Arbetet har genomförts i samarbete med Malmö Gatukontor med målet att samla in information om fiberförstärkta plastkompositer (fiber-reinforced polymer; FRP). FRP-kompositer kan vara ett intressant alternativ till konventionella byggnadsmaterial på grund av sina goda materialegenskaper. FRP har inte använts i gångbroar i Sverige tidigare och materialet är därför relativt okänt för byggbranschen. Studiens syfte var att undersöka och dokumentera beständigheten för FRP-gångbroar som påverkas av den omgivande miljön. Arbetet har genomförts som en litteraturstudie. Huvuddelen av studien fokuserade på att utvärdera olika nedbrytningsprocesser för att kunna bedöma potentiella svagheter hos FRP kompositer i gångbroar. Kopplingspunkter mellan olika delar i FRP broar har också studerats och dess inverkan på den totala beständigheten av konstruktionen har evaluerats. Studien ger en överblick av hur beständighetsparametrar för FRP-kompositer påverkas av olika typer av nedbrytning. Från denna överblick värderades nedbrytning genom fuktabsorption, höga och/eller cykliska temperaturer och UV-strålning som de faktorer som mest påverkar materialegenskaperna för FRP-kompositer. Studien konstaterar även att effekten av samverkan mellan olika nedbrytningsprocesser måste beaktas då materialet utsätts för flera olika angrepp i naturliga miljöer. Denna synergi gör att det är svårt att värdera effekten av varje enskilt angrepp. På grund av brist på information kunde inte kopplingspunkterna mellan komponenter i överbyggnadskonstruktionen i gångbroar fullständigt utvärderas, med avseende på dess påverkan på den totala beständigheten. Studien kunde dock konstatera att kopplingspunkter bör undvikas om det är möjligt, då vibrationer, utmattning och termisk expansion kan orsaka högre spänningsnivåer i kopplingspunkterna. Resultaten från studien syftar till att ge vägledande information vid projektering av gångbroar med FRP-kompositer. / This bachelor thesis was written in cooperation with Malmö Streets and Parks Department to collect information on fiber-reinforced polymer (FRP) composites. In today’s building industry, FRP composites provide an interesting alternative to conventional building materials because of their superior material properties. FRPs are suggested to be a sustainable solution meeting the future requirements in infrastructure and especially bridge design. The use of FRP composites in pedestrian bridge applications have not previously been utilized in Sweden and thus the material is relatively unknown to the building industry. The aim of this study was primarily to examine the performance in terms of durability of FRP pedestrian bridges subjected to the effects of the surrounding environment by conducting a literature review. The main part of this study was to evaluate different types of degradation to assess the potential weaknesses of FRP composites during in-service use in pedestrian bridges. The connections between the different members and components in FRP bridges were also studied and their impact on the overall durability of the construction was evaluated. The results from this study provided an overview of the durability characteristics of FRP composites subjected to different types of degradation. From this overview it was concluded that degradation by moisture absorption, high and/or cyclic temperature, and UV-radiation had the most significant impact on the material properties in FRP composites. This study also concludes that the effects of synergism between the different types of degradation need to be considered since FRP composites are subjected to many types of degradations in natural environments. Because of the effects of synergism, the individual effects of the different types of degradations can be difficult to evaluate. Due to lack of information, the impact on overall durability in pedestrian bridges from the connections between components in the superstructure could not be fully evaluated. However, it was found that connections should be avoided if possible due to vibrations, fatigue, and thermal expansions that may cause higher stress levels in the connection points. The results of this study aims to provide guidance when designing FRP composite pedestrian bridges.

Corrosion is a major challenge in the use of molten fluoride salt as a coolant in molten salt reactors (MSRs). A promising way of satisfying the two requirements of high strength and corrosion resistance is to clad structural alloys with a corrosion resistant material. Four candidate cladding and structural alloy combinations—stainless steel 316L and Incoloy 800H structural alloys either diffusion bonded to Hastelloy N or electroplated with nickel—were thermally aged at 700 °C for two to eight months. Based on measured concentration profles, the diffusion resistance of the four material combinations was compared and diffusion results were extrapolated to an end of reactor lifetime. The most important conclusion from this work is that Hastelloy N is highly likely to be signifcantly more diffusion resistant than nickel. The difference in diffusion resistance between Incoloy 800H and stainless steel 316L is relatively small. Two methods were used for extrapolating experimental diffusion results: (1) a diffusion model and calculated diffusion coeffcients and (2) simulations with Thermo-Calc DICTRA. Some simulations were carried out with a corrosion boundary condition of near-zero chromium concentration, demonstrating the potential of simulations for predicting diffusionlimited corrosion in molten fluoride salts. A surprising result of these simulations is that decreasing the thickness of Ni plating did not increase the thickness of diffusion zones in underlying structural alloys. / Thesis / Master of Applied Science (MASc)

