This research is focused on investigating the mechanical behavior of Fused Deposition Modeling (FDM) processed CFRP/Al hybrid riveted joints at elevated temperatures. A two-pronged approach was adopted entailing experimental and computational domains. In the experimental thrust, the developed joint was evaluated for its mechanical behavior by employing Digital Image Correlation, micro-XCT, and fractographic analysis. The tensile testing was performed at four different temperatures, i.e., Room Temperature (RT), 50°C, 75°C, and 100 °C. At RT, the joint experienced net-sectioning in the CFRP sheet along with minute secondary bending. Further, distinct failure modes were noticed for each ply orientation where the inherent porosity/voids appeared as the governing factor for the damage progression. Novel constitutive models were developed using accrued strain and change in energy dissipation to estimate the damage progression. The damage accumulation was found to be more uniform in the 0° layer as compared to 90°. Moreover, the 90° layer exhibited a more catastrophic damage pattern toward final failure. At elevated temperatures, a significant reduction in mechanical properties along with a non-uniform warping/bending of the plies was noticed due to viscoelastic behavior change. The computational analysis, having a hierarchical approach, was performed for the validation of the experimental results, and both were found to be in good agreement.

This research focused on developing a novel Friction Stir Riveting (FSR) technique, viz., Friction Stir Blind Riveting for pre-drilled holes (FSBR-pH), to improve the mechanical performance of hard-to-access aircraft joints. This objective is realized through a hierarchal four-pronged experimental and numerical analysis approach. Firstly, the existing FSBR process was evaluated where the existing process was found infeasible for pre-drilled holes. The existing process was then modified to develop good quality joints in case of pre-drilled holes. In the second step, a process window was created for FSBR-pH joints through (a) microscopic analysis of joint cross section to observe the presence of any defects/gaps and (b) numerical simulation. Microstructural and mechanical characterization (i.e., tensile strength and microhardness) of the optimized joints were performed in the third step where the presence of dynamic recrystallization was found responsible for the formation of submicron-sized grain in the stir region. The strain-hardening phenomenon was observed in the stir region which occurred due to extensive stirring at high spindle speeds. Finally, a comparison of the developed joints was drawn with existing Blind Riveted (BR) joints in terms of failure modes and tensile strength where the FSBR-pH joints performed better than their existing counterparts. 

The environmental, social and economic sustainability of our infrastructure network is clearly of paramount importance to the road-engineering sector as well to society at large. Sustainable road materials and reduced transport of those materials therefore play a significant role. Cold mix asphalt (CMA) emulsion technology could be one of the better options for the road industry to explore more thoroughly. Given its lower start-up and equipment installation costs, lower energy consumption and reduced environmental impact, CMA should offer a reliable alternative to some of the Hot Mix Asphalt (HMA) or Warm Mix Asphalt (WMA) options. As CMA is not a new technology, there are many reasons why this material is not currently being used as extensively as it might be. Though risk adverseness of the market may be partly to blame for this, a number of technical challenges and uncertainties related to material behavior are certainly responsible. This thesis has addressed some of the important technical challenges, aiming to provide more guidance in material selection and design, and prediction of the behavior of emulsion-based CMAs. To do so, this research has focused on aspects of the correct formulation of the bitumen emulsions, how to select the correct combinations of material components, and how to control the breaking and coalescence processes in bitumen emulsions better, resulting in usable and predictable adhesive and cohesive bond strengths. Though most of the laboratory and modeling choices that were made in this thesis are based on theoretical considerations, the main contribution is the test protocol development. The systematic surface free energy measurements of the material components, combined with the test set-up to monitor controllably the breaking and coalescence behavior of bitumen droplets in an emulsified environment, gives a new way to approach the design of CMA. It is recommended that future research is focused on taking the developed protocols as a basis for enhanced mix design and making a direct link to validated long-term mechanical properties on the asphalt mixture scale.

