<p>The mechanical behaviour of coated papers during folding has been investigated. This problem has been studied with experimental techniques and numerical analyses in order to give a better understanding of the folding properties of coated papers pertinent to the mechanical behaviour in general, and particularly cracking along the fold. </p><p>A microscopy investigation has been performed. The surface of the folded paper has been carefully examined to study the event of fracture and related issues. The influence of the grammage on the cracking event has been studied and it was shown that the coating material would not fail if the paper sample was sufficiently thin. It was found that a stress or strain based criterion is sufficient to describe the cracking of the coating layers and that the anisotropy of paper should be taken into account when studying the folding process. </p><p>The finite element method has been used for the numerical analyses remembering that the geometry of the problem is rather complicated, excluding a solution in analytical form. Using different constitutive models for the base stock, it has been shown that the deformation of the coated paper during folding is much governed by the paper substrate. The numerical results also suggested that particular forms of plastic anisotropy can substantially reduce the maximum strain levels in the coating. Furthermore, it has also been shown that delamination buckling, in the present circumstances, has a very small influence on the strain levels in the coating layer subjected to high tensile loading. </p><p>Dynamic effects have also been studied and it has been shown that a quasi-static analysis of the problem is sufficient in order to describe many of the important features related to cracking. An attempt to model strong anisotropy of paper has been presented and the results indicate that the large anisotropy in the thickness direction of coated papers needs to be taken into account in order to fully understand the mechanics of folding. </p><p>Finally, an experimental investigation has been presented in order to study if important mechanical properties of the coating material could be determined by microindentation techniques. The results presented indicate that microindentation can be a powerful tool for characterization of these materials, but only if careful efforts are made in order to account for the influence from plasticity as well as from boundary effects. </p><p><b>KEYWORDS:</b> folding, coated papers, finite element method, cracking, indentation, anisotropy, plasticity.</p>

<p>This thesis work aimed at increasing the knowledge regarding phenomena occurring when gas is injected using a top-blown lance on to a bath. All results are based on physical modeling studies carried out both using low and high gas flow rates and nozzle diameters ranging from 0.8 mm to 3.0 mm. At the low gas flow rates, the penetration depth in the bath was studied. The experiments focused on studying the effect of nozzle diameter, lance height and gas flow rate on the penetration depth. It was found that the penetration depth increases with decreasing nozzle diameter, decreasing lance height and with increasing gas flow rate. The results were also compared with previous work. More specifically, it was studied how the previous published empirical relationships fitted the current experimental data. It was found that the relationships of Banks [1], Davenport [2], Chatterjee [3] and Qian [4] agreed well with the experimental data of this investigation for nozzle diameters of 2.0 mm and 3.0 mm. However, for smaller nozzle diameters there were considerable deviations. Therefore, a new correlation heuristically derived from energy conservation consideration was suggested and showed better agreement for small nozzle diameters.</p><p>The experiments carried out at higher gas flow rates focused on the study of swirl motion. The effects of nozzle diameter, lance height, gas flow rate and aspect ratio on the swirl motion were investigated. The amplitude and period of the swirl as well as the starting time and the damping time of the swirl were determined. The amplitude was found to increase with an increased nozzle diameter and gas flow rate, while the period had a constant value of about 0.5 s for all nozzle diameters, gas flow rates and lance heights. The starting time for the swirl motion was found to decrease with an increased gas flow, while the damping time was found to be independent of gas flow rate, nozzle diameter, lance height and ratio of depth to diameter.</p>

No description available.

<p>The creep of paper is accelerated by moisture content changes. This acceleration is known as mechano-sorptive creep, which is also found in wood and some other materials. Mechano-sorptive creep has been known for several decades but it is still not well understood, and there is no generally accepted model explaining the effect. </p><p>In this thesis, it is assumed that mechano-sorptive creep is the result of transient redistributions of stresses during moisture content changes in combination with non-linear creep behaviour of the material. The stress redistributions are caused by the anisotropic hygroexpansion of the fibres, which will give a mismatch of hygroexpansive strains at the bonds and hence large stresses each time the moisture content changes. This redistribution will lead to an uneven stress state. If the creep of the material depends non-linearly on stresses this will give an increase in creep rate where the stresses are high, that is larger than the decrease of creep rate where stresses are low, so in average there will be an increase in creep rate. The stress distribution evens out as the stresses relax during creep, and the moisture content has to change again to create a new uneven stress state and maintain the accelerated creep. </p><p>Two different network models based on this mechanism are developed in this thesis. Numerical simulations show that the models produce results similar to the mechano-sorptive creep found in paper. In the first model it is assumed that creep takes place in the fibre-fibre interfaces at the bonds, in the second the creep of the fibres themselves is accelerated. The second model is further developed. Experiments verify model predictions of the dependence of the amplitude of moisture changes. </p><p>The second model shows a linear relationship between mechanical load and deformation, although creep of the fibres depends non-linearly on stresses. This linear behaviour is also found in applications. Further analysis shows that the mechanical load can be treated as a small perturbation of the internal stress state caused by moisture content changes. This can be used to develop a linearized model, from which a continuum model can be derived. This leads to a reduction of the necessary number of variables, and a significant increase in speed of calculations. Hence, this linearized continuum model can be used as a constitutive law of paper in problems with complicated geometries, for example a corrugated board box in varying humidity.</p>

