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Fall-related injuries are common problems in elderly care in particular. These can cause brain damage and hip fractures, which in many cases can be serious. To reduce or mitigate the damage, various safety measures have been developed. One of them concerns a change in the surroundings, more specifically, the floor. At KTH within the Division of Neuronic Engineering, research has been done on how the impact of the case can be minimized and a shock absorbing floor (SAF) was developed. Diving problems with this type of flooring are that heavy medical beds sink into the floor, which means increased rolling resistance and thus long-term damage to both the floor and the medical staff. The aim of this thesis was to investigate how much rolling resistance can be minimized by building a downscaled hovering device based on hovercraft technology. The purpose was to enable the device to possibly be mounted under hospital beds and create a lifting force. To evaluate the performance, force measurements were performed on KTH SAF with different weights and with the use of a dynamometer. The results showed that the device reduced rolling resistance by up to 57.4% with additional weight. Four axial fans were used together with manual control of the speed of each fan. The selected components were made taking into account, in particular, cost, weight and dimensions and can thus also be limiting factors for this thesis. For future work, effective soundproofing is needed for this solution to be possible to be implemented in a hospital environment. Furthermore, studies needs to be carried out for a full-scale prototype to confirm that an equally large reduction in rolling resistance can be achieved.

Energy dissipation, fuel consumption, real-estate property prices and health issues are some of the aspects related to the tyre/pavement interaction and its functional properties of rolling resistance and noise. The first two aspects are affected by the tyre/road interaction as energy is dissipated mostly by hysteretic losses as the tyre is subjected to dynamic deformations when contacting the pavement surface. The other effect of this contact system that is analysed in this thesis is noise. Excessive noise exposure leads to a decrease in real-estate property values and even health issues such as increased blood pressure, sleep disturbance, cognitive impairment in children, among others. To mitigate such issues, a good understanding of the underlying causes is crucial and therefore a holistic approach was used to analyse the contact interaction in a more comprehensive way, encompassing the pavement, tyre, environmental and contact media (contaminations). Both noise and rolling resistance were analysed after subjecting the contact system to controlled interventions in one variable while maintaining the other variables constant and then comparing to a reference condition. In the first part of the investigative work, different tyres were tested while maintaining the pavement, environment and contact media constant, allowing an evaluation of the impact of winter tyres on noise and rolling resistance. In the second part, an intervention in the pavement was applied while maintaining the other variables constant. allowing an evaluation of the impact of surface grinding on noise and rolling resistance. The first part quantified how noisier studded tyres are in comparison to non-studded tyres, yet no substantial difference in rolling resistance was found. The second part revealed the potential of the horizontal grinding to reduce noise and rolling resistance, having a limitation, on the duration of such effects, especially for Swedish roads where studded tyres are used. / Energiförluster, bränsleförbrukning, fastighetspriser och hälsoproblem är några av de effekter som följer av däckens interaktion med vägytan och som relaterar till de funktionella egenskaperna för rullmotstånd och buller. De första två effekterna uppkommer av väg- och däckinteraktionen eftersom energi förbrukas mestadels genom hysteresförluster när däcken utsätts för dynamiska deformationer vid kontakt med vägytan. Den andra effekten av däck/vägkontakten som analyseras i avhandlingen är buller. Alltför hög bullerexponering intill boendemiljöer leder till minskning av fastighetspriser och även till hälsoproblem såsom ökat blodtryck, sömnstörning, kognitiv försämring hos barn, med mera. För att mildra sådana problem, är det avgörande att ha en god förståelse av de bakomliggande orsakerna, och därför används här ett helhetsgrepp för att genomföra en mer omfattande analys av interaktionen. Analysen inkluderar egenskaper hos vägytan, däcken, omgivande miljö samt kontaktmedier (förorenande skikt).. Både buller och rullmotstånd har analyserats efter att på ett kontrollerat sätt ha varierat en viss variabel medan de andra variablerna hållits konstanta, och sedan jämföra resultaten med referensförhållandet. I den första delen av denna undersökning provades flera olika däck medan vägytan, miljö- och kontaktmedier hölls konstanta. Detta möjliggjorde en utvärdering av effekterna av olika vinterdäck på rullmotstånd och buller. I den andra delen beskrivs effekter av en förändring av vägytan, utförd genom att slipa bort topparna i vägtexturen, medan de andra variablerna hålls konstanta.. Den första delen kvantifierar bullerökningen vid användning av dubbdäck i jämförelse med odubbade vinterdäck. Några betydande skillnader i rullmotstånd hittades däremot inte mellan de två däckgrupperna. Den andra delen av texten visar på potentialen av horisontell slipning för att minska buller och rullmotstånd, dock är varaktigheten begränsad; särskilt för svenska vägar där dubbdäck används. / <p>QC 20180212</p>

<p>Sheet specimens of alloy AZ31 were cross-rolled to equivalent strains of 0.05, 0.10, 0.30, 0.40, 0.56, and 0.77. The microstructure evolution was examined using a combination of optical metallography (OM), Electron Backscattered Diffraction (EBSD), Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD). The results revealed significant activity of basal and non-basal slip as well as twinning. The twins were mainly of the contraction and double-twin (contraction-extension) types. In addition to the micron scale (1-5μm) twins observed on EBSD patterns, nano-scale twins were observed. The nano twins had a width of less than 0.20μm and existed either as individual/isolated twins or as twin-bundles that are several microns thick. The number of nano twin-bundles increased with increasing strain. Shear bands were also observed to form at high strains and eventually led to the failure of the sheet. As for the texture evolution, analysis of the pole figures shows an evident strengthening of the basal texture during the cross-rolling.</p> <p>Specimens of Mg alloy AZ31 cold-rolled to equivalent strains of 0.10 and 0.30 were selected and annealed at 250^oC. The progress of recrystallization was followed using OM, EBSD and TEM with special emphasis on the nucleation of recrystallization. The distribution of recrystallization nuclei was very heterogeneous due to the heterogeneity of the as-deformed microstructure. Twin/grain-boundary and twin/twin intersections as well as twin interiors were the dominant recrystallization nucleation sites. Significant recovery was observed in the non-recrystallized regions and this limited the growth of the recrystallized grains.</p> / Master of Applied Science (MASc)