Endre søk
Begrens søket
12 1 - 50 of 90
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.
    Alfredsson, Bo
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Fretting fatigue of a shrink-fit pin subjected to rotating bending: Experiments and simulations2009Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 31, nr 10, s. 1559-1570Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fretting fatigue initiation was studied for a shrink-fit pin at rotating bending. Eight assemblies with four different grips were manufactured from soft normalized steel and tested at loads well below bending endurance. All pins displayed rust-red fretting oxides deep into the contact and black oxidised fretting scars with fretting fatigue cracks at the rim. The slip evolution was simulated in a three-dimensional FE model including assembly, bending and sufficiently many rotations to reach a steady-state. The extension of cyclic slip agreed with the black oxidised scar. Deeper into the contact a monotonic slip developed to the positions with rust-red oxides. Asymmetric slip and traction on the interface sides together with a slight twist of the pin in the hub and the slip development process, illustrated that a three-dimensional analysis was required for the interface. Both the stress amplitude and the Findley multi-axial criterion predicted fretting fatigue of the pin although the rotating bend stress was well below the endurance limit.

  • 2.
    Alfredsson, Bo
    et al.
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Cadario, Alessandro
    KTH, Tidigare Institutioner, Hållfasthetslära.
    A study on fretting friction evolution and fretting fatigue crack initiation for a spherical contact2004Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 26, nr 10, s. 1037-1052Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new design for fretting experiments is presented. The normal and tangential contact loads as well as the specimen bulk stress are separately controlled. The separate control of load systems enables more accurate simulations of the fretting situations in component interfaces. Also, the influence of the salient parameters can be investigated individually. The initial test series comprised a spherical indenter and constant normal load and bulk stress. The evolution of the slip zone coefficient of friction at a spherical fretting contact was evaluated in four different ways. For two of these methods new equations were derived. The importance of a correct coefficient of friction and the advantages of each evaluation method are discussed. The experimental results were evaluated with respect to fretting fatigue crack initiation. Five multi-axial fatigue criteria were evaluated and ranked with respect to their ability to predict fretting fatigue initiation properties. The endurance limits of all criteria were too high as compared to the experimental fretting fatigue endurance level. A qualitative explanation for the discrepancy was found in the surface profile of the slip zone.

  • 3.
    Alfredsson, Bo
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Linares Arregui, Irene
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Hazar, Selcuk
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Numerical analysis of plasticity effects on fatigue growth of a short crack in a bainitic high strength bearing steel2016Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 92, s. 36-51Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Plasticity effects on fatigue growth were simulated for a physically short crack. The material description comprised the Drucker-Prager yield surface, non-associated flow rule and non-linear combined hardening. The simulated development of the growth limiting parameter agreed with the experimental crack behaviour with early rapid propagation followed by a transition to slow R-controlled growth. The crack was open to the tip without any crack face closure throughout all load cycles. Instead compressive residual stresses developed at the unloaded tip which supplied an explanation to the slow rate of the propagated short crack in this bainitic high strength bearing steel. The material's strength differential effect was the key difference explaining why compressive residual stresses instead of crack face closure was responsible for the short crack effect in this material.

  • 4.
    Alfredsson, Bo
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Olsson, Erik
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Multi-axial fatigue initiation at inclusions and subsequent crack growth in a bainitic high strength roller bearing steel at uniaxial experiments2012Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 41, s. 130-139Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The behaviour of inclusion initiated fatigue was studied for a high strength bearing steel with a bainite micro-structure. The analysis included experiments and numerical simulations. It was realized that the stress-state was multi-axial in the matrix material that met the inclusion also for a uniaxial far field stress. Fatigue initiation risk at the interface between the inclusion and matrix material was therefore predicted with the Findley multi-axial critical plane criterion. The fatigue parameters were determined from independent experiments on smooth specimens with tensile surface stress gradients. Crack growth from the inclusion to final rupture was modelled as a penny shaped crack with closure compensated effective material parameters. The growth simulations suggested that the majority of the fatigue life was consumed as fatigue crack initiation at the non-metallic inclusion.

  • 5.
    Alfredsson, Bo
    et al.
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Olsson, Mårten
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Applying multiaxial fatigue criteria to standing contact fatigue2001Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 23, nr 6, s. 533-548Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The ability of some multiaxial fatigue criteria to predict initiation of standing contact fatigue cracks is investigated. In the standing contact fatigue test an indenter subjects a case-hardened rest specimen to a stationary but pulsating contact load. The initiation of two axi-symmetric crack types appearing in the test specimen is investigated. The surface initiated ring/cone cracks circumscribe the contact area, whereas the lateral cracks are horizontal sub-surface cracks. The effect of the stress-state history at possible crack Locations is evaluated through the Sines, Haigh principal stress, Findley, Me Diarmid and Dang Van multiaxial fatigue criteria. The material fatigue parameters of each criterion are determined from independent bending and torsion fatigue testing. Finally, the mean and spread in radial position of the ring/cone crack are evaluated by considering the statistical effects of a weakest link assumption using a three parameter Weibull distribution. The investigation shows that it is hard to distinguish a single criterion that well describes all aspects of the experimental results. For the current contact situation with highly compressive mean stresses in combination with tensile maximum values the Findley criterion shows the best overall performance followed by the Haigh principal stress criterion

  • 6.
    Alfredsson, Bo
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Wåtz, Veronica
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Olsson, Erik
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Fatigue crack initiation and growth at holes in a high strength bainitic roller bearing steel when loaded with non-proportional shear and compressive cycles2011Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 33, nr 9, s. 1244-1256Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fatigue initiation from an artificial defect was investigated for a bainitic high strength roller bearing steel. Thin walled pipe specimens with small holes were subjected to multi-axial and non-proportional load cycles. The experimental fatigue crack positions around the hole were predicted with the Findley critical plane criterion. The criterion also ranked the severeness of three load sequences with respect to fatigue risk. Crack growth simulations and crack life measurements with strain gauges confirmed the ranking between the load sequences. Three uni-axial fatigue series with stress gradients were used to determine surface endurance data for the Findley criterion.

