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  • 1601.
    Åstrand, Max
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik. ABB Corp Res, Control Optimizat & Analyt, Automat Solut, Vasteras, Sweden.
    Johansson, Mikael
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Greberg, J.
    Lulea Univ Technol, Dept Civil Environm & Nat Resources Engn, Div Min & Geotech Engn, Lulea, Sweden..
    Underground mine scheduling modelled as a flow shop: a review of relevant work and future challenges2018Ingår i: The Southern African Journal of Mining and Metallurgy, ISSN 2225-6253, E-ISSN 1543-9518, Vol. 118, nr 12, s. 1265-1276Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Advanced planning and automation are increasingly important in modern mines. Sophisticated methods for long-term mine planning are often used, and the advent of autonomous machines makes the actual operation more predictable. However, the interface between these two timescales, i.e. the scheduling of the mobile production fleet, often limits the ability to operate mines at maximum profitability. We show how scheduling the production fleet in an underground mine can be modelled as a flow shop. A flow shop is a general abstract process formulation that captures the key properties of a scheduling problem without going into specific details. Thus, the flow shop enables mine scheduling to reap the benefits of scheduling research from other industries. We review recent results from the mining community and the flow shop community, and introduce scheduling methods used in these two fields. This work aims at providing value to researchers from the mining community who want to leverage their skill set, as well as to theoretical researchers by presenting the mining process as a potential application area. Lastly, we discuss the results, and outline some future challenges and opportunities facing the industry.

  • 1602.
    Åström, August
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Sten, Morgan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Macro segregation in continuous cast HSLA steels: With correlation to impact toughness2019Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Denna rapport granskar makrosegringar i stränggjutet stål och eventuella kopplingar till slagseghet. Centrumsegringar och V-segringar undersöks för att undersöka vilken segringstyp som har störst effekt på slagseghet, vilket är syftet med denna avhandling. Förutom en litteraturstudie, hämtades Charpy-V data med SSAB’s medgivande från två olika stålsorter, kvalitet A och kvalitet B, med respektive dominant segringstyp. Datan som inhämtades erhölls från tre stycken Charpy-V tester för varje plåt, från ett närliggande område. Medelvärdet för dessa datapunkter användes i statistisk analysför att obeservera spridningen av datapunkter i olika charger av de två stålen. Dessutom, erhölls segringsbilder för respektive slab från SSAB. Resultaten visade att datapunkterna för kvalitet A, som hade centrumsegring som domiant segringstyp, var mer spridd än datan för kvalitet B. Således, är slutsatsen att centrumsegring är värre i relation till slagseghet eftersom en högre avvikelse leder till mindre förutsägbara egenskaper från en kunds perspektiv.

  • 1603.
    Öberg, Christian
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Zhu, B. H.
    Jonsson, Stefan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Plastic deformation and creep of two ductile cast irons, simo51 and simo1000, during thermal cycling with large strains2018Ingår i: 11th International Symposium on the Science and Processing of Cast Iron, SPCI-XI 2017, Trans Tech Publications, 2018, Vol. 925, s. 361-368Konferensbidrag (Refereegranskat)
    Abstract [en]

    Cyclic deformations of two ferritic, ductile cast irons, SiMo51 and SiMo1000, were studied in air and Ar using a new method, SRTC (stress relaxation with thermal cycling). Locked specimens were thermally cycled up to 800 °C with isothermal holds, varying temperature interval, heating/cooling rates and hold times. A description of the mechanical response to thermal cycling of a locked specimen is given.

  • 1604.
    Örnek, Cem
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. The University of Manchester, United Kingdom.
    Burke, M. G.
    Hashimoto, T.
    Engelberg, D. L.
    748 K (475 A degrees C) Embrittlement of Duplex Stainless Steel: Effect on Microstructure and Fracture Behavior2017Ingår i: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, nr 4, s. 1653-1665Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    22Cr-5Ni duplex stainless steel (DSS) was aged at 748 K (475 A degrees C) and the microstructure development correlated to changes in mechanical properties and fracture behavior. Tensile testing of aged microstructures confirmed the occurrence of 748 K (475 A degrees C) embrittlement, which was accompanied by an increase of strength and hardness and loss of toughness. Aging caused spinodal decomposition of the ferrite phase, consisting of Cr-enriched alpha aEuro(3) and Fe-rich alpha' and the formation of a large number of R-phase precipitates, with sizes between 50 and 400 nm. Fracture surface analyses revealed a gradual change of the fracture mode from ductile to brittle delamination fracture, associated with slip incompatibility between ferrite and austenite. Ferrite became highly brittle after 255 hours of aging, mainly due to the presence of precipitates, while austenite was ductile and accommodated most plastic strain. The fracture mechanism as a function of 748 K (475 A degrees C) embrittlement is discussed in light of microstructure development.

