Endre søk
Begrens søket
1 - 23 of 23
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.
    Barbier, Christophe
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörs- och kemivetenskaper, 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.
    Larsson, Per-Lennart
    Östlund, Sören
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Karathanasis, Michael
    On material characterization of paper coating materials by microindentation testing2005Inngår i: JCT: Journal of Coatings Technology, ISSN 0361-8773, Vol. 2, nr 6, s. 463-471Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Microindentation as a method for determining important material properties of paper coating materials is studied experimentally and numerically. The bulk of the investigation is concentrated upon the short-lived elastic part of a spherical indentation test, but determination of the failure stress of the coating is also discussed. The results indicate that microindentation can be a powerful tool for material characterization of these materials, but only if careful efforts are made to account for the influence from plasticity as well as from boundary effects

  • 2. Girlanda, Orlando
    et al.
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Östlund, S.
    Tryding, J.
    Defect sensitivity and strength of paperboard in the out-of-plane tension and shear2005Inngår i: Journal of Pulp and Paper Science, 31(2), 100-104 (2005)Artikkel i tidsskrift (Fagfellevurdert)
  • 3.
    Gåård, Anders
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Hallbäck, Nils
    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.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap.
    Temperature effects on adhesive wear in dry sliding contacts2010Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 268, nr 7-8, s. 968-975Artikkel i tidsskrift (Fagfellevurdert)
  • 4.
    Gåård, Anders
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Krakhmalev, Pavel
    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, Avdelningen för maskin- och materialteknik. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap.
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap.
    Galling resistance and wear mechanisms - cold work tool materials sliding against carbon steel sheets2007Inngår i: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 26, nr 1, s. 67-72Artikkel i tidsskrift (Fagfellevurdert)
  • 5.
    Hallbäck, Nils
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Girlanda, Orlando
    Tryding, J
    Finite element Analysis of Ink-Tack Delamination of Paperboard2006Inngår i: International Journal of Solids and Structures, 43(5), 899–912 (2006)Artikkel i tidsskrift (Fagfellevurdert)
  • 6.
    Hallbäck, Nils
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik.
    Korin, Christer
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik.
    Barbier, Christophe
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörs- och kemivetenskaper.
    Nygårds, Mikael
    KTH.
    Finite Element Analysis of Hot Melt Adhesive Joints in Carton Board2014Inngår i: Packaging technology & science, ISSN 0894-3214, E-ISSN 1099-1522, Vol. 27, nr 9, s. 701-712Artikkel i tidsskrift (Fagfellevurdert)
  • 7.
    Hallbäck, Nils
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Korin, Christer
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Paper Surface Centre.
    Vähä-Nissi, Mika
    Seppänen, Rauni
    Laine, Christiane
    Influence of paperboard on bond formation and strength of adhesive joint2009Konferansepaper (Fagfellevurdert)
    Abstract

    Knowledge about the glueability of fiber-based materials is limited. Factors affecting the adhesive joint between adhesive and paperboard are presented here through two cases: strength of hot melt adhesive joint and consolidation of dispersion adhesive. The hot melt joint was investigated by Y-peel testing, while shear testing was applied for dispersion adhesives. A set of supplementing tools was used to understand the adhesive joints, their development and failure. The results show, for example, the importance of paperboard roughness on the hot melt joint strength. Formation of an adhesive joint with dispersion adhesives is affected by the rheological properties of the adhesive layer and the structure and absorbation properties of the board surface. Both case studies indicate that it can actually be better to apply the adhesive first on a rough surface and the press the smooth surface on the adhesive, which is in contrast with the common practice today

  • 8.
    Hallbäck, Nils
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik.
    Tofique, Muhammad Waqas
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik.
    Development of a distributed dislocation dipole technique for the analysis of multiple straight, kinked and branched cracks in an elastic half-plane2014Inngår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 51, s. 2878-2892Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A distributed dislocation dipole technique for the analysis of multiple straight, kinked and branched cracks in an elastic half plane has been developed. The dipole density distribution is represented with a weighted Jacobi polynomial expansion where the weight function captures the asymptotic behaviour at each end of the crack. To allow for opening and sliding at crack kinking and branching the dipole density representation contains conditional extra terms which fulfil the asymptotic behaviour at each endpoint. Several test cases involving straight, kinked and branched cracks have been analysed, and the results suggest that the accuracy of the method is within 1% provided that Jacobi polynomial expansions up to at least the sixth order are used. Adopting even higher order Jacobi polynomials yields improved accuracy. The method is compared to a simplified procedure suggested in the literature where stress singularities associated with corners at kinking or branching are neglected in the representation for the dipole density distribution. The comparison suggests that both procedures work, but that the current procedure is superior, in as much as the same accuracy is reached using substantially lower order polynomial expansions.