  • 7.
    Alfredsson, Bo
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Öberg, Martin
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Lai, J.
    Propagation of physically short cracks in a bainitic high strength bearing steel due to fatigue load2016Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 90, s. 166-180Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Physically short cracks in a bainitic high strength bearing steel were fatigue loaded. The rapid propagation rate of early open short cracks agreed with that of long closure free cracks. After some rapid growth, the short cracks entered a transition period to the rate of growth limited long cracks. Potential drop showed that the short cracks were open to the tip throughout the growth sequence, which excluded crack face closure in the wake as the growth limiting mechanism in this material. Instead the short crack effect was related to residual stresses and other mechanisms at the crack tip. Crack manufacturing procedures were determined for straight long and short start cracks in the present material. LEFM with effective material parameters and limit compensation predicted the short crack lives.

  • 8. Aygül, M.
    et al.
    Al-Emrani, M.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Leander, John
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Investigation of distortion-induced fatigue cracked welded details using 3D crack propagation analysis2014Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 64, s. 54-66Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The behaviour of distortion-induced fatigue cracks in welded details in an existing bridge was studied analytically by performing crack propagation analysis based on linear elastic fracture mechanics. The real load history of the bridge was obtained from strain measurements. These loads were utilised to examine the crack growth rate and the residual service life of the cracked detail. Moreover, the effectiveness, accuracy and applicability of the crack propagation analysis on bridge structures were investigated by simulating a complex case of fatigue cracking using several crack propagation analyses. The results of the analyses revealed that the fatigue crack in the studied details had significantly different crack growth characteristics in different directions. In the thickness direction, for instance, the crack was seen to propagate at a certain rate, which increased with the propagated crack from the beginning and, as expected, the crack propagation rate decreased when the crack grew longer. The crack was subsequently arrested half way through the thickness of the plate. In the longitudinal direction, the crack was not, however, arrested in the same way as in the thickness direction and it continued to propagate at a reduced yet constant crack growth rate. The results also revealed that, even though distortion-induced fatigue cracking was usually caused by a mixed-mode condition (i.e. a combination of modes I, II and III), the governing propagation mode is still mode I. Furthermore, it was also observed that the contribution of modes II and III to crack propagation was very little and dependent on the location of the propagated crack front, as well as the geometrical configuration of the cross-beam.

  • 9.
    Azar, Amin S.
    et al.
    SINTEF Mat & Chem, Oslo, Norway.
    Svensson, Lars-Erik
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avd för industriell produktion.
    Nyhus, Bård
    SINTEF Mat & Chem, Oslo, Norway.
    Effect of crystal orientation and texture on fatigue crack evolution in high strength steel welds2015Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 77, s. 95-104Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present study, electron backscattered diffraction is used to analyze the fatigue crack evolution in a high strength steel weld that was loaded cyclically in the plastic regime. Three prominent regions of a fatigue crack are investigated separately: crack tip, crack trajectory and crack initiation. Taylor and Schmid factors are mapped with respect to the defined loading matrix. Possible effective mechanisms are proposed based on the local plasticity properties like lattice rotation and misorientation. The analyses of the crack tip and trajectory regions show that although the critical resolved shear stresses in some regions are low, small deformation resistance of these regions can compromise the dislocation immobility and cause local fracture. It is shown that if the crack grows transgranularly, at least one side of the crack may show low lattice rotation or strain equivalent values, which indicates the relaxation of elastic stresses after fracture. The crack initiation is determined to be dominantly controlled by transcrystalline mechanism of initiation that takes place under plastic loading conditions. It is also shown that the secondary < 123 >11 (1) over bar type of slip systems were the most activated under such loading conditions. (C) 2015 Elsevier Ltd. All rights reserved.

  • 10. Baumgartner, J.
    et al.
    Yıldırım, H. C.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Fatigue strength assessment of TIG-dressed welded steel joints by local approaches2019Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 126, s. 72-78Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fatigue strength assessment methods by local approaches are widely used in the literature. This paper provides a comprehensive evaluation of published data for welded steel joints improved by TIG dressing methods. Fatigue classes for the local assessment methods with the available fatigue data are recommended. The available fatigue data extracted for transverse non-load carrying welds, cruciform joints as well as butt joints. In total, 17 published test series of weld details with various yield strengths and stress ratios are presented. Fatigue strength assessment is performed by considering the weld profile geometry within Finite Element models and taking the resulting stress gradients as basis for the evaluation. In addition, the influence of the steel grade is included. The most reliable results are derived by using the critical distance approach. Fatigue classes and critical distances are recommended as a result of the evaluations.

  • 11.
    Busse, Christian
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Palmert, Frans
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Sjodin, B.
    Siemens Ind Turbomachinery AB, Sweden.
    Almroth, P.
    Siemens Ind Turbomachinery AB, Sweden.
    Gustafsson, D.
    Siemens Ind Turbomachinery AB, Sweden.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Leidermark, Daniel
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Evaluation of the crystallographic fatigue crack growth rate in a single-crystal nickel-base superalloy2019Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 127, s. 259-267Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cracks in single-crystal nickel-base superalloys have been observed to switch cracking mode from Mode I to crystallographic cracking. The crack propagation rate is usually higher on the crystallographic planes compared to Mode I, which is important to account for in crack growth life predictions. In this paper, a method to evaluate the crystallographic fatigue crack growth rate, based on a previously developed crystallographic crack driving force parameter, is presented. The crystallographic crack growth rate was determined by evaluating heat tints on the fracture surfaces of the test specimens from the experiments. Complicated crack geometries including multiple crystallographic crack fronts were modelled in a three dimensional finite element context, The data points of the crystallographic fatigue crack growth rate collapse on a narrow scatter band for the crystallographic cracks indicating a correlation with the previously developed crystallographic crack driving force.

