Endre søk
Begrens søket
1 - 27 of 27
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Akhtar, Farid
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Synthesis, microstructure and mechanical properties of Al 2 O 3 reinforced Ni 3 Al matrix composite2009Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 499, nr 1-2, s. 415-420Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new method to synthesize alumina reinforced Ni3Al intermetallic matrix composites has been described. The powder mixture of nickel and aluminium was mechanically alloyed. The powder mixture was excessively heated during mechanical alloying and then exposed to atmosphere for oxidation. The oxidized powder mixture was transformed into alumina reinforced nickel aluminide matrix composite on subsequent pulse current processing. Alumina reinforcements were generated in the nickel aluminide matrix by in situ precipitation. The microstructure of the composite showed that the alumina reinforcements were 50–150 nm in size. The fine alumina reinforcements were homogeneously distributed in the matrix phase. The mechanical properties of the alumina reinforced nickel aluminide matrix composite fairly exceeded the nickel aluminide alloys. This novel synthesis approach allowed the rapid and facile production of high strength alumina reinforced Ni3Al matrix composites.

  • 2.
    Akhtar, Farid
    et al.
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Du, Xueli
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Jawid, Askari Syed
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Tian, Jianjun
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Guo, Shiju
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Microstructure and property evolution during the sintering of stainless steel alloy with Si 3 N 42008Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 472, nr 1-2, s. 324-331Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper describes the sintering of a martensitic stainless steel alloy with addition of Si3N4. Sintering behavior was studied at different sintering temperatures ranging from 1250 to 1400 °C with different holding times (20–80 min) and with varying Si3N4. Results showed that the samples were densified rapidly via liquid phase sintering mechanism. Nearly full density was obtained at 1300 °C after 60 min of holding time with 5 wt% Si3N4. Temperature above 1350 °C and Si3N4 content 10 wt% caused slumping of the samples. Two weight percent Si3N4 was found chemically stable in steel alloy. Above 2 wt% Si3N4 dissolved in the steel matrix. The distribution of dissolved Si and N was characterized by XMAP. When N content reached much above its solubility limit in steel alloy it diffused out leaving pores in steel alloy with considerable decrease in the sintered density. The mechanical properties of the sintered product with varying Si3N4 were measured. A maximum ultimate tensile strength of 1011 MPa was achieved with 2 wt% Si3N4 sintered at 1300 °C after 60 min of holding time. Fracture morphologies of tensile samples are also reported.

  • 3.
    Akshantala, Nagendra V.
    et al.
    Goodyear Tire and Rubber Company, Akron, OH.
    Talreja, Ramesh
    A micromechanics based model for predicting fatigue life of composite laminates2001Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 285, nr 1-2, s. 303-313Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The current practice, as well as the hitherto proposed models, for assessment of fatigue life of composite laminates rely largely on experimental fatigue life data. In this paper, we propose a methodology for fatigue life prediction that utilizes a micromechanics based evaluation of damage evolution in conjunction with a semi-empirical fatigue failure criterion. The specific case treated is that of cross ply laminates under cyclic tension. The predicted results are compared with experimental data for several glass/epoxy and carbon/epoxy laminates, and good agreement is found. Published by Elsevier Science S.A. The current practice, as well as the hitherto proposed models, for assessment of fatigue life of composite laminates rely largely on experimental fatigue life data. In this paper, we propose a methodology for fatigue life prediction that utilizes a micromechanics based evaluation of damage evolution in conjunction with a semi-empirical fatigue failure criterion. The specific case treated is that of cross ply laminates under cyclic tension. The predicted results are compared with experimental data for several glass/epoxy and carbon/epoxy laminates, and good agreement is found.

  • 4.
    Almqvist, Nils
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Rubel, M.
    Franconi, E.
    Surface characterization of SiC composites exposed to deuterium ions, using atomic force microscopy1995Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 201, nr 1-2, s. 277-285Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the influence of deuterium plasma on the surface structure of SiC based composites. The substrates are silicon carbides doped with titanium diboride, aluminium nitride or graphite. A number of surface sensitive techniques are used to characterize the substrates, before and after exposure to low-energy deuterium ions, the main method being atomic force microscopy. The microscope reveals distinct morphological changes on the irradiated samples. The density and surface area of the samples probably influence the content of deuterium in the surfaces. However, this study shows that the amount of graphite aggregated on the surfaces is of crucial importance for the uptake of deuterium.

