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Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 251.
    Krakhmalev, Pavel
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Gåård, Anders
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Influence of tool steel microstructure on origin of galling initiation and wear mechanisms under dry sliding against a carbon steel sheet, WOM 20072009Konferansepaper (Fagfellevurdert)
  • 252.
    Krakhmalev, Pavel
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Rodil, Adeva
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap.
    Influence of microstructure on the abrasive edge wear of WC–Co hardmetals2007Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 263, nr 1-6, s. 240-245Artikkel i tidsskrift (Fagfellevurdert)
  • 253.
    Krakhmalev, Pavel
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Ström, E.
    Li, C.
    Microstructure and properties stability of Al-alloyed MoSi2 matrix composites2004Inngår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 12, nr 2, s. 225-233Artikkel i tidsskrift (Fagfellevurdert)
  • 254.
    Krakhmalev, Pavel
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Ström, E.
    Sundberg, M.
    Li, C.
    Microstructure, hardness and indentation toughness of C40 Mo(Si,Al)2/ZrO2 composites prepared by SPS of MA powders2003Inngår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 48, nr 6, s. 725-729Artikkel i tidsskrift (Fagfellevurdert)
  • 255.
    Krakhmalev, Pavel
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Ström, E.
    Sundberg, M.
    Li, C.
    Microstructure, hardness and indentation toughness of high-temperature C40 Mo(Si,Al)2/SiC composites prepared by SPS of MA powders2003Inngår i: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 57, nr 22-23, s. 3387-3391Artikkel i tidsskrift (Fagfellevurdert)
  • 256.
    Krakhmalev, Pavel
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Ström, E.
    Sundberg, M.
    Li, C.
    Processing, microstructure and properties of C40 Mo(Si,Al)2/Al2O3 composites, Materials Science and Engineering A, Volume 360, Issues 1-2, Pages 207-213, 20032003Artikkel i tidsskrift (Fagfellevurdert)
  • 257.
    Krakhmalev, Pavel
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Sukumaran, J.
    Gåård, Anders
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Effect of microstructure on edge wear mechanisms in WC-Co2007Inngår i: International Journal of Refractory Metals and Hard Materials, ISSN 0958-0611, Vol. 25, nr 2, s. 171-178Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Edge wear of nano to coarse WC–Co grades was investigated under two-body abrasion conditions using SiC abrasive at 2 and 15 N loads. With the fine abrasive utilized, a transition from homogeneous plowing in submicron grades to inhomogeneous grains pullout in coarse hardmetals was observed at the beginning stages. At final stages, plowing was detected in all the grades. When using the coarse abrasive, for all grades, flaking at the beginning and plowing at the final stages occurred. The performed numerical finite element simulation of the microstructural mechanical response showed good agreement to experimental results and was discussed in relation to the operative wear mechanisms observed. The found results demonstrated a remarkable influence of microstructure and abrasive size on the heterogeneous to homogeneous wear mechanisms transition at initial stages

  • 258.
    Krakhmalev, Pavel
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Sukumaran, J.
    Gåård, Anders
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    How hardmetals react to wear: Nano is not always the best2007Inngår i: Metal Powder Report, ISSN 0026-0657, E-ISSN 1873-4065, Vol. 62, nr 2, s. 30-35Artikkel i tidsskrift (Fagfellevurdert)
  • 259.
    Krakhmalev, Pavel
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Yadroitsava, Inna
    Central University of Technology, Free State, South Africa.
    Fredriksson, Gunnel
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Yadroitsev, Igor
    Central University of Technology, Free State, South Africa.
    Microstructural and thermal stability of selective laser melted 316L stainless steel single tracks2017Inngår i: South African Journal of Industrial Engineering, ISSN 1012-277X, E-ISSN 2224-7890, Vol. 28, nr 1, s. 12-19Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To remove residual stresses, an as-built SLM object is usually posttreated. This treatment can affect the microstructure, changing the final mechanical characteristics. This investigation is focused on the microstructural characterisation of 316L austenitic stainless steel in as-built and annealed conditions. The SLM microstructure was relatively stable up to 900°C, when cell boundaries start to disappear. At higher temperatures, an insignificant grain coarsening was detected. These microstructural changes caused a gradual drop in the hardness. The obtained result is background for the future development of post-treatment regimens to achieve a high level in the final mechanical properties of SLM objects.

  • 260.
    Krakhmalev, Pavel
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Yadroitsava, Inna
    Central University of Technology, South Africa.
    Fredriksson, Gunnel
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Yadroitsev, Igor
    Central University of Technology, South Africa.
    Microstructural and thermal stability of selective laser melted 316L stainless steel single tracks2015Inngår i: Additive Manufacturing Transforming ideas into business: RAPDASA Rapid Product Development Association of South Africa, 16th Annual International Conference 4-6 November 2015, Roodevallei, Pretoria, South Africa, Pretoria: University , 2015, s. 91-Konferansepaper (Fagfellevurdert)
  • 261.
    Krakhmalev, Pavel
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Yadroitsava, Inna
    Central University of Technology, South Africa.
    Fredriksson, Gunnel
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Yadroitsev, Igor
    Central University of Technology, South Africa.
    Microstructure of SLM manufactured 316L and 420 grades stainless steels2014Inngår i: PROCEEDINGS 15th Annual International Conference 6 November – 7 November 2014 Stellenbosch, South Africa / [ed] Dimitrov, Dimitar; Becker, Thorsten, Stellenbosch: Stellenbosch University , 2014Konferansepaper (Fagfellevurdert)
  • 262.
    Krakhmalev, Pavel
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Yadroitsev, I.
    Univ Lyon, Ecole Natl Ingn St Etienne ENISE, DIPI Lab, F-42023 St Etienne, France..
    Microstructure and properties of intermetallic composite coatings fabricated by selective laser melting of Ti-SiC powder mixtures2014Inngår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 46, s. 147-155Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Transition metal silicides and carbides are attractive advanced materials possessing unique combinations of physical and mechanical properties. However, conventional synthesis of bulk intermetallics is a challenging task because of their high melting point. In the present research, titanium carbides and silicides composites were fabricated on the titanium substrate by a selective laser melting (SLM) of Ti -(20,30,40 wt.%)SiC powder mixtures by an Ytterbium fiber laser with 1.075 mu m wavelength, operating at 50 W power, with the laser scanning speed of 120 mm/s. Phase analysis of the fabricated coatings showed that the initial powders remelted and new multiphase structures containing TiCx, Ti5Si3C5, TiSi2 and SIC phases in situ formed. Investigation of the microstructure revealed two main types of inhomogeneities in the composites, (i) SiC particles at the interlayer interfaces and, (ii) chemical segregation of the elements in the central areas of the tracks. It was suggested and experimentally proven that an increase in laser power to 80 W was an efficient way to improve the laser penetration depth and the mass transport in the liquid phase, and therefore, to fabricate more homogeneous composite. The SLM Ti (20,30,40 wt.%)SiC composites demonstrated high hardness (11-17 GPa) and high abrasive wear resistance (3.99 x 10(-7)-9.51 x 10(-7) g/Nm) properties, promising for the applications involving abrasive wear. (C) 2013 Elsevier Ltd. All rights reserved.

