Several fatigue criteria were evaluated with experimental fatigue test data. The fatigue tests contained many different geometries with different degrees of stress concentration. It was concluded that the differences between the criteria were neglectable when compared to the differences between the specimens. The stress concentrations with the stress gradients and sizes of the highly stresses volumes that resulted were very important. In order to understand this, gradient and volume methods were investigated. The gradient methods showed some improvement over the strictly local evaluation first attempted. The volume method, a weakest link application with a Weibull distribution of the fatigue strength, yielded results useable for actual design situations. The volume method is strongly recommended and the choice of criterion does not seem to be very important. / <p>QC 20101122</p>

This licentiate thesis is generally concerned with the ductile failure and rupture mechanisms encountered under combined tension and torsion loading. In the first part entitled Paper A, an experimental investigation of the rupture mechanisms in a mid-strength and a high strength steel was conducted employing a novel test configuration. The specimen used was a double notched tube specimen loaded in combined tension and torsion at a fixed ratio. The effective plastic strain, the stress triaxiality and the Lode parameter was determined in the centre of the notch at failure. Scanning electron microscopy of the fractured surfaces revealed two distinctively different ductile rupture mechanisms depending on the stress state. At high stress triaxiality the fractured surfaces were covered with large and deep dimples, suggesting that growth and internal necking of voids being the governing rupture mechanism. At low triaxiality it was found that the fractured surfaces were covered with elongated small shear dimples, suggesting internal void shearing being the governing rupture mechanism. In the fractured surfaces of the high-strength steel, regions with quasi-cleavage were also observed. The transition from the internal necking mechanism to the internal shearing mechanism was accompanied by a significant drop in ductility. In the second part entitled Paper B, a micromechanics model based on the theoretical framework of plastic localization into a band introduced by Rice is developed. The model employed consists of a planar band with a square array of equally sized cells, with a spherical void located in the centre of each cell. The periodic arrangement of the cells allows the study of a single unit cell for which fully periodic boundary conditions are applied. The micromechanics model is applied to analyze failure by ductile rupture in experiments on double notched tube specimens subjected to combined tension and torsion carried out by the present authors. The stress state is characterized in terms of the stress triaxiality and the Lode parameter. Two rupture mechanisms can be identified, void coalescence by internal necking at high triaxiality and void coalescence by internal shearing at low triaxiality. For the internal necking mechanism, failure is assumed to occur when the deformation localizes into a planar band and is closely associated with extensive void growth. For the internal shearing mechanism, a simple criterion based on the attainment of a critical value of shear deformation is utilized. The two failure criteria capture the transition between the two rupture mechanisms successfully and are in good agreement with the experimental result. / <p>QC 20101109</p>

The aim of the present work was to clarify the mechanisms of hydrogen removal during vacuum degassing. The main reason for this was because the primary source of hydrogen pick-up in steel-making is the moisture in the furnace atmosphere and the raw material charged into the ladle furnace. Previous studies showed that the presence of hydroxyl ions in the ladle slag results in hydrogen transfer from the slag back into the steel bath. The main focus of this thesis was therefore to gain deeper knowledge of the ladle slag and its properties. For this purpose a number of slag compositions were examined in order to clarify whether these slags were single liquids at 1858 K. 14 out of 27 compositions in the Al2O3 CaO MgO SiO2 system was completely melted. These results were in disagreement with the existing phase diagrams. Water solubility measurements were carried out by employing a thermo gravimetric technique. The temperature was found to have negligible effect on the water solubilities. The experimental results showed that the water capacity values varied between 1x103 and 2x103 in the majority of the composition range. However, for compositions close to CaO saturation the water capacity value could reach higher than 3x103. The experimental determined water capacity was further used to develop a water capacity model for the quaternary slag system Al2O3 CaO MgO SiO2. The model was constructed by considering the affects of the binary interactions between the cations in the slag on the capacity of capturing hydroxyl ions. The model calculations agreed well with the experimental results as well as with the literature data. An attempt was made to develop a preliminary process model for dehydrogenation by using the results from CFD calculation. For this purpose industrial sampling was made during vacuum treatment. The hydrogen concentrations decreases fast in the initial stages of the degassing, but is slowed down in the final stage. The model calculations fit the initial stage of the dehydrogenation process well. In the final stage of the process the predicted values are somewhat lower than the plant data. The results from the model prediction showed that a dynamic process model could be satisfactorily constructed using the results from CFD calculation. The present work aimed at determining how big impact hydroxyl ions in the slag have on the final hydrogen concentration in the liquid steel. It was found that the effect is of less importance regarding the final concentration of the metal after the degassing treatment. / <p>QC 20101110</p>

