för material- och tillverkningsteknik; Chalmers University of Technology / Department of Materials and Manufacturing TechnologyWEEE is a complicated waste stream from a recycling point of view. About 20-35 wt% of WEEE is usually plastics, which previously have been found possible to mechanically recycle. One way to recycle the WEEEBR plastic is to improve the mixing state by extrusion compounding, such as previously done at Chalmers. The influence of combined accelerated aging and repeated extrusion on mechanical and thermal performance is studied in this work. Although the onset temperature of the thermo-oxidative degradation was almost the same for different accelerated aging times, the difference in mechanical properties was significant. The aging performed was found to cause a substantial decrease in elongation at break, an increase in stiffness and an unchanged ultimate tensile strength, also after relatively low aging times corresponding to 2-4 years use time at room temperature. For longer aging times, corresponding to 10-16 years use time at room temperature, there was a small decrease in both tensile strength and elongation at break, while the stiffness remained at about 1,2GPa. After the combined extrusion and accelerated aging corresponding to 2 years cycles, the elongation at break decreased after aging, while stiffness and tensile strength decrease after the extrusion of the third cycle. The thermal evaluation indicated the state of physical aging of the amorphous styrenic polymers part of the material.
- PostIntroducing composite material in car bonnet(2016) Schulz, Johan; Kalay, Hakan; Chalmers tekniska högskola / Institutionen för material- och tillverkningsteknik; Chalmers University of Technology / Department of Materials and Manufacturing TechnologyThe cars of today tend to be quite heavy in the front meanwhile light in the rear, mainly due to the location of the engine compartment and powertrain in the front of the car. If the front weight of the car could be reduced, the car could be more balanced and also the most discussed parameter for cars, namely emission of carbon dioxide, can be reduced,. This study aims to investigate how to introduce a composite materials in the bonnet, with the focus on reducing the weight, while meeting important demands on the bonnet. In this study it was chosen to consider the demands related to pedestrian safety and the stiffness of the bonnet. Pedestrian safety is a complex demand saying that the bonnet should be able to absorb a certain amount of energy from a head impact without getting the pedestrian injured. From an extensive literature study three potential material structures were found to be appropriate regarding impact resistance and flexural stiffness. Carbon fibre reinforced epoxy (CFRP)/Polyvinylchloride (PVC) foam sandwich material, aluminium/polycarbonate sandwich material and Hybrix micro-sandwich material are the materials explored in the literature study to be appropriate candidates for the demands chosen in this study. As seen in recent research based on simulations of impact resistance, some materials are especially interesting. Considering those more interesting materials, it was decided to purchase and build beam sections of each material sharing the same geometry to perform impact tests in the drop tower facility at Volvo Cars Corporation (VCC) in Gothenburg. Of those three materials selected only two materials could be compiled due to the time limit of the project. The material excluded from testing was the Al/PC sandwich material. In additional to the potential stiff and impact resistant materials, also an aluminium beam was built sharing the same geometry as the other materials and the impact resistance and stiffness of samples were measured and compared with the aluminium material used in the current bonnets at VCC. Additional to the impact tests, also a three point bending test was performed on the different materials samples according to VCC and ASTM standards, in order to determine the stiffness of the structures studied. The results showed that the CFRP/PVC foam sandwich material absorbed least amount of energy at the impact test. The amount of energy absorbed was only in the elastic region of the material, but the structure did not have the ability to deform plastically. It was interesting to note that this kind of structure indicated a possibility to reduce weight, by approximately 24 % lighter than the current aluminium material. The Hybrix material combined with steel absorbed most amount of energy but was 27 % heavier than the current aluminium material. Finally, the three point bending showed that the aluminium structure had the highest stiffness of the samples studied.
- PostInvestigation of hot cracking in additive manufactured nickel-base superalloys(2018) Hallberg, Emil; Chalmers tekniska högskola / Institutionen för industri- och materialvetenskap; Chalmers University of Technology / Department of Industrial and Materials ScienceAdditive manufacturing (AM) offers an unprecedented freedom of design and enables production of complex geometries with competitive mechanical properties, such as components for aerospace engines and gas turbines. Some commonly used materials, such as γ’ precipitation strengthened Ni-base superalloys, are susceptible to cracking during both AM processing and subsequent densification and/or heat treatment. Therefore, to fully utilize the potential that AM offers, it is crucial to optimize the manufacturing process in order to minimize the amount of defects in the final product. The aim of this study is to reduce the amount of defects, primarily micro-cracks, in a laser powder bed fusion (LPBF) processed γ’ precipitation strengthened Ni-base superalloy. LPBF process parameter optimization, by using a design of experiment approach lead to reduction of defect density to very low levels. This was followed by a statistical data analysis to investigate how different parameters relate to defect formation. Furthermore, it is shown that post-AM hot isostatic pressing (HIP) can completely eliminate remaining micro-cracks. In addition, after HIP above a certain temperature and pressure (1210°C and 1000 bar), cracks did not re-open during subsequent high temperature heat treatment. SEM/EDX analysis showed that only small non-metallic inclusions remained after HIP+HT at these conditions. Finally, it is shown that by applying a tailored temperature-pressure profile, strain age cracking during HIP and heat treatment can be completely avoided.
- PostLignin-based bio composites: Exploring compatibility and potentials in a batch system(2019) Torstensson, Alexandra; Chalmers tekniska högskola / Institutionen för industri- och materialvetenskap; Chalmers University of Technology / Department of Industrial and Materials ScienceThe growing concern of the depletion of fossil resources as well as the increasing awareness of the environmental impact of petroleum-based products has led to an increased interest in materials based on renewable resources. One of the most abundant natural resources in Sweden is wood, providing, among other, material for the paper and pulp industry. The processes used in this industry creates lignin as a byproduct, most of which is used as a low-cost bio-fuel. An attractive alternative to this use would be to modify the lignin to be used as a value-added thermoplastic polymer. The Swedish company RenCom is contributing to this work by developing a thermoplastic lignin that can potentially be blended with ordinary thermoplastics, creating bio-composites. This master thesis aims to produce and investigate different thermoplastic composites containing modified lignin. The final material properties will be analyzed to find potential matrices of interest for the further development of ligninbased composites.