  • 12.
    Chai, Guocai
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. R&D Center, Sandvik Materials Technology, Sandviken, Sweden.
    Forsman, Tomas
    R&D Center, Sandvik Materials Technology, Sandviken, Sweden.
    Gustavsson, Fredrik
    R&D Center, Sandvik Materials Technology, Sandviken, Sweden.
    Microscopic and Nanoscopic Study on Subsurface Damage and Fatigue Crack Initiation During Very High Cycle Fatigue2016Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 83, nr 2, s. 288-292Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    “Fish eye” is a typical phenomenon of fatigue crack initiation at a subsurface defect such as inclusion during very high cycle fatigue. The formation of a fine grained area and micro-debonding is believed to cause fatigue crack initiation. This paper provides a basic study on the formation of the fine grained area in a martensitic stainless steel during very high cycle fatigue using scanning electron microscopy, SEM, focused ion beam technique, FIB, electron backscatter diffraction, EBSD, and electron channeling contrast imaging, ECCI. The results show that the formation of a fine grained zone is a local behavior. The fine grained zone is very near the fatigue crack initiation origin. In the transversal direction (cross section), the depth of the fine grained zone is only few micrometers. In the longitudinal direction (crack propagation direction), the depth of the fine grain zone is about one micrometer. ECCI analysis shows that in the fine grained area with high retained strain, high plastic deformation can be found. Dislocation slip bands can be observed. They interact with grain boundaries and cause the formation of damage due to impingement cracking. The results indicate that occurrence of plastic deformation in metallic material during very high cycle fatigue is very localized, mainly near the front of the crack tip or a defect.

  • 13.
    Dahlberg, Johan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Alfredsson, Bo
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Influence of a single axisymmetric asperity on surface stresses during dry rolling contact2007Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 29, nr 5, s. 909-921Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect from contact loading of some single axisymmetric asperities as a potential mechanism for surface initiated rolling contact fatigue was investigated numerically using FEM. Computational results were compared to properties of some rolling contact fatigue craters, or spalls, in the teeth surfaces of four driving gear wheels. The gears were geometrically identical but had experienced slightly varying load conditions. The residual surface stresses of a used teeth with spalls were measured using the hole drilling technique. The combined cylinder asperity contact was first modelled with a stationary model in which an asperity was introduced at the contact rim. By varying asperity height, width, position and contact load dangerous asperity configurations were sought for. The gear contact close to the rolling circle was modelled as two rolling cylinders. A single asperity was introduced into the contact surface of one of them. Due to the presence of the asperity a three-dimensional contact model was required. The simulation included residual stresses from heat treatment and plastic deformation due to the first roll cycle. Thus, the stress results were computed from the second roll cycle. The important overall conclusion was that a single asperity may serve as a stress raiser in the contact surfaces. Furthermore, the computed values of the increased surface stresses were comparable to those that are reported in the literature to give cracks. Example of dangerous asperity dimensions were noted and changes in residual stresses from moderate plastic deformation during rolling were estimated. The asperity deformed plastically during over-roll but remained sufficiently high. The trajectory of the largest principal stress was computed, starting from the position in front of a loaded asperity with maximum tensile stress. The trajectory was compared to the spalling entry angle of a representative spall. For some asperity-cylinder configurations a convex region with large stress was found in the surface. The presence of such a convex stress region was compared to the convex shaped of the spalling tip that sometimes could be found.

  • 14.
    Dahlberg, Johan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Alfredsson, Bo
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Surface stresses at an axisymmetric asperity in a rolling contact with traction2008Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 30, nr 9, s. 1606-1622Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Rolling contact between a smooth cylinder and a cylinder with an axisymmetric surface asperity was modelled numerically. The influence of tangential slip and friction was investigated through relative contact movement between the cylinders. As the asperity entered the rolling contact it acted as a point type contact force, which gave a tensile surface stress in the forward rolling direction. The tensile stress maximum was greatly influenced by slip and coefficient of friction.

    Data for the simulations were captured from a gear example with surface initiated rolling contact fatigue or spalling. The cylindrical contact load and geometry corresponded to that at the roll-circle of the gear. The geometrical properties of the asperity were based on surface profiles of the gear flank. The combined isotropic and non-linear kinematic Chaboche material model was used with parameters determined from cyclic compression-tension tests on the gear material. The residual stress profile due to heat-treatment of the gear was included into the model.

    Two different frictional set-ups were investigated. One contained a non-zero coefficient of friction throughout the rolling contact. This was believed to compare to dry contacts. The other set-up was supposed to model lubricated rolling with asperity break-through to metal contact. Here friction was non-zero on the asperity and zero elsewhere in the contact. With traction throughout the cylindrical contact a sufficiently long start distance had to be travelled before the asperity interaction. Thus, the transient rolling distance was determined together with the slip limit for sliding in the cylindrical contact. Numerical predictions of residual stresses and surface distress angles suggested that the asperity friction model agreed with gear conditions.

    Evaluation of elastic-plastic asperity indentation suggested that the asperity deformation was approximately as severe as repeated macro-scale experiments with fatigue cracks. Since the stresses at the asperities were of the same size as those at the repeated indentations and since the Findley multi-axial fatigue criteria predicted fatigue damage, it was concluded that the stresses in front of the asperity could be sufficient to initiate rolling contact fatigue cracks in applications. The influences of some parameters on the stress maximum were also evaluated.