A large proportion of the food that is consumed daily is bought ready-madeand is served on some sort of disposable container. ConServ AB developsand produces sustainable food packaging made from Areca palm leaves.The company wonders how durable the product is so that they can further investigate on their own what form the product should have for thebest durability. They also wonder how durable the product is during usage.The aim is to conduct a pilot study to investigate and identify trends regarding the material’s durability and mechanical behaviour during and as aresult of simulated useage. The goal is to use tensile tests and photograhicmethods to produce a basis with data on the material’s behaviour for ConServ.In order to be able to evaluate the durability and behavior of the product,a systematic study has been carried out where tensile tests were performedon test pieces exposed to a food simulant in the form of water or vinegarsolution. The test pieces were exposed for 0, 1, 6, 24 or 48 hours and testswere performed immediately after exposure.Experimental data show that the durability of the product depends to alarge extent on the fiber direction, where the test pieces taken perpendicularto the fiber direction performed worse in the tensile test. The mechanicalbehavior of the material is affected by the time it is exposed to liquid andbecomes more ductile with time.

Modern durability and damage tolerance predictions for composite material systems rely on accurate estimates of the local stress and material states for each of the constituents, as well as the manner in which the constituents interact. In this work, an number of approaches to estimating the stress states and interactions are developed. First, an elasticity solution is presented for the problem of a penny-shaped crack in an N-phase composite material system opened by a prescribed normal pressure. The stress state around such a crack is then used to estimate the stress concentrations due to adjacent fiber fractures in a composite materials. The resulting stress concentrations are then used to estimate the tensile strength of the composite. The predicted results are compared with experimental values. In addition, a cumulative damage model for fatigue is presented. Modifications to the model are made to include the effects of variable amplitude loading. These modifications are based upon the use of remaining strength as a damage metric and the definition of an equivalent generalized time. The model is initially validated using results from the literature. Also, experimental data from APC-2 laminates and IM7/K3B laminates are used in the model. The use of such data for notched laminates requires the use of an effective hole size, which is calculated based upon strain distribution measurements. Measured remaining strengths after fatigue loading are compared with the predicted values for specimens fatigued at room temperature and 350°F (177°C). / Ph. D.

Structural adhesive bonding offers several advantages over other types of joining. These include improved stress distribution and increased design flexibility. Adhesive bonding is important in aerospace, automotive, and packaging applications. However, the full potential of the technology has not been exploited because the understanding of the basic mechanisms of adhesion and adhesion failure is incomplete. This investigation elucidates the chemical and mechanical mechanisms responsible for durable adhesion of epoxy resins to phosphorus oxo acid treated aluminum alloys. By systematically altering the adherend surface chemistry, surface topography, and adhesive formulation, combined with accelerated testing, the chemical and mechanical factors that influence the properties of adhesively bonded aluminum are isolated and assessed. It is postulated that a combination of two factors determines the strength and environmental durability of epoxy-bonded aluminum. One is the formation of hydrolytically stable, primary bonds between the adhesive and the adherend, and the second is the hydrolytic stability of the surface oxide, which is always present on the surface of aluminum and aluminum alloys. These conditions can best be met by chemical pretreatment of the oxide surface, which renders the oxide insoluble and creates, at the same time, functional surface sites. These sites can form chemical bonds with reactive components of the adhesive. Morphological and mechanical alteration of the metal surface oxide through hydroxide formation requires liquid water. Liquid water can only form by capillary condensation in interfacial gaps from molecularly diffusing water. A hydrolytically stable oxide will prevent bond failure due to mechanical weakening of the substrate surface, while a high density of hydrolytically stable surface bonding sites will minimize the occurrence of capillary gaps at the interface, thus decreasing the formation of liquid water. It is shown that highly chemically active, although not inherently stable, oxide surfaces can provide environmentally stable adhesive bonds. Conversely, certain highly stable oxide surfaces with few chemically active sites provide no environmental stability to adhesive joints, regardless of the topography of the surface. / Ph. D.

