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  • Wallström, Lennart (författare)
  • Cell wall bulking and distribution of different chemicals in pine, Pinus Sylvestris
  • 1998
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • <p>The interaction between wood, Pinus sylvestris, (60% RH) and polyethyleneglycol (PEG) of different molecular weights (PEG 200 and PEG 1500), pentaerythritol and glycerol, impregnated into the wood, has been investigated using Scanning Electron Microscopy, EDS-analysis, dynamical mechanical techniques (DMTA), X-ray diffraction (WAXS) and macroscopic dimensional measurement. Reduced dimensional changes after impregnation when exposed to environments with changing moisture content, showed that the stabilization effect of glycerol and PEG 200 impregnation is very good. The other chemicals used, especially pentaerythritol, were not as effective as glycerol and PEG 200. Cell wall measurements using SEM show that an increase in cell wall thickness gives a corresponding increase in stabilization effect. DMTA-measurements showed that interaction between wood molecules and the chemicals used differs. In general, a higher degree of cell wall penetration of the chemicals gives a better stabilization effect. WAXS- investigations showed free crystalline pentaerythritol, PEG 1500, glycerol and PEG 200. Examination using SEM/EDS-linescan of potassium stained chemicals confirmed the results from the cell wall thickness measurements. However, the better resolution obtained in the STEM/EDS-linescan showed an inhomogenous distribution of the chemical in the cell wall. High temperature dried and green wood of Swedish pine was impregnated with glycerate and silver nitrate. Silver was precipitated in the cell wall by a new method. A significant difference in the distribution, size and location of the silver was observed. The silver particles are small and dispersed in the green wood samples but clustered and irregulary spaced in the dried specimens. The inhomogenous distribution in the dried specimens is believed to be the result of damage inside the wood cell walls due to drying stresses, which in turn will negatively affect the dimensional stabilizing result. The strength and energy to fracture is increased by a factor of two if wood not is allowed to be dried before cell wall bulking. This is because the impregnating chemical (glycerol in the present case) in the cell wall substitutes some of the moisture and therefore limits drying stresses. The glycerol is believed to be soluble inbetween the hemicellulose. The average distance between the silver particles in the impregnated green wood indicates that the impregnant is distributed in the cell wall at the microfibrilar level. Experimental results showed that the fastest diffusion path into the cell wall is from the lumen over the pit membrane through the compound middle lamell and not from the lumen through the secondary wall layer S3. The darker compound middle lamella seen in TEM is believed to be an artefact, as it is possible that the ML is thicker than the other layers in the wood cell wall after microtoming.</p>
  • Wallström, Peter (författare)
  • On Value and Waste
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • <p>Value and waste are concepts that are used in improvement projects. In lean the concepts are fairly simple. Reduce the waste and the value has increased. However, value is both multidimensional and differs over time. If the concepts value and waste are to be used, the concepts must be clearly defined and measured. Otherwise, value can be reduced for the customer/user and the cost increased for the producer/seller. The purpose in this thesis is to investigate how value and waste are perceived by different stakeholders, how value and waste are related, and how value and waste are measured. The focus of the study is the improvement of production and services. The study does not investigate the product/service development. The conclusions are based on a number of cases and research from different fields such as resource-based view and marketing. The study use mix of qualitative and quantitative methods. Measures of forecasting accuracy and their relations where explored with different statistical tools in order to understand the influence of measures and dimensions. The view of value concerning energy efficiency was examined in a statistical analysis of a survey concerning stakeholders’ view of a specific value, energy efficiency, as well as their influence on the value creation process. A multiple qualitative case study explores the relation between value and waste in different settings and the consequences of waste focus. The findings in the multiple case study are confirmed and elaborated further by an additional case study, both qualitative and quantitative, of value stream mapping.Value and waste are analysed with the use of order winners and qualifiers. Also, a model to clarify the consequences of mixing value creation and value exchange for customer/user and producer/seller have been defined and used in the analysis.Depending on the