| 1. |
- Chedid, Michel, 1977-
(författare)
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Wearable Systems in Harsh Environments : Realizing New Architectural Concepts
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wearable systems continue to gain new markets by addressing improved performance and lower size, weight and cost. Both civilian and military markets have incorporated wearable technologies to enhance and facilitate user's tasks and activities. A wearable system is a heterogeneous system composed of diverse electronic modules: data processing, input and output modules. The system is constructed to be body-borne and therefore, several constraints are put on wearable systems regarding wearability (size, weight, placement, etc.) and robustness rendering the task of designing wearable systems challenging. In this thesis, an overview of wearable systems was given by discussing definition, technology challenges, market analysis and design methodologies. Main research targeted at network architectures and robustness to environmental stresses and electromagnetic interference (EMI). The network architecture designated the data communication on the intermodule level - topology and infrastructure. A deeper analysis of wearable requirements on the network architecture was made and a new architecture is proposed based on DC power line communication network (DC-PLC). In addition, wired data communication was compared to wireless data communication by introducing statistical communication model and looking at multiple design attributes: power efficiency, scalability, and wearability.The included papers focused on wearable systems related issues including analysis of present situation, environmental and electrical robustness studies, theoretical and computer aided modelling, and experimental testing to demonstrate new wearable architectural concepts. A roadmap was given by examining the past and predicting the future of wearable systems in terms of technology, market, and architecture. However, the roadmap was updated within this thesis to include new market growth figures that proved to be far less than was predicted in 2004. User and application environmental requirements to be applied on future wearable systems were identified. A procedure is presented to address EMI and evaluated solutions in wearable application through modelling and simulation. Environmental robustness and wearability of wearable systems in general, and washability and conductive textile in particular are investigated. A measurement-based methodology to model electrical properties of conductive textile when subjected to washing was given.Employing a wired data communication network was found to be more appropriate for wearable systems than wireless networks when prioritizing power efficiency. The wearability and scalability of the wired networks was enhanced through conductive textile and DC-PLC, respectively. A basic wearable application was built to demonstrate the suitability of DC-PLC communication with conductive textile as infrastructure. The conductive textile based on metal filament showed better mechanical robustness than metal plated conductive textile. A more advanced wearable demonstrator, where DC-PLC network was implemented using transceivers, further strengthened the proposed wearable architecture. Based on the overview, the theoretical, modelling and experimental work, a possible approach of designing wearable systems that met several contradicting requirements was given.
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| 2. |
- Pinate, Santiago
(författare)
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Control of particles codeposition and strengthening mechanisms in nickel based nanocomposite coatings
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Surface durability is a key factor in the service life of components. Depending on the aggressiveness of the environment, surface deterioration by wear or corrosion leads to failure of the bulk material and eventually to the loss of functionality of the component. Therefore, designing surfaces to withstand service requirements is a critical aspect for industrial product realisation.Electroplating is an attractive technique to mass-produce affordable protective coatings due to its low cost and high performance, easy maintenance of the process, and adjustable production times. Producing nanocomposite coatings by electroplating has received significant attention for decades due to their potential to provide excellent wear and corrosion protection.Nanocomposites provide the possibility of combining different materials to achieve multifunctionality and, due to the nanometer size of the reinforcer phase, promote additional strengthening effects in the matrix not present in microcomposites. Additionally, the reduction in the size of the reinforcer provides advantages in wear protection as the risk of third-body abrasion is reduced. However, the industrial applicability remains limited due to the lack of control in their production process.The present work focuses on the relationship between the input parameters and the codeposition of SiC, MoS2 and graphite particles, identifying critical factors and providing methods to control the process better. Furthermore, a correlation between the nickel matrix microstructure and codeposition is established, linking them to the strengthening effects and final performance of the nanocomposite coating.New methods were developed to provide a reproducible electroplating process. A surface treatment for the reinforcing powder minimised the differences between the particles surface state deriving from different batches, supplier or production routes. Composites produced with surface-treated nanoparticles showed reproducible results displaying similar codeposition rate andhardness values. Additionally, a pulse-reverse plating waveform, adapted to the SiC particles average size, was designed and optimised to deposit a reproducible and improved particles content even in the presence of anionic surfactants, typically used to reduce coatings porosity and defects.The study of the impact of the reinforcer phase on the electrocrystallisation of the nickel matrix showed that the microstructure was significantly affected by the size, chemistry and dispersion of the particles, promoting changes in the preferred crystal orientation, grains morphology and size. The strengthening mechanisms were linked to the microstructural changes resulting from the process parameters, particles codeposition and the agitation mode. Different models were used to predict the hardness of the composites based on the contribution and combination of each strengthening factor: Hall-Petch, Orowan, enhanced dislocation density and particles incorporation, showing a good agreement with the experimental data.Furthermore, the wear behaviour of the composites was analysed and connected to the hardening effects. The analysis highlighted how particles content, dispersion, type and size of the reinforcer contribute to the protection against wear.A novel multifunctional composite coating based on a dual dispersion mix of hard SiC particles and self-lubricant MoS2 particles was designed, resulting in a surface with high hardness, low friction and low wear.