In this dissertation, novel approaches to PEMFC durability research are summarized. These efforts are significantly different from most other studies on durability in that rather than focusing on chemical degradation, more attention is given to the mechanical aspects of the PEMFC system. The tensile stress-strain behavior of Nafion® 117 (N117) and sulfonated poly(arylene ether sulfone) random copolymer (BPSH35) membranes is explored under ambient conditions, with respect to the effects of initial strain rate, counterion type, molecular weight and the presence of inorganic fillers. A three-dimensional "bundle-cluster" model is proposed to interpret the tensile observations, combining the concepts of elongated polymer aggregates, proton conduction channels as well as states of water. The rationale focuses on the polymer bundle rotation/interphase chain readjustment before yielding and polymer aggregates disentanglement/ reorientation after yielding. In addition, the influence of uniaxial loading on proton conductivity of N117 and BPSH35 membranes is investigated. When the membranes are stretched, their proton conductivities in the straining direction increase compared to the unstretched films, and then relax exponentially with time. The behavior is explained on the basis of the morphological variations of hydrophilic channels, accompanied by the rotation, orientation and disentanglement of the copolymer chains in the hydrophobic domains, as illustrated with the help of our bundle-cluster model. Finally, the long-term aging of hydrogen-air PEMFCs is examined with a cyclic current profile and under constant current conditions. The end-of-period diagnosis is performed for both MEAs at 100h aging intervals, including a series of cell polarization, impedance and electrochemical experiments. The results demonstrate that hydrogen crossover is the most significant result of degradation for the MEA under cyclic aging mode due to the formation of pinholes at approximately 500-600h, and mass transport limitations are the major degradation sources for constant current mode. A phenomenological mathematical model is set up to describe the PEMFC aging process under both cyclic and constant conditions. / Ph. D.

Porous ceramics and porous ceramic composites are emerging functional materials that have found numerous industrial applications, especially in energy conversion processes. They are characterized by random microstructure and high porosity. Examples are ceramic candle filters used in coal-fired power plants, gas-fired infrared burners, anode and cathode materials of solid oxide fuel cells, etc. In this research, both experimental and theoretical work have been conducted to characterize and to model the mechanical behavior and durability of this novel class of functional material. Extensive experiments were performed on a hot gas candle filter material provided by the McDermott Technologies Inc (MTI). Models at micro-/meso-/macro- geometric scales were established to model the porous ceramic material and fiber reinforced porous ceramic material. The effective mechanical properties are of great technical interest in many applications. Based on the average field formalism, a computational micromechanics approach was developed to estimate the effective elastic properties of a highly porous material with random microstructure. A meso-level analytical model based on the energy principles was developed to estimate the global elastic properties of the MTI filament-wound ceramic composite tube. To deal with complex geometry, a finite element scheme was developed for porous material with strong fiber reinforcements. Some of the model-predicted elastic properties were compared with experimental values. The long-term performance of ceramic composite hot gas candle filter materials was discussed. Built upon the stress analysis models, a coupled damage mechanics and finite element approach was presented to assess the durability and to predict the service life of the porous ceramic composite candle filter material. / Ph. D.