  • 263.
    Krakhmalev, Pavel
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Yadroitsev, I.
    Central University of Technology, Free State, South Africa.
    Baker, I.
    Thayer School of Engineering, USA.
    Yadroitsava, I.
    Central University of Technology, Free State, South Africa.
    Manufacturing of intermetallic Mn-46%Al by laser powder bed fusion2018Inngår i: Procedia CIRP, Elsevier, 2018, Vol. 74, s. 64-67Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Laser powder bed fusion (LPBF) provides an excellent opportunity to use custom powders for complex objects without extensive machining. This opportunity is attractive for brittle and hard intermetallics, but is challenging due to cracking, anisotropy, and the formation of non-equilibrium phases. The present investigation is focused on a development of the process parameters for pre-alloyed Mn-46 at.%Al gas atomized intermetallic powder, which is a promising magnetic material. A hierarchical approach involving optimization of the process parameters for a single track, a single layer, and then a 3D specimen was applied. The manufacturing of single tracks was performed at scanning speeds of 0.06-3.4 m/s and laser powers of 50-350 W. Test parameters guaranteeing stable single track with constant width and height, and sufficient remelting depth were selected for further manufacturing. Surface morphology, chemical composition, crack density and distribution, and the microstructures in the final materials were investigated. It was shown that the consists mostly of the ε-phase with some amounts of equilibrium γ2 and β phases and the ferromagnetic τ-phase. The presence of the ε-phase shows a potential to use heat treatment to form τ-phase magnetic phase in AM Mn-46 at.%Al. Future investigations will clarify the applicability of LPBF to manufacture Mn-46%Al for magnetic applications. 

  • 264.
    Krakhmalev, Pavel
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik, Science, Mathematics and Engineering Education Research (SMEER).
    Yadroitsev, Igor
    Yadroitsava, Ina
    de Smidt, Olga
    Functionalization of Biomedical Ti6Al4V via In Situ Alloying by Cu during Laser Powder Bed Fusion Manufacturing2017Inngår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 10, nr 10, artikkel-id 1154Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The modern medical industry successfully utilizes Laser Powder Bed Fusion (LPBF) to manufacture complex custom implants. Ti6Al4V is one of the most commonly used biocompatible alloys. In surgery practice, infection at the bone-implant interface is one of the key reasons for implant failure. Therefore, advanced implants with biocompatibility and antibacterial properties are required. Modification of Ti alloy with Cu, which in small concentrations is a proven non-toxic antibacterial agent, is an attractive way to manufacture implants with embedded antibacterial functionality. The possibility of achieving alloying in situ, during manufacturing, is a unique option of the LPBF technology. It provides unique opportunities to manufacture customized implant shapes and design new alloys. Nevertheless, optimal process parameters need to be established for the in situ alloyed materials to form dense parts with required mechanical properties. This research is dedicated to an investigation of Ti6Al4V (ELI)-1 at % Cu material, manufactured by LPBF from a mixture of Ti6Al4V (ELI) and pure Cu powders. The effect of process parameters on surface roughness, chemical composition and distribution of Cu was investigated. Chemical homogeneity was discussed in relation to differences in the viscosity and density of molten Cu and Ti6Al4V. Microstructure, mechanical properties, and fracture behavior of as-built 3D samples were analyzed and discussed. Pilot antibacterial functionalization testing of Ti6Al4V (ELI) in situ alloyed with 1 at % Cu showed promising results and notable reduction in the growth of pure cultures of Escherichia coli and Staphylococcus aureus.

  • 265.
    Krakhmalev, Pavel
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Yi, D.
    Nyborg, L.
    Preparation of nanocrystalline/amorphous structure in soft magnetic Fe-based alloys by mechanical alloying, 22nd Risoe International Symposium on Materials Science2001Konferansepaper (Fagfellevurdert)
  • 266.
    Kvarnlöf, Niklas
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för kemiteknik.
    Germgård, Ulf
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för kemiteknik.
    Aspects on the reactivity of dissolving pulps prior to viscose preparation2012Konferansepaper (Annet vitenskapelig)
  • 267.
    Land, Cecilia
    Karlstads universitet, Institutionen för kemi.
    Laboratory method for the study of moisture-induced waviness in paper2004Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Paper that is subjected to moisture undergoes dimensional changes. It expands during moistening and shrinks during drying. When the paper is under tension between rollers, the effects are complex since shrinkage and expansion are restricted in the width direction. Waves can then appear on the paper web. This can be a problem in heatset web offset printing. The problem is known as waviness or fluting. The printed papers exhibit a wavy shape, which is visually disturbing due to light reflections which create glossy streaks. The aim of the work described in this thesis was to develop a method suitable for studying the moisture- and tension-induced waviness. Experiments were carried out on a laboratory scale to study how such waves develop during moistening and drying. The experimental setup was based on a modified tensile tester. A CCD camera and image analysis based on the STFI-OptiTopo technique was used to characterise the waviness. Moistening and drying were achieved by changing the surrounding air humidity. The method was used to study the effect of moisture uptake by the paper, and to evaluate the effect of tension on the waviness. It was found that increasing moisture resulted in a higher waviness amplitude, but that the web tension controlled the wavelength of the waviness. A high tension gave rise to a shorter wavelength. The measured wavelength was compared with a previously suggested model and the predicted wavelength was about twice as high as the measured wavelength.