<p>The shrinkage during solidification of aluminium and iron based alloys has been studied experimentally and theoretically. The determined shrinkage behaviour has been used in theoretical evaluation of shrinkage related phenomena during solidification. </p><p>Air gap formation was experimentally studied in cylindrical moulds. Aluminium based alloys were cast in a cast iron mould while iron based alloys were cast in a water-cooled copper mould. Displacements and temperatures were measured throughout the solidification process. The modelling work shows that the effect of vacancy incorporation during the solidification has to be taken into account in order to accurately describe the shrinkage. </p><p>Crack formation was studied during continuous casting of steel. A model for prediction of crack locations has been developed and extended to consider non-equilibrium solidification. The model demonstrates that the shrinkage due to vacancy condensation is an important parameter to regard when predicting crack formation. </p><p>The centreline segregation was studied, where the contributions from thermal and solidification shrinkage were analysed theoretically and compared with experimental findings. In order to compare macrosegregation in continuous casting and ingot casting, ingots cast with the same steel grade was analysed. However, the macrosegregation due to A-segregation is driven by the density difference due to segregation. This is also analysed experimentally as well as theoretically.</p>

<p>Further increase of erbium concentrations in Er-doped amplifiers and lasers is needed for the design of efficient, reliable, compact and cost-effective components for telecommunications and other photonic applications. However, this is hindered by Er concentration dependent loss mechanism known as upconversion. The upconversion arises due to non-radiative energy transfer (ET) interactions (migration and energy-transfer upconversion) among the Er ions exited to the metastable level that is used for amplification. The upconversion deteriorates the conversion efficiency of Er doped gain medium and may even totally quench the gain. The upconversion can be significantly intensified if the Er distribution in glass is non-uniform, which can be minimized by optimizing the fabrication process and the glass composition. The optimization requires detailed characterization techniques capable to distinguish between the effects caused by the uniformly distributed ions (homogeneous upconversion, HUC) and non-homogeneously distributed ions (pair induced quenching, PIQ)</p><p>The thesis deals with rigorous statistical modeling of the HUC and development of experimental methods that can provide accurate and detailed data about the upconversion, which are needed for the characterization of the upconversion. </p><p>The presented model interprets the homogenous upconversion as an interplay of ET interactions between randomly distributed Er ions, which is affected by stimulated emission/absorption of the radiation propagating in the medium. The model correspondingly uses the ET interactions parameters as the main modeling parameters. </p><p>The presented analytical model is verified by Monte-Carlo simulations. It explains strongly non-quadratic character of the upconversion observed in experiments and variety of the associated effects. The model is applicable to the interpretation of the upconversion measurements in various experimental conditions, which facilitates the upconversion characterization. The thesis also presents an advanced experimental method for accurate and detailed characterization of the upconversion in both continues-wave pumping conditions and during the decay of Er population inversion. Using the method the upconversion modeling is experimentally verified by correlating the measurements results with the modeling predictions in the whole range of the practical Er doping levels. This also allows to estimate the parameters for the ET interactions in silica. Finally, it is shown that the presented method can serve as a basis for discrimination of HUC and PIQ effects, which is crucial for optimizing the fabrication process and the glass composition.</p>

<p>In the present work studies were performed to provide understanding for further model development of the two-phase phenomena, film formation from o/w emulsions and slag foaming.</p><p>The drying of o/w emulsions of different oil viscosities on hydrophobic and hydrophilic substrates was studied. The hydrophobic substrate was found to destabilise the oil droplets and to result in a different mechanism for forming continuous oil film. Studies of adsorption behaviour of a series of non-ionic diblock copolymers at relevant interfaces showed that the adsorption behaviour at hydrophobic and hydrophilic solid surfaces differed at high polymer concentration. Emulsion droplets were found to interact with the hydrophobic interface. Adsorption at silicone oil-water interface resembled adsorption at solid hydrophobic surfaces.</p><p>Gas was generated through chemical reaction at the interface between two immiscible liquids and the bubbles formation from the generated was studied optically. The gas bubble size was seen to be uninfluenced by the reaction rate. However, bubble formation was seen to take place in one of the phases, held up at the interface before detaching from the interface with a surrounding aqueous film. It was argued that this may affect the final bubble sizes.</p><p>Slag foaming at high temperatures was studied in laboratory scale with X-ray imaging under dynamic conditions. The foam displayed a fluctuating behaviour, which the presently available models are not able to take into account. The concept of foaming index was found to be unsatisfactory in describing the foaming behaviour under dynamic conditions, thus emphasizing the need for alternative theories. The rate of fluctuations was seen to be related to the difference between rate of gas generation and rate of gas escape from the system (U_g-U_e) as well as the bubble sizes. Thus, it seems like model development of dynamic foaming phenomenon has to take the effective chemical reaction rate as well as the bubble sizes into consideration</p>