  • 15.
    Dahlin, Peter
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Olsson, Mårten
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Fatigue crack growth: mode I cycles with periodic mode II loading2008Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 30, nr 5, s. 931-941Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of periodic Mode II loading on Mode I fatigue crack growth is studied using a new type of loading device. The average rate of crack growth is found to be governed mainly by four parameters; Delta K-I and the Mode I R-ratio, the magnitude of the Mode II load and the Mode II period, M (M = number of Mode I load cycles per Mode II load). The Mode 11 load has to be large enough to create residual tangential displacements of the crack faces otherwise no effect occurs at all. Two mechanisms are found, Mode II-induced crack closure that reduces the crack propagation rate (long range) and a mechanism that increases the growth rate temporarily at every Mode I I load (short-range). For a specific Mode I load and Mode I I magnitude, it is possible to find a minimum crack growth rate for a certain Mode II period, M-opt. At high R-ratios the Mode II-induced closure mechanism disappears, but the temporary increase in growth rate at every Mode II load is still active. A semi-analytical model for the average crack growth rate during sequential Mode I and Mode II loading is presented.

  • 16.
    Dahlin, Peter
    et al.
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Olsson, Mårten
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Reduction of mode I fatigue crack growth rate due to occasional mode II loading2004Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 26, nr 10, s. 1083-1093Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of mode 11 loading on subsequent mode I crack growth is experimentally investigated on steel AISI 01. The results show that the mode I crack growth rate decreases after a single mode 11 load cycle. This effect remains also after the crack has propagated through the mode 11 plastic zone. The crack growth reduction is shown to be caused by crack closure due to tangential displacement of crack-surface irregularities. The durability of this reduction has a decisive influence on the fatigue life when the mode I R-ratio is not as high as to keep the entire load cycle above the closure level.

  • 17.
    Ericsson, Mats
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Jin, Lai-Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Sandström, Rolf
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Fatigue of friction stir welded T-joints2005Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452Artikkel i tidsskrift (Annet vitenskapelig)
  • 18.
    Ericsson, Mats
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Jin, Lai-Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Sandström, Rolf
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Fatigue properties of friction stir overlap welds2007Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 29, nr 1, s. 57-68Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Friction stir welding (FSW) is currently used for many applications involving lap or T-joints, e.g. hermetically closed boxes such as cooling elements and heat exchangers. The frequent pressure changes in these make them susceptible to fatigue. The fatigue characterization of lap joints involves a combination of shear and bending. Forces applied to the ends of lap joints result in non-axial stresses in the connection area. FSW lap joints of Al-Mg-Si alloy 6082 in the artificially aged condition T6 were studied. A pin (probe) based on the Triflute (TM) concept was used with two modifications to the pin, the pin end being either convex or concave. Tool shoulders of 15 and 18 turn respectively were utilized, producing four different weld series. Fracture was initiated in the highly stressed area where the weld cuts through the interface between the two sheets. The cracks typically propagated through the weld in the upper sheet (tool side). The broadest tool shoulder with a concave end of pin design gave the best fatigue performance. This was due to an improved flow path provided by the hollowed out end of the pin; allowing material flow around the pin which resulted in minimal hooking of the sheet interface adjacent to the weld nugget. Additionally heat energy was supplied by the increased contact area. The stress intensity factor Delta K was determined. It was found that a simplified approach, developed to estimate Delta K for overlap spot welds, could be applied to friction stir overlap joints. The corresponding crack propagation rates were in fair accordance with the experimental results.

  • 19.
    Ericsson, Mats
    et al.
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Sandström, Rolf
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Influence of welding speed on the fatigue of friction stir welds, and comparison with MIG and TIG2003Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 25, nr 12, s. 1379-1387Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The objective of this investigation was to determine whether the fatigue strength of friction stir (FS) welds is influenced by the welding speed, and also to compare the fatigue results with results for conventional arc-welding methods: MIG-pulse and TIG. The Al-Mg-Si alloy 6082 was FS welded in the T6 and T4 temper conditions, and MIG-pulse and TIG welded in T6. The T4-welded material was subjected to a post-weld ageing treatment. According to the results, welding speed in the tested range, representing low and high commercial welding speed, has no major influence on the mechanical and fatigue properties of the FS welds. At a significantly lower welding speed, however, the fatigue performance was improved possibly due to the increased amount of heat supplied to the weld per unit length. The MIG-pulse and TIG welds showed lower static and dynamic strength than the FS welds. This is in accordance with previous comparative examinations in the literature on the fatigue strength of fusion (MIG) and FS welds. The TIG welds had better fatigue performance than the MIGpulse welds. The softening, of the alloy around the weldline has been modelled. Using a model without adjustable parameters, a fair description of the hardness profiles across the weld as a function of welding speed was obtained. The softening in front of the Friction Stir Welding tool was also estimated. At the low and high welding speeds a full and partial softening is predicted, respectively.

  • 20.
    Eriksson, Robert
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Chen, Zhe
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    A low cycle fatigue life model for a shot peened gas turbine disc alloy2019Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 124, s. 34-41Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Turbine disks in gas turbines are subjected to cyclic load at high temperature, making, especially the fir tree type blade attachments, susceptible to fatigue. Shot peening of the fir tree attachments may be used to increase the fatigue life by introducing compressive residual stresses. In the current study, both polished and shot peened notched specimens made from alloy 718 were subjected to low cycle fatigue at 450-550 degrees C. The shot peening generally increased the fatigue life, although the effect diminished for high loads. It was shown that the effect of shot peening could be handled as mean stress effects in a life model based on a Smith-Watson-Topper (SWT) type parameter, sigma(max)Delta epsilon/2. A material model which captured the mean stress was set up to get the SWT parameter at the notch root. It was shown that thermal relaxation of residual stresses and initial strain hardening from cold work could be excluded from the finite element analysis used to establish the mean stress; this since the plasticity in the first cycle dominated the plastic deformation of the specimen. Overall, the SWT-based life model worked satisfactorily. However, the prediction of correct mean stresses at 550 degrees C proved somewhat difficult as the degree of mean stress relaxation at this temperature varies widely in available literature data.

