This thesis investigates, using finite element modelling and experimental investigation, the fracture of mesh reinforcement in composite floor slabs at elevated temperatures. The main objective of the research is the study of the bond strength between the welded mesh reinforcement and concrete at elevated temperatures, since this was found to be the principal behaviour that governs the fracture of the reinforcement in a composite floor slab.The experimental programme included steady state and transient pull-out tests carried out at temperatures varying from 20°C to 1000°C. However, unlike previous work, which concentrated on the bond of single bars, rectangular normal concrete prisms were constructed with one longitudinal bar, ensuring a bond length of 200 mm, and one transverse bar welded centrally. As a result, the influence of the weld of the mesh reinforcement in the bond strength between reinforcement and concrete was studied. The bond strength-slip-temperature relationship was obtained for various sized ribbed and plain bars. It was found that the 6, 7 and 8mm diameter ribbed mesh failed by fracture of the longitudinal bar at all temperatures, including ambient temperature. It was shown that the reduction of bond strength of ribbed mesh was similar to the reduction in strength of the bar, which together with the observed modes of failure, lead to the conclusion that ribbed mesh can be assumed to be fully bonded at all temperatures. The 10mm diameter ribbed mesh failed by splitting due to the cover-bar diameter ratio being small. In contrast, all the plain bars failed by fracture of the weld followed by pull-out of the bar. Therefore the correct bond stress-slip relationship should be modelled for smooth bars to accurately predict global structural behaviour.The investigation using finite element modelling utilizes the DIANA program. The incorporation by the author of the bond strength-slip-temperature relationship within the models permits a better prediction of fracture of the reinforcement in composite floor slabs. It has been shown that smooth bars are more beneficial since the bond is broken before fracture of the bar allowing strains to be distributed along the bar. In the case of ribbed bars the bond is such that localised strain will occur in the bar at crack locations leading quickly to fracture of the reinforcement.

Zirconium is used inside nuclear reactors as fuel cladding. The in-reactor performance of zirconium alloys is strongly influenced by the properties that develop during thermo-mechanical processing, such as the microstructure and crystallographic texture. Optimising the combination of properties would enable improved reactor efficiency, longer component lifetimes and reductions in nuclear waste. Achieving the desired texture and microstructure requires a mechanistic understanding of the processes that govern them: deformation and recrystallisation. These mechanisms are influenced by numerous variables including temperature, strain-rate, and the initial state of the material. This work aims to clarify how texture develops as a result of the active deformation mechanisms of slip and twinning and how these mechanisms are influenced by temperature. The alloy chosen for this is Zircaloy-4.This work has shown that texture evolution varies with deformation temperature. The activation of {10-12}<10-11> tensile twinning dramatically alters the texture up to at least 300°C. In the absence of much twinning at 500°C prismatic slip appears to govern the texture evolution up to moderately high strain. Prismatic slip is generally considered the easiest slip system in zirconium. This work highlights its distinct effect upon both texture and microstructure evolution. In particular the extent of grain fragmentation by prismatic slip is shown to depend upon the initial grain orientation. As a result the break-up of the microstructure takes place heterogeneously. This then has implications for the microstructure and texture development during subsequent recrystallisation treatments. Experimental data indicates that the slip anisotropy between <c+a> and prismatic <a> slip increases with temperature. Crystal Plasticity simulations suggest that the variation of both the twin variant selection and the grain fragmentation with temperature are consistent with increasing slip anisotropy, in contrast to previous experimental and modelling studies on high purity zirconium alloys. The character of {10-12}<10-11> tensile twins and the texture change they induce is influenced by temperature, strain path and weakly influenced by the neighbouring orientations. Increasing temperature causes twin fraction variation, thicker twins and an increased frequency of less favourable twin variants. Plane strain compression also causes less favourable variants to activate more often. Looking at the twinned orientations highlights the importance of grain orientation. Poorly orientated grains do still twin. This work shows that in these instances neighbouring interactions can play a role. In summary, this work contributes to the current understanding of deformation in hexagonal close packed metals. It is hoped that this aids the development of improved physically based crystal plasticity models.

Wall slip in the die of a capillary rheometer was investigated. Corn meal and water were mixed to a moisture content of 35% wet basis. Oil was then added at 0%, 2.5%, and 5% of the total mass. A capillary rheometer was used to extrude the mixture at 100C. Three die diameters were studied: 2mm, 4mm, and 8mm. Two length to diameter ratios were studied: L/D=4 and L/D=8. Pressure and flow rate in grams per 30 seconds were collected from the capillary rheometer to perform the Bagley correction, determine the flow behavior index, and correct for slip using the Mooney slip analysis method. Several slip analysis methods were considered prior to the selection of the Mooney method. Overall, the Bagley correction was successful for all die diameters except 2mm. The Mooney method was successful for the 5% added oil content samples. An increase slip velocity was observed as shear stress increased. Mooney plots for 0% and 2.5% resulted in negative shear rate values. An empirical model was developed to predict apparent viscosity of the mixture as a function of total oil content.