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| 3. |
- Zhu, Baiwei
(författare)
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On the influence of Si on anodising and mechanical properties of cast aluminium alloys
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The combination of two cost-effective processes, i.e. casting and anodising, would be an interest for the aluminium component applications. However, there are some obstacles in the application of anodising on cast Al alloys. The challenges mostly relate to the alloying elements especially Si and the surface quality. With the development of casting process, cast aluminium alloys with low Si content can be casted, and a complex geometry component with reasonably good surface finish can be achieved. This study aims to identify the influence of Si on anodising and mechanical properties of Al-Si alloys.In this study, six Al-Si alloys with three different Si level and two different Sr level were investigated. Sr acts as a modifier to change the morphology of Si particles. The directional solidification technology was used to vary the microstructure coarseness by controlling the cooling rate to study the influence of Si level, Si particle morphology and cooling rate on mechanical properties, oxide layer formation and corrosion protection performance in cast Al-Si alloys.This study has observed that Si has a significant influence on anodising. During anodising, Si particles are anodised at a lower rate than the Al phase. The presence of Si particles in eutectic phase make the oxide layer locally thinner and more defected due to the low oxide growth rate in eutectic phase. This study observed the presence of residual metallic Al phase beneath or between Si particles. Due to their presence and their geometry, Al can be shielded by Si particles and prevented from oxidation. Si particles also act as a key role in the corrosion protection of oxide layer in Al-Si alloys. The corrosion attack propagates along Si particles as well as oxide defects to the Al substrate.It is found that the morphology of Si particles has a significant influence on the oxide layer formation and corrosion protection performance of the oxide layer on cast Al-Si alloys. A substantially improvement the corrosion resistance of anodised layer on Al-Si alloys is attributed to the morphology change from interconnected flakes to disconnected Si fibres when Sr is added, with less oxide defects and better oxide distribution.The Si level governs the mechanical properties of Al-Si based alloys. An increase of Si content in Al alloys improves the mechanical properties such as ultimate tensile and yield strength as well as hardness of the materials, but decreases the ductility. However, an increase of Si level in Al alloys decreases the thickness of oxide layer, and thereby, the corrosion protection of the oxide layer is deteriorated.
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| 4. |
- Arwidson, Jonas, 1972-
(författare)
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Thermal Fatigue Life Prediction of Solder Joints in Avionics by Surrogate Modeling : A Contribution to Physics of Failure in Reliability Prediction
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Manufacturers of aerospace, defense, and high performance (ADHP) equipment are currently facing multiple challenges related to the reliability of electronic systems. The continuing reduction in size of electronic components combined with increasing clock frequencies and greater functionality, results in increased power density. As an effect, controlling the temperature of electronic components is central in electronic product development in order to maintain and potentially improve the reliability of the equipment. Simultaneously, the transition to lead-free electronic equipment will most probably propagate also to the ADHP industry. Compared to well-proven tin-lead solder, the knowledge about field operation reliability of lead-free solders is still limited, as well as the availability of damage evaluation models validated for field temperature conditions. Hence, the need to fill in several knowledge gaps related to reliability and reliability prediction of lead-free solder alloys is emphasized. Having perceived increasing problems experienced in the reliability of fielded equipment, the ADHP industry has suggested inclusion of physics-of-failure (PoF) in reliability prediction of electronics as one potential measure to improve the reliability of the electronic systems.This thesis aims to contribute to the development of reliable ADHP systems, with the main focus on electronic equipment for the aerospace industry. In order to accomplish this, the thesis provides design guidelines for power distribution on a double-sided printed circuit board assembly (PBA) as a measure to improve the thermal performance without increasing the weight of the system, and a novel, computationally efficient method for PoF-based evaluation of damage accumulation in solder joints in harsh, non-cyclic field operation temperature environments.Thermal fatigue failure mechanisms and state‑of‑the‑art thermal design and design tools are presented, with focus on the requirements that may arise from avionic use, such as low weight, high reliability, and ability to sustain functional during high vibration levels and high g-forces. Paper I, II, and III describes an in-depth investigation that has been performed utilizing advanced thermal modeling of power distribution on a double-sided PBA as a measure to improve the thermal performance of electronic modules.Paper IV contributes to increasing the accuracy of thermal fatigue life prediction in solder joints, by employing existing analytical models for predicting thermal fatigue life, but enhancing the prediction result by incorporating advanced thermal analysis in the procedure.Papers V and VI suggest and elaborate on a computational method that utilizes surrogate stress and strain modeling of a solder joint, to quickly evaluate the damage accumulated in a critical solder joint from non-cyclic, non-simplified field operation temperature profiles, with accuracy comparable to finite element modeling. The method has been tested on a ball grid array package with SnAgCu solder joints. This package is included in an extensive set of accelerated tests that helps to qualify certain packages and solder alloys for avionic use. The tests include -20°C to +80°C and -55°C to +125°C thermal cycling of a statistically sound population of a number of selected packages, assembled with SnAgCu, Sn100C, and SnPbAg solder alloys. Statistical analysis of the results confirms that the SnAgCu-alloy may outperform SnPbAg solder at moderate thermal loads on the solder joints.In Papers VII and VIII, the timeframe is extended to a future, in which validated life prediction models will be available, and the suggested method is expected to increase the accuracy of embedded prognostics of remaining useful thermal fatigue life of a critical solder joint.The key contribution of the thesis is the added value of the proposed computational method utilized in the design phase for electronic equipment. Due to its ability for time-efficient operation on uncompressed temperature data, the method gives contribution to the accuracy, and thereby also to the credibility, of reliability prediction of electronic packages in the design phase. This especially relates to applications where thermal fatigue is a dominant contributor to the damage of solder joints.