  • 268.
    Land, Cecilia
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för kemiteknik.
    Stolpe, Lennart
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap.
    Beghello, Luciano
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för kemiteknik.
    Modeling of bagginess due to storage of paper reels with ridges2009Inngår i: TAPPI Journal, ISSN 0734-1415, Vol. 8, nr 9, s. 18-22Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Paper is subjected to stress relaxation during storage in reels. Ridges in the paper reel subject the paper in the ridge to a higher strain than the paper adjacent to the ridge. The strain difference can become a permanent strain difference, resulting in a baggy web after unwinding. Researchers used a geometrical model based on stress relaxation test results to determine when the bagginess is substantial enough to cause problems. The results showed that runnability problems will appear if the ridge is about 1–2 mm high. This applies for a reel with a diameter of 1.2–1.8 m stored for 1 week.

  • 269.
    Land, Cecilia
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för kemiteknik.
    Wahlström, Torbjörn
    Stora Enso, Karlstad, Sweden.
    Stolpe, Lennart
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap.
    Moisture streaks and their relation to baggy paper webs2008Inngår i: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 34, nr 4, s. 234-239Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Significant and controlled wet streaks were imparted to laboratory-made kraft paper sheets having an initial moisture content of 50 %. The sheets were then dried under a specified strain according to different drying strategies. Both the wet streaks and the drying strain were applied in the CD in order to amplify the observed effects. The bagginess of the paper sheet, or the length profile, was measured after drying and relaxation. Moisture streaks remaining after unloading resulted in short streaks in the paper. Drying of the paper beyond moisture equilibrium also led to an uneven paper length, particularly when the paper was allowed to shrink during drying. No correlation was found between the tensile stiffness profile and the permanent length profile.

  • 270.
    Land, Cecilia
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för kemiteknik.
    Wahlström, Torbjörn
    Stora Enso, Karlstad, Sweden.
    Stolpe, Lennart
    Beghello, Luciano
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för kemiteknik.
    Plastic strain of moisture streaks at different moisture contents2010Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, nr 4, s. 481-487Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An uneven moisture profile in the paper web during drying can cause runnability problems due to slack areas in the paper web. This study aims at indentifying the moisture level at which it is most important to keep the moisture even. This was evaluated with a laboratory study of plastic strain after loading wet paper samples to strains between 0.3-4% and unloading. The papers tested were made from softwood bleached kraft pulp and the moisture content varied between 9 and 50%. The plastic strain was highest at a moisture content of 20-30%, but the sensitivity to moisture variations was highest at a moisture content of 10-20%. The paper was also sensitive to moisture variations above a moisture content of 30%.

    According to calculations based on the laboratory results, moist streaks appearing at a high moisture content would turn into short streaks, and moist streaks appearing at a low moisture content would turn into long streaks. A machine trial with moist streaks applied at high moisture resulted in short streaks in the paper, confirming the qualitative results of the laboratory study.

  • 271.
    Larsson, Karl
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Nötning av verktygsstål vid plåtformning: Inverkan på arbetsmaterialets sträckgräns och påkletningsmotstånd för verktygsstål2019Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    I dagens industri utsätts verktyg vid plåtformning för allt större krafter. Material som ska formas blir starkare behövs också större krafter för at åstadkomma en geometrisk förändring. Detta har medfört att nötningseffekter vid tillverkning har ökat, och ett av dessa problem är galling. Galling, som är ett av huvudproblemen, är en nötningseffekt på verktygen där både adhesiv och abrasiv nötning förekommer. Detta innebär att material lossnar från värdmaterialet och fastnar på verktyget. Då material har överförts till verktyget har det inte längre ursprungsformen och kan leda till ojämnheter i materialet som ska formas. Hittills har företag använt sig av smörjmedel för att minska galling. Eftersom smörjmedel regleras allt hårdare av miljöskäl, måste industrin hitta nya lösningar. En lösning är att skapa verktygsstål som är motståndskraftiga mot galling genom sin mikrostruktur. Det finns fortfarande begränsad kunskap inom området och den här studien syftar till att jämföra två verktygsstål för att avgöra vilket som är mest beständigt mot galling. Verktygsstålen Caldie och Vancron Superclean kommer glida mot materialen DP600 och DP1000. De sistnämnda är de material som formas vid plåtformningen. Där materialen har olika sträckgränser, detta för att se om den har en inverkan vid plåtformning. För att avgöra vilket verktygsstål som är mest lämpligt vid plåtformning kommer en glidsträcka tas fram med hjälp av SOFS metoden. Glidsträckan kommer att ange hur snabbt galling uppstår och således kan ett bättre material bestämmas. Nötningsspåren hos materialen analyserades med hjälp av ett elektronmikroskop för att se hur galling hade påverkat verktygsstål och ytmaterial.Resultatet visade att Vancron Superclean var mer beständigt mot galling, då verktygsstålen gled över DP600, medan ingen slutsats kunde dras när de gled över DP1000.

  • 272. Larsson, Linda
    et al.
    Sjödahl, L.
    Thuvander, Fredrik
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Paper Surface Centre. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Microscopic 3-D Displacement Field Measurements using Digital Speckle Photography2004Inngår i: Optics and Lasers in Engineering, 41, 767-777 (2004)Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A technique to measure object shape and 3-D displacement fields in micro-scale is offered by microscopic stereo digital speckle photography. The displacement of the random features that are often present on many engineering surfaces when viewed in a microscope is measured with the system, using image correlation. In this paper the equipment, physical model and calibration routines are described. The technique can be applied for sub-mm sized objects of arbitrary shape for small deformation fields. As a verifying experiment, an in-plane rotation of a flat calibration plate is presented. The expected in-plane errors are shown to be less than 0.1 ?m and the corresponding out-of-plane errors about three times larger. As a pilot experiment, micro-structural paper expansion is studied, when exposed to humidity. The scaling properties of the microscope as well as the sampling criteria and reliability of the system are discussed in detail

  • 273.
    Larsson, Markus
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap.
    Kullander, Johan
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap.
    Utbytets och malningens inverkan på NSSC-massans egenskaper2010Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [sv]

    Neutralsulfitkokning av björk möjliggör ett högt utbyte av hemicellulosa, vilket bidrar positivt till flutingens egenskaper och minskar vedkostnaden. Neutralsulfitkoket ska avbrytas när delignifieringen nått tillräckligt långt för att veden ska kunna defibreras skonsamt med en rimlig energiinsats, men innan nedbrytningen av hemicellulosa hunnit accelerera. Syftet med detta examensarbete var att undersöka utbytets och malningens inverkan på NSSC-massans egenskaper.