Regarding the use of material, modern lightweight car bodies are becoming more and more complex than previous constructions. The materials nowadays are used for a more specific field of application and more high strength steels are used and also other materials like aluminium, stainless steel, reinforced polymers are used more frequent. The joining of these materials often requires new or modified joining processes. The aim with this thesis is concerned with the development of simulation models of the joining process as well as mechanical properties of self piercing riveted (SPR) joints and pierce nut joints. In both of these joining methods problems occur when introducing more high strength steel sheets. For SPR, fractures occur in the rivet, and for pierce nut the thread will be damaged. Since both the SPR process and the pierce nut process expose the material for plastic deformation up to 150%, correct material properties for very large strain and a simulation program that could handle this was required. With the commercial finite element program Deform2D an axi-symmetric model has been built for the SPR process and the pierce nut process. Because of the computational time, 3D simulations were only used where it was necessary. The developed 3D models use the commercial finite element program ABAQUS-Explicit. All simulation models have been verified with satisfactory agreement to experimental results. For SPR, an axi-symmetric simulation model was used for evaluating and optimising the setting process in the stainless steel sheets EN1.4301, HyTens 800 and HyTens 1200. Subsequently, 3D models were used for predicting the mechanical properties of new SPR joints that have showed reduced risk for rivet cracking. In pierce nut simulations, nuts with hardness 8 and 10 have been set in the high strength steel sheet DP600. An axi-symmetric simulation model was used for centred nut setting and two different simulation models in 3D were used to evaluate eccentric nut setting and torque resistance. This work resulted in more knowledge about the fracture risk in the rivet and how to reduce it. The strain and stress, which was used as fracture indicators, were reduced to the half with modifications of the rivet and the die geometry. Mechanical property simulations in shear and peel load resulted in satisfactory results for new SPR joints that have showed reduced fracture risk during rivet setting. New die and rivet designs can be developed effectively by combining the process and mechanical property simulations. For a pierce nut joint in high strength steel sheets (1.5mm DP600), the simulations show that the cutting of the sheet in combination with eccentric setting over the die causes the thread damage. The thread damage can be avoided by changing the dimension of the nut or by increasing the strength of the nut material. The simulation models can also be used to develop new nut and die geometries for future applications. / QC 20101115

This work has been conducted to study the effect of different types of iron ore pellets on an EAFbased steel production. The study has focused on how the chemical composition of the raw materialsinfluences the slag amount and as a result the EAF operation. It is also shown that the raw materialselection can be optimized for a better slag practice. The advantage of slag former additions that arestrictly adapted to the EAF charge composition is also demonstrated.This work is based on a MgO-saturation model for slag, developed by Dr Roger Selin. The model hasbeen implemented in RAWMATMIX®, a software developed by Kobolde &amp; Partners AB in Stockholm.In this report I discuss the following studies: i) A study and comparison between different basicityindices and MgO-saturation for EAF slags, ii) a comparison between different DR-pellets and mixesbetween them and their corresponding DRI, iii) a parameter study on how different properties for theDR-pellet and DRI influence the EAF process, and iv) a case study of two hypothetical steel plants toillustrate the value of an adaptive slag former addition based on the raw material input. Overall,these studies describe the value of using DRI based on DR-pellets, containing low amount of acidicoxides and balanced amounts of MgO, for an EAF based steel production.

The demand of renewable fuels is increasing. Catalytic Fast Pyrolysis is a growing technology that could supply with high quality bio crude that can be used in the already existing infrastructure. The process of choice in this paper to implement this technology is insitu circulating fluidized bed using saw dust as feed. Two cases are designed and then modelled in ASPEN Plus. The first case uses steam as fluidizer and the second uses recycled pyrolysis gas as fluidizer. Both cases are found to be self-sustainable with biomass as the only energy source. According to the parameter study, this is only true for biomass feed up to 40% moisture content. / Efterfrågan om förnyelsebara bränslen ökar. Catalytic Fast Pyrolysis är en växande teknologisom skulle kunna förse med bio-crude av hög kvalité för att användas med dagensinfrastruktur. Den process som valdes för att implementera denna teknologi är in-situcirculating fluidized bed med sågspån som inmatning. Två fall blev utformade och sedanmodellerade i ASPEN Plus. Det första fallet använder sig av ånga som flödare och andrafallet använder sig av återvunnen pyrolysgas. Båda fallen var självförsörjande med endastbiomassa som energikälla. Enligt parameterstudien stämmer detta endast för biomassa medmindre än 40% fuktinnehåll.