The fiber suspensions in the production line from wood topaper are subjected to many types of chemical and mechanicalprocesses, in which the flow of the suspension is of vitalimportance. The flow of the suspension determines the degree ofuniformity of the fibers through the processing, which inreturn affects the properties of the fiber suspension. In orderto optimise the process, thorough knowledge of the suspensionflow is necessary, both on the level of suspension, fibernetworks and individual fibers. Knowledge of the fibersuspension behaviour combined with commercial CFD simulationprovides an efficient design method for any unit operation inthe papermaking process. This work concentrates on macroscopic modeling of thebehaviour of fiber suspensions from 0.5-5% dry content, purefiber suspensions without fillers or additives. Any mechanismscausing the characteristic behaviour of the pulp suspensionhave not been included, they are only included through theirinfluence on the suspension parameters. Excluded mechanismsare, for instance, the fiber-fiber coupling mechanisms that arethe reason for the formation of fiber networks and parts offiber network, flocs. By combining a rheology model for the bulk suspension, awall function that accounts for the slip layer and finallyintroducing turbulence, a model has been created that is ableto simulate the flow of most fiber suspensions. The flow of thesuspension is not constrained to any particular flowconditions; the models discussed in this work aim at describingthe behaviour of the suspension for all flow rates and flowtypes. The models are developed under simple flow conditions,where all variables can be controlled, but the models areintended for usage within the industry-based flows in real pulpand papermaking applications. Keywords:rheology, fiber, suspension, CFD, model, wall,slip, turbulence / <p>QCR 20161026</p>

För att öka köreffektivitet och säkerhet samt minska bromsarnas slitage är de flesta av Scanias lastbilar och bussar utrustade med en hjälpbroms, så kallad retarder. En retarder arbetar generellt sett enligt någon av följande två principer. Dels en elektromagnetisk variant av retarder som bromsar bilens kardanaxel, drivaxlar eller växellåda genom att utnyttja elektromagnetisk induktion, eller som i Scanias fall där man använder sig av en hydrodynamisk tillsatsbroms som bromsar bilens kardanaxel genom att slunga vätska inom ett skovelsystem. Bromsenergin övergår då till värmeenergi som i sin tur kyls bort av bilens ordinarie vattenkylsystem. Bromsmomentet styrs via trycket som råder mellan skovelbladen. Som mest överträffar retardern den effekt som bilens motor kan leverera. Då retardern inte används är skovelsystemet trycklöst. Men även då skapas det dock ett litet släpmoment i retardern eftersom den fortfarande roterar med växellådan. Detta släpförlustmoment är en bråkdel jämfört med det moment som skapas vid bromsning men ur bränslebesparingssynpunkt är det ändå viktigt att det hålls på minimal nivå. Detta examensarbete syftar till att utreda hur dessa släpförluster kan minimeras genom att via konceptstudier ta fram den bäst lämpade släpförlustreduceringsmetoden för Scanias retarder. En studie på konkurrenter och andra applikationer där inspiration skulle kunna inhämtas genomfördes och ett antal koncept togs fram. Därefter genomfördes en provkörning av en konkurrentretarder för ytterligare fördjupade kunskaper om problemet. Där samtidigt ett av koncepten med en bländarskiva mellan rotor och stator provades, dock med ett resultat som inte kunde anses tillräckligt. Efter detta kunde det konstateras att den bäst lämpade släpförlustreduceringsmetoden för Scania bör vara att helt frikoppla retardern från växellådan vid avaktivering då ett flertal av de största förlusterna som mättes upp kunde härledas in diverse tätningar och lager och inte till själva retardern. Denna frikoppling bör förslagsvis ske genom någon form av synkroniseringsinkoppling för att minimera vikt, storlek och kostnad. Slutligen kan det konstateras att kunskapen om vad som exakt sker i en retarder är begränsad och att det är ett komplext område. Vidare bör simuleringsmodeller användas för att minimera utvecklingsarbetet och ytterligare studier på hur en effektiv frikoppling kan användas bör genomföras. Nyckelord: retarder, släpförluster, växellåda / In order to increase the drive efficiency and safety as well as to minimize the brake wear, most Scania trucks and busses are equipped with a complementary brake system, also known as a retarder. A retarder generally works under one of the following two principles. An electromagnetic retarder that brakes the propeller shaft, drive axles or the gearbox using electromagnetic induction or as in Scania's case using a hydrodynamic brake that brakes the propeller shaft by pumping a fluid thru a rotating turbine shaped system. The braking energy then turns to heat which then cools off by the engine’s cooling system. The brake power is controlled by the fluid pressure in the retarder. At its maximum, the brake power exceeds the power of the engine. When the retarder is deactivated, the system is not pressurized. But even then, it creates a small slip loss, because the retarder is still rotating with the gearbox. This slip loss is a fraction compared to the braking torque than can be used, but from a fuel efficiency standpoint it is still important that it is kept at a minimum. The goal of this master thesis is to investigate how to minimize these losses. To find out which the best suited solution for Scania would be, different concept studies has been carried out. A study of competitors and other applications where further inspiration could be obtained was conducted and a number of concepts were developed. Thereafter a test run of a retarder from a competitor for further in-depth knowledge was conducted. At the same time one of the concepts with an aperture plate between the rotor and stator was tested on the competitor retarder. With a result that could not be considered sufficient. After this it was found that the most appropriate slip reduction method should be to completely disengage the retarder from the gearbox at deactivation since most of the losses that was measured could be traced to various seals and bearings and not to the retarder itself. The decoupling should be done through some kind of synchronization unit to minimize weight, size and cost. Finally it was observed that the knowledge about what’s exactly happening in the retarder is limited and that it is a complex area. Furthermore should the use of simulation models enhance to minimize the development work and further studies about how to disengage the retarder in the most effective way should be worked out Keywords: losses, retarder, slip