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| 5. |
- Mølmen, Live
(författare)
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Durability evaluation of PEM fuel cell components
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Proton exchange membrane fuel cells (PEMFCs) are used to convert hydrogen and oxygen to electricity, heat, and water. There are no greenhouse gas emissions, given that the hydrogen is produced from renewable sources, such as water electrolysis from wind, hydro or solar energy. PEMFCs can be found on the commercial market today, predominantly in applications such as forklifts, passenger cars and combined heat and power units. The PEMFC is a new technology, and there are hurdles to overcome, mainly with regard to price and durability.In this work, two PEMFC components are the main focus: the bipolar plate and the catalyst. For the bipolar plate, the effect of defects from fabrication is investigated to further understand the critical factors for corrosion and how to avoid it. Droplets from laser cutting and cracks in the coating due to the forming of pre-coated plates are both identified as possible sources of corrosion. However, by correct design, both can be avoided or made less critical. Laser welding stainless steel 304 is, on the other hand, found not to be a source of corrosion under simulated PEMFC bipolar plate conditions. Furthermore, tailoring the properties of a multicomponent alloy coating by additions of Ta and W is explored to stabilise the coating at higher potentials in the acidic environment of the PEMFC. Ta is found to achieve a protective passive layer at a lower concentration than W. However, it does significantly increase the interfacial contact resistance. One-step synthesis of a ternary alloy by electrodeposition is studied for the catalyst to allow for facile screening of new alloy compositions, both in- and ex-situ. The ternary alloy gives comparable results to the binary alloy even at lower Pt content.As the PEMFC has entered the commercial market relatively quickly, there is a lack of standardised tests, both on the component and system level. The procedure for testing the interfacial contact resistance of the bipolar plate is studied in detail, and the methodology is further developed to ensure reliable and comparable results.
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| 6. |
- Mølmen, Live
(författare)
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Materials Reliability in PEM Fuel Cells
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As part of the global work towards reducing CO2 emissions, all vehicles needs to be electrified, or fueled by green fuels. Batteries have already revolutionised the car market, but fuel cells are believed to be a key energy conversion system to be able to electrify also heavy duty vehicles. The type of fuel cell commercially available for vehicles today is the polymer electrolyte membrane fuel cell (PEMFC), but for it to be able to take a larger market share, the cost must be reduced while sufficient lifetime is ensured.The PEMFC is a system containing several components, made of different materials including the polymer membrane, noble metal catalyst particles, and metallic bipolar plate. The combination of different materials exposed to elevated temperature, high humidity and low pH make the PEMFC components susceptible to corrosion and degradation.The noble metal catalyst is one of the major contributors to the high cost. In this work, the latest research on new catalyst materials for PEMFCs are overviewed. Furthermore, electrodeposition as a simple synthesis route to test different Pt-alloys for the cathode catalyst in the fuel cell is explored by synthesis of PtNi and PtNiMo. The gas diffusion layer of the PEMFC is used as substrate to reduce the number of steps to form the membrane electrode assembly.In addition to cheaper and more durable materials, understanding of how the materials degrade, and how the degradation affects the other components is crucial to ensure a long lifetime. Finding reliable test methods to validate the lifetime of the final system is necessary to make fuel cell a trusted technology for vehicles, with predictable performance.In this work, commercial flow plates are studied, to see the effect of different load cycles and relative humidities on the corrosion of the plate. Defects originating from production is observed, and the effect of these defects on the corrosion is further analysed. Suggestions are given on how the design and production of bipolar plates should be made to reduce the risk of corrosion in the PEMFC.