The necessity for synthesis of nanoparticles with well controlled size and morphology emerged with the development in recent years of novel advanced applications especially in biomedical related fields. These applications require nanoparticles with more complex architecture such as multifunctional nanoparticles (i.e. core–shell structures) that can carry several components with different embedded functionalities. In this thesis, we developed core–shell nanoparticles (CSNPs) with finely tuned silica shell on iron oxide core as model system for advanced applications in nanomedicine such as MRI, drug delivery and hyperthermia. The synthesis of monodispersed, and well separated, single iron oxide core–silica (SiO2) shell nanoparticles for biomedical applications is still a challenge. Substantial amount of aggregated and multicore CSNPs are generally the undesired outcome. In this thesis, synthesis of monodispersed, free of necking, single core iron oxide-SiO2 different distinct overall size and tuneable shell thickness was performed using an inverse microemulsion method. The influence of the reaction time, hydrodynamic conditions and precursor concentration on the synthesis process and thickness of the silica layer was investigated and the process was optimised. The residual reactions during the post synthesis processing were inhibited using a combination of pH adjustment and alternating shock freezing with ultracentrifuging. The second part of the thesis is concerning thorough characterisation of the CSNPs with different shell thickness. The non-aggregated tuneable shell CSNPs maintained the superparamagnetic character of the cores with high magnetisation, showing great potential for their applications in nanomedicine. Magnetic measurements and relaxivity tests were performed and the comparison of the CSNPs with commercial products revealed the fact that relaxation time ratios (r2/r1) obtained are higher than those of the commercially available MRI contrast agents which indicates a better T2 contrast. In the last part of the thesis the in-vitro toxicity investigation results are reported. For the investigation of cytotoxicity (3- 4, 5-dimethyldiazol-2-yl)-2, 5 diphenyl-tetrazolium bromide (MTT) assay was performed and the secretion of pro-inflammatory cytokines TNF-α and IL-6 was determined using enzyme-linked immunosorbent assay (ELISA). The cells were exposed to a wide range of concentrations of nanoparticles (between 0.5 μg/ml to 100 μg/ml). The cell toxicity results indicated no severe toxic effects on human monocyte-derived macrophages (HMDM) as model system. The internalisation of the nanoparticles by HMDM was monitored using transmission electron microscopy (TEM). The CSNPs have the capacity of forming stable colloidal dispersions at physiological pH, with desired magnetic properties, low toxicity, and the potential for further functionalisation via surface modification of the silica shell or by adding new components (i.e. quantum dots, therapeutics). These characteristics make them highly promising for drug delivery, medical imaging, hyperthermia, magnetic cell marking and cell separation as well as many other biomedical applications. / <p>QC 20100506</p>

In recent years the material graphite has been heavily studied since its use in widespread applications have increased, for example batteries, vehicles, and solar cells. When the need for this type of material increases the efficiency and the sustainability of the production methods must be taken into consideration. This thesis presents an alternative method to produce graphite from biochar which is renewable. Biochar in combination with a catalyst was used rather than the more traditional method, which is known for its high temperatures and time-consuming procedures. The weight ratio of pure iron (catalyst) to biochar was approximately 22.4 wt-% in the graphite production process. The result was analyzed using X-Ray Diffraction and showed that the method managed to produce a high crystalline graphite at a temperature of 1300 °C within 3 hours. The result also showed that by using a catalyst a graphite sample with a high “degree of graphitization” with a moderate crystal size was produced. / Under senare år har materialet grafit studerats omfattande eftersom dess användning i diverse applikationer har ökat. Detta omfattar områden som batterier, bilar och solceller. När behovet av denna typ av material ökar måste metodernas effektivitet beaktas för processen. Denna avhandling presenterar en alternativ metod för att framställa grafit från biokol som är förnybar. Biokol i kombination med en katalysator användes istället för den traditionella metoden som är känd för sina höga temperaturer och tidskrävande processer. Ett viktförhållande av rent järn till biokol på cirka 22,4 viktprocent i grafit användes i produktionsprocessen. Resultatet analyserades med röntgendiffraktion och metoden lyckades producera en högkristallin grafit vid en temperatur av 1300 ° C och inom ett tidsintervall på ca 3 timmar. Resultatet visade även att genom användningen av en katalysator i processen uppnåddes en hög "grad av grafitisering" med en måttlig kristallstorlek.

No description available.

No description available.