stakeholder there is a difference between whether value can be regarded as a use value, exchange value or both. Even if exchange value is related to a specific moment in time, use value is not. The view of value differs among stakeholders which increase the risk of sub-optimisation in production.Value and waste have multi-dimensional properties and there are links between the different dimensions. The relationships depend upon the situation in question. The lean seven types of waste are not independent dimensions. Also, the concept of waste as anti-value is too simplistic. In all cases studied the focus is on waste, not value. Also, it is often the symptoms of waste that are of interest in measures taken not the root causes. Reduction of waste without considering the value can create new waste. Since waste is a dependent variable, it should not be measured without considering value. Another complication is that value and waste often occurs at different points in time and in different settings.Single measures are sensitive to its environment. Several measures are more robust. Measures distort and influence the perception and thereby the decision of the studied phenomena. Also, the notion of value and waste becomes harder to define and trace as the resolution and detailing of the studied process increases.</p>
  • Wallström, Åsa (författare)
  • Industrial buying behavior of large Swedish firms case studies of the purchase of educational services
  • 2002
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • <p>The lack of studies focusing on industrial buying behavior in the purchase of professional services, coupled with the increased corporate need of investing in employee training and education, created the foundation for the research problem of this thesis: How can the buying behavior of large Swedish firms be characterized when they purchase educational services in the area of sales and marketing? Based on this research problem, five research questions were developed. A frame of reference describing industrial buying behavior in the purchase of professional services was then created, based on the literature review. A qualitative research approach was adopted, and case studies were conducted in four large Swedish firms: Scandic Hotels, Telia Mobile, Ericsson, and SEB. The empirical data were collected through personal interviews with 29 respondents. Results from this study demonstrate that the buying process when large Swedish firms purchase educational services in the area of sales and marketing can be described as a sequential process comprising eleven stages. A variety of strategies to reduce the perceived uncertainty in purchasing educational services were identified. Several similarities and some dissimilarities were found with respect to the composition, roles, and influence in the buying center, both in comparisons among the four cases and in comparison with previous research. Moreover, as proposed in existing research, the results from this study indicate that the selection of a supplier should be viewed as a process and not as an event. The selection process was found to contain five sequential stages: search for and identify potential suppliers; a first evaluation; contact selected suppliers; evaluation of proposal(s); and finally the selection. Results show that most members of the buying center focused on the supplier's firm, or a combination of the supplier's firm and their services at the beginning of the selection process. However, their attention gradually shifts towards the supplier's services and the persons providing these services. Furthermore, the findings show that a certain set of criteria was used to evaluate and compare potential suppliers (selection criteria), but other criteria may be used to reject a potential supplier (rejection criteria). In addition, the findings clearly indicate that the selection and rejection criteria vary across the stages in the selection process. Moreover, individual members of the buying center, to a large extent, apply their own distinct selection and rejection criteria. As proposed in previous research, more subjective assessments were employed during the later stages of the selection process. The results indicate that some criteria were perceived as difficult to assess before a purchase, and a number of cues were used to assess these criteria. Long-term supplier relationships were found to be important in the purchasing of educational services, but at the same time firms actively search for new potential suppliers. Moreover, the selection process involved the evaluation of a combination of new and long-term suppliers. However, new suppliers were usually evaluated in a more detailed manner. Results also show that suppliers can easily be rejected at the beginning of the selection process, and known suppliers were usually selected when time pressure was intense. Finally, findings from this study indicate that several factors can affect buying behavior (i.e., the buying process, the buying center, and/or the selection and rejection criteria) in a number of ways when firms purchase educational services in the area of sales and marketing.</p>