    En laboratoriestudie genomfördes där massan kokades till olika utbyten och maldes vid olika insatser. Resultatet av den studien användes sedan för att ställa om kokaren och raffinörerna på lämpligt sätt vid fabriksförsöken. Massaprover togs ut efter det andra kvarnsteget och skickades för analys. De mest väsentliga egenskaperna för fluting testades genom CCT (Corrugated Crush Test), CMT (Concora Medium Test) och SCT (Short Span Compression test) men övriga konventionella egenskaper testades likväl. En avgörande egenskap för fluting är också dess krypstyvhet som undersöktes på laboratorie genom isokrona kryptester. För att få en djupare förståelse för NSSC-massans egenskaper samt kokningens och malningens inverkan på dessa utfördes även fiberkaraktärisering.

    Resultatet visar att styrkan på NSSC-massan kan påverkas genom att variera både utbytet och effekten i raffinörerna. För att åstadkomma en signifikant styrkeökning krävs ett lågt utbyte tillsammans med en hög effekt i raffinörerna. Kraftiga ändringar av dessa parametrar leder dessvärre till att papperets egenskaper förändras i den grad att körbarheten på maskin kan påverkas. Studien visar även att fluting som uppfyller dagens riktvärden kan framställas kostnadseffektivt genom ett högt utbyte i kokaren och en hög insats i raffinörerna. Samtidigt erhålls då en ljusare massa, vilket kan vara betydande i vissa fall. Krypmätningarna visar samtidigt att malningen i positiv bemärkelse påverkar krypstyvheten medan utbytets inverkan är mer svårtolkat. Ett allt för högt utbyte verkar dock vara negativt ur krypstyvhetssynpunkt.

  • 274.
    Lestelius, Magnus
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörs- och kemivetenskaper (from 2013).
    Ytbehandling av papper och papper som leder ström2012Konferansepaper (Annet (populærvitenskap, debatt, mm))
  • 275.
    Lestelius, Magnus
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörs- och kemivetenskaper (from 2013), Paper Surface Centre.
    Nyflött, Åsa
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörs- och kemivetenskaper (from 2013).
    Moons, Ellen
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Järnström, Lars
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörs- och kemivetenskaper (from 2013), Paper Surface Centre.
    Carlsson, Gunilla
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörs- och kemivetenskaper (from 2013).
    Bonnerup, Chris
    Govindarajan, Venkatesh
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörs- och kemivetenskaper (from 2013).
    Oxygen permeabilityand economic-environmental impact studies of some polyvinyl alcohol dispersionbarrier coatings for packaging applications2017Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Purposes of employing barrier coatings in packaging, and in particular food packaging, can be to increase the shelf life, preserve colour, odour, and taste, and to protect from a harmful environment in general. Barrier coatings can thus help to reduce food waste along the value chain until end use. Including both materials choice for packaging and the possible fates of the used package, even further steps to provide greater knowledge for decisions on choices of packaging solutions. To that end, we have conducted several experimental and transport modeling studies on oxygen barrier coatings performance. The coating system of choice    has been dispersion coatings of poly vinyl alcohol (PVOH), with additions of kaolin. Physical and chemical features of the coatings were characterized to obtain information on polymer crystallinity, free volume and filler orientation as these characteristics are influential to the oxygen mass transport performance. In turn, the oxygen mass transport was also measured, both in steady state and dynamically. In so doing, we obtained information    useful for developing a general model to describe the oxygen permeability taking into account the physical and chemical features, described above, of the coating layer. Attempts on describing the interdependence and impact, for instance between crystalline and amorphous polymer regions and moisture, was added to the model. The model showed agreement to experimental data for PVOH-kaolin coating in this particular case. However, the basic permeability model has been applied to  many different polymers.

    To further explore the potential of these types of coating, which are technically possible to    produce in paperboard production, an economic-environmental impact comparison to other existing material solutions was made. Four barrier material alternatives – starch, polyethylene, ethyl vinyl alcohol (chosen as an alternative for PVOH, where data was difficult to obtain) and kaolin, and latex and kaolin, were analyzed with respect to cost and global warming potential. Weighting and comparing cost to environmental aspect, weighting    factors based on interviews with experts in the packaging value chain, starch emerges as the most sustainable alternative. However, previous coating and mass transport studies also shows how these renewable materials require some further technical development to be competitive.

    The mass transport model can serve as a tool for customizing barrier coatings and to predict the barrier performance, as permeability is obtained and thus shelf-life estimation is    possible. The overall concept, the combination of assessment of structural performance and the environmental studies, can be employed to find sustainable food packaging solutions.

  • 276.
    Lin, Wamei
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörs- och kemivetenskaper (from 2013).
    Nilsson, Lars
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörs- och kemivetenskaper (from 2013). Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för miljö- och livsvetenskaper (from 2013).
    Malutta, Raffaelle
    Waste heat recovery by organic rankine cycle (ORC) for moist exhaust gases from paper industry2017Inngår i: ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE), American Society of Mechanical Engineers (ASME) , 2017, Vol. 6Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Large potential exists in recovering waste heat from paper industry processes and machinery. If the overall energy efficiency would be increased, it could lead to significant fuel savings and greenhouse gas emission reduction. The organic Rankine cycle (ORC) system is a very strong candidate for converting low-grade waste heat into power. However, there is a lot of water vapor containing latent heat in the exhaust gases from the drying process in the paper industry. Thus, the aim of this research work is to increase the efficiency of the ORC system by recovering not only the sensible heat but also the latent heat from the exhaust gases in the paper drying process. In order to recover the latent heat from the moist exhaust gases, one idea of this article is to introduce a direct contact condensing unit into the ORC system. The performance of ORC system with the direct contact condensing unit was analyzed by using the CHEMCAD software. A case study was conducted based on data of the exhaust gases from a tissue production / drying machine. Latent heat will be recovered when the evaporating temperature of the ORC working fluid is lower than the dew point of the water vapor in the exhaust gases. The results showed that the available heat load was increased when the evaporating temperature was reduced. Furthermore, a performance comparison of the ORC systems with and without the direct contact condensing unit was carried out in the case study as well. The results showed that the ORC system with the direct contact condensing unit not only could recover latent heat from the water vapor in the exhaust gases but also could have a small size and small volume evaporator in the ORC system.

  • 277.
    Lind, Sofia
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013).
    Wear reduction between disc edge and seat in a butterfly valve2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This thesis was written on behalf of SOMAS instruments AB. SOMAS develops, manufactures and markets valves. The mission was to reduce the wear between the disc edge and the seat in a butterfly valve that are used at high temperatures. This study investigated the possibility of using a surface treatment or coating that can reduce wear or if a new base material is better to use than the current steel 316 material.

