The large number of vehicles operating on the roads cause high emissions and consequently a negative effect on the environment. When developing and optimizing internal combustion engines, certain requirements must be considered, which are environmental regulations, reduced fuel consumption and increased specific power. In order to meet these demands, an increase of the engine combustion pressure will occur usually accompanied with a temperature increase. During start-up and shut-down of an engine, it is subjected to cyclic thermo-mechanical fatigue (TMF) loads. The turbo manifold and exhaust manifolds connected to the engine is also subjected to these thermo-mechanical fatigue loads and thereby exposed to alternating tensile and compression loads. As these TMF loads will increase in the near future due to the development and optimization of internal combustion engines, it is important to understand the limitations of the material for these loads. In collaboration with Scania CV AB in Södertälje, this thesis covers the investigation of influence of nitrocarburizing (NC) on TMF properties of three ductile irons (DCI) labelled HiSi, SiMo51 and SiMo1000 intended to be used for components in the exhaust system. Nitrocarburizing is a thermo-chemical process where nitrogen and carbon diffuses from the process medium into the surface zone of a ferrous metal. The purpose of the NC is to increase the wear properties in contact areas between different parts. The oxidation with and without nitrocarburizing are studied both after isothermal and stress free oxidation tests at 780 °C and after TMF loads with combined cyclic variation of mechanical and thermal loads. In addition, the properties such as hardness, defects, porosity, microstructure, composition of both the materials and of the oxide layer have been investigated. For SiMo1000+NC cracks formed during nitrocarburizing were positioned parallel to the surface edge in the diffusion zone and consequently an increased diffusion of nitrogen into the material, i.e. deeper diffusion depth. SiMo1000+NC showed highest hardness, highest compressive residual stresses and thickest oxide layer. SiMo1000 showed highest resistance against oxidation due to the protective aluminum oxide layer. Oxide crack initiations after thermo-mechanical tests with a protective silicon oxide layer around the cracks for HiSi and SiMo51 and a protective aluminum oxide layer around the cracks for SiMo1000. In materials with nitrocarburizing, these protective layers of either silicon oxide or aluminum oxide were more distributed into the material. In SiMo1000+NC, crack initiations were not oxidized.