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| 7. |
- Pinate, Santiago
(författare)
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Study of particle-current-electrocrystallization interactions in electroplating of Ni/SiC coatings
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Composite coatings have great potential due to the possibility to combine properties of two different materials in one coating. This way, new surface properties can be tailored and applied to any material's surface. Among different manufacturing routes, electrodeposition has the biggest potential in creating composite metal matrix coatings, especially nanocomposites. Nevertheless, there is a knowledge gap between the deposition of composite coatings in laboratory conditions, described in the literature, and those that are now in place on an industrial level. While micro-composites have been industrialised for about ten years, the production of Ni/SiC nanocomposite coatings by electroplating is still far from an industrial manufacturing floor. This is due to the lack of understanding of the mechanisms of nanoparticles codeposition leading to scattering results.The production of nanocomposite coatings is much more sensitive to the process parameters compared to microcomposite. The correlation between parameters and their influence on the codeposition are still not fully identified and understood. The codeposition models proposed in the literature are only valid in specific conditions, but composite depositions behave differently, or even opposite if some of the variables are modified.The main objective of this work is to identify the particle-current-electrocrystallization interactions in the production of Ni/SiC nanocomposites. A series of experiments are designed to isolate single variables and identify the controlling parameters of these interactions and their impact on the final properties.In this thesis, the effect of current density, type of current and particles size are identified as primary variables controlling the metal crystallisation and coatings properties.Among many parameters, a specific current waveform in pulse reverse mode proved to increase the codeposition rate effectively, doubling the content of nanoparticles compared to other techniques. Ultrasound assistance is also considered as stirring method when particles are suspended in the deposition bath to increase their stability and dispersion. The effect of Ultrasound on the particles codeposition and metal crystallisation is studied and compared to silent condition.Moreover, a surface treatment for the particle has been proven successful in making any particle to behave similarly in the Ni deposition bath. Furthermore, the codeposition rate doubled or tripled compared to untreated ones thanks to this treatment. Both ultrasonic agitation and surface treatment reduce the formation of aggregates, improving the particle dispersion and metal microstructure thus increasing the final hardness.The work proved the synergistic effect between particle and metal microstructure which affected the final properties of the coating. Therefore, when tailoring the composite coating to improve hardness, it is not only the amount of the particles that should be considered but also their influence on the electrocrystallisation process.
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| 8. |
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| 9. |
- Gunnarsson Sarius, Niklas, 1976-
(författare)
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Surface Technology for Optical and Electrical Connectors
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis treats surface engineering with the purpose of improved quality of optical and electricalconnectors with a focus on electroplated and magnetron sputtered materials. In electroforming of tools formanufacturing optical connectors, the influence of ultrasonic agitation on intrinsic stresses and fillingproperties of electroplated Ni has been studied. It is established that the ultrasonic agitation at the substratesurface during deposition impacts the intrinsic stresses making it possible to increase deposition rate viacurrent density, with stress-free or low-stress levels in the Ni layers. Reduced variations of the intrinsicstress over the surface with the current density is a further important result. Filling of grooves byelectroplating of Ni using ultrasonic agitation is demonstrated. This is due to increasing mass transport ofspecies into the grooves compared to conventional pumped agitation. The enhanced filling propertiesmakes it possible to electroplate Ni in the bottom of high-aspect-ratio grooves. In order to industriallyimplement new nanocomposite coatings on electronic connectors, studies have been performed regardingthe thermal diffusion barrier properties against Cu for Ti-Si-C and Ti-Si-C-Ag nanocomposites, depositeddirectly onto Cu substrates or with sputtered Ni, Ti or electroplated Ni as an intermediate coating. Theapplication of an electroplated Ni diffusion barrier coating, hinders Cu from reaching the surface of thenanocomposites. Also, Ti-Si-C-Ag nanocomposite deposited on magnetron sputtered Ni or Ti on Cusubstrates hinder Cu from diffusing to the surface after annealing. The contact resistance of Ag-Pdtopcoated Ti-Si-C-Ag-Pd and Ti-Si-C-Ag nanocomposite coatings in contact with hard gold is shown tocompete with hard gold in contact with itself, as electrical contact coatings at contact forces around 5 N.Ag-Pd topcoated Ti-Si-C-Ag-Pd in contact with hard gold is shown to have approximately the same contactresistance as hard gold in contact with hard gold at contact forces around 0.1 N, which here is in the 10 mΩrange, while Ti-Si-C-Ag nanocomposite coatings in contact with hard gold has a contact resistance that isup to 10 times higher. The overall contribution of this thesis can be summarised as a deeper knowledge andunderstanding of techniques and coatings, that help reduce cost and increase reliability of electronics.
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| 10. |
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