    Possible materials, surface treatments and coatings were investigated and compared in a material study. In discussion with the company, four test pairs were chosen;

    • Steel 316 - Steel 316

    • Steel 316 - Nitronic 60

    • Nitronic 60 - Nitronic 60

    • Steel 316 - Steel 316 with a surface coating of Tribaloy T-400

    The wear behavior of the selected materials was investigated using a test rig at Karlstad University based on the method of block-on-ring. The machine spins a cylinder that corresponds to the seat against a block which in this case corresponds to the disc edge. The tests were carried out at room temperature, 250 ˚C and 500 ˚C. The cylinder was spinning at a speed of 100 rpm while the block pressed against with a load of 50 N.

    A profilometer, micro-hardness tester and scanning electron microscope (SEM) were used to investigate the wear. A comparison was made based on the volume of material removed from the blocks, the maximum wear depth of the blocks and the maximum wear depth of the cylinder. Wear mechanisms, chemical composition and hardness profiles were used to explain differences in results.

    The results were compared with the steel 316 to steel 316 solution. The Tribaloy T-400 showed good properties to reduce the wear at room temperature. Block made of Tribaloy T-400 showed no wear, instead steel from the cylinder had been adhered to the blocks. At higher temperatures, the amount of adhered material on the tribaloy T-400 increased, resulting in more wear at the surface of the cylinder than at room temperature. The wear on the cylinder was comparable to the wear of a steel cylinder that slid against a steel block. Nitronic 60 against nitronic 60 exhibited a significant reduction in wear compared with steel to steel at room temperature. At higher temperatures, nitronic 60 against nitronic 60 was the test pair that exhibited least wear.

    Nitronic 60 is recommended for further examination as a material in both the disc edge and the seat in a butterfly valve to be used at both room temperature and elevated temperatures.

  • 278.
    Lind, Sofia
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik.
    Zinklegering i åldrat och kylt tillstånd: Identifiering av parametrar som förändrar materialegenskaperna i Zamak52015Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Bilsäkerhet är en viktig fråga i dagens samhälle. Det enklaste sättet att skydda sig vid en bilfärd är genom att använda säkerhetsbälte. En säkerhetsbältesrulle är uppbyggd av flera olika komponenter, en av dessa kallas torque tube som tar energi när kroppen fångas upp av bältet vid en eventuell kollison. Säkerhetsbältet ska skydda passagerarna i bilen i många år och vid olika temperaturer. Torque tuben är i detta fall gjuten i en zinklegering som heter Zamak5 som förändrar sina materialegenskaper i åldrat och kylt tillstånd. Målet med arbetet är att hitta de parametrar som förändrar materialegenskaperna i Zamak5.

    Olika metoder användes för att få fram ett resultat på en torque tube som är specialtillverkad med försvagad geometri. Provobjekten som testades var både åldrade och oåldade. Ett pendelprov kan motsvara en kollision mellan ett säkerhetsbälte och en tyngd. För att hitta den kritiska temperatur då Zamak5 förändrar materialegenskaperna gjordes det pendelprov vid olika temperaturer för att se vilka provobjekt som gav brott. Brottytorna studerades sedan i mikroskop för att se vilka parametrar som orsakat egenskapsförändringarna.

    Resultatet visade att brottet var sprött. Det beror på att temperaturen understigit omslagstemperaturen. Det åldrade och kylda provobjektet visade på sämre hållfasthet och detta beror på att inkoherenta partiklar bildats och lagt sig i korngränser och i kritiska skjuvplan.

  • 279. Lindskog, P
    et al.
    Barbier, Christophe
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Paper Surface Centre. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för kemiteknik. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Jelagin, D
    Larsson, P.L.
    Optimization as a tool for characterization of advanced constitutive models describing powder compaction2007Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The applicability of optimization procedures used in combination with advanced constitutive models, describing dry pressing powder compaction, is investigated by aid of standard finite ele- ment and optimization commercial packages. It is found that, at fairly general conditions, this can be expected to be a very advantageous approach at material characterization

  • 280.
    Lindvall, Fredrik W.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Measurement and mechanisms of galling in sheet metal forming: A literature reviewManuskript (preprint) (Annet vitenskapelig)
  • 281.
    Lindvall, Fredrik W.
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Krakhmalev, Pavel
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Tool steel and contact geometry influence on galling initiation in lubricated sliding on carbon steel sheets2009Inngår i: Proceedings of the 8th International Tooling Conference, Vol 1, 2009, s. 189-198Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In sheet metal forming operations, sliding contact may cause adhesive wear of sheet materials with transfer of worn material to the tool surface, a wear damage process named galling. It results in loss of product quality, process performance and tool lifetime. The industrial experience of the optimal combination of sheet metal grades, tool steel grades, tool geometry and lubrication to increase the tool performance is not clearly understood. Accordingly, simulation of wear of sheet metal forming operation in laboratory conditions in order to quantify tendency of a tool material to galling is not a trivial problem neither. In the present study two tool steel grades, an ESR made 8%Cr cold work tool steel and a superior PM made high speed steel, were tested with different test tool geometries to obtain different contact pressure conditions. A slider on flat sheet (SOFS) test equipment was utilized, where a disc made of tool steel was slid along lubricated carbon steel sheets of different strengths. The sliding tool discs were prepared so that one elliptical and two linear contacts were simulated, in order to study their influence on distance to galling initiation. Normal and friction force data were collected, galling initiation was detected by analysis of the friction curve and verified by SEM and OP analysis of the tool surfaces and sheet sliding tracks. It was found that under selected test conditions, galling initiation was remarkably dependent on tool material as well as geometry.

  • 282.
    Lindvall, Fredrik W.
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Krakhmalev, Pavel
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Bay, Niels
    Department of Mechanical Engineering, Technical University of Denmark.
    The effect of grinding and polishing procedure of tool steels in sheet metal forming2010Inngår i: ICTPM 2010, 2010, s. 603-612Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The surface finish of tools in sheet metal forming has a large influence on the performance of the forming tool. Galling, concern of wear in sheet metal forming, is a severe form of adhesive wear where sheet material is transferred on to the tool surface. By polishing the tools to a fine surface finish, material pick-up has traditionally been reduced, but some surface preparations withstand adhesive wear better. To investigate the effect on galling performance of different surface preparations lubricated tests have been performed using a strip reduction rig. Two different tool materials, Vancron 40 and Vanadis 6 and up to ten different grinding and polishing treatments were tested against AISI 316 stainless steel. The tests showed that an optimum surface preparation might be found at the transition between abrasive and adhesive wear.