  • 21.
    Ewest, D.
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten. Siemens Ind Turbomachinery AB, Sweden.
    Almroth, P.
    Siemens Ind Turbomachinery AB, Sweden.
    Sjodin, B.
    Siemens Ind Turbomachinery AB, Sweden.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Leidermark, Daniel
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    A modified compliance method for fatigue crack propagation applied on a single edge notch specimen2016Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 92, s. 61-70Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Crack length measurements with high accuracy are often difficult to achieve during fatigue crack propagation testing under non-isothermal conditions. In this work a modified approach to the compliance method defined in e.g. ASTM E647 is described, which is better suited for high loads, varying temperatures and for taking the scatter in Youngs modulus into account. A numerical finite element study is performed for a single edge notch specimen, to investigate the influence of initiation locations on the accuracy of the method. The change in cracked area versus change in stiffness for three different cases are numerically shown to collapse to one curve, i.e. the result is not significantly affected by how the crack is initiated. The numerical study is compared to results from two experiments using different materials, with heat tinting during the tests for extracting snapshots of the crack fronts. A good agreement between the experiments and the numerical study is shown. A new compliance curve and a new geometry function for the stress intensity factor is proposed for the single edge notch specimen. (C) 2016 Elsevier Ltd. All rights reserved.

  • 22.
    Ewest, Daniel
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten. Siemens Ind Turbomachinery AB,Finspång, Sweden.
    Almroth, P.
    Siemens Ind Turbomachinery AB, Finspång, Sweden.
    Leidermark, Daniel
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjodin, B.
    Siemens Ind Turbomachinery AB, Finspång, Sweden.
    Fatigue crack propagation in a ductile superalloy at room temperature and extensive cyclic plastic flow2015Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 80, s. 40-49Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fatigue crack propagation experiments under both force and displacement control have been performed on the wrought superalloy Haynes 230 at room temperature, using a single edge notched specimen. The force controlled tests are nominally elastic, and the displacement controlled tests have nominally large plastic hysteresis at the beginning of the tests, but saturates towards linear elastic conditions as the crack grows. As some tests are in the large scale yielding regime, a non-linear fracture mechanics approach is used to correlate crack growth rates versus the fracture parameter Delta J. It is shown that crack closure must be accounted for, to correctly model the crack growth seen in all the tests in a unified manner. For the force controlled small scale yielding tests the Newman crack closure model was used. The Newman equation is however not valid for large nominal cyclic plasticity, instead the crack closure in the displacement controlled tests is extracted from the test data. A good agreement between all tests is shown, when closure is accounted for and effective values of Delta J are used.

  • 23.
    Ewest, Daniel
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten. Siemens Ind Turbomachinery AB, Sweden.
    Almroth, P.
    Siemens Ind Turbomachinery AB, Sweden.
    Sjodin, B.
    Siemens Ind Turbomachinery AB, Sweden.
    Leidermark, Daniel
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Isothermal and thermomechanical fatigue crack propagation in both virgin and thermally aged Haynes 2302019Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 120, s. 96-106Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fatigue crack propagation tests under both isothermal and non-isothermal thermomechanical fatigue conditions have been performed on wrought Haynes 230, a ductile combustor material. A number of specimens were thermally aged by pre-straining and subsequent furnace exposure for 3000 h at 600 degrees C. The tests were performed both under load and strain control, between room temperature and 600 degrees C. The thermally aged notched specimens show a decrease in the crack initiation life, similar to results previously reported for smooth test specimens at room temperature. For the crack growth rates, the effects of thermal ageing were less pronounced than for crack initiation. Further, the tests have been simulated using the finite element method to calculate the crack driving force, where the plasticity induced crack closure is handled with a full history description. A temperature dependent linear kinematic hardening plasticity law has been adopted for describing the material behaviour between room temperature and 600 degrees C. A post-processing tool was used in which the plasticity induced crack opening level was calculated, followed by a calculation of the effective Delta J range for each crack length. The adopted procedure yields good correlation between the different tests, under both isothermal and non-isothermal conditions.

  • 24.
    Gamstedt, E. Kristofer
    et al.
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Sjogren, B. A.
    An experimental investigation of the sequence effect in block amplitude loading of cross-ply composite laminates2002Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 24, nr 04-feb, s. 437-446Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Palmgren-Miner rule has been shown to be inexact in many cases for various composite materials. Several empirical models have been conceived to account for this discrepancy, as well as the effect of block sequence. The approach taken here is based on the underlying mechanisms. A cross-ply laminate was used as a model material. In general, composites show both initiatory and progressive mechanisms under fatigue loading. The former is active at high static stresses, whereas the latter predominates at lower stress amplitudes where they are given sufficient time to propagate, Initiatory mechanisms give rise to damage from which the progressive mechanisms can start, and conversely the progressive mechanisms continually alter the local stress state which results in further damage accumulation caused by the initiation controlled mechanisms. In a cross-ply laminate, the initiatory mechanism is the formation of transverse cracks, and the progressive mechanism is mainly delamination growth initiated from the transverse cracks. In an experimental investigation of carbon fiber/epoxy cross-ply laminates, the interaction of these mechanisms has shown why a sequence of high-low amplitude levels results in shorter lifetimes than a low-high order. Such a sequence effect seems to be a common behavior for many other composite materials, and can be mechanistically explained by a similar kind of interaction. Advantages and drawbacks of the mechanistic approach compared with empirical rules are also discussed.