Miljömässig, social och ekonomisk hållbarhet är av största betydelse för vår infrastruktur både inom vägbyggnadsområdet och inom samhället i stort. Där kan hållbara vägbyggnadsmaterial och minskade transporter av vägbyggnadsmaterial ge ett betydande bidrag. Tekniken med kallblandade asfaltemulsionsbeläggningar (CMA) är en av de bättre lösningarna för vägbyggnadsindustrin som skulle kunna användas i större utsträckning än som görs för närvarande. Givet teknikens låga uppstarts- och investeringskostnader, minskad energiförbrukning och minskad miljöpåverkan, kan CMA bli ett attraktivt alternativ till varmblandade (HMA) och halvvarma (WMA) asfaltmassor. Då CMA inte är någon ny teknik, finns många skäl att fundera över varför denna teknik inte praktiseras i så stor omfattning idag. Obenägenheten att ta risker med ny teknik på marknaden delvis kan beskyllas för detta, men också ett flertal osäkerheter kopplade till materialegenskaper hos CMA kan också bidra. Denna avhandling har studerat några viktiga tekniska utmaningar med syfte att ge mer vägledning vid materialval och utformning, samt att förutse materialbeteenden hos emulsionsbaserade CMA. För att nå detta har denna forskning fokuserats på sammansättningen av bitumenemulsioner, hur man väljer rätt kombination av materialkomponenter och hur man får en bättre kontroll på brytförloppet och koalescensen, med målet att kunna förutsäga adhesiv och kohesiv bindningsstyrka. Då de flesta laborativa och modelleringsmässiga valen i denna avhandling är baserade på teoretiska överväganden, är det viktigaste bidraget i denna rapport utvecklingen av testprotokollen. De systematiska mätningarna av fri ytenergi hos materialkomponenterna, kombinerat med testmetoder för att på ett kontrollerat sätt studera bryt- och koalescensbeteendet hos droppar i en emulsionsmiljö, ger en ny möjlighet att optimera sammansättningen av CMA. Det rekommenderas att framtida forskning fokuseras på att ta de föreslagna protokollen som bas för förbättrad proportionering och att göra en direkt koppling till validerade mekaniska långtidseffekter på asfaltbeläggningen.

Nyckelord

Bitumen, Kallblandad Asfalt, Mineraler/Aggregat, Fri Ytenergi, Sorption, Kontaktvinkel, Bitumenemulsioner, Brytning och Koalescensen, Emulgatorer, Adhesionsegenskaper.

Several roads in Iceland with bio-oil modified surface dressings exhibited severe distresses such as bleeding, binder drain down, and eventually as surface dressing sticking to tires. Samples from six road sections were evaluated in the laboratory to determine the causes of the failure. Binders with and without bio-oil, rapeseed oil and fish oil, were evaluated through a comprehensive rheological and chemical characterization. Both oils, exhibited solubility issues with the bitumen; consequently, the oils covered the aggregates, preventing bonding between binder and stones. It appears that fish oil worked a little better than rapeseed oil for binder modification.

The performance of asphalt mixtures is strongly influenced by the physical and chemical properties of the minerals and binders used, at various micro to macro scales. In cold asphalt mixtures a process that particularly strongly influences adherence between the minerals and binders (and thus performance) is the wetting of bitumen on the minerals’ surfaces. Their adhesion is influenced by numerous factors and parameters, such as surface free energies of both binders and aggregates in the presence of moisture or dust on the surface of aggregates, mixing temperatures, surface textures including open porosity, nature of the minerals and their surface chemical composition, as well as additives present in the binder phase. However, the relationships involved are not fully understood. Thus, iowever

n this study the surface free energies of both minerals/aggregates and binders were characterized using two approaches, one based on contact angles and the other on vapor sorption methods. Precise specific surface areas of four aggregates and seven minerals were determined using BET (Brunauer, Emmett and Teller) theory, by measuring the physical adsorption of selected gas vapors on their surfaces, and calculating amounts of adsorbed vapors corresponding to monolayer occupancy on the surfaces. Interfacial bond strengths between bitumen and aggregates were also calculated, based on measured surface free energy components of minerals/aggregates and binders, in both dry and wet conditions. The adhesive bond strength for the binder with each mineral/aggregate combination in wet condition has been improved by using additives. The presented study has highlighted the need for accurate measurements of aggregates’ and minerals’ specific surface areas and (hence) requirements to develop new approaches to resolve problems associated with BET-based methods.

Cold mix bitumen emulsion technology is getting a lot of focus by the road industries since a few decades due to the diminished environmental impacts and reduced energy associated with it. The durability and mechanical performance of cold asphalt mixtures very much depend on the breaking, coalescence and phase separation processes in bitumen emulsions; however, the exact nature of the breaking mechanism of bitumen emulsion is not completely understood today. During coalescence or relaxation process, two bitumen droplets are completely fused into a unique spherical droplet and their kinetic is usually recorded in terms of time, denoted as relaxation time or τ_relaxation.  In this work, a two dimensional Phase Field model was used to simulate the coalescence process of two bitumen droplets in water phase. The numerical model is based on Finite Element Method and solves Navier-Stokes system of equations coupled with the Cahn-Hilliard equation. The model predictions are validated by direct comparison with the experimental measurements performed in our previous work. Moreover, the study was extended to the small size (order μm) bitumen droplets which are difficult to produce and handle via experimental methods.  