Um novo ciclo de tratamento térmico denominado como têmpera e partição vem sendo desenvolvido em aços com elevados teores de silício, como rota para obtenção de estruturas com frações consideráveis de austenia retida. Essa rota de tratamento m térmico consiste em realizar uma têmpera temperaturas intermediárias entre Ms e Mf, seguido de um reaquecimento com manutenção em patamares isotérmicos por certos intervalos de tempo, objetivando estabilizar a austenita remanescente através da partição do carbono a partir da martensita supersaturada. No presente trabalho, duas ligas de ferros fundidos nodulares convencionais, com diferentes teores de silício e manganês, foram submetidas a ciclos de têmpera e partição. As amostras foram austenitizadas a 900°C por duas horas. Uma das ligas foi temperada em óleo a 160°C e a outra a 170°C por 2 minutos. Imediatamente após a têmpera as amostras foram reaquecidas em temperaturas entre 300 e 450°C por intervalos de tempo que variaram entre 2 e 180 minutos. A caracterização microestrutural foi realizada através de microscopia eletrônica de varredura (MEV) e difração de raios x. A caracterização mecânica foi feita através de ensaios de energia absorvida ao impacto, dureza HRC e ensaios de tração. A caracterização microestrutural evidenciou que os ciclos de têmpera e partição são viáveis na obtenção de frações consideráveis de austenita retida nos ferros fundidos nodulares. A caracterização mecânica evidenciou que foi possível obter boas combinações de energia absorvida ao impacto, resistência à tração e alongamento. Em todas as condições testadas é possível perceber uma janela de processo bem definida caracterizada por valores crescentes das propriedades mecânicas nos primeiros minutos do ciclo de partição e que decrescem após certo intervalo de tempo. O conjunto de propriedades mecânicas obtidas através dessa rota de tratamentos térmicos indica que os ferros fundidos nodulares submetidos ao ciclo de têmpera e partição podem se constituir como alternativa tecnológica para aplicações comerciais nas quais os ferros fundidos nodulares austemperados já são materiais consolidados. / A new heat treatment cycle known as quenching and partitioning has been developed in commercial steel alloys containing silicon as a way to obtain structures with controlled fractions of retained austenite. This heat treatment cycle consists in performing a quenching in temperatures between Ms and Mf, followed by a reheating with isothermal holding by different time intervals. The aim of this cycle is to achieve the austenite stabilization by diffusion of carbon from the supersaturated plates of martensite. In this work, two conventional ductile cast iron alloys, with two different contents of silicon and manganese were heat-treated in quenching and partitioning cycle. The samples were austenitized at 900°C for two hours, followed by quenching in oil at 160° C and 170° C for two minutes. Immediately after quenching, the samples were reheated at temperatures between 300 and 450°C for time intervals between 2 and 180 minutes. The microstructural characterization was performed using electronic microscopy (SEM) and x-ray diffraction. The mechanical characterization was performed using impact tests, hardness and tensile strength tests. The microstructural characterization showed that the cycles of quenching and partitioning are viable to obtain considerable fractions of retained austenite in nodular cast by this heat treatment route. The mechanical characterization showed that it was possible to obtain good combinations of energy absorbed in the impact, tensile strength and elongation. In all tested conditions was possible to perceive a well-defined process window characterized by increasing values of mechanical properties in the first minutes of the partitioning step, and decrease after certain time intervals. The set of mechanical properties obtained by this route of heat treatments indicates that nodular cast iron subjected to tempering and partitioning cycle can be constituted as an alternative technology for commercial applications in which austempered ductile irons are already consolidated materials.

Industrial metal forming operations generally require several deformation steps in order to create the final product. The mechanical behavior of materials undergoing strain path changes can be very different from those deformed in a given direction to fracture. The work presented here employed laser drilled model materials to better understand the effect of pre-strains and strain path changes on void growth and linkage leading to fracture is studied. The experimental results show that increasing pre-strain results in faster void growth which was justified in terms work hardening rate in the sample. Scanning electron microscope images revealed that the ductility of the sample decreased with increasing pre-strain but only slightly compared to the large decrease in far field strain at failure. This suggests that pre-strain affects strain localization significantly and to a lesser extent the ductility. Finally a finite element model has been built to predict the linkage between voids.

The Sibiel Shear Zone is a 1-3km wide, ductile shear zone located in the South Carpathian Mountains, Romania. In the Rsinari area, the ductile shear zone juxtaposes amphibolite facies rocks of the Lotru Metamorphic Suite against greenschist facies rocks of the Rauorul Cisndioarei Formation. The first represents the eroded remnants of Peri-Gondwanan arcs formed between the Neoproterozoic-Silurian (650-430Ma), regionally metamorphosed to amphibolite facies during the Variscan orogeny (350-320Ma). The second is composed of metasedimentary and metavolcanic Neoproterozoic-Ordovician (700-497Ma) assemblages of mafic to intermediate bulk composition also resembling an island arc metamorphosed during the Ordovician (prior to similar to 463Ma). Between these lie the epidote amphibolite facies mylonitic and ultramylonitic rocks of the Sibisel Formation, a tectonic melange dominated by mafic actinolite schists attenuated into a high strain ductile shear zone. Mineral Rb-Sr isochrons document the time of juxtaposition of the three domains during the Permian to Early Triassic (similar to 290-240Ma). Ductile shear sense indicators suggest a right lateral transpressive mechanism of juxtaposition; the Sibiel shear zone is a remnant Permo-Triassic suture between two Early Paleozoic Gondwanan terranes. A zircon and apatite U-Th/He age transect across the shear zone yields Alpine ages (54-90Ma apatite and 98-122Ma zircon); these data demonstrate that the exposed rocks were not subjected to Alpine ductile deformation. Our results have significant implications for the assembly of Gondwanan terranes and their docking to Baltica during Pangea's formation. Arc terranes free of Variscan metamorphism existed until the Early Triassic, emphasizing the complex tectonics of terrane amalgamation during the closure of Paleotethys.