  • 25.
    Gustafsson, David
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Lundström, Erik
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Correction: Corrigendum to High temperature fatigue crack growth behaviour of Inconel 718 under hold time and overload conditions [Int. J. Fatigue 48 (2013) 178–186]2013Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 52, s. 157-157Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    n/a

  • 26.
    Gustafsson, David
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Lundström, Erik
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    High temperature fatigue crack growth behaviour of Inconel 718 under hold time and overload conditions2013Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 48, s. 178-186Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Inconel 718 is a frequently used material for gas turbine applications at temperatures up to 650°C. For such components, the main load cycle is typically defined by the start-up and shut-down of the engine. In this main loading cycle, hold times at high temperature are commonly present in critical components. These high temperature hold times may greatly increase the fatigue crack growth rate with respect to the number of cycles unless other beneficial factors such as for example initial overloads are present. The latter can be caused by abnormal service conditions but can also occur on a more regular basis and are then typically observed in components with strong thermal transients during engine start-up. In this paper, focus has been placed on the effect of overloads on the hold time fatigue crack growth behaviour and its subsequent description. More specifically, crack propagation in Inconel 718 has been studied at the temperatures 550°C and 650°C with and without an overload at the start of the cycle. The effect of initial overloads was found to be substantial. A simple model for describing the effect of these loading conditions has also been developed based on the concept of the damaged zone, present around the crack tip. Irregular crack fronts and unbroken ligaments left on the fracture surfaces seen in complementary microscopy studies seem to support this approach. Furthermore, the stress state in front of a crack tip in a 2D model was investigated both with and without an initial overload. The results were related to the observed crack growth retardation behaviour found in the material testing.

  • 27.
    Gustafsson, David
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Lundström, Erik
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Modelling of high temperature fatigue crack growth in Inconel 718 under hold time conditions2013Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 52, s. 124-130Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Inconel 718 is a frequently used material for gas turbine applications at temperatures up to 650 °C. The main load cycle for such components is typically defined by the start-up and shut-down of the engine. It generally includes hold times at high temperatures, which have been found to have a potential for greatly increasing the fatigue crack growth rate with respect to the number of load cycles. However, these effects may be totally or partly cancelled by other load features, such as overloads or blocks of continuous cyclic loading, and the actual crack propagation rate will therefore depend on the totality of features encompassed by the load cycle. It has previously been shown that the increased crack growth rate found in hold time experiments can be associated with a damage evolution, where the latter is not only responsible for the rapid intergranular crack propagation during the actual hold times, but also for the increased crack growth during the load reversals. In this paper, modelling of the hold time fatigue crack growth behaviour of Inconel 718 has been carried out, using the concept of a damaged zone as the basis for the treatment. With this conceptually simple and partly novel approach, it is shown that good agreement with experimental results can be found.

  • 28.
    Gustafsson, David
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Johansson, Sten
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Hornqvist, M
    Volvo Aero Corp.
    Mansson, T
    Volvo Aero Corp.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Influence of high temperature hold times on the fatigue crack propagation in Inconel 7182011Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 33, nr 11, s. 1461-1469Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High temperature fatigue crack growth in Inconel 718 has been studied at the temperatures 450 degrees C, 500 degrees C, 550 degrees C and 650 degrees C. The tests were conducted both without hold times and with hold times of different lengths and with a mix of both. Focus has been on quantifying the effect the hold time has upon the crack growth rate and how much it damages the material. Furthermore, it has been investigated how this damage influences the actual cracking behavior, i.e. where in the loading cycle the damage contributes most to the crack growth. This damage is related to the concept of a damaged zone in front of the crack tip. The size of the damaged zone has been derived from the tests and a microscopy study to confirm the findings has also been carried out. It is found that the concept of a damaged zone can be a successful explanatory model for the observed crack growth behavior under high temperature hold time.

  • 29.
    Harati, Ebrahim
    et al.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för svetsteknologi (SV).
    Karlsson, Leif
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för svetsteknologi (SV).
    Svensson, Lars-Erik
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för svetsteknologi (SV).
    Dalaei, Kamellia
    ESAB AB, Lindholmsallen 9, 40227 Gothenburg.
    Applicability of Low Transformation Temperature welding consumables to increase fatigue strength of welded high strength steels2017Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 97, s. 39-47Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Application of Low Transformation Temperature (LTT) consumables in welding is a recent approach to increase the fatigue strength of welds. In this paper high strength steels with yield strengths ranging from 650-1021 MPa were fillet and butt welded using different LTT and conventional consumables. The effects of weld metal chemical composition on phase transformation temperatures, residual stresses and fatigue strength were investigated. Lower transformation start temperatures and hence lower tensile or even compressive residual stresses were obtained close to the weld toe for LTT welds. Fatigue testing showed very good results for all combinations of LTT consumables and high strength steels with varying strength levels. For butt welds, the characteristic fatigue strength (FAT) of LTT welds at 2 million cycles was up to 46% higher when compared to corresponding welds made with conventional filler materials. In fillet welds, a minimum FAT improvement of 34% and a maximum improvement of 132% was achieved when using LTT wires. It is concluded that different LTT consumables can successfully be employed to increase fatigue strength of welds in high strength steels with yield strength up to 1021 MPa. Weld metals with martensite transformation start temperatures close to 200°C result in the highest fatigue strengths.

