Diss. (sammanfattning) Uppsala : Univ., 2007. / Härtill 6 uppsatser.

Diss. (sammanfattning) Uppsala : Univ., 2002. / Härtill 8 uppsatser.

Diss. (sammanfattning) Uppsala : Univ., 2003. / Härtill 6 uppsatser.

There are a number of experiments showing that the ductility of aluminum alloys decreases during age-hardening heat treatment. Observing the grains of age-hardened aluminum alloys at the micron scale, one can notice that there are precipitate-free zones (PFZs) along the grain boundaries. PFZ has yield stress three times lower than the grain interior (bulk) due to absence of alloying elements. As a result, PFZ is suspected to be the reason for ductility reduction of alloys. On the other hand, a number of experiments performed on specimens with micron-scale dimensions have shown that the plastic deformation of crystalline materials is size-dependent. These micron-scale dimensions which can influence the mechanical behavior, such as yield stress or hardening, are not taken into account in the conventional plasticity theory, therefore another theory has been developed. That theory is Strain Gradient Plasticity (SGP). The specific SGP theory used here is a so called ‘higherorder theory’ in the sense that higher order stresses as well as additional boundary conditions are included in the theory. SGP theory also includes length scale parameters in order to be dimensionally consistent. On a recent study conducted by Fourmeau et al. (Fourmeau, 2015), transmission electron microscopy (TEM) is used to display the geometrical properties and the chemical composition of PFZ in the AA7075-T651 aluminum alloy. It is observed that the width of PFZ is about 20 to 40 nm. In the present thesis, the properties for PFZ and bulk material provided by that study are used for a micromechanical finite element model of a microstructure including the bulk, PFZ and the grain boundary (GB). A uniaxial loading condition is applied to the representative volume element (RVE) and SGP theory is hired in order to capture the plastic strain fields as well as the stress triaxiality in PFZ and bulk region. Moreover a damage criterion is employed and studied for models with PFZ and without PFZ to understand the role of PFZ in reduction of the ductility of aluminum alloys. It is found that the damage parameter is much higher in the presence of PFZ. Finally, the void growth is studied by adding voids at critical locations to the model.

<p>The objective of this thesis was to improve a paraffin actuated micropump design, to be able to pump against extreme pressures (above 100 bar). This was accomplished by initially studying the membrane activation, using video capturing. The micropump has been improved to withstand pressures high enough, to enable use in an high-performance liquid chromatography (HPLC) system. The micropump has been shown to pump against back pressures up to 150 bar, with a positive net-flow. This should be compared with the previously recorded maximum back pressure of 50 bar. The pumping against high back pressures was possible due to an increased understanding of the sealing of the membranes. This resulted in a new design that was manufactured and characterised. Without clamping the pump was measured to manage back pressures of 10 bar, and then starting to leak in a bond at the flow channel. With supporting clamping, the managed back pressures increased ten folded.</p><p>When measured on the different valves, pressure above 200 bar has been possible to withhold. Although the valves were below their maximum limit, the pressure was not possible to be further increased due to a limitation in the equipment, i.e. risk of damaging the connections. When examined after pressurised at extreme pressures (above 100 bar) several times, no signs of fatigue or damage of the membrane was seen.</p><p>A new behaviour of the valves was discovered. Above certain pressures some designs self sealed, i.e. withholding the pressure after the voltage was turned off. For these valves the pressure had to be released by some other means.</p>

The objective of this thesis was to improve a paraffin actuated micropump design, to be able to pump against extreme pressures (above 100 bar). This was accomplished by initially studying the membrane activation, using video capturing. The micropump has been improved to withstand pressures high enough, to enable use in an high-performance liquid chromatography (HPLC) system. The micropump has been shown to pump against back pressures up to 150 bar, with a positive net-flow. This should be compared with the previously recorded maximum back pressure of 50 bar. The pumping against high back pressures was possible due to an increased understanding of the sealing of the membranes. This resulted in a new design that was manufactured and characterised. Without clamping the pump was measured to manage back pressures of 10 bar, and then starting to leak in a bond at the flow channel. With supporting clamping, the managed back pressures increased ten folded. When measured on the different valves, pressure above 200 bar has been possible to withhold. Although the valves were below their maximum limit, the pressure was not possible to be further increased due to a limitation in the equipment, i.e. risk of damaging the connections. When examined after pressurised at extreme pressures (above 100 bar) several times, no signs of fatigue or damage of the membrane was seen. A new behaviour of the valves was discovered. Above certain pressures some designs self sealed, i.e. withholding the pressure after the voltage was turned off. For these valves the pressure had to be released by some other means.