Research areas within the automotive industry are dedicated to reducing the weight and emissions of vehicles. Through the application of lightweight materials, such as polymers, fuel consumption and production costs can be decreased. Therefore, understanding the mechanical responses and failure mechanisms of these materials is significant to the development and design of vehicular structural components. Experimental tests were performed to capture the time, temperature, and stress state dependence, as well as failure mechanisms and large-strain mechanical responses of polypropylene (PP) and copolymer polypropylene (co-PP). Alongside studying the mechanical responses of PP and co-PP, the deformation mechanisms associated with the ductile and brittle failures were also examined. By applying an Internal State Variable (ISV) model, the mechanical behavior of PP and co-PP under various strain rates and temperatures was predicted. Phenomenological, mechanics based failure criteria were also applied to the model to predict the ductile or brittle failure of the materials.

Scania wants to lower the weight of their trucks, including the goal to reduce the carbon dioxide emissions, and one way to do that is to use laser welding instead of fastenings.This bachelor thesis work is about laser welding of ductile cast iron, or spheroidal graphite cast iron or nodular cast iron, to QT-steels and case hardening steel and evaluation of the mechanical properties of the weld. Also laser welding of cast steel to the same two materials are being evaluated in this work. Tests are done to evaluate the effect on the material from laser welding. The tests are tensile tests and Vickers hardness test; both across and along the weld and in some areas of interest. EDS (Energy Dispersive X-Ray Spectroscopy) is used to analyze the composition in the weld and light optical microscope is used to look at the fusion zone (FZ) and the heat affected zone (HAZ). The results shows that the hardness is high in the heat affected zone due to the formation of martensite and that the materials mix more towards the root of the weld. The materials also mix more if the weld depth is deeper. The width of the heat affected zone seems to be longer if the heat input is higher. It is also clear that welding of cast steel is less complicated than the welding of ductile cast iron. That is because ductile cast iron gets a hard and brittle heat affected zone (HAZ) while the cast steel does not. The cast steel can also be welded without filler wire without getting to hard or to brittle. If laser welding is to be used in the future the component should be constructed in such a way that the fusion zone is not carrying the main load. Tests on fatigue strength should also first be done on a finished component as it cannot be tested on the samples in this work. This work was conducted at Scania AB and the royal institute of technology, KTH, in Sweden. / Scania vill sänka vikten på sina lastbilar, bland annat för att minska utsläppen av koldioxid, och ett sätt att göra det är att lasersvetsa istället för att använda bultar. Detta kandidatexamensarbete handlar om lasersvetsning av segjärn, eller nodulärt gjutjärn som det också kallas, till seghärdningsstål och sätthärdningsstål samt utvärdering av svetsens mekaniska egenskaper. Även lasersvetsning av gjutstål till samma stålsorter som ovan utvärderas i detta arbete.Tester görs för att utvärdera effekten på materialet från lasersvetsningen. Testerna är dragprov och Vickers hårdhetstestning; både tvärs över och längs med svetsen samt även i vissa områden av särskilt intresse. EDS (Energy Dispersive X-Ray Spectroscopy) används för att analysera sammansättningen i svetsen och ljusoptiskt mikroskop används för att se svetsgodset och den värmepåverkade zonen. Resultaten visar att hårdheten går upp i den värmepåverkade zonen på grund av martensit bildning och att materialen blandar sig mer närmare svetsroten. Materialen blandar sig också mer om svetsdjupet är djupare. Den värmepåverkade zonens bredd verkar vara större om sträckenergin är hög. Det står också klart att svetsning av gjutstål är mindre komplicerat än svetsning av segjärn eftersom segjärnet får en hög hårdhet i den värmepåverkade zonen medan det inte alls blir så för gjutstålet. Gjutstålet kunde också svetsas utan tillsatsmaterial utan att få ett för hårt eller sprött svetsgods. Om man vill använda lasersvetsning i framtiden ska komponenter konstrueras så att svetsen inte bär huvudvikten eftersom resultatet visar att svetsgodset får lägre brottgräns. Utmattningstester borde också göras på en färdig komponent eftersom det inte kan testas på proven från det här arbetet. Detta arbete utfördes på Scania AB och Kungliga Tekniska Högskolan, KTH, i Sverige.