  • 30.
    Harati, Ebrahim
    et al.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avd för tillverkningsprocesser.
    Karlsson, Leif
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avd för tillverkningsprocesser.
    Svensson, Lars-Erik
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avd för tillverkningsprocesser.
    Dalaei, Kamellia
    ESAB AB, Gothenburg.
    The relative effects of residual stresses and weld toe geometry on fatigue life of weldments2015Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 77, s. 160-165Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The weld toe is one of the most probable fatigue crack initiation sites in welded components. In this paper, the relative influences of residual stresses and weld toe geometry on the fatigue life of cruciform welds was studied. Fatigue strength of cruciform welds produced using Low Transformation Temperature (LTT) filler material has been compared to that of welds produced with a conventional filler material. LTT welds had higher fatigue strength than conventional welds. A moderate decrease in residual stress of about 15% at the 300 MPa stress level had the same effect on fatigue strength as increasing the weld toe radius by approximately 85% from 1.4 mm to 2.6 mm. It was concluded that residual stress had a relatively larger influence than the weld toe geometry on fatigue strength.

  • 31.
    Harati, Ebrahim
    et al.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för svetsteknologi (SV).
    Svensson, Lars-Erik
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för svetsteknologi (SV).
    Karlsson, Leif
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för svetsteknologi (SV).
    Widmark, Mattias
    Material Technology, Volvo Group Trucks Technology, Gothenburg, Sweden.
    Effect of high frequency mechanical impact treatment on fatigue strength of welded 1300 MPa yield strength steel2016Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 92, s. 96-106Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High frequency mechanical impact (HFMI) is a recent post weld treatment method which can be employed to increase the fatigue strength of welded components. In this paper the fatigue strength of as-welded and HFMI treated fillet welds in a 1300 MPa yield strength steel was compared. Fatigue testing was done under fully reversed, constant amplitude bending load. Finite element analysis was used to calculate the stress distribution in the weld toe region to permit evaluation of the fatigue data with the effective notch stress approach. As-welded samples showed a mean fatigue strength of 353 MPa and a characteristic fatigue strength of 306 MPa. HFMI treatment increased the mean fatigue strength by 26% and the characteristic fatigue strengths by 3%. The weld toe radii in as-welded condition were large. HFMI only increased the weld toe radii slightly but resulted in a more uniform weld toe geometry along the weld. A depth of indentation in the base metal in the range of 0.15–0.19 mm and a width of indentation in the range of 2.5–3 mm, were achieved. Maximum compressive residual stresses of about 800 MPa in the longitudinal and 250 MPa in the transverse direction were introduced by HFMI treatment, adjacent to the weld toe. The surface hardness was increased in the entire HFMI treated region. It is concluded that the increase in fatigue strength is due to the combined effects of the weld toe geometry modification, increase in surface hardness and creation of compressive residual stresses in the treated region.

  • 32.
    Kahla, Hiba Ben
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Institut Jean Lamour, SI2M, Université de Lorraine.
    Ayadi, Z.
    Edgren, F.
    GKN Aerospace.
    Pupurs, Andrejs
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Statistical model for initiation governed intralaminar cracking in composite laminates during tensile quasi-static and cyclic tests2018Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 116, s. 1-12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A simple model for predicting intralaminar cracking in laminates under cyclic loads is proposed and validated. The model is limited to low stresses and low crack density and is based on the assumption that the non-uniformity of the fiber distribution is the main reason for the observed large variation of cracking resistance along the transverse direction of the layer. Hence, the resistance variation in quasi-static and in cyclic loading can be described by the same parameter. At low crack density the failure resistance variation is more significant than the variation of the stress state in the specimen, the latter becoming dominant at high crack density. At low crack density the Weibull distribution for probability of intralaminar cracking is used for crack density growth simulation during cyclic loading. Assuming the non-uniformity of the fiber distribution as the cause for variation of cracking resistance, the Weibull shape parameter in cyclic loading is the same as in quasi-static loading case while the scale parameter is assumed to degrade with the applied number of cycles and this dependence is described by a power function. Thus, the determination of parameters is partially done using quasi-static tests and partially using cyclic tests, significantly reducing the necessary testing time. The predictions of dependency of the cracking on the stress and number of cycles are validated against experimental observations of cracking in the 90-plies of quasi-isotropic non-crimp fabric (NCF) laminates as well as in tape based cross-ply laminates.

  • 33.
    Kahlin, Magnus
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling. Linköpings universitet, Tekniska fakulteten. Saab AB, Aeronaut, SE-58188 Linkoping, Sweden.
    Ansell, Hans
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten. Saab AB, Aeronaut, SE-58188 Linkoping, Sweden.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Fatigue behaviour of additive manufactured Ti6Al4V, with as-built surfaces, exposed to variable amplitude loading2017Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 103, s. 353-362Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Additive Manufacturing (AM) allows for great design freedom compared to conventional manufacturing. This is very attractive for the aerospace industry in which AM could contribute to lightweight designs and thereby reduce fuel consumption, increase payload and extend flight range. The fatigue behaviour for rough as-built AM surfaces has previously been characterized with constant amplitude testing but in aerospace applications, most parts are exposed to variable amplitude loading. The fatigue behaviour for variable amplitude is not always consistent with the behaviour for constant amplitude due to effects of overloads and local plastic deformations. Therefore, variable amplitude loading behaviour of laser sintered and electron beam melted Ti6Al4V, with rough as-built surfaces have been investigated in this study using the Short-FALSTAFF (Fighter Aircraft Loading STAndard For Fatigue) load sequence. The predicted and the experimental fatigue life was overall consistent even though most experimental results exceeded the predicted life, especially for the laser sintered material. These findings show that conventional cumulative damage fatigue life predictions give reliable predictions for AM materials with rough as-built surfaces for the type of tension dominated load sequence used. (C) 2017 Elsevier Ltd. All rights reserved.