  • 5.
    Bergquist, Bjarne
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Industriell Ekonomi.
    The importance of experimental design2002Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 328, nr 1-2, s. 348-349Artikkel i tidsskrift (Annet vitenskapelig)
  • 6.
    Dini, Hoda
    et al.
    Department of Materials and Manufacturing, School of Engineering, Jönköping University.
    Svoboda, Ales
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Andersson, Nils-Eric
    Department of Materials and Manufacturing, School of Engineering, Jönköping University.
    Ghassemali, Ehsan
    Department of Materials and Manufacturing, School of Engineering, Jönköping University.
    Jarfors, Anders E.W.
    Department of Materials and Manufacturing, School of Engineering, Jönköping University.
    Optimization and validation of a dislocation density based constitutive model for as-cast Mg-9%Al-1%Zn2018Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 710, s. 17-26Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A dislocation density-based constitutive model, including effects of microstructure scale and temperature, was calibrated to predict flow stress of an as-cast AZ91D (Mg-9%Al-1%Zn) alloy. Tensile stress-strain data, for strain rates from 10-4 up to 10-1 s-1 and temperatures from room temperature up to 190 °C were used for model calibration. The used model accounts for the interaction of various microstructure features with dislocations and thereby on the plastic properties. It was shown that the Secondary Dendrite Arm Spacing (SDAS) size was appropriate as an initial characteristic microstructural scale input to the model. However, as strain increased the influence of subcells size and total dislocation density dominated the flow stress. The calibrated temperature-dependent parameters were validated through a correlation between microstructure and the physics of the deforming alloy. The model was validated by comparison with dislocation density obtained by using Electron Backscattered Diffraction (EBSD) technique.

  • 7.
    Du, Xueli
    et al.
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Qin, Mingli
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Akhtar, Farid
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Humail, Islam S
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Qu, Xuanhui
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Study of rare-earth oxide sintering aid systems for AlN ceramics2007Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 460-461, s. 471-474Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present work, effects of Y2O3 and Dy2O3 sintering aid systems on density and thermal conductivity of AlN ceramics sintered at low temperature were investigated. The AlN powder synthesized by self-propagating high-temperature synthesis (SHS) was mixed individually with six different sintering aids, which were Y2O3, Dy2O3, CaF2–Y2O3, CaF2–Dy2O3, CaF2–Li2CO3–Y2O3 and CaF2–Li2CO3–Dy2O3, and then fabricated by employing press forming technique. The specimens were sintered at 1650 °C in nitrogen atmosphere at atmospheric pressure for 4 h. X-ray diffraction (XRD) was used to identify the secondary phases. The microstructure of the specimen was observed by scanning electron microscopy (SEM). The thermal diffusivity at room temperature was measured by a laser flash technique. Density of sintered specimen was measured by Archimedes displacement method. The result reveals that the density and thermal conductivity of AlN ceramics sintered with one component sintering aids were lower than those of sintered with multiple components sintering aids. The thermal conductivity of AlN ceramics sintered with CaF2–Li2CO3–Y2O3 and CaF2–Dy2O3 were 141 W m−1 K−1 and 142 W m−1 K−1, which were higher than that of any others.

  • 8.
    Forouzan, Farnoosh
    et al.
    Department of Materials Engineering, Isfahan University of Technology.
    Najafizadeh, Abbas
    Department of Materials Engineering, Isfahan University of Technology.
    Kermanpur, Ahmad
    Department of Materials Engineering, Isfahan University of Technology.
    Hedayati, Ali
    Department of Materials Engineering, Isfahan University of Technology.
    Surkialiabad, Roohallah
    Department of Materials Engineering, Isfahan University of Technology.
    Production of nano/submicron grained AISI 304L stainless steel through the martensite reversion process2010Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 527, nr 27-28, s. 7334-7339Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Production of nano/submicron grained AISI 304L austenitic stainless steel through formation of strain-induced martensite and its reversion to austenite are studied in this paper. The effects of annealing parameters on the microstructural development and mechanical properties are also investigated. Heavily cold rolling at 0 °C is employed to induce the formation of martensite in the metastable austenitic material, followed by reversion treatment at the temperature range of 700-900 °C for 0.5-300. min. Microstructural evolutions are analyzed using Feritscope, X-ray diffraction, and scanning electron microscopy, whereas the mechanical properties are determined by hardness and tensile tests. The smallest grain size (about 135. nm) is obtained in the specimen annealed at 700 °C for 20. min. The resultant nano/submicron grained steel not only exhibits a high strength level (about 1010. MPa) but also a desirable elongation of about 40%. Moreover, an annealing map is developed which indicates the appropriate range of annealing parameters for grain refinement of AISI 304L stainless steel through the martensite reversion process.