  • 9.
    Hämäläinen, Pyry
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörs- och kemivetenskaper (from 2013).
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Barbier, Christophe
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörs- och kemivetenskaper (from 2013).
    Development and evaluation of a high-speed creping simulator for tissue2016Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, nr 3, s. 448-458Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An innovative creping simulator for tissue has been developed to meet the requirements set by both industrial needs, such as speed and process step duration, and research ambitions, such as flexibility for modifications and efficient operation. Some of these factors can be difficult to achieve with the previously introduced simulators. Lower speeds and much longer process step times can jeopardize results when, for instance, the drying time of chemicals is longer and the speed of creping is slower than in a tissue mill. The newly developed simulator has been used to investigate the effects of paper grammage, creping angle, temperature of dryer, speed and the horizontal force experienced during tissue creping. Results show good agreement with results of industrial-scale tissue production, with the exception of shrinkage which was greater. It was observed that the grammage influences the final thickness and the shrinkage of creped sheets, and that creping speed affects the creping frequency, thickness and shrinkage. The temperature of the surface of a sled mimicking the Yankee cylinder was shown to influence creping frequency and thickness. The horizontal friction force during creping appears to increase if drying temperature is lowered.

  • 10.
    Hämäläinen, Pyry
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörs- och kemivetenskaper (from 2013).
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Gåård, Anders
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Lestelius, Magnus
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörs- och kemivetenskaper (from 2013).
    On the determination of transverse shear properties of paper using the short span compression test2017Inngår i: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 107, s. 22-30Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present paper explores the short span compression tester (SCT) as a means to experimentally determine the transverse shear moduli of paper. These moduli, which are known to be difficult to determine by any other means, are of importance for the behavior of paper during tissue manufacturing and in the converting and embossing of paperboard. Testing was conducted on paper of two different grammages both in MD and in CD. By applying the Timoshenko-Engesser theory for buckling of shear compliant materials, estimates of the transverse shear moduli were obtained through the measured SCT values and standard measurements of the Young's modulus and the thickness. These estimates were evaluated by detailed FE-analyses of the SCT setup incorporating initial geometrical imperfections representative for real test conditions. It was found that the Timoshenko-Engesser theory gives estimates of the transverse shear moduli that are within an accuracy well applicable for most engineering purposes. The results suggest that the method is at least as accurate as any other, more involved, method that could be used for the purpose.