  • 283.
    Lindvall, Fredrik W.
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik.
    Gåård, Anders
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik.
    Krakhmalev, Pavel
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik.
    Study of the influence of contact geometry and contact pressure on sliding distance to galling in the Slider-On-Flat-Surface wear tester2013Inngår i: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 56, nr 6, s. 1137-1145Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One of the major causes of tool failure in sheet metal forming is wear in the form of galling. Galling is gradual buildup of adhered sheet material on the tool and leads to unacceptable scratches on the sheet surface and to components that fail to meet tolerances. Because it is difficult to reproduce operational and interactional conditions in laboratory test equipments it is hard to test, model, and predict galling initiation.Here the authors examine how changes from elliptical to line contact geometry influenced galling initiation under dry sliding by using a slider-on-flat surface (SOFS) wear tester. A micro clean tool steel was tested against ferritic low-strength and martensitic high-strength steel sheets.The sliding distance to galling initiation was extracted from friction data and verified by scanning electron microscopy (SEM) observations. The presence of adhesive wear on worn tools after completed tests was used as a criterion. Experimental results showed that the elliptical contact causes galling quicker than the line contact.Applicability of experimental results depends on the relevance of test conditions, so contact pressures calculated for the described tests were compared to calculated contact pressures in a semi-industrial U-bending test and to literature data relevant to industrial applications. Good agreement between values observed for SOFS and for most selected industrial applications was found, which assume that contact pressures typical for most common industrial applications can be successfully simulated by selection of tool geometry and normal load in the SOFS tester.

  • 284. Ljungqvist, Carl-Henrik
    et al.
    Lyng, Reidar
    Thuvander, Fredrik
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Paper Surface Centre. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Evaluation of PFI beating on the strain to failure of spruce fibres using single fibre fragmentation2005Annet (Annet (populærvitenskap, debatt, mm))
  • 285. Ljungqvist, Carl-Henrik
    et al.
    Lyng, Reidar
    Thuvander, Fredrik
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Paper Surface Centre. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Influence of fibre damage in latewood spruce tracheids on strain to failure of wood fibres determined be Weiull modeling2004Inngår i: Nordic Pulp and Paper Research Journal, 19 2004 pp 164-169Artikkel i tidsskrift (Fagfellevurdert)
  • 286. Ljungqvist, Carl-Henrik
    et al.
    Lyng, Reidar
    Thuvander, Fredrik
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Paper Surface Centre. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Influence of observable damage on mature latewood spruce fiber properties2003Konferansepaper (Fagfellevurdert)
  • 287. Ljungqvist, Carl-Henrik
    et al.
    Lyng, Reidar
    Thuvander, Fredrik
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Paper Surface Centre. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Measuring the strain to failure for wood fibres - influence of fibre wall damage2003Annet (Annet (populærvitenskap, debatt, mm))
  • 288.
    Marques da Silva Näsman, Aline Fernanda
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap.
    Effects of refining energy, pH and different types of fibers on the strength of paper2011Independent thesis Advanced level (degree of Master (Two Years)), 30 poäng / 45 hpOppgave
    Abstract [en]

    This report is the result of an examination work at Karlstad University. This thesis was performed in cooperation with Billerud Gruvön. The purpose of this project was to investigate how refining energy, pH and different types of fibers affect the strength of the final paper. A laboratory study was performed where softwood and hardwood unbeaten pulps and broke had their pH adjusted after disintegration and then they were refined with different energy inputs in a laboratory pulp refiner. Mixtures containing softwood and broke or hardwood and broke were prepared to produce hand sheets. As reference, refined pulp and broke from Billerud Gruvön were taken and hand sheets were also produced. The results indicate that it is possible to affect the strength properties of paper by varying pH, different types of fibers and energy input in the refiner.

  • 289.
    Mattsson, Josephie
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap.
    Technical Analysis of Flax Fiber Reinforced Polypropylene: Prerequisites for Processing and Recycling2014Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Nowadays, when environmental concerns are becoming increasingly important are there great interest in natural materials and recyclability. The possibility of reusing materials with maintained mechanical properties are essential for sustainability. Today produced approximately 90,000 tons of natural fiber reinforced composites in Europe of those are 40,000 tons compression molded of which the automotive industry uses 95%. Natural fiber reinforced composites is recyclable and therefore interesting in many applications. Also, natural fiber reinforced composites is inexpensive, light in weight and shows decent mechanical properties which makes them attractive to manufactures. However, the problem with natural fiber reinforced composites is the poor adhesion between fiber and matrix, the sensitivity of humidity and their low thermal stability. Those problems could be overcome by addition of compatibilizer and reactive filler. This study will examine the technical requirement in order to develop a sustainable and recyclable biocomposite. It investigates the composition of matrix (polypropylene), fiber (flax), compatibilizer (maleic anhydride grafted polypropylene) and reactive filler (CaO) in order to obtain various combinations of stiffness, strength and processability. The two main methods used for preparing samples were compounding and injection molding. Results shows that 20 wt% flax was the optimal fiber content and that maleic anhydride grafted polypropylene is a very good compatibilizer by enhancing the strength significant. Surprisingly was the strength impaired due to the addition of CaO. The composition of 20 wt% flax, 1 wt% maleic anhydride grafted polypropylene and 79 wt% polypropylene is the technically most favorable composition.

  • 290.
    Medvedeva, Anna
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Performance of advanced tool steels for cutting tool bodies2010Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Performance of indexable insert cutting tools is not only about the performance of cutting inserts. It is also about the cutting tool body, which has to provide a secure and accurate insert positioning as well as its quick and easy handling under severe working conditions. The common damage mechanisms of cutting tool bodies are fatigue and plastic deformation. Cutting tools undergo high dynamic stresses going in and out cutting engagement; as a result, an adequate level of fatigue strength is the essential steel property. Working temperatures of tool bodies in the insert pocket can reach up to 600°C, why the tool steel requires high softening resistance to avoid plastic deformation. Machinability is also essential, as machining of the steel represents a large fraction of the production cost of a cutting tool.

    The overall aim of the study is to improve the tool body performance by use of an advanced steel grade with an optimized combination of all the demanding properties. Due to the high-temperature conditions, the thesis concerns mostly hot-work tool steels increasing also the general knowledge of their microstructure, mechanical properties and machinability.

    Knowing the positive effect of sulphur on machinability of steels, the first step was to indentify a certain limit of the sulphur addition, which would not reduce the fatigue strength of the tool body below an acceptable level. In tool bodies, where the demand on surface roughness was low and a geometrical stress concentrator was present, the addition of sulphur could be up to 0.09 wt%.

    Fatigue performance of the cutting tools to a large extent depended on the steel resistance to stress relaxation under high dynamic loading and elevated temperatures. The stress relaxation behaviour, material substructure and dislocation characteristics in low-alloyed and hot-work tool steels were studied using X-ray diffraction under thermal and mechanical loading.  Different tool steels exhibited different stress relaxation resistance depending on their microstructure, temper resistance and working temperature. Hot-work tool steels showed to be more preferable to low-alloyed tool steels because of their ability to inhibit the rearrangement and annihilation of induced dislocations.

    High-temperature softening resistance of the hot-work tool steels was investigated during high-temperature hold-times and isothermal fatigue and discussed with respect to their microstructure. Carbide morphology and precipitation were determined using scanning and transmission electron microscopy.

    Machinability of a prehardened hot-work tool steel of varying nickel content from 1 to 5 wt% was investigated in end milling and drilling operations. Machining the higher nickel containing steels resulted in longer tool life and generated lower cutting forces and tool/workpiece interface temperature. The difference in machinability of the steels was discussed in terms of their microstructure and mechanical properties. 

  • 291.
    Medvedeva, Anna
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Properties of tool steel for tool holder application: A litterature review2008Rapport (Annet vitenskapelig)
    Abstract [en]

    Large improvements in cutting tool design and technology have been achieved in the last decades. But the problem of improving the tool body material is not adequately studied. In the present study, the different aspects associated with the steel properties as related to the milling cutter body application are reviewed. The working performance of a tool holder depends in particular on the fatigue strength, high temperature properties and machinability of the tool steel used.

    Rotating tools, tool going in and out of cutting engagement, impose dynamic stresses and require adequate fatigue strength off the tool. Different publications, as well as internal investigation at Uddeholm Tooling AB show that the working temperatures of milling cutter bodies in the insert pocket vary from 300 to 600 degrees Celsius depending on the cutting conditions and material of the workpiece. As a result, steel for this application needs good hot properties such as high temper resistance, high hot hardness values, etc. Machinability is also essential as machining of steel represents a large fraction of the production cost of a milling cutter. Its complex shape with flutes and insert pockets as well as small thread holes and small deep holes for cooling channels require time consuming and advanced machining operations.

    The essential properties mentioned above were characterized with the emphasis to the steel type, its microstructure and purity, processing and surface treatment and strong interrelations between them.

  • 292.
    Medvedeva, Anna
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Tool steel for tool holder applications: microstructure and mechanical properties2008Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Large improvements in cutting tool design and technology, including the application of advanced surface engineering treatments on the cemented carbide insert, have been achieved in the last decades to enhance tool performance. However, the problem of improving the tool body material is not adequately studied.

    Fatigue is the most common failure mechanism in cutting tool bodies. Rotating tools, tool going in and out of cutting engagement, impose dynamic stresses and require adequate fatigue strength of the tool. Working temperatures of milling cutter bodies in the insert pocket can reach up to 600°C depending on the cutting conditions and material of the workpiece. As a result, steel for this application shall have good hot properties such as high temper resistance and high hot hardness values to avoid plastic deformation in the insert pocket of the cutting tool. Machinability of the steel is also essential, as machining of steel represents a large fraction of the production cost of a milling cutter.

    This thesis focus on the improvement of the cutting tool performance by the use of steel grades for tool bodies with optimized combination of fatigue strength, machinability and properties at elevated temperatures.

    The first step was to indentify the certain limit of the sulphur addition for improved machinability which is allowable without reducing the fatigue strength of the milling cutter body below an acceptable level. The combined effect of inclusions, surface condition and geometrical stress concentrator on the fatigue life of the tool steel in smooth specimens and in tool components were studied in bending fatigue.

    As the fatigue performance of the tools to a large extent depends on the stress relaxation resistance at elevated temperature use, the second step in this research was to investigate the stress relaxation of the commonly used milling cutter body materials and a newly steel developed within the project. Compressive residual stresses were induced by shot peening and their response to mechanical and thermal loading as well as the material substructures and their dislocation characteristics were studied using X-ray diffraction.

    Softening resistance of two hot work tool steels and a newly developed steel was investigated during high temperature hold times and isothermal fatigue and discussed of with respect to their microstructure. Carbide morphology and precipitation as well as dislocation structure were determined using transmission electron microscopy and X-ray line broadening analysis.

  • 293.
    Medvedeva, Anna
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap.
    Gunnarsson, Staffan
    Research and Development, Uddeholm Tooling AB.
    Inclusions, Stress Concentrations and Surface Condition in Bending Fatigue of an H13 Tool Steel2008Inngår i: Steel research, ISSN 0177-4832, ISSN 1869-344X, Vol. 79, nr 5, s. 376-381Artikkel i tidsskrift (Fagfellevurdert)
  • 294.
    Medvedeva, Anna
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Gunnarsson, Staffan
    Research and Development, Uddeholm Tooling AB.
    Andersson, Jörgen
    Research and Development, Uddeholm Tooling AB.
    High-temperature properties and microstructural stability of hot-work tool steels2009Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 523, nr 1-2, s. 39-46Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    Indexable insert tools for machining operations are in service exposed to high temperatures and cyclic mechanical loads. Secondary hardening steels such as hot-work steels are commonly used for tools subjected to thermal exposure. However, these steels, highly alloyed with strong carbide forming elements as Cr, V and Mo, are generally difficult to machine and machining represents a large fraction of the production cost of a tool. Thus, the present study concerns the development of a new steel with improved machinability and meeting the requirements for high-temperature properties.

    Softening resistance of the THG2000 and QRO90 tool steels, commonly used in hot-work applications, and a newly developed tool steel MCG2006 with lower alloying content of carbide forming elements, was investigated by tempering and isothermal fatigue testing. Mechanisms of high-temperature softening of the tested tool steels were discussed with respect to their microstructure and high-temperature mechanical properties. Carbide morphology and precipitation as well as dislocation structure were determined using transmission electron microscopy and X-ray line broadening analysis.