  • 9.
    Forouzan, Farnoosh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Vuorinen, Esa
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mücklich, Frank
    Department for Materials Science, Functional Materials, Saarland University.
    Post weld-treatment of laser welded AHSS by application of quenching and partitioning technique2017Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 698, s. 174-182Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two-step quenching and partitioning (Q&P) treatment was applied on specimens of an advanced high strength steel (AHSS) after laser welding, for post welding treatment. In order to avoid formation of brittle martensite phase, which usually form due to very high cooling rate of laser welding. To simulate the effect of different Q&P parameters after welding in the most critical part of HAZ, several cycles were performed in Gleeble simulator and analyzed in advance. Subsequently some of the cycles were repeated after laser welding by using an induction heater close to the weld. Different techniques including SEM, EBSD and XRD were used to analyze the microconstituents of the structure and mechanical properties were investigated by micro-hardness measurements across the weld, tensile and impact toughness tests. The final structure consists of controlled amount of tempered martensite with precipitates, bainite laths and small amount of fresh martensite depending on the thermal cycles. In addition, samples heated at a temperature between Ms and Bs (in this case 540C) showed the best mechanical properties. Therefore, this technique not only improves the microstructure and mechanical properties of the fusion zone (FZ) and heat affected zone (HAZ) but gives also a quick industrial processing method for post welding treatments.

  • 10.
    Gaddam, Raghuveer
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Influence of alpha–case layer on the low cycle fatigue properties of Ti–6Al–2Sn–4Zr–2Mo alloy2014Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 599, s. 51-56Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Strain–controlled low cycle fatigue properties of Ti–6Al–2Sn–4Zr–2Mo with different thickness of alpha–case layers were investigated. Results show that at strain amplitudes 0.3 and 0.4%, the fatigue life of the alloy is reduced for the specimens with alpha–case layer compared to the ones without any alpha–case. It was noted that with a 2 μm thick alpha–case layer the low cycle fatigue life is reduced about 50% at the higher strain amplitude. The degrading effect of the alpha–case layer on fatigue life increased with increasing thickness. The alpha–case layer at the surface is enriched with oxygen making the surface harder and brittle, which results in easier crack initiation and thus decrease in fatigue life.

  • 11. Gaddam, Raghuveer
    et al.
    Hörnqvist, M.
    Department of Applied Physics, Chalmers University of Technology.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Influence of High-pressure gaseous Hydrogen on the low-cycle fatigue and fatigue crack growth properties of a cast titanium alloy2014Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 612, s. 354-362Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present study, the effect of gaseous hydrogen on the fatigue properties of a commonly used aerospace titanium alloy (Ti–6Al–4 V) was studied. The low-cycle fatigue and fatigue crack growth properties were investigated at room temperature in ambient air and 15 MPa gaseous hydrogen. Results showed that the low-cycle fatigue life was significantly reduced in hydrogen, and the detrimental effect was larger at higher strain amplitudes. The fatigue crack growth rate in hydrogen remained unaffected below a critical stress intensity ΔK⁎≈17 MPa√m, while beyond this value, the fatigue crack growth rate fluctuated and increased with increasing ΔK. Fractography analysis clearly showed that gaseous hydrogen mainly affected the fatigue crack growth rate. On the fracture surfaces, striations were noted over the entire crack growth region in air, whereas in hydrogen striations were noted at stress intensities lower than ΔK⁎. Above ΔK⁎, secondary cracks and brittle flat surfaces with features similar to crack arrest marks were mostly observed in hydrogen. Microstructural analysis along the crack growth direction showed that the crack followed a transgranular path in air, i.e. through α colonies. In hydrogen, the crack also grew along the prior β grain boundaries and at α/β interface within the α colonies. Thereby, the detrimental effect of hydrogen in cast titanium alloy was attributed to a change in the fracture process during crack propagation