  • 11.
    Korin, Christer
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för kemiteknik.
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Barbier, Christophe
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för kemiteknik.
    Nygårds, Mikael
    KTH Royal Institute of Technology, Solid Mechanics.
    Finite Element Analysis of Hot Melt Adhesive Joints in Carton BoardManuskript (preprint) (Annet (populærvitenskap, debatt, mm))
  • 12.
    Korin, Christer
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Paper Surface Centre.
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Junghans, R
    Failure Modes of Adhesively Joined Carton Board2008Inngår i: Journal of Adhesion Science and Technology, 2008Artikkel i tidsskrift (Fagfellevurdert)
  • 13.
    Korin, Christer
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för kemiteknik.
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Junghans, Robert
    Failure Modes of Adhesive Joints in Carton Board2008Inngår i: Journal of Adhesion Science and Technology, ISSN 0169-4243, E-ISSN 1568-5616, Vol. 22, s. 2079-2104Artikkel i tidsskrift (Fagfellevurdert)
  • 14.
    Korin, Christer
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Paper Surface Centre.
    Lestelius, Magnus
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för kemiteknik. Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Paper Surface Centre. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap.
    Tryding, J
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Y-peel Characterization of Adhessively-bonded Carton Board an objective Method2007Inngår i: Journal of Adhesion Science and Technology 21 2007 (2) 197-210Artikkel i tidsskrift (Fagfellevurdert)
  • 15.
    Korin, Christer
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för kemiteknik.
    Seppänen, Rauni
    YKI, Institute for Surface Chemistry.
    Vähä-Nissi, Miki
    VTT Technical Research Centre of Finland.
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Influence of surface treatments on the mechanical strength of hotmelt adhesive joints made of cartonboards2012Inngår i: Journal of Adhesion Science and Technology, ISSN 0169-4243, E-ISSN 1568-5616, Vol. 26, nr 20-21, s. 2339-2356Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of surface treatments including pigment coating, surface sizing and calendering on the mechanical strength of hotmelt adhesive joints in pilot made cartonboards was studied. The mechanical strength of the joints was investigated using the Y-peel test device at 23 degrees C and 50% relative humidity. Some of the samples were investigated with respect to the failure mode by scanning electron microscopy. The surfaces were characterized in terms of surface roughness, surface chemical composition, and adhesion behaviour. A strong adhesive bond displayed fibre tear. In addition to fibre tear, interfacial failure, i.e., failure between the cartonboard and the adhesive, was the main reason for fracture in the bonded assembly. The most important factor controlling the integrity of adhesive joints seemed to be the real contact area. The adhesive joints showed significantly higher strength when the hotmelt adhesive was first applied onto the rougher cartonboard of the assembly and then the smoother cartonboard was pressed on the adhesive than vice versa. The surface roughness of cartonboards mainly depended on whether the surface was pigment coated or not. Calendering displayed only a minor effect. No clear influence of surface chemical composition of the cartonboards on the adhesive joint strength was found due to the fact that changes in surface chemistry in this study also led to changes in surface roughness. The strongest adhesive joint was created between two medium-rough and surface-sized cartonboards.

  • 16. Nygårds, M
    et al.
    Just, M.
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Tryding, J.
    A finite Element Model for simulations of Creasing and Folding of PaperBoard2005Konferansepaper (Fagfellevurdert)
  • 17.
    Sadek, Mohamed
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Bergström, Jens
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Burman, Christer
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    20 kHz 3-point bending fatigue of automotive steels2018Inngår i: MATEC Web of Conferences, EDP Sciences, 2018, Vol. 165, s. 1-7, artikkel-id 22020Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The 20 kHz load frequency enables fatigue tests for very high cycle fatigue life, 109-1013 cycles, within conveniently short time. In automotive applications, many components are subjected to flexural loading and hence bending fatigue is an important test mode. Ultrasound fatigue test instruments have been used successfully in several assessments of fatigue strength and more commonly in uniaxial loading. Here, a 3-point bending fatigue test rig operating in resonance at 20 kHz load frequency has been designed to test plane specimens at R=0.1 loading. The test rig design and stress calculations are presented. Testing for fatigue strength was conducted using the staircase method with 15 specimens of each steel grade, specimens reaching 108 cycles were considered run-outs giving fatigue strength at 108 cycles. Additional 15 specimens of each grade were tested for S-N curves with the upper limit above 109 cycles. Two different common automotive steels, 38MnSiV5, a micro-alloyed ferritic-pearlitic steel, and 16MnCr5, a carburizing martensitic steel, were tested. The fatigue strengths achieved from the staircase testing are 340 and 419 MPa stress amplitudes for the 38MnSiV5 and 16MnCr5 steels, respectively. The S-N curves of the steels appear to be quite flat in the tested life range 107 - 109.