New materials, optimized for increased strength, ductility, and other desirable properties, have the potential to improve every aspect of modern living. To achieve these optimums, the necessary technological advancements are impeded mainly by the limits of available material models. Innovations in this field rely on research into the nature of material behavior. While a typical model of material behavior in the region near yield involves the initial linear elastic response, followed by yield and isotropic hardening, this fails to explain various important phenomena that manifest in a range of materials, such as pre-yield nonlinearity, anelasticity, yield point phenomena, hardening stagnation, and the Bauschinger effect. These effects have been explained over the past century with the theories of Cottrell atmospheres, the Orowan by-pass mechanism, and back stress. This manuscript compares data from experimental observation in tantalum to these theories to better understand the micromechanisms occurring near yield. Understanding deformation in this region has significant implications in structural and mechanical engineering, as well has having direct applications in the forming of metals. Forty-four dogbone-shaped samples were cut from 99.99% pure tantalum and pulled in load-unload-load and multi-cycle loop tensile tests at room temperature. The specimens were either single crystal, whose orientations were chosen based on desired active slip mode determined by Schmid factors, or bicrystal, based on the orientation of the single grain boundary. Sample behavior was simulated in both crystal plasticity and General Mesoscale finite element models to assist in interpreting results and in suggesting plausible micromechanisms. The experimental results and crystal plasticity simulations suggest alternate explanations to some of the discussed mechanical theories of near-yield deformation. The combined experimental / modeling approach indicates that other slip systems, besides the conventionally assumed {110}, are activated upon yield; particularly the {112} system. The breakaway model traditionally associated with the yield point phenomenon may also be better explained through a different mechanism; back stress development during deformation is shown to result in the observed behavior. Lastly, as is well-known, the Taylor formulation, upon which most crystal plasticity models are based, does not adequately predict yield stress behavior in the presence of grain boundaries; once again, an internal stress mechanism matches much better with the experimental results on single and bicrystals. While not all observations could be fully explained by simply adding internal stress generation to a standard crystal plasticity model, this work anticipates further studies to enable more accurate predictive modeling capabilities and increase understanding of the mechanisms driving the fundamental material properties necessary for future progress.