Cold mix asphalt (CMA) emulsion technology could become an attractive alternative for the road industry due to low startup and equipment installation costs, diminished energy consumption and reduced environmental impact. The performance of cold asphalt mixtures produced from emulsions is strongly influenced by a good control of the breaking and coalescence process. The wetting of bitumen on the surface of the aggregates is hereby of major importance for the performance of the asphalt. Premature coalescence of the bitumen emulsions away from the surface, could lead to poor adhesion and decreased mechanical strength of the asphalt. Today, the breaking and coalescence mechanisms of bitumen emulsions are still not fully understood due to their complexities and the lack of fundamental experimental methods and existing models. However, in the past years efforts have been made in defining relationships for understanding the bitumen emulsions. In this paper, a new experimental method is presented to study coalescence of bitumen by using shape relaxation of bitumen droplets in an emulsion environment. The coalescence of spherical droplets of different bitumen have been correlated with neck growth, densification and surface area change during the coalescence process. The test protocol was designed in a controlled climate chamber, to study the coalescence process with varying environmental conditions. The kinetics of the relaxation process was influenced by the temperature as well as other parameters. The research showed that the developed test procedure is repeatable and able to study the coalescence process on a larger scale. However, the relationship between the measured parametric relationships at the larger scale and the bitumen emulsion scale still needs further investigation.

Cold mix asphalt (CMA) emulsion based technology is a potential option to replace traditional hot mix asphalt due to environmental benefits and less energy consumption of producing it. However, there are some issues concerned with CMA, for instance, pre-mature coalescence of bitumen emulsions while mixing with minerals or aggregates, which might need more attention to improve the performance of CMA. Actually, the adhesion between the binder and the aggregate surface is largely dependent on the breaking process of bitumen emulsions and the water push-out from the mixtures. This breaking process helps to predict the materials behavior as well as the long term mechanical performance of the mixtures; however, the exact nature of the breaking mechanism of bitumen emulsion is not completely understood until today. The objective of this research is to develop understanding of the structural changes during the phase separation and coagulation stages of the bitumen emulsion. Wettability of bitumen was analyzed by changing the substrate climate conditions. Moreover, this study was extended with the addition of emulsifier and other additives to the binder itself as well as to the water phase. Similar kinds of experiments were setup for exploring the coalescence of bitumen drops in water and emulsifier with other additives.

Nanostructured powders of thermoelectric (TE) CoSb3 compounds were synthesized using a chemical alloying method. This method involved co-precipitation of oxalate precursors in aqueous solution with controlled pH, followed by thermochemical treatments including calcination and reduction to produce stoichiometric nanostructured CoSb3. Moreover, CoSb3 nanoparticles were consolidated by spark plasma sintering (SPS) with a very brief processing time. Very high compaction densities (>95%) were achieved and the grain growth was almost negligible during consolidation. An iterative procedure was developed to maintain pre-consolidation particle size and to compensate Sb evaporation during reduction. Significant changes in particle size and morphology were observed, and the post-reduction cooling was found to be an important stage in the process. The spark plasma sintering (SPS) parameters were optimized to minimize the grain growth while achieving sufficient densification. Grain sizes in the range of 500 nm to 1 mu m, with compaction density of 95-98% were obtained. Preliminary measurements of thermal diffusivity and conductivity showed the dependence on grain size as well as on porosity. TE transport properties were measured in the temperature range of 300-650 K. Sample showed p-type behavior with a positive Seebeck coefficient, which increases with increasing temperature. Electrical conductivity measurements indicate metallic behavior and it decreases with increasing temperature. Thermal conductivity also decreases with increasing temperature and major contribution is due to the lattice component. A TE figure of merit of 0.15 was achieved for high purity CoSb3 nanostructured TE material at 650 K and these results are comparable with the values reported for the best unfilled/undoped CoSb3 in the literature.

For environmental reasons, low installation cost and initial investment; low energy infrastructure materials are becoming of high interest. A potential option to replace current hot mix asphalts is emulsifications, where bitumen binder is dispersed in a water phase aided by emulsifier and shear forces, and mixed at ambient temperature with unheated stones. Long term performance must, however, be guaranteed, otherwise the application benefits will be significantly diminished. In this paper, the main issues of cold mix (emulsion based) asphalt, like wetting in the presence of moisture and dust, and coalescence issues are discussed. Since both bitumen droplets and mineral surfaces were upscaled, pure mineral surfaces were investigated as stone material consists of different minerals. As a measure of the interfacial bond strength, surface free energies of different mineral aggregates and bitumen have been investigated in this paper as a stepping stone for further analyses of emulsions. From the analyses it was found that bitumen has only dispersive forces whereas most of the minerals surfaces have polar nature. According to Fowke's additive nature of the forces, bitumen and water are roughly equally strongly adsorbed to plagioclase and calcite, whereas water will displace bitumen from quartz, gypsum, potassium feldspar and mica surface.