  • 18.
    Sadek, Mohamed
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Bergström, Jens
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Burman, Christer
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Computation of and testing crack growth at 20 kHz load frequency2016Inngår i: 21ST EUROPEAN CONFERENCE ON FRACTURE, (ECF21) / [ed] F. Iacoviello, L. Susmel, D. Firrao, G. Ferro,, Elsevier, 2016, s. 1164-1172Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Fatigue properties are evaluated in a large span of fatigue lives ranging from a few load cycles to more than 1013 load cycles. If the interest is focused on fatigue lives above 10(7) load cycles, we speak of the very high cycle fatigue (VHCF) range. For evaluation of properties in the VHCF range one often needs to use higher load frequencies to be able to perform testing within a reasonable time. Therefore, the influence of load frequency on fatigue strength and fatigue crack growth is an important issue, both from testing and design perspectives. Within an EU-RFCS research project on the frequency influence on high strength steel fatigue properties the present study has been conducted on fatigue crack growth testing to determine threshold values and crack growth material parameters. The testing was analyzed by FE-computation to determine geometry factors for AK-determination. The testing was performed in a 20 kHz ultrasound resonance instrument. In such a system the whole load train needs to be designed to run at a resonance frequency of 20 kHz, and it implies that the specimen needs to be designed and computations performed by dynamic computational methods. As the crack grows the dynamic response of the specimen will change, and hence calculation to obtain the geometry factor is made with a progressing crack length. A uniaxial tensile load at 20 kHz frequency is applied to a single edged notched side-grooved flat specimen. The specimen dimensions are calculated in order to have a resonance frequency of 20 kHz, which is the frequency used for the experiments. Dynamic FEM computation, with a 3D-model and a quarter symmetry was used with one of the symmetry planes parallel to and in the crack growth line. To avoid crack surface interpenetration during the simulations a rigid thin sheet was introduced and used as a counter-face to the crack surface. The solution obtained was then combined with the breathing crack model proposed by Chati et. al. (1997) in order to solve for the irregularities observed when crack surface interpenetration occurs. Finally, the whole load train was considered. Thus, also the computed frequencies were very close to frequencies observed in experiments. The computation of stress intensities was made for varying crack lengths in a series of simulations. The geometry factor relation was determined and used in 20 kHz crack growth testing to control the actual stress intensity at the advancing crack tip. Comparison of computations and experimental results were made.

  • 19.
    Sadek, Mohamed
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Bergström, Jens
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Burman, Christer
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Crack growth rates and mechanisms in 20 kHz FCP testing of automotive steels2019Inngår i: Proceedings of the 13th International Conference on the Mechanical Behaviour of Materials, 2019, Melbourne: ICM13 conference proceeding , 2019, , s. 10Konferansepaper (Fagfellevurdert)
    Abstract [en]

    During the past decades, Very High Cycle Fatigue (VHCF) research has developed into an active and prioritized research area. An increased interest in testing up to 107-1010 load cycles, realized within a reasonably short amount of time, has been enabled by the development of 20-30 kHz ultrasonic fatigue testing equipment. Here, a study is presented on fatigue crack propagation at 20 kHz of three different automotive steels tested at R=-1 and R=-0.24 load ratios. However, the high load rates provokes new challenges, as theoretically finding the best practice method to compute the stress intensity factor considering 20 kHz dynamic effects (inertia forces and damping). Calibrating the fatigue load system, monitoring, controlling and performing precise measurements of the growing crack during the tests are some examples of experimental challenges encountered. Here, a best practice method for computing the stress intensity factor is presented together with a complete 20 kHz fatigue crack growth testing procedure.Three different bar steel grades have been tested; a ferritic-pearlitic, a quenched and tempered martensitic and a carburizing steel grade. Crack propagation test results differentiated between the three steel grades and were depending on load ratio R. The obtained test results at 20 kHz were found to agree with results of the same steel grades tested at conventionally used load frequencies. The SEM fractography analysis revealed ductile transgranular crack propagation mechanisms, also this in agreement with the same steel grades tested at lower frequencies.

  • 20.
    Tofique, Muhammad Waqas
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik.
    Bergström, Jens
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap.
    Burman, Christer
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik.
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap.
    Gåård, Anders
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Fatigue strength, crack initiation, and localized plastic fatigue damage in VHCF of duplex stainless steels2016Inngår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 87, nr 7, s. 899-910Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The fatigue strength of two-duplex stainless steel grades, 2304 SRG and LDX 2101, with austenitic–ferritic microstructure is tested using ultrasonic fatigue testing equipment operating at 20 kHz. The testing is conducted in tension-compression mode with the load ratio R=-1. The fatigue strength is evaluated at 107, 108, and 109 load cycles and the estimates of fatigue strength are higher for the LDX 2101 grade. The fatigue crack initiation mechanisms are analyzed using a scanning electron microscope. The fatigue cracks, in all cases, appear to initiate due to accumulation of plastic fatigue damage at the surface. In the 2304 SRG grade, accumulation of fatigue damage occurs at the external surface of fatigued specimens in the form of extrusions at the grain/phase boundaries and in the form of individual slip lines in the austenite phase. Meanwhile, in the LDX 2101 grade accumulation of plastic fatigue damage in the form of extrusions and intrusions occurs mainly within the ferrite grain. When the crack is microstructurally short, the crack growth appears to be crystallographic in nature and the crack appears to change its direction propagating from one grain into another.