    No difference in softening behaviour was found among the QRO90 and MCG2006 regarding hot hardness measurements. The THG2000 indicated some stabilization of the hardness between 450 and 550 °C and a considerable hardness decrease at higher temperatures.

    The short-time cyclic softening in isothermal fatigue was controlled by dislocation rearrangement and annihilation. The alloying composition of the steels presently tested had no influence on the dislocation density decrease.

    The long-time softening was affected by the material's temper resistance and strongly depended on the carbide morphology and their over-ageing resistance. The QRO90 with greater molybdenum and lower chromium contents than in the THG2000 show the best resistance to softening among the tested grades at all temperatures. The MCG2006, leaner alloyed with the carbide forming elements and alloyed with 4 wt% nickel, has better temper resistance than THG2000 at higher temperatures and longer tempering times.

  • 295.
    Medvedeva, Anna
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap.
    Gunnarsson, Staffan
    Research and Development, Uddeholm Tooling AB.
    Andersson, Jörgen
    Research and Development, Uddeholm Tooling AB.
    Krakhmalev, Pavel
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Stress relaxation resistance of tool steels for tool holder applications2009Inngår i: Proceedings of the 8th International Tooling Conference, 2-4 June, Aachen, Germany, 2009, 2009, s. 697-712Konferansepaper (Fagfellevurdert)
  • 296.
    Medvedeva, Anna
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Gunnarsson, Staffan
    Research and Development, Uddeholm Tooling AB.
    Höglund, Dan
    Materials and Process Engineering, AB Sandvik Coromant.
    Stress relaxation resistance for improved fatigue performance of shot peened tool components2008Inngår i: Proceedings of the 10th International Conference on Shot Peening, 15-18 September, Tokyo, Japan, 2008 / [ed] Tosha K, Tokyo: Academy Common Meiji University , 2008, s. 286-295Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Shot peening is an extensively used process in the production of mechanical components to improve their fatigue strength at ambient temperature. At higher working temperatures of some mechanical components, e.g. from 300 to 600°C, the influence and behaviour of the compressive residual stresses are more uncertain, since they tend to relieve at higher temperatures. The response to shot peening induced residual stresses of low alloyed and hot work tool steels was evaluated with respect to stress relief heat treatments and isothermal high temperature fatigue testing. Not only the residual stresses, but also the material substructure and its dislocation characteristics are of importance. Dislocation structures were determined using X-ray diffraction to explain the preference of the different steel grades. Also, results obtained from bending fatigue testing at ambient temperature of tool components after shot peening and stress relief heat treatments demonstrated the different ability of retaining the fatigue strength.

  • 297.
    Medvedeva, Anna
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap.
    Gunnarsson, Staffan
    Research and Development, Uddeholm Tooling AB.
    Krakhmalev, Pavel
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Thermally activated relaxation behaviour of shot peened tool steels for cutting tool body application2011Inngår i: materials science and engineering A: Structural Materials: Properties, Microstructures and Processing, ISSN 0921-5093, Vol. 528, nr 3, s. 1773-1779Artikkel, forskningsoversikt (Annet vitenskapelig)
  • 298.
    Medvedeva, Anna
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap.
    Gunnarsson, Staffan
    Research and Development, Uddeholms Tooling AB.
    Krakhmalev, Pavel
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Nordh, Lars Göran
    Research and Development, Uddeholm Tooling AB.
    Influence of nickel content on machinability of a hot-work tool steel in prehardened condition2011Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 32, nr 2, s. 706-715Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present study, the influence of nickel content on the machinability of a prehardened hot-work tool steel was investigated. The machinability with varying nickel content from 1 to 5 wt% was characterized in end milling and drilling by evaluating tool life, cutting forces, and tool/chip interface temperature.

    Nickel content showed to have a positive effect on the machinability of the hot-work tool steel; with increasing nickel content in the steel, the longer tool life was reached in end milling and drilling operations. Machining the higher nickel containing steels generated lower cutting forces and tool/workpiece interface temperature. In addition, less adhesive wear and built-up edge formation were observed on the tools.

    The difference in the steel machinability was discussed in terms of their microstructure and mechanical properties. Increasing nickel content tends to decrease the carbon in the martensite and to retain a fine distribution of small primary carbides. It resulted in a reduction in yield strength with increasing nickel content related to the cutting force reduction and machinability improvement.

  • 299. Mitterer, C
    et al.
    Barbist, R.
    Björk, T
    Sundqvist, M
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Hagler, JA
    A comparative study on the evaluation of the tribological behaviour of polymer/zinc coated steel sheets1997Annet (Annet (populærvitenskap, debatt, mm))
  • 300.
    Moletsane, M G
    et al.
    Cent Univ Technol, Dept Mech & Mech Engn, Bloemfontein, Free State, South Africa.
    Krakhmalev, Pavel
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Kazantseva, N
    Urals Branch Acad Sci, Inst Met Phys, Ekaterinburg, Russia.
    du Plessis, Anton
    Univ Stellenbosch, CT Scanner Facil, Stellenbosch, South Africa.
    Yadroitsava, I
    Cent Univ Technol, Dept Mech & Mech Engn, Bloemfontein, Free State, South Africa.
    Yadroitsev, I
    Cent Univ Technol, Dept Mech & Mech Engn, Bloemfontein, Free State, South Africa.
    Tensile properties and microstructure of direct metal laser-sintered TI6AL4V (ELI) alloy2016Inngår i: South African Journal of Industrial Engineering, ISSN 1012-277X, E-ISSN 2224-7890, Vol. 27, nr 3, s. 110-121Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Direct metal laser sintering (DMLS) is an additive manufacturing technology used to melt metal powder by high laser power to produce customised parts, light-weight structures, or other complex objects. During DMLS, powder is melted and solidified track-by-track and layer-by-layer; thus, building direction can influence the mechanical properties of DMLS parts. The mechanical properties and microstructure of material produced by DMLS can depend on the powder properties, process parameters, scanning strategy, and building geometry. In this study, the microstructure, tensile properties, and porosity of DMLS Ti6Al4V (ELI) horizontal samples were analysed. Defect analysis by CT scans in pre-strained samples was used to detect the crack formation mechanism during tensile testing of as-built and heat-treated samples. The mechanical properties of the samples before and after stress relieving are discussed. 

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