  • Wamala, Caroline (författare)
  • Does IT count? complexities between access to and use of information technologies among Uganda's farmers
  • 2010
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • <p>Drawn from a year of ethnographic fieldwork among farmers in Uganda, this study engages with developing an understanding on how access to and use of media and information technologies are negotiated in their separate profiles. Oftentimes the two entities, access and use, are laminated into one statistical representation, depicting both terms as either use or access. However, these terms are nodal points in two discourses and should not by necessity be understood as one. Media and information technologies in the current study refer to computers/internet and mobile phones which are situated in the information technologies part of the phrase. Radios, newspapers and television form part of the media phrase. Access to information carries similar weight as having access to other crucial resources such as land and capital for the farmer, which is why media and information technologies which have the ability to deliver information in real time are encouraged for Uganda's farmers by development efforts.Agriculture is Uganda's economic bedrock and is a practice that Ugandans identify with. Situating a study of access to and use of media and information technologies in this sector may give an indication of the diffusion process of the media and information technologies among Ugandans. Uganda like other developing regions are encouraged to adapt the use of media and information technologies, particularly the Internet, in light of the socioeconomic progress, associated with the ability to use the information from this medium towards self-progression. This study is partly motivated by the requests for more studies that give an indication to what level socioeconomic progress can be measured in line with access to information from media and information technologies. The methods that informed this research include interviews, observations, survey research methods and focus group discussions. Farmers in the eastern, northern and central regions of Uganda informed this research. The farmers were initially asked what information sources were available to them with regards to their farming practices. This question produced a range of responses and from the responses an indication of where farmers locate media and information technologies was analysed. It was also possible to discern that a positive influence on the farming practices can be traced to use of information from the media and information technologies. From the descriptions given by the farmers as well as the observations made, the social environment in which the media and information technologies operate is influential towards the farmer's relationship with the technology. As farmers' negotiated access and use in very innovative ways in light of the fact that the communications infrastructure is still developing specific relations with the technologies emerged. For example the search for signals for radios and mobile phones in some of the rural areas may require tree-climbing or going up a hill. Women are culturally barred from some of these practices deemed to be uncouth and unflattering for the pious nature of women. The technologies for which signals must be sought gain an inherently masculine symbolism to which women enjoy limited associations. In this case having access to the physical device, may not always result in women being able to use the radio or mobile phone. Critically analysing access in this way also brings to question who a user is. Because access and use require various social negotiations, this brings forth the understanding that technology is culturally embedded. The current research gives specific focus to gender, at the same time as it is acknowledged that gender intersects with other social categories such as age and ethnicity and aims to contribute to studies that give attention to the cultural embeddedness of gender and technology from a development perspective.</p>
  • Wang, Chuan (författare)
  • Possibilities of CO2 emission reduction process integration analysis and carbon trading schemes
  • 2007
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • <p>Climate change is one of the greatest challenges faced by today's society. With more evidence from scientists, the need to manage greenhouse gas emissions has been increasing in response to international climate change negotiations. With the aid of the Kyoto Protocol's entry into force in February 2005, more efforts on greenhouse gas emission reduction can be expected from nations. In this thesis, possibilities of reducing carbon dioxide emission in Sweden have been analysed: via the internal abatement from domestic efforts; and through international collaboration with the aid of carbon trading schemes. For the former, the Swedish steel industry was chosen and the Process Integration (PI) method was applied to analyse possibilities of CO2 emission