  • 12.
    Golling, Stefan
    et al.
    Gestamp R&D, Box 828, 97 125 Luleå.
    Frometa, David
    Fundació CTM Centre Tecnològic, Plaça de la Ciència 2, 08243 Manresa, Spain.
    Casellas, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Fundació CTM Centre Tecnològic, Plaça de la Ciència 2, 08243 Manresa, Spain.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Influence of microstructure on the fracture toughness of hot stamped boron steel2019Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 743, s. 529-539Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The automotive industry's desire for weight reduction while maintaining crashworthiness demands development of materials and material properties within the economic framework of consumers. The industrial process of hot stamping provides a technique to utilize steel in an efficient way. In hot stamping, microstructural characteristics of a steel blank are influenced by controlling the cooling rate. Hot stamping has become a prevalent method for lightweight solutions in car bodies without sacrificing passenger safety. The process of hot stamping applies sequential forming and quenching in a single production step. During the cooling of the blank, various microstructures can be formed depending on the cooling rate or holding temperature. Special tooling allows the application of different cooling rates within the same blank. Thus, the microstructure and mechanical properties can be influenced in designated areas of a blank.

    Fracture toughness properties of sheet metal are necessary to better understand fracture initiation and crack propagation during crash loading as well as improve crashworthiness predictions. This paper focus on fracture toughness of low-alloyed boron steel sheet common in the automotive industry. A heat treatment process is used to form different microstructures, predominately consisting of one single phase or mixed microstructures with two distinct phases. The fracture toughness of the present microstructures is evaluated using the Essential Work of Fracture methodology. Results are discussed in terms of the different microstructures obtained and the consequent part performance.

    Results show a strong connection between microstructure and fracture toughness. The bainitic grade shows favorable fracture toughness while a mixed microstructure of bainite and martensite shows a very brittle fracture behavior. A post heat treatment in the form of paint bake curing shows a negligible effect on fracture toughness of martensite.

  • 13.
    Golling, Stefan
    et al.
    Gestamp R&D, Luleå.
    Frómeta, David
    Fundació CTM Centre Tecnològic, Plaça de la Ciència 2, 08243 Manresa, Spai.
    Casellas, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Fundació CTM Centre Tecnològic, Plaça de la Ciència 2, 08243 Manresa, Spai.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Investigation on the Influence of Loading-Rate on Fracture Toughness of AHSS Grades2018Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 726, s. 332-341Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The automotive industry is striving for light body-in-white structures while maintaining or improving passenger safety. The aim of this paper is to investigate the influence of the loading rate on the fracture toughness of thin steel sheet metal of three advanced high strength steels. Although steel is a heavy material it plays a significant role for lightweight solutions in car bodies. Three different advanced high strength steel (AHSS) grades, namely dual-phase (DP), quench-partitioning (Q&P) and TRIP-assisted bainitic-ferritic (TBF), are investigated in the present paper. For crash relevant components it is of importance to know the material response under high loading velocities i.e. high strain rates. A standard tensile test system is used for low loading rates, a high-speed tensile testing setup is used to obtain high loading rates. The fracture toughness of the three AHSS grades is evaluated using the methodology of the Essential Work of Fracture (EWF). The tensile specimen used in the present work is the double edge notched tensile (DENT) geometry with a pre-developed crack. High-speed imaging is applied to verify the validity of the evaluation method Essential Work of Fracture at high rates of loading. Results from this work show that knowledge of fracture toughness would improve the understanding of fracture and crack propagation mechanisms for third generation high strength steels used for automotive components