During the past decade, new advanced combustion systems that share the same basic concept of using a substantially diluted and high-temperature oxidizer in the reaction volume have gained a great deal of interest regarding their application in industrial and power systems. These novel combustion technologies have proved to offer significant benefits compared to traditional combustion techniques. These benefits include reductions in pollutant emissions and energy consumption, as well as a higher and more uniformly distributed heat flux. This entails the potential to, for example, reduce the size of equipment in industrial units or increase production rates while fuel consumption and the subsequent CO2 emissions are decreased or maintained at the same level. Although the development of these new combustion technologies has occurred fairly recently, it has gained worldwide recognition. During the past few years the technique has been used commercially with several different types of burners. Despite its widespread use, the basic understanding of the chemical-physical phenomena involved is limited, and a better understanding of the combustion phenomena is required for more effective utilization of the technology. The objectives of this work have been to obtain fuel-jet characteristics in combustion under high-temperature, low-oxygen conditions and to develop some theoretical considerations of the phenomena. The effect of the preheat temperature of the combustion air, combustion stoichiometry and the fuel-jet calorific value on flame behavior was investigated. Temperature and heat-flux distribution were also studied using a semi-industrial test furnace to see if similar flame features would be found for the small- and large-scale experiments. Particle Image Velocimetry (PIV) was used for the first time to obtain information on the flow dynamics of a fuel jet injected into a crossflow of oxidizer at either a normal temperature or a very high temperature. Light emission spectroscopy was used to collect information on time-averaged radical distributions in the combustion jet. Jet turbulence, time-averaged velocity distribution, fuel-jet mixing, the distribution of radicals such as CH, OH and C2, and flame photographs were investigated. The results showed delayed mixing and combustion under high-temperature low-oxygen-concentration conditions. The combustion air preheat temperature and oxygen concentration were found to have a significant effect on the burning fuel-jet behavior. The results of the semi-industrial-scale tests also showed the features of even flame temperature and heat flux. / QC 20100610

<p>Case hardening distortions are a major problem for gear manufacturers. The aim of the current work is to create a simulation model, able to predict how and when case hardening distortions arise. The results presented in this thesis form a basis for such a model.</p><p>Two case hardening steels, with base carbon contents of 0.20 and 0.21 % C were studied using dilatometer experiments. One of them was carburized to 0.36, 0.52 and 0.65 % C in order to investigate the influence of carbon content. Experiments were performed during both isothermal and continuous heating and cooling conditions. The results were used to evaluate phase transformations, heat expansion behaviors and phase transformation strains. The expansion behavior of the material was modeled as a function of temperature, carbon content and phase fractions. The phase transformations to martensite and bainite were modeled, using the Koistinen-Marburger equation and a transformation rate equation based on Austin-Rickett kinetics, respectively. Experiments were simulated using the COMSOL Multiphysics software, to verify the model with respect to martensite and bainite transformations, heat expansion behavior and phase transformation strains.</p>

This Thesis presents two different deposition techniques for the synthesis of Ti2AlC coatings. First, I have fabricated Ti2AlC coatings by high velocity oxy-fuel (HVOF) spraying. Analysis with scanning electron microscopy (SEM) show dense coatings with thicknesses of ~150 µm when spraying with a MAXTHAL 211TM Ti2AlC powder of size ~38 µm in an H2/O2 gas flow. The films showed good adhesion to stainless steel substrates as determined by bending tests and the hardness was 3-5 GPa. X-ray diffraction (XRD) detected minority phases of Ti3AlC2, TiC, and AlxTiy alloys. The use of a larger powder size of 56 µm resulted in an increased amount of cracks and delaminations in the coatings. This was explained by less melted material, which is needed as a binding material. Second, magnetron sputtering of thin films was performed with a MAXTHAL 211TM Ti2AlC compound target. Depositions were made at substrate temperatures between ambient and 1000 °C. Elastic recoil detection analysis (ERDA) shows that the films exhibit a C composition between 42 and 52 at% which differs from the nominal composition of 25 at% for the Ti2AlC-target. The Al content, in turn, depends on the substrate temperature as Al is likely to start to evaporate around 700 °C. Co-sputtering with Ti target at a temperature of 700 °C, however, yielded Ti2AlC films with only minority contents of TiC. Thus, the addition of Ti is suggested to have two beneficial roles of balancing out excess of C and to retain Al by providing for more stoichiometric Ti2AlC synthesis conditions. Transmission electron microscopy and X-ray pole figures show that the Ti2AlC grains grow in two preferred orientations; epitaxial Ti2AlC (0001) // Al2O3 (0001) and with 37° tilted basal planes of Ti2AlC (101̅7) // Al2O3 (0001). / Report code: LIU-TEK-LIC-2008:15.