  • 34.
    Kahlin, Magnus
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Ansell, Hans
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Fatigue Behaviour of Notched Additive Manufactured Ti6Al4V with As-built Surfaces2017Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, nr 101, s. 51-60Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Additive manufacturing (AM) allows the manufacturer to produce parts with complex geometries that are difficult to produce with conventional production methods. Generally, AM is considered to have great potential for the aerospace industry by contributing to reduced weight and lower costs. There are a number of challenges to be solved before AM can be fully utilized in the aerospace industry, and the understanding of fatigue behaviour is one of the major challenges. Although the fatigue properties of flat additive manufactured specimens with rough as-built surfaces already have been widely studied, in practice, few aerospace components have a simple flat geometry with no corners or radii that would act as stress concentrations. Therefore, the combined effect on fatigue life of a rough as-built surface and a geometrical notch needs to be established. In this study, the fatigue properties of both laser sintered and electron beam melted Ti6Al4V have been investigated and a combined effect of a rough as-built surface and a geometrical notch has been determined. In addition, hot isostatic pressing was found to have no impact on fatigue life for rough as-built surfaces. These findings can be directly applied to predict fatigue behaviour of an AM industrial component.

  • 35.
    Karlén, Kristoffer
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Olsson, Mårten
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    A probabilistic model for the entire HCF domain based on equivalent stress - Simulations and experiments2012Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 36, nr 1, s. 9-17Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A probabilistic model for fatigue life is presented. It allows for inhomogeneous stress fields. The stressing of the whole body is summarized in an equivalent stress. The model is calibrated with experiments and can be formulated for a variety of different types of equivalent stresses (point, gradient, area and volume). Finite life experiments at constant load levels as well as tests around the infinite life fatigue limit are used. Using this new model, the PES-model (Probabilistic and based on Equivalent Stress), it is shown that the choice of equivalent stress has a small influence on the fit for finite fatigue life, i.e. the constant load level results. The fit for all tested equivalent stresses are similar over the entire failure probability domain. For the fatigue limit part, however, there is a larger difference between the choices of equivalent stress. It is found that a gradient adjusted point stress is most suited for the PES-model, and that it can be used in the entire SN-domain.

  • 36.
    Karlén, Kristoffer
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Olsson, Mårten
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    A study of the volume effect and scatter at the fatigue limit: experiments and computations for a new specimen with separated notches2011Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 33, nr 3, s. 363-371Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper a new fatigue specimen is presented that has been developed in order to conduct detailed investigations of the volume effect and the scatter of fatigue data in the fatigue limit regime The specimen has two separated notches A and B with different size of the loaded volume associated with them respectively By changing the location of the applied load the fatigue failure in the experiments can be controlled to occur in either notch A or B Comparisons were made with simulations based on statistical weakest link (WL) theory In the weakest link statistics the three parameter Weibull distribution is used for estimation of the fatigue failure probability It is shown that the predictive capability of WL-models is poor for high and low failure probabilities when the two separated notches A and B are considered If only one notch (either A or B) is considered and the other one is disregarded the predictive capability of WL is drastically improved Experiments with almost equal failure WL-probability in A and 8 (28% and 27%) did not result in equal experimental failure probability WL-statistics can not predict the experimental outcome when separated notches are present.

  • 37.
    Karlén, Kristoffer
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Olsson, Mårten
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    An investigation of a fatigue model with two competing failure mechanisms2014Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 64, s. 131-139Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new combined fatigue model that considers a global and a local fatigue mechanism is presented. The global mechanism is assumed to describe fatigue failure from internal defects. It is modeled using weakest link theory. The local mechanism describes fatigue failure occurring in a very clean material (i.e. almost defect-free). This mechanism is described by the normal distribution, where the stress is the largest occurring stress value, the point stress, or the point stress adjusted with the stress gradient, denoted the gradient adjusted point stress. Experiments have been performed on notched specimens with different notch root radii. At high failure probabilities, the local model dominates in the combined model. At low failure probabilities, results are less clear. There, the local model is not accurate and the global model dominates. Using the gradient adjusted point stress as the local model and the volumetric weakest link integral as the global model gives the best overall fit to the probability of failure. It is noted that for design with respect to high failure probabilities (> 20%), it is enough to use only the gradient adjusted local model.

  • 38.
    Karlén, Kristoffer
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Olsson, Mårten
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    An investigation of the location of fatigue initiation - Deterministic and probabilistic aspects2014Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 66, s. 65-77Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fatigue limit tests where there are two competing fatigue failure locations, two notches of different size, are performed in this paper. The normal distribution is used for describing the experimental outcome, where the largest occurring stress value or the gradient adjusted stress is used as a stress measure. Another model for describing the experimental outcome is the Weakest Link (WL)-integral where the integration is performed over the specimen surface area or the specimen volume. In addition, the positions of the fatigue failure initiation sites are measured and investigated. The predictive capabilities of the different models are evaluated with respect to determination of the longitudinal failure location. A notable result is that the longitudinal location of fatigue failure differs considerably from one experiment to the other, even when they are numerically equal. Nominally the stress at the fatigue failure site is much lower than the maximal stress. The load cases where there should be an equal amount of failures in both notches according to the models used do not agree with the experimental findings. Neither the point stress model nor the gradient adjusted point stress, nor the WL-integral can explain the experimental outcome from the competing notch tests.

  • 39.
    Karlén, Kristoffer
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Olsson, Mårten
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Ahmadi, Hamidreza
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Härkegård, Gunnar
    On the effect of random defects on the fatigue notch factor at different stress ratios2012Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 41, s. 179-