reduction. For the latter, case studies were performed to demonstrate CO2 emission reduction by using Kyoto market mechanisms and EU ETS. A process integration method was developed and used to analyse CO2 emission for the steel industry with consideration of the material and energy system. This model was initially designed based on a specific steel plant. However, the model can be used to analyse other steel plants with different processes, either for the whole steel process system or some sub-systems. The modelling work on optimising residue material flows and ferrous burden materials use for the BF-BOF system was focused on analysing CO2 emission reduction. The model covering the carbon trading systems shows that internal changes and the Kyoto CDM mechanism will both contribute to help steel plants to meet their emission allowance and future reduction commitments. The carbon trading schemes will play a critical part in future efforts against climate change since they can offer lower cost. CDM is the only operative Kyoto mechanism at the moment, and it will probably be the largest carbon trading market. In addition, it is the only mechanism through which the developing countries have been involved in the climate change mitigation arena. The Swedish government has already declared its desire to contribute to making CDM work and become an effective instrument in work on the international climate. Sweden will keep a leading position in the bioenergy technology field by implementing more CDM projects and will also gain more experience of international collaboration related to the CDM. The calculated potential reduction of CO2 emission by using Swedish bioenergy technologies can be used as a guideline to develop CDM projects in developing countries. Two case studies of bioenergy CDM projects demonstrate how Sweden can reduce CO2 emission via CDM. In summary, it is possible to reduce the industrial CO2 emissions at lower cost through carbon trading schemes. However, it is important to preserve the competitiveness of industry. Therefore, domestic actions/internal abatement should be encouraged since they can further improve the efficiency and promote the discovery of new technologies for creating a more sustainable energy supply both from an economic and an environmental point of view.</p>
  • Wang, Jinhui (författare)
  • Technology-based self-service and its impact on service firm performance a resource-based perspective
  • 2007
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • <p>Improving productivity is crucial for service firms to be competitive. To have customers perform certain tasks normally undertaken by employees is an important means to achieving this objective. With the aid of technology, the scale and scope of self-service has significantly increased in recent years. Despite the size and importance of technology-based self-service (TBSS) investments in service firms, the absence of empirical studies on TBSS and its impact on company performance has resulted in a significant gap in knowledge. The aim of this thesis therefore was to increase our understanding of this important research area. Drawing from a resource-based view, this thesis proposed a framework that shows how firm resources and capabilities are leveraged via customer performing self-service to deliver superior value to employees, customers and/or business owners. To ground the research, three Swedish TBSS case studies (i.e., SAS self- check-in, Nordea Net Bank, and ICA self-scanning) were conducted. The findings of these case studies helped further refine the framework and a more elaborate model illustrating the impact of TBSS on firm performance was proposed. To test this model, a survey was conducted to understand self-scanning system and its impact on firm performance. Questionnaires were sent to managers and employees at ICA and Coop, the two biggest food chain stores in Sweden. The results of the survey show that employee training and dynamic capabilities of the service provider are crucial to the success of self- scanning implementation. TBSS promotion was found to have no relationship with customer usage and weak relationship with accuracy of customer performing self-service. Furthermore, improved service quality, rather than reduction of labor costs, was found to be the primary value of self- scanning in Swedish retail food stores. Finally, employees and customers are positively affected by using TBSS, although the impact on financial performance is hard to pin down.</p>
  • Wang, Zheng (författare)
  • Molecular sieve films and zoned materials synthesis and characterization
  • 2004