  • 1605.
    Örnek, Cem
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. University of Manchester, UK.
    Burke, M. G.
    Hashimoto, T.
    Lim, J. J. H.
    Engelberg, D. L.
    475 degrees C Embrittlement of Duplex Stainless Steel-A Comprehensive Microstructure Characterization Study2017Ingår i: Materials Performance and Characterization, ISSN 2379-1365, Vol. 6, nr 3, s. 409-436Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of 475 degrees C embrittlement on microstructure development of grade 2205 duplex stainless steel was investigated. Spinodal decomposition products and associated precipitates in ferrite, austenite, and at interphase boundaries were characterized using analytical transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques. Microanalyses confirmed the presence of Cr-enriched alpha'' and Cr-depleted alpha' spinodal structures in the ferrite after 5 h of aging at 475 degrees C. Long-term aging for 255 h resulted in heavily-faulted R-phase precipitates with sizes of similar to 50-400 nm, chi-phase, and epsilon-Cu in the ferrite, TiN and Cr2N precipitates in the austenite, and a continuous network of M23C6-carbides at interphase boundaries. A significant hardness increase was observed after 255 h of aging, which was accompanied by a reduction of ferrite fraction. X-ray diffraction (XRD) stress measurements showed a general reduction of residual stresses in both ferrite and austenite with aging. Electron backscatter diffraction (EBSD) showed increased local misorientations, primarily close to precipitate interfaces within the ferrite, indicating the development of strain heterogeneities in the microstructure. The data presented provided a better understanding of 475 degrees C embrittlement in duplex stainless steel, suggesting that not only the ferrite alone is responsible for embrittlement. A comprehensive microstructure characterization study has been provided and the explanation for 475 degrees C embrittlement of duplex stainless steel has been discussed.

  • 1606.
    Örnek, Cem
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap.
    Leygraf, Christopher
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap.
    Pan, Jinshan
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap.
    Passive film characterisation of duplex stainless steel using scanning Kelvin probe force microscopy in combination with electrochemical measurements2019Ingår i: npJ Materials Degradation, ISSN 2397-2106, Vol. 3, nr 1, s. 1-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The characterisation of passive oxide films on heterogeneous microstructures is needed to assess local degradation (corrosion, cracking) in aggressive environments. The Volta potential is a surface-sensitive parameter which can be used to assess the surface nobility and hence passive films. In this work, it is shown that the Volta potential, measured on super duplex stainless steel by scanning Kelvin probe force microscopy, correlates with the electrochemical properties of the passive film, measured by electrochemical impedance spectroscopy and potentiodynamic polarisation. Natural oxidation by ageing in ambient air as well as artificial oxidation by immersion in concentrated nitric acid improved the nobility, both reflected by increased Volta potentials and electrochemical parameters. Passivation was associated with vanishing of the inherent Volta potential difference between the ferrite and austenite, thereby reducing the galvanic coupling and hence improving the corrosion resistance of the material. Hydrogen-passive film interactions, triggered by cathodic polarisation, however, largely increased the Volta potential difference between the phases, resulting in loss of electrochemical nobility, with the ferrite being more affected than the austenite. A correlative approach of using the Volta potential in conjunction with electrochemical data has been introduced to characterise the nobility of passive films in global and local scale.

  • 1607.
    Örnek, Cem
    et al.
    KTH.
    Reccagni, Pierfranco
    Kivisakk, Ulf
    Bettini, Eleonora
    Engelberg, Dirk L.
    Pan, Jinshan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Hydrogen embrittlement of super duplex stainless steel - Towards understanding the effects of microstructure and strain2018Ingår i: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 43, nr 27, s. 12543-12555Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effects of austenite spacing, hydrogen charging, and applied tensile strain on the local Volta potential evolution and micro-deformation behaviour of grade 2507 (UNS 532750) super duplex stainless steel were studied. A novel in-situ methodological approach using Digital Image Correlation (DIC) and Scanning Kelvin Probe Force Microscopy (SKPFM) was employed. The microstructure with small austenite spacing showed load partitioning of tensile micro-strains to the austenite during elastic loading, with the ferrite then taking up most tensile strain at large plastic deformation. The opposite trend was seen when the microstructure was pre-charged with hydrogen, with more intense strain localisation formed due to local hydrogen hardening. The hydrogen-charged microstructure with large austenite spacing showed a contrasting micro-mechanical response, resulting in heterogeneous strain localisation with high strain intensities in both phases in the elastic regime. The austenite was hydrogen-hardened, whereas the ferrite became more strain-hardened. SKPFM measured Volta potentials revealed the development of local cathodic sites in the ferrite associated with hydrogen damage (blister), with anodic sites related to trapped hydrogen and/or micro voids in the microstructure with small austenite spacing. Discrete cathodic sites with large Volta potential variations across the ferrite were seen in the coarse-grained microstructure, indicating enhanced susceptibility to micro-galvanic activity. Microstructures with large austenite spacing were more susceptible to hydrogen embrittlement, related to the development of tensile strains in the ferrite.

30313233 1601 - 1607 av 1607
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