<p> Small shear zones located northwest of the Grenville Front Mylonite Zone exhibit both a brittle and ductile deformation history. Textures reveal that an earlier mylonitic rock has been overprinted by one which demonstrates textures typical of brittle cataclasis.</p> <p> ductile deformation has occurred under greenschist facies conditions, while a later, brittle event has occurred below lower greenschist temperatures. These produce high shear strain values which lie between 14.44 and 10.79.</p> <p> Upper and lower age limits for the initiation of shear zones have been determined as being prior to the emplacement of pegmatite dykes, and up until the formation of brittle-ductile shear zones found locally. Thus, they have developed between 1400 ± 50 Ma and approximately 1100 + ? Ma.</p> / Thesis / Bachelor of Arts (BA)

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No description available.

The mechanism of metal material failure due to inelastic cyclic deformations is commonly described as Low-Cycle Fatigue (LCF). Fracture in steel structures caused by earthquakes can be associated with this mechanism. Mathematical expressions describing the material deterioration due to LCF are often referred to as LCF laws. The accurate determination of the safety of steel structures against earthquake-induced failure requires the use of LCF laws which have been sufficiently validated with experimental test data. The present study combined experimental testing and computational simulation to enhance the understanding of structural steel fracture due to LCF. The experiments were conducted in specimens extracted from the flat and corner regions of two rectangular steel hollow sections with different thickness. A total of 60 cylindrical specimens with a circumferential notch were subjected to different combinations of axial and torsional loading. The loading protocols and notch geometry were designed to produce different stress states at the location of fracture initiation. Finite element analyses were conducted to obtain the stress state and inelastic strains at the fracture initiation location. This information was then used for the calibration of five existing LCF laws. The calibration also allowed the comparative evaluation of the capability of the different laws to capture fracture initiation for different stress states, with a single set of values for the various parameters. The accuracy of the calibrated LCF laws to predict fracture initiation in a large-scale test was also investigated. To this end, a test was conducted on a rectangular steel tube subjected to cyclic axial loading. A finite element analysis of this test was conducted, and predictions of the instant and location of fracture initiation using the calibrated LCF laws were compared with the experimental observations. / Doctor of Philosophy / The mechanism of material failure due to repeated cycles of large deformations is denoted as Low-Cycle Fatigue (LCF); this failure mechanism can occur in steel structures subjected to loading conditions such as those induced by earthquakes. Mathematical expressions that evaluate the material deterioration due to LCF are often used to predict the instant and location of fracture initiation in small-scale and large-scale tests. An experimental program was conducted for the study of fracture associated with LCF. A total of 60 specimens were fabricated with material extracted from the flat and corner regions of two rectangular steel tubes; the applied loads elongated and/or twisted the specimens until they ruptured. Computational simulations of these tests were conducted to obtain key information at the location of the observed fracture initiation. This information was used to adjust five mathematical expressions suggested by previous researchers that could predict the same instant of fracture initiation observed in the experiments. The accuracy of the predictions from each of these mathematical expressions was evaluated. The accuracy of these mathematical expressions to predict fracture initiation in a large-scale test was also investigated. To this end, an experiment was conducted on a rectangular steel tube subjected to repeated cycles of deformation. A computational simulation of this test was also developed, and predictions of the instant and location of fracture initiation were compared with the experimental observations.