  • 14.
    Golling, Stefan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Östling, Rickard
    Gestamp Hardtech AB, Luleå.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Characterization of ductile fracture properties of quench-hardenable boron steel: Influence of microstructure and processing conditions2016Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 658, s. 472-483Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Developments of the hot stamping technology have enabled the production of components with differential microstructure composition and mechanical properties. These can increase the performance of certain crash-relevant automotive structures by combining high intrusion protection and energy absorption. This paper presents a comprehensive experimental investigation on the flow and ductile fracture properties of boron-alloyed steel with a wide range of different microstructure compositions. Three types of dual phase microstructures at three different volume fractions, and one triple phase grade, were generated by thermal treatment. Flow curves extending beyond necking and the equivalent plastic strain to fracture for each grade was determined by tensile testing using full-field measurements. The influence of phase composition and microstructural parameters were further investigated by means of a multi-scale modeling approach based on mean-field homogenization in combination with local fracture criteria. Inter-phase and intra-phase fracture mechanisms were considered by adopting two separate fracture criteria formulated in terms of the local average stress field. The micromechanical model captures with useful accuracy the strong influence of microstructure and processing conditions on the flow and fracture properties, implying promising prospects of mean-field homogenization for the constitutive modeling of hot stamped components.

  • 15.
    Golling, Stefan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Östlund, Rickard
    Gestamp HardTech.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A stress-based fracture criteria validated on mixed microstructures of ferrite and bainite over a range of stress triaxialities2016Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 674, s. 232-241Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hot stamping is a sequential process for formation and heat-treatment of sheet metal components with superior mechanical properties. By applying different cooling rates, the microstructural composition and thus the material properties of steel can be designed. By controlling the cooling rate in different sections of a blank, the material properties can be tailored depending on the desired toughness. Under continuous cooling, various volume fractions of ferrite and bainite are formed depending on the rate of cooling. This paper focuses on the ductile fracture behavior of a thin sheet metal made of low-alloyed boron steel with varying amounts of ferrite and bainite. An experimental setup was applied in order to produce microstructures with different volume fractions of ferrite and bainite. In total, five different test specimen geometries, representing different stress triaxialities, were heat treated and tensile tested. Through full field measurements, flow curves extending beyond necking and the equivalent plastic strain to fracture were determined. Experimental results were further investigated using a mean-field homogenization scheme combined with local fracture criteria. The mean-field homogenization scheme comprises the influence of microstructure composition and stress triaxiality with usable accuracy, connoting auspicious possibilities for constitutive modeling of hot-stamped components

  • 16.
    Gunnars, Jens
    et al.
    Luleå tekniska universitet.
    Wiklund, U.
    Department of Materials Science, Uppsala University.
    Determination of growth-induced strain and thermo-elastic properties of coatings by curvature measurements2002Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 336, nr 1-2, s. 7-21Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Curvature measurements on bimaterial specimens are examined for determination of residual strain/stress and thermo-elastic properties of coatings and layered materials. By using specimens with material layers of comparable thickness, large deflections and thereby high measurement accuracy are obtained. Strain-curvature relations are given for beam and plate specimens at different deformation modes. A robust fitting method for simultaneous determination of the mismatch strain and the modulus of elasticity is described. Experiments are performed on a titanium nitride (TiN) coating deposited on a thick high-speed steel substrate by PVD. The modulus of elasticity and the thermal expansion coefficient for the TiN coating are determined to 500 GPa and 7.4 x 10 exp -6 K exp -1 , respectively. The characteristic residual stress, i.e. the thin-film stress at room temperature, is -3.8 GPa, for this material combination and deposition conditions. The temperature independent growth-induced strain is determined to -0.0045, which is 75% of the mismatch strain at room temperature.

  • 17.
    Hansson, T.
    et al.
    Nagaoka University of Technology.
    Ramamurty, U.
    University of California.
    Bull, C.
    Brown university.
    Warren, Richard
    Luleå tekniska universitet.
    Elevated temperature fracture behavior of monolithic and SiCW- reinforced silicon nitride under quasi-static loads1996Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 209, nr 1-2, s. 137-148Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fracture behavior of a monolithic and SiCw-reinforced Si3N4 over the 1000-1550 °C temperature range with monotonically increasing loads was investigated. Peaks in the fracture initiation toughness, Kc, were found to occur owing to the brittle-to-ductile transition in the fracture behavior. This transition is associated with the onset of viscous deformation of the secondary intergranular amorphous phase present in the microstructure and the concomitant relaxation of the crack-tip stresses. The brittle-to-ductile transition temperature (BDTT) depends on the loading rate. Damage accumulation in terms of nucleation and growth of cavities ahead of the crack-tip promote stable crack growth at temperatures higher than the BDTT. The length of the subcritical crack increases with increasing temperature. Experiments involving the introduction of stable cracks at elevated temperatures followed by room-temperature fracture toughness testing reveal that shielding owing to the crack-wake bridging increases the apparent fracture resistance above the BDTT. Micromechanisms of the brittle-to-ductile transition and subcritical crack growth at elevated temperatures in the Si3N4 ceramics were discussed.