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • <p>Molecular sieve films and colloidal particles have great potential for utilization in novel, technological sophisticated applications such as structured catalysts, sensors and membranes. The work in this thesis mainly concerns the synthesis of molecular sieve films and the crystallization of zoned MFI materials. Films are also evaluated in an FTIR-ATR application. A previously developed preparation method has been adapted for the preparation of MFI and FAU type films on various steel types and crystals (Si, ZnS, ZnSe and Ge) for ATR spectroscopy. The films were characterized by SEM, XRD and gas sorption. The type of substrate did not affect the film morphology, the thickness or the preferred orientation of the crystals in the film, whereas the thermal stability was dependent on the substrate. Zeolite (MFI) coated ATR crystals were investigated using ATR-FTIR spectroscopy to detect low amounts of organic molecules in a gas flow. It was demonstrated that these novel materials could be used as a sensor with high sensitivity. The sensor offers the possibility to study both the adsorbate and the adsorbent, and can be used for in-situ studies of sorption, diffusion and reaction in zeolites. The sensor combines the strengths of IR spectroscopy with the high sensitivity of zeolite coated ATR elements. Zoned (epitaxial) MFI materials in the form of colloidal crystals and films were also synthesized in this work. The materials were characterized by SEM, TEM and XRD. A two-step crystallization method was developed, in which acid treated precursor colloidal particles or films of ZSM-5 were grown in a silicalite-1 synthesis solution. It was shown that zoned MFI materials did not form when the ZSM-5 surface had high aluminum content. In this case, polycrystalline aggregates or a sandwich film formed due to secondary nucleation. After acid treatment of ZSM-5, which reduced the surface aluminum content to half, zoned MFI material was obtained by epitaxial growth.</p>
  • Wanhainen, Christina (författare)
  • On the origin and evolution of the palaeoproterozoic Aitik Cu-Au-Ag deposit, northern Sweden a porphyry copper-gold ore, modified by multistage metamorphic-deformational, magmatic-hydrothermal, and IOCG-mineralizing events
  • 2005
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • <p>The Aitik Cu-Au-Ag mine in the Gällivare area in northern Sweden is the biggest open pit operation in northern Europe and one of Europe’s largest metal producers. The open pit is almost 3 km long, 930 m wide and 345 m deep. Approximately 424 million tonnes of ore averaging 0.4% Cu, 0.2 g/t Au and 4 g/t Ag has been produced, and the metal production in year 2004 was 64,805 tons of copper, 2,035 kg of gold, and 45,110 kg of silver. Although multiply deformed, metamorphosed and hydrothermally altered, characteristic features of two major mineralization styles, porphyry copper and iron oxide-copper-gold (IOCG), have been identified by using field and microscopic observations in combination with techniques such as fluid inclusion microthermometry, sulphur isotopic analyses, U-Pb and Re-Os geochronology, and major and trace element geochemistry. Results from this study indicate that the Aitik deposit is of mixed origin, with a major part of the copper ore originating from an early porphyry copper system, and a second, minor part, originating from an overprinting IOCG-system. The Aitik porphyry Cu-Au-Ag deposit and its host rocks, situated approximately 200 km north of the Archaean-Proterozoic palaeoboundary in the Fennoscandian shield, are considered to have formed in a volcanic arc environment related to subduction of oceanic crust beneath the Archaean craton at ca. 1.9 Ga. An intrusion related to the formation of porphyry copper mineralization is situated in the footwall of the deposit. This source intrusion and related volcaniclastic rocks are mafic-intermediate in composition and belong to the regionally widespread Haparanda suite and Porphyrite group, respectively. The quartz monzodiorite intrusion is porphyritic and comprises younger, but comagmatic, phases of micro-quartz monzodiorite and diorite, and is suggested to represent a cupola protruding from a larger pluton at depth. High salinity fluids (30-38 eq. wt% NaCl + CaCl2) responsible for chalcopyrite-pyrite mineralization was released contemporaneously with quartz monzodiorite emplacement and quartz stockwork formation at ca. 1.89 Ga, and caused potassic alteration of the intrusive and surrounding volcaniclastic rocks. Potassic alteration is manifested by early biotitization and K-feldspatization, in close association with disseminated sulphides and magnetite. Remnants of this primary porphyry copper mineralization are best preserved in the footwall (micro-) quartz monzodiorite, in units of micro-quartz monzodiorite within the volcaniclastic rocks of the ore zone, and in quartz stockworks at the margins of the quartz monzodiorite. The Aitik IOCG mineralizing event occurred about 100 Ma later, when eastward subduction resulted in compression, monzonitic-granitic magmatism, ductile deformation, and tectonic block movements in Northern Norrbotten. Extensive deformation of rocks and redistribution of metals occurred. Magnetite enrichment locally found within late veins of mainly amphibole, K-feldspar, and epidote, together with late scapolite alteration within the deposit, implies that fluids responsible for IOCG-mineralization and extensive Na-Ca alteration in the region during this tectonic event also affected the Aitik deposit, and probably involved addition of copper and gold. This late mineralizing fluid was highly saline, and contained ferropyrosmalite in addition to NaCl + CaCl2. Hydrothermal fluids continued to affect the Aitik area for another ca. 60 Ma, forming minerals such as zeolite, calcite, and thaumasite, indicating low-temperature conditions at the end of the Aitik evolution. It is here concluded that the Aitik Cu-Au-Ag deposit is a strongly deformed and metamorphosed porphyry copper-gold deposit related to a 1.9 Ga quartz monzodiorite, with at least 160 Ma of post-ore modification, including an overprinting mineralizing event of IOCG-type at ca. 1.8 Ga.</p>
  • Wattanasen, Kamhaeng (författare)
  • Environmental and hydrogeological geophysics with applications in Thailand, Laos, and Sweden
  • 2007
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • <p>This thesis presents applications of geophysical methods in the fields of environment and hydrogeology. In relation to environmental problems, two different geophysical surveys have been carried out; one to study an arsenic contaminated area in the southern Thailand (paper I) and a second to locate shallow faults in Quaternary sediments in an area around the Ongkharak Nuclear Research Centre, central Thailand (paper II). For hydro-geological problems, surveys were conducted in southern Sweden (paper III) and in the Vientiane basin, Laos (paper IV). In the arsenic contaminated area, tin and associated minerals, i.e. arsenopyrite and pyrite, have been extracted from granites and natural processes and the mining activities led to arsenic contamination in the environment. Electrical resistivity and self potential (SP) have been used to define the distribution of arsenic contamination in the groundwater. Resistivities of 25 - 100 ohm-m and a positive SP anomaly of 66.0 mV were observed in an area where the arsenic content in auger water at 3.5 to 5.0 m depths was high, 0.5 - 5.0 mg/l. Integrated interpretation of resistivity, seismic refraction, GPR, and gravity data gave a clear image of subsurface structures at a depth to 30 m. There was a good correlation between the resistivity and the gravity data. A subsurface rise was found, which possibly acts as a naturally buried dam, separating a high contaminated area from a low contaminated area. This study has demonstrated that the combination of geophysical methods is successful in delineating contaminated areas and contributes to the understanding of a possible mechanism for the distribution of arsenic. In the Ongkharak Nuclear Research Centre area combined GPR and resistivity pseudosections (dipole-dipole and pole-pole arrays) have given a good image of shallow faults in Quaternary sediments, faults that were originally indicated from regional remote sensing interpretations. Horizontal discontinuities of reflected signals obtained by GPR and images of lateral resistivity variation have been correlated to faults or subsurface movement identified by geological mapping in trenches. This signature of the faults is caused by contrasts in dielectric permittivity and/or in resistivity, which originates from vertical displacement at sedimentary layers and from sediments filling the faults. The positions of sub-faults as identified by GPR and their strike directions obtained from the trenching data (N60°W - N70°W, N65°W - N70°W, and N30°W) agree with the general NW-SE trend of the major faults, the Mae Ping Fault Zone, the Nakhon Nayok-Prachinburi and the Ongkharak faults in central Thailand. Thermoluminescence (TL) dating showed that sub-faults in the area have been active at about 7,500-2,400, 4,800- 1,750, and 9,700-2,300 years ago. Thus, these sub-faults have been classified to be of the same generation and they are defined as "capable faults" with reference to the criteria of U.S. Nuclear Regulatory Commission. Magnetic Resonance Sounding (MRS) has been successfully tested for detecting groundwater and in combination with Vertical Electrical Sounding to characterizing aquifer in southern Sweden and in the Vientiane basin, Laos. The combination of MRS and VES in the southern areas of Sweden shows that low resistivity layers interpreted as clay are sometimes identified close to the surface. The results here have shown that the MRS signals penetrate through the clay and that deeper aquifer can still be detected. The MRS data suggest aquifers that are not only hosted in soft sediment materials (moraine, sand, and mixed materials), but also hosted in basement rocks. Based on the MRS and borehole pumping test data, the hydraulic conductivity of aquifers has been estimated and the results agree with yield, average water content and subsurface geological data. The results from the measurement in the Vientiane basin have shown that there is usually two - three water bearing layers, and the "best aquifer" is found at depths between 15 and 25 m, with regard to high water content, permeability and resistivities indicating fresh water. MRS has also shown to be an important tool in constraining layer thickness and distinguishing low resistive layers of impermeable rock from what could have been interpreted as water in the VES interpretation. MRS data also suggest a clay layer at depths between 30 and 50 m, which is overlying halite deposits. This clay layer may act as a naturally sealing layer to protect the fresh water in above aquifer from salt contamination. On the basis of this drilling for fresh water is recommended not to penetrate deeper than 20 to 40 m, depending of the local depth to the clay layer.</p>
  • Wedberg, Dan (författare)
  • Modelling of high strain rate plasticity and metal cutting
  • 2013
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • <p>Metal cutting is one of the most frequently used forming processes in the manufacturing industry. Extensive effort is made to improve its process and simulation has become an integrated part, not only in the product development process but also in the customer relations. However, simulation of metal cutting is complex both from numerical as well as physical point of view. Furthermore, modelling the material behaviour has shown to be crucial. Errors in the material model cannot be reduced by the numerical procedures. The magnitudes of strain and strain rate involved in metal cutting may reach values of 1-10 and 103-106 s-1. The dissipative plastic work together with the chip tool friction also leads to locally high temperatures. These extreme ranges of conditions imply that a diversity of physical phenomena is involved and it is a challenge to develop a material model with adequate accuracy over the whole loading range. Furthermore, this intense and severe deformation represents thermo-mechanical behaviour far from what is generated from conventional material compression and tension testing. A highly desirable feature is also a material model that can be extrapolated outside the calibration range. This is not trivial since materials exhibit different strain hardening and softening characteristics at differentstrains, strain rates and temperatures. Models based on modelling some aspects of the underlying physical process, e.g. the generation of dislocations, are expected to have a larger range of validity than engineering models. Though, engineering models are the far most common models used in metal cutting simulations.The scope of this work includes development of validated models for metal cutting simulations of AISI 316L stainless steel. Particular emphasis is placed on the material modeling and high strain rate plasticity phenomena. The focus has been on a physically based material model. The approach has been to review the literature about flow stress models and phenomena and particularly at high strain rates. A previous variant of a dislocation density model has thereafter been extended into high strain rate regimes by applying different mechanisms. Some of the models have been implemented in commercial finite element software for orthogonal cutting simulations. Experimental measurements and evaluations that include SHPB-measurements, cutting force measurements, quick-stop measurements and some microstructural examinations has been conducted for calibration and validation. The compression tests, within a temperature and strain rate range of 20-950 °C and 0.01-9000 s-1 respectively, showed that the flow stress increased much more rapidly within the dynamic loading range and hence depends on the strain rate. The dynamic strain aging (DSA) that has been observed at lower strain rates is non-existent at higher strain rates. The temperature and strain-rate evolution is such that the DSA is not necessary to include when modelling this process. Furthermore the magnetic balance measurements indicate that the martensite transformation-strengthening effect is insignificant within the dynamic loading range.In the present work the concept of motion of dislocations, their resistance to motion and substructure evolution are used as underlying motivation for description of the flow stress. A coupled set of evolution equations for dislocation density and mono vacancy concentration is used rendering a formulation of a rate-dependent yield limit in context of rate-independent plasticity. Dislocation drag due to phonon and electron drag, a strain rate dependent model of the subcell formation, a strain rate and temperature dependent recovery function and a structural dependent thermally activated stress component have among others been considered. Best predictability was obtained with a strain rate dependent subcell formulation. Dislocation drag did not improve the predictability within the measured testing range. Although showed to has a greater influence outside the range of calibration when extrapolated. It has been shown that extrapolation is uncertain. Results from experiments and modelling of material behaviour and metal cutting together with the literature indicate that the predictability of the material behaviour within and outside the measured testing range can be further tuned by implementing models of the phenomenon mechanical twining and recrystallization.</p>
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