The mechanical properties of unaged and aged constituent materials for solid oxide fuel cells were evaluated using microindentation, plate tensile, four-point bend, ball on ring and pressure on ring tests. The Vickers hardness of the anode, interconnect and electrolyte was determined before and after 1000 hours aging at 1000 oC in air. The fracture toughness KIC was found for the electrolyte materials. Finite element analysis (FEA) was validated and used to calculate the stress distribution and peak stress for the biaxial strength test. A Weibull analysis was carried out on the test/FEA-predicted peak stresses, and Weibull strength, modulus and material scale parameters were found for each test methodology. The methodologies were evaluated based on the results of the Weibull analysis and the pressure on ring test is preferred one for brittle thin film fracture strength testing. Half cell SOFCs with composite cathode (Pr0.7Sr0.3)MnO3±Î´ /8YSZ on the 8YSZ electrolyte were aged 1000 hours at 1000 oC in air with/without polarization and investigated using Electrochemical Impedance Spectroscopy (EIS), Scanning Electron Microscopy (SEM), Brunauer-Emmett-Teller (B.E.T.) method and X-ray Diffraction (XRD). The performance of the half cell SOFCs degraded after aging with/without polarization compared to the initial state, which was ascribed to the decrease of the electrolyte conductivity. The current load was shown to have impact on the performance by slowing down the decreasing rate of the polarization resistance of the SOFCs. After aging, the microstructural properties - pore size and pore volume changed, and growth of grains was found on the (Pr0.7Sr0.3)MnO3 phases, which may have contributed to the decrease of the activation polarization by decreasing the capacitance and increasing the number of active sites. After aging the high frequency EIS arcs/peaks shifted to a lower frequency range, and the low frequency arcs/peaks became unapparent compared to before aging. A 3-D multiphysics finite element model was used to simulate the performance of the half cell SOFC. The effective exchange current density and the effective ionic conductivity of the cathodes showed much influence on the performance of the SOFC. Predicted and observed performance was compared. Suggestions were given for the further experiments on the composite cathode. / Ph. D.

The objective of this study is to evaluate the bond durability of an epoxy-based polymer concrete wearing surface bonded to aluminum bridge decks. In the bridge design, an aluminum alloy bridge deck is used with a polymer concrete wearing surface. A modified mixed mode flexure fracture test was developed to assess the bond durability of specimens aged in the following environmental conditionings: 30°C [86°F], 98% RH; 45°C [113°F], 98% RH; 60°C [140°F], 98% RH; freezing and thawing; salt (NaCl) water soak; and 60°C [140°F], dry. The exposure times varied from none to twelve months. The critical strain energy release rate (Gc) of the bond was determined using a compliance technique. In spite of considerable scatter in the data, the results suggested that the interfacial bond toughness had been degraded by exposure conditions. The aging appeared to affect the polymer concrete overlay (silica aggregates/epoxy bond) as well. Fracture analysis and finite element modeling were completed for linear elastic behavior. Analytical and numerical solutions were in reasonably good agreement. Characterization of the bridge components and failure specimens were accomplished using analytical measurements including thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Techniques employed in the surface analysis included x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). / Master of Science

Proton exchange membrane fuel cells typically consist of stacks of membrane electrode assemblies sandwiched between bipolar plates, effectively combining the individual cells in series to achieve the desired voltage levels. Elastomeric gaskets are commonly used between each cell to insure that the reactant gases are isolated; any failure of a fuel cell gasket can cause the reactants to mix, which may lead to failure of the fuel cell. An investigation of the durability of these fuel cell seals was performed by using accelerated characterization methods. A hydrocarbon sealant was tested in five different environments to simulate fuel cell conditions. Viscoelastic properties of these seals were analyzed using momentary and relaxation compressive stress tests. Material properties such as secant modulus at 100% strain, tensile strength, and strain at failure were determined using dog-bone samples aged at several different imposed strains and aging times in environments of interest. Tearing energy was evaluated using trouser test samples tested under different rates and temperatures after various environmental aging conditions. Additionally, tearing tests were conducted on samples tested in liquid environment. A viscoelastic and mechanical property characterization of these elastomeric seals under accelerated aging conditions could help understand the behavior and predict durability in the presence of mechanical and environmental loading. Additionally, the effects of confinement have been evaluated for a bonded joint with varying thickness along the bonded direction. The Dreaming project is a glass art project in Fredrick, MD which incorporates such a varying thickness joint where thermal expansion of the adhesive has caused the glass adherend to break and debonding of the sealant. To examine this joint design, finite element analysis has been used to determine the effects of thermal expansion on such a complex geometry. Nine different test geometries have been evaluated to determine the effect of confinement coupled with thermal expansion on joint design with an elastomeric adhesive. Once evaluated, design changes were performed to try to reduce the loading while maintaining the general joint design. Results of this analysis can be used to determine the effects of confinement on a complex elastomeric joint. / Master of Science