  • 18.
    Larsson, C.
    et al.
    Linköping University.
    Holden, T.M.
    Los Alamos National Laboratory.
    Bourke, M.A.M.
    Los Alamos National Laboratory.
    Stout, M.
    Los Alamos National Laboratory.
    Teauge, J.
    Los Alamos National Laboratory.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Measurement and modeling of residual stress in a welded Haynes® 25 cylinder2005Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 399, nr 1-2, s. 49-57Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An experimental and simulation study of residual stresses was made in the vicinity of a gas tungsten arc weld, used to join a hemispherical end cap to a cylinder. The capped cylinder is used in a satellite application and was fabricated from a Co-based Haynes® 25 alloy. The cylinder was 34.7 mm in outer diameter and 3.3 mm in thickness. The experimental measurements were made by neutron diffraction and the simulation used the implicit Marc finite element code. The experimental resolution was limited to approximately 3 mm parallel to the axis of the cylinder (the weld was 6 mm in the same direction) and comparison over the same volume of the finite element prediction showed general agreement. Subject to the limited spatial resolution, the largest experimentally measured tensile residual stress was 180 MPa, located at the middle of the weld. However, the predictions suggest that there are regions in the weld where average tensile residual stresses as much as 400 MPa exist. One qualitative disparity between the model and the experiments was that the measurement included a larger degree of asymmetry on either side of the weld than predicted by the model.

  • 19.
    Larsson, C
    et al.
    Linköping universitet.
    Odén, Magnus
    Hardness profile measurements in functionally graded WC-Co composites2004Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 382, nr 1-2, s. 141-149Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Micro- and nanoindentation were used to determine hardness as a function of depth in two functionally graded WC-Co composites. The gradients were continuous (extended over ~70 and ~40 μm, respectively) and consisted of varying WC and Co phase volume fractions. Five comparable homogeneous samples with different Co contents and different average WC grain sizes were also used for direct comparison. A relationship between hardness and Co content was established for both the graded and the homogeneous samples wherein the hardness decreased with increasing Co content. The magnitude of the hardness was the same (for a given Co content) for the functionally graded and the homogeneous materials. The hardness measurements were also correlated with X-ray diffraction studies of thermal residual stresses and the absence of any major influence explained. It is generally concluded that the hardness values are dominated by the local Co content. Additionally, the examination of surface cracks around indents suggests that compositional gradients in WC-Co composites offer increased toughness

  • 20.
    Meara, C.O.
    et al.
    Chalmers University of Technology.
    Suihkonen, T.
    Chalmers University of Technology.
    Hansson, T.
    Nagaoka University of Technology.
    Warren, Richard
    Luleå tekniska universitet.
    Microstructural investigation of the mechanisms of tensile creep deformation in an Al2O3/SiCW composite1996Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 209, nr 1-2, s. 251-259Artikkel i tidsskrift (Fagfellevurdert)
  • 21.
    Odenberger, Eva-Lis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Pederson, Robert
    Volvo Aero Corporation, Trollhättan.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Thermo-mechanical material response and hot sheet metal forming of Ti-62422008Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 489, nr 1-2, s. 158-168Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermo-mechanical response of a Ti-6242 alloy has been studied in elevated temperature compression tests (CT) together with cold and hot sheet metal forming tests (FT) to evaluate the suitability of different cold and hot sheet metal forming processes. The CT are designed to function as input for the estimation of material model parameters such as the parameters of constitutive equations. Furthermore, results from the FT will be used in correlation of finite element (FE) models for the prediction of sheet metal forming. Experiments were performed in a broad range of temperatures and strain rates. In CT at 400-900 °C and strain rates 0.05-1 s-1. In FT at 20-1000 °C in both isothermal and non-isothermal forming, at forming velocities of 5 and 10 mm/s. The microstructures of as-received material and deformed specimens were examined using optical microscopy. Experimental results of the CT show that initial material hardening was followed by specimen failure where cracks have formed in deformation bands or by flow softening, depending on the temperature. Compressive logarithmic strains of 10-50% were achieved. The FT reveals that optimal forming conditions are a combination of forming velocity, temperature and holding time. Hence increasing forming temperatures alone does not necessary imply better forming characteristics. A change in spring-back characteristics occurred at elevated temperatures. It can be concluded that, under the current conditions in this study, Ti-6242 is suitable to be formed by hot sheet metal forming.

