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- Nilsson, Maria, 1984-
(författare)
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Tribology in Metal Working
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on the tribological performance of tool surfaces in two steel working operations, namely wire drawing and hot rolling. In all forming operations dimensions and surface finish of the products are of utmost importance. Forming basically includes three parts – forming conditions excluded – that may be changed; work material, tool and (possibly) lubricant. In the interface between work material and tool, the conditions are very aggressive with – generally or locally – high temperatures and pressures. The surfaces will be worn in various ways and this will change the conditions in the process. Consequently, the surface finish as well as the dimensions of the formed product may change and in the end, the product will not fulfil the requirements of the customer. Therefore, research and development in regard to wear, and consequently tribology, of the forming tools is of great interest.The investigations of wire drawing dies focus on coating adhesion/cohesion, surface characteristics and material transfer onto the coated steel both in laboratory scale as well as in the wire drawing process. Results show that it in wire drawing is possible to enhance the tribological performance of drawing dies by using a lubricant together with a steel substrate coated by a polished, dual-layer coating containing both hard and friction-lowering layers.The investigations of hot rolling work rolls focus on microstructure and hardness as well as cracking- and surface characteristics in both laboratory scale and in the hot strip mill. Results show that an ideal hot work roll material should be made up of a matrix with high hardness and a large amount of complex, hard carbides evenly distributed in the microstructure. The surface failure mechanisms of work rolls are very complex involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation.This knowledge may be used to develop new tools with higher wear resistance giving better performance, lower costs and lower environmental impact.
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| 3. |
- Sehlin, Staffan, 1950-
(författare)
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Förebygger medling återfall i brott bland unga gärningsmän : En återfallsstudie av medlingsverksamheterna i Hudiksvall & Örnsköldsvik
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The purpose of this study is to investigate mediation’s crime prevention effects. The question that has been answered is: which crime prevention effects mediation has had on young criminals who have participated in mediation programs? The investigation was made in relation to a comparable control group and included a reoffence analysis based on a multivariate analysis. This reoffence study mainly focuses on that the mediation prevents crime through the feelings of shame that the young perpetrator has due to the fact that the crime has been made clear and reinforced at the mediation meeting. The following hypothesis is addressed in this study: Mediation involves the trust between the young perpetrator and his/her parents and has a conflict-solving and crime-prevention effect. By committing a crime, the youth has broken the trust with his/her parents, who have condemned the action. The parents feel the shame from those around them, and because of this resume their position against the youth. The main conclusion is that the total population of youths who participated in mediation programs relapsed into crime to a lesser extent than the youths who did not participate in mediation. The risk for a relapse was twice as high for the youths who did not participate in mediation. A statistically significant relationship emerged between mediation and relapse with regard to party and person plaintiff status, but it is not possible to draw any conclusions whether mediation has a better or worse effect between plaintiff status. The significant effect of relapse for respective gender showed that girls relapsed to a lesser extent than boys. It was not possible to statistically determine whether the youths who were born abroad respective born i Sweden have relapsed to a greater extent. Regarding the age groups there was no statistically significant relationship as to whether youths relapsed to a greater or lesser extent depending on whether they were under or over fifteen years of age. Furthermore, it has not been possible to statistically determine whether group mediation has had a different outcome in relapse frequency as compared to individual mediation, and it has not been possible to distinguish whether compensation at mediation has had any effect. There emerged significant relationships between mediation and relapse for the crime categories ‘crime against life and health’, ‘crime against freedom and peace’, ‘burglary, robbery and other theft crimes’ and ‘vandalism’.
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