  • 21.
    Tofique, Muhammad Waqas
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Bergström, Jens
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Burman, Christer
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Fatigue initiation and strength of duplex stainless steel strip specimens in the very high cycle fatigue regime2014Inngår i: Very high cycle fatigue 6 (VHCF6), 2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Fatigue studies of cold-rolled duplex stainless strip steel were performed in the very high cycle fatigue life region. The duplex austenitic-ferritic microstructure gives this grade a combination of high mechanical strength and high corrosion resistance. Fatigue properties of thin steel strips are particular due to cold rolling introducing a very fine microstructure. Crack initiation and fatigue strength are controlled by steel microstructure and alloying. The initiation and growth of the very short initial fatigue crack in very high cycle fatigue are unclear and subject to different descriptions. Fatigue test data of thin strip specimens at very high fatigue lives are scarce due to testing difficulties. For practical reasons testing must be performed at ultrasound test frequencies which involves fixturing problems. A test setup including the load chain ultrasonic horn, fixture and specimen was designed for resonance with a horse-shoe design of a screw fixture. The design of the horse-shoe fixture and the specimens along with FEM calculation of eigenfrequency are presented. Fatigue testing was performed at 20 kHz in R=-1 conditions up to fatigue life of 107 to 5*109 cycles. Fatigue strength was tested and crack initiation was studied on the fracture surface using FEG-SEM at the initiation site.

  • 22.
    Tofique, Muhammad Waqas
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Materialvetenskap. Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Development of the distributed dislocation dipole technique for the analysis of closure of complex fractures involving kinks and branches2018Inngår i: European journal of mechanics. A, Solids, ISSN 0997-7538, E-ISSN 1873-7285, Vol. 69, s. 168-178Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the development of the distributed dislocation dipole technique (DDDT) for the analysis of straight, kinked and branched cracks where parts of the cracks may close during loading. The method has been developed for plane problems. Crack cases in which closure occurs are analyzed by reformulating the Buecicner's principle, taking into account the contact stresses at the contacting portions of the crack surfaces. Stress intensity factors corresponding to opening and the in-plane sliding mode of deformation at the crack tips are computed. Several test cases involving straight, kinked and/or branched cracks where parts of the cracks undergoes crack surface closure when subjected to the outer loading are analyzed. The results obtained from the DDDT are compared to those obtained from a Finite Element Method (FEM) analysis of the same crack cases. This comparison shows that the computation of stress intensity factors for the cases involving crack surface closure are less accurate than those for fully open crack cases. However, for the cases under consideration, the stress intensity factors were still computed with a maximum difference of approximately 2 per cent compared to the FEM calculations if Jacobi polynomial expansions of at least the twelfth order were used to represent the crack surface opening and sliding displacements. In most cases under consideration, sixth order Jacobi polynomial expansions were sufficient to obtain results within that margin of deviation.

  • 23.
    Tofique, Muhammad Waqas
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Hallbäck, Nils
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Development of the distributed dislocation dipole technique for the analysis of closure of complex fractures involving kinks and branchesManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    This paper presents the development of the distributed dislocation dipole technique (DDDT) for the analysis of crack surface closure of crack cases involving kinks and branches. Crack cases in which closure occurs are analyzed by reformulating the Bueckner's principle taking the contact stresses at the contacting portions of the crack surfaces into account. Stress intensity factors corresponding to opening and sliding mode of deformation at the crack tips are computed. Three test cases involving kinked and/or branched cracks with at least one of the crack segments undergoing crack surface closure when subjected to remote tensile loading are analyzed. The results obtained from the DDDT are compared to those obtained from the Finite Element Method (FEM) analysis of the same crack cases. This comparison shows that the computation of stress intensity factors for the crack cases involving crack surface closure are less acurate compared to fully open crack cases. However, the stress intensity factors are still computed to an accuracy of within 2 percent if the Jacobi polynomial expansions of at least the sixth order are used to represent the crack surface opening and sliding displacements. Higher order Jacobi polynomials lead to increased accuracy.

1 - 23 of 23
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