The geometry and mineralization features of small left-lateral strike-slip faults and associated fractures in Lake Edison Granodiorite of the central Sierra Nevada, California, were examined in order to model the three-dimensional structure of strike-slip faults. These faults, which are reactivated joints, were also examined to determine fault sizes, starting joint size, and evidence for fluid flow. The associated secondary fractures are usually found in the dilational quadrants of fault-tip regions. The longest fault-segment trace is 32.14 m; the longest joint trace is 22 m. The joint population length (l) is represented by a power-law distribution (l-n) and it is l-1.22. The fault-segment distributions are l-0.23~0.79, and the compiled fault-segment distribution is l-1.18. The data on fracture and fault spacing, along with the joint power-law distribution, will aid in the simulation and analysis of fault evolution. The splay-fracture traced in the faults are linear at depth and the average splay-fracture angle is 39° ± 13°. The dihedral angle of the splay plane and fault plane ranges from 20° to 65°. There is a high concentration of splay fractures near the fault. As distance increases perpendicular form the fault, the splay-fracture spacing increases and splay-fracture frequency decreases. The splay tracelength distributions have a high short tracelength concentration with a rapid decrease of long tracelengths. The maximum tracelength of multiple splay-fracture groups is restricted by their distance orthogonal to the fault trace. The three-dimensional relationship between the splay-fracture plane and fault plane can be inferred from these data. When present, mineralized quartz appears largely as lenses and few as single continuous veins along the faults. No consistent pattern exists between fault displacement and the locations and dimensions of quartz cavities. There is no visible damage zone near the fault termination or around the faults. Microstructures in the fault zone consist of cataclasites and patchy gouges, and zones of dynamically recrystallized fault walls. The three-dimensional geometry, along with quartz cavity distribution and thin section analysis, has led to the conclusion that fluid migrates vertically among the faults and fractures.

Friction Stir Welding (FSW) is a solid-state joining process that is of special interest in joining aluminum and other alloys that are traditionally difficult to fusion weld. The energy required for this joining process is transmitted to the work-pieces through a rotating FSW tool. Modeling attempts, aimed at perfecting the process, rely on assumptions of the contact conditions present between the work-pieces and the FSW tool. Various studies have attempted to define these contact conditions. Both theoretical and experimental studies indicate the contact conditions between the work-piece and weld tool are unknown and may vary during the FSW process. To provide insight into the contact conditions, the objective of this study is to characterize the FSW nugget in terms of swept volume as indicated by the cross-sectional area and symmetry of the FSW nugget over a range of processing conditions.

The San Andreas fault forms the right lateral transform boundary between the North American and Pacific tectonic plates. At various locations along the San Andreas fault the geometry of the fault surface is much more complex than a straight, vertical, plane. The San Bernardino Mountain segment of the San Andreas fault, in the San Gorgonio Pass region has one of the most complex active fault geometries in southern California due to a left-stepping restraining bend in the San Andreas fault. The evolution of the actively faulting pass has created an intricate network of active and formerly active, dipping and vertical, three-dimensionally irregular fault surfaces. The purpose of this research is to gain a better understanding of the mechanics of the present day active fault geometry and the evolution in the San Gorgonio pass region, through numerical modeling. We use the three-dimensional Boundary Element Method modeling code Poly3D to simulate different fault configurations. We see that fault geometries that include geologically observed and inferred fault dips match geologic data more accurately than simplified, vertical faults in the San Gorgonio Pass region of the San Andreas fault. The evolution of the San Andreas Fault in the San Gorgonio Pass region over the past million years may follow the principle of work minimization in the Earth’s crust up until the present day configuration.

Superhydrophobic surfaces are a class of surfaces that have a microscale roughness imposed on an already hydrophobic surface, akin to a lotus leaf. These surfaces have been shown to produce significant drag reduction for both laminar and turbulent flows of water through large and small-scale channels. The goal of this thesis was to explore how these surfaces alter the vortex shedding dynamics of a cylindrical body when coated on its surface, thus leading to an alteration in drag and lift on these surfaces. A cylindrical body was chosen as it is a very nice representative bluff body and sets the stage for predicting the behavior of hydrofoils and other bluff bodies under flow with a slip boundary condition. In this work, a series of experiments were performed which investigated the effect of superhydrophobic-induced slip on the flow past a circular cylinder. In these experiments, circular cylinders were coated with a series of superhydrophobic surfaces fabricated from PDMS with well-defined micron-sized patterns of surface roughness or random slip surfaces fabricated by sanding Teflon cylinders or spray painting superhydrophobic paint on a smooth cylinder. The presence of the superhydrophobic surface was found to have a significant effect on the vortex shedding dynamics in the wake of the circular cylinder. When compared to a smooth, no-slip cylinder, cylinders coated with superhydrophobic surfaces were found to delay the onset of vortex shedding and increase the length of the recirculation region in the wake of the cylinder. For superhydrophobic surfaces with ridges aligned in the flow direction the separation point was found to move further upstream towards the front stagnation point of the cylinder and the vortex shedding frequency was found to increase. For superhydrophobic surfaces with ridges running normal to the flow direction, the separation point and shedding frequency trends were reversed. The vortices shed from these surfaces were found to be weaker and less interlaced leading to reduced circulation and lift forces on these cylinders. The effect of slip on bluff bodies and separating flow was dealt with in detail in this thesis and the results could be used to predict the impact of these surfaces on the flow past hydrofoils which combine skin friction dominated flow with separating flow.