This study explores the performance of porous Paptic paper materials composed of a mixture of softwood and lyocell fibers. The investigation involves laboratory experiments and numerical simulations to analyse the impact of various parameters on the paper's characteristics. Tensile and hygroexpansion tests were conducted on sheets with different binder quantities and drying methods. VTT aided in the analysis of mechanical properties using tomography images. The objective was to determine the optimal binder content, to understand the behaviour of the paper under different drying conditions and to optimise the pulp mixture through numerical simulations. Experimental tests involved producing paper sheets with varying binder amounts and different drying methods. Tensile tests were conducted to assess the elastic stiffness, strength, and strain at break. Constrained dried and freely dried papers were compared to evaluate the influence of drying conditions. Hygroexpansion tests were performed to examine the water storage behaviour of papers with added binders. Tomography measurements provided the density profile, which was replicated in the numerical sheets. A micro-mechanical model was employed for numerical simulations, representing each fiber as a beam. The model was calibrated using stress-strain data from VTT's tensile testing of the paper with the highest binder content. The influence of altering the amount and length of lyocell fibers was examined to optimise the pulp. From the tensile tests, an optimal binder content was identified that yielded the highest elastic stiffness while considering the density increase caused by binders. Further additions of binders did not enhance elastic stiffness. However, no optimal value was found for strength and strain at break, as both parameters continued to increase with additional binders. Tensile tests comparing constrained dried and freely dried papers showed similar behaviour, suggesting inadequate constraint in the former. Hygroexpansion tests confirmed the similarities between the two drying methods and revealed that papers with added binders stored less water at a given humidity. Additionally, the drying-moistening cycling exhibited an unusual behaviour not observed in conventional paper, with irreversible expansion occurring during the first drying cycle. Numerical simulations using a micro-mechanical model demonstrated that higher amounts of lyocell fibers improved performance, increasing strength and strain at break. However, varying fiber length did not yield significant improvements in these parameters, although stiffness showed a slight increase. While the literature suggests that the addition of long lyocell fibers decreases paper strength, this study found that when maintaining constant bulk, strength increased under the assumption that the bonding strength was unaffected by lyocell fibers. Furthermore, numerical simulations indicated that an even density profile throughout the paper thickness resulted in higher strength and strain at break. The tomography data revealed that the density profile is affected by the binder quantity. With the addition of binders, the thickness decreased even though the grammage increased. The density is high on the top and bottom surface of the papers which contain more binders while the density is lower in the middle. This difference in density is more pronounced with higher amounts of binders. / Denna studie undersöker prestandan hos porösa pappersmaterial från Paptic som består av en blandning av barrträd och lyocell-fibrer. Undersökningen innefattar laboratorieexperiment och numeriska simuleringar för att analysera effekten av olika parametrar på papperets egenskaper. Drag- och hygroexpansionstester utfördes på ark med olika mängder bindemedel och torkningsmetoder. VTT hjälpte till med analysen av mekaniska egenskaper genom tomografibilder. Målet var att bestämma optimalt innehåll av bindemedel, att förstå papperets beteende under olika torkningsförhållanden och att optimera pappersmassan genom numeriska simuleringar.  De experimentella testerna innefattade framställning av pappersark med varierande mängder bindemedel och olika torkningsmetoder. Dragtester utfördes för att bedöma elastisk styvhet, styrka och töjning vid brott. Inspännt samt fritt torkade papper jämfördes för att utvärdera inflytandet av torkningsförhållanden. Hygroexpansionstester utfördes för att undersöka vattenlagringsbeteendet hos papper med tillsatt bindemedel. Tomografimätningar gav papprens densitetsprofilen, som återskapades i de numeriska arken. En mikromekanisk modell användes för de numeriska simuleringarna, där varje fiber representeras som en balk. Modellen kalibrerades med hjälp av spännings-töjnings-data från VTT:s dragprovning av papperet med högst mängd bindemedel. Inflytandet av att ändra mängden och längden på lyocell-fibrer undersöktes för att optimera pappersmassan.  Från dragtesterna identifierades en optimal mängd bindemedel som gav högst elastisk styvhet när den densitetsökning som orsakas av bindemedel har tagits till hänsyn. Ytterligare tillsatser av bindemedel förbättrade inte den elastiska styvheten. Dock hittades ingen optimal värde för styrka och brottsträckning, eftersom båda parametrarna fortsatte öka med ytterligare bindemedel. Dragtester som jämförde inspännt och fritt torkat papper visade liknande beteende, vilket tyder på otillräcklig begränsning i det förstnämnda fallet. Hygroexpansionstester bekräftade likheterna mellan de två torkningsmetoderna och avslöjade att papper med tillsatt bindemedel lagrade mindre vatten vid en given luftfuktighet. Dessutom uppvisade torknings-fuktnings-cykeln ett ovanligt beteende som inte observerats i konventionellt papper, där irreversibel expansion inträffade under den första torkningscykeln. Numeriska simuleringar med en mikromekanisk modell visade att högre mängder lyocell-fibrer förbättrade prestandan genom att öka styrka och töjning vid brott. Ändringar i fibrernas längd gav dock inte märkvärda förbättringar i dessa parametrar, även om styvheten visade en liten ökning. Medan litteraturen föreslår att tillsatsen av långa lyocell-fibrer minskar papperets styrka, fann denna studie att när densiteten hålls konstant ökar styrkan under antagandet att bindestyrkan inte påverkas av lyocell-fibrer. Dessutom indikerade de numeriska simuleringarna att en jämn densitetsprofil genom papperets tjocklek resulterade i högre styrka och töjning vid brott. Tomografidata visade att densitetsprofilen påverkas av mängden bindemedel. När mängden bindemedel ökade, minskade tjockleken trots att ytvikten ökade. Densiteten är hög på papperets över- och undersida, medan densiteten är lägre i mitten. Skillnaden i densitet är mer uttalad med högre mängder bindemedel.