  • 22.
    Pederson, Robert
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Niklasson, F.
    Volvo Aero.
    Skystedt, F.
    Volvo Aero Corporation, Materials Technology.
    Warren, R.
    University of Malmö, Department of Technology and Society.
    Microstructure and mechanical properties of friction- and electron beam welded Ti-6Al-4V and Ti-6Al-2Sn-4Zr-6Mo2012Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 552, s. 555-565Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work presents mechanical data and microstructural characterization of friction welded (FRW) and electron beam welded (EBW) post weld heat treated (PWHT) specimens of Ti-6Al-2Sn-4Zr-6Mo and Ti-6Al-4 V. PWHT Ti6246/Ti6246 welds and Ti64/Ti6246 welds were evaluated with tensile-, creep-, Charpy-V, and microhardness tests. The PWHT treatments were 593 °C/2 h, 640 °C/2 h and 704 °C/2 h, respectively. The microstructure of the different weld types and alloy combinations where examined and characterized using optical microscope and SEM.Tensile strength and yield strength were within specification for both material combinations. The elongation for Ti6246 welded to Ti6246 is below specification. Only small variations in tensile properties were found for the different PWHTs. Fracture occurred in base material of the Ti64 alloy for the combination of Ti64 welded to Ti6246.Charpy-V tests shows that the welds are more brittle compared with the base material. The largest difference was found in Ti6246 welded to Ti6246.No significant variation in creep properties for the different PWHTs has been found. Ti64 welded to Ti6246 shows poor creep properties due to the high testing temperature for the Ti64 alloy. Ti6246 welded to Ti6246 shows good creep properties compared to the base material.The general trend for the weld microhardness was a decreasing hardness with increasing PWHT temperature. One exception though was the FRW Ti64/Ti6246 combination, were the hardness of the Ti6246 side of the HAZ, close to the interface between the two alloys, was highest after a PWHT temperature of 593 °C, then decreasing in hardness for 640 °C, not PWHT and being least hard for the PWHT temperature of 704 °C. The hardness of the Ti64 base material showed no decrease after the PWHTs, but the hardness of the Ti6246 bulk material decreased after PWHT at 704 °C.

  • 23.
    Pineda Huitron, Rosa Maria
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Lopez, Pavel E. Ramirez
    Casting and Flow Simulation Group, Process Metallurgy Department, SWERIM AB, Luleå, Sweden. Materials Science and Engineering, Royal Institute of Technology (KTH), Stockholm, Sweden.
    Vuorinen, Esa
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Jentner, Robin
    Luleå tekniska universitet.
    Kärkkäinen, Maija E.
    SSAB Europe Oy Raahe works, Raahe, Finland.
    Converging criteria to characterize crack susceptibility in a micro-alloyed steel during continuous casting2020Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 772, artikkel-id 138691Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The ductility drop and decrease in strength that lead to crack formation during continuous casting of steel is typically investigated by means of the hot ductility test. In this study, hot ductility tests are performed by using a thermo-mechanical Gleeble system to simulate the deformation of steels at high temperatures and low deformation rates similar to those during continuous casting. Thus, temperature was varied between 600 and 1000°C while strain rates covered a range from 0.001 to 0.1s−1. Tests are carried out to identify the temperature range at which the steel is susceptible to crack formation as well as the effect of strain rate. Characterization of fractured surfaces and phase transformation after thermo-mechanical tests are conducted in the SEM and Optical Microscope. The combination of these techniques makes possible to formulate cracking mechanisms during hot processing which show critical strain for failure at temperatures between 700 and 900°C based on the convergence of three different criteria: I) Reduction of area, II) True fracture strength-ductility and III) True total energy. This approach provides a better understanding of crack formation in steels at the high temperatures experienced during continuous casting. This information is key to productivity losses and avoid defect formation in the final cast products.

  • 24.
    Singh, Gaurav
    et al.
    Department of Materials Engineering, Indian Institute of Science, Bangalore.
    Satyanarayana, D.V.V.
    Defence Metallurgical Research Laboratory, Hyderabad.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Datta, Ranjan
    International Centre for Materials Science, JNCASR, Jakkur PO, Bangalore.
    Ramamurty, Upadrasta
    Department of Materials Engineering, Indian Institute of Science, Bangalore.
    Enhancement in creep resistance of Ti-6Al-4 V alloy due to Boron addition2014Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 597, s. 194-203Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The addition of B, up to about 0.1 wt.%, to Ti-6Al-4 V reduces its as-cast grain and colony sizes by an order of magnitude. In this paper, the creep resistance of this alloy modified with 0.06 and 0.11 wt.% B additions was investigated in the temperature range of 475–550 °C and compared with that of 0B alloy. Conventional dead-weight creep tests as well as stress relaxation tests were employed for this purpose. Experimental results show that the B addition enhances both elevated temperature strength and creep properties of Ti64, especially at the lower end of the temperatures investigated. The steady state creep rate in the alloy with 0.11 wt.% B was found to be an order of magnitude lower than that in the base alloy, and both the strain at failure as well as the time for rupture increases with the B content. These marked improvements in the creep resistance due to B addition to Ti64 were attributed primarily to the increased number of inter-phase interfaces – a direct consequence of the microstructural refinement that occurs with the B addition – that provide resistance to dislocation motion

  • 25. Talreja, Ramesh
    A conceptual framework for interpretation of MMC fatigue1995Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 200, nr 1-2, s. 21-28Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A previously developed conceptual framework for interpretation of fatigue of polymer matrix composites (PMCs) is revisited for the purpose of the interpretation of fatigue in metal matrix composites (MMCs). With appropriate modifications, the basic features in the mechanisms based fatigue life diagrams of PMCs are found to hold for MMCs as well. Fatigue data for different MMC systems are examined with the interpretative framework and some observed trends are clarified. Approaches to fatigue life modeling are discussed for the different regions of behavior interpreted by the fatigue life diagram concept.

  • 26.
    Tan, Zheng
    et al.
    Luleå tekniska universitet.
    Magnusson, Claes
    Persson, Bengt
    Volvo Company, Olofström.
    Bauschinger effect in compression-tension of sheet metals1994Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 183, nr 1-2, s. 31-38Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is important to know how sheet metals behave under complicated loading conditions, since yielding and hardening of a metal are actually dependent upon the stress state and deformation history. An example is the Bauschinger effect, which is manifested as a loss of yield strength during reverse loading upon plastic prestraining. Quantitative analysis of the Bauschinger effect is required for better understanding of this problem. In this study, experiments carried out by subjecting sheet metals to uniaxial compression-tension tests show that the Bauschinger effect varies with the material properties and the magnitude of prestrain. On the basis of the experiments and the continuum theory of plasticity, parameters defining the Bauschinger effect are proposed, which interpret the combined effect of work hardening and work softening of a material during forward and reverse straining, and a model revealing the Bauschinger effect on the subsequent yield surface is finally presented

  • 27.
    Åkerfeldt, Pia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Influence of microstructure on mechanical properties of laser metal wire-deposited Ti-6Al-4V2016Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 674, s. 428-437Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present paper laser metal wire deposition of Ti-6Al-4V has been studied and the mechanical properties evaluated. The yield strength, ultimate tensile strength and tensile elongation were all found to depend on the orientation of the specimens with respect to the deposition direction. Two orientations in the deposited material were evaluated in the study, perpendicular and parallel to the deposition direction. The specimens in the perpendicular orientation showed 25–33% higher elongation than the specimens parallel to the deposition direction. The parallel specimens on the other hand showed both higher (4%) ultimate tensile strength and higher (2–5%) yield strength. Furthermore, the anisotropic mechanical properties were correlated to the microstructural constituents of the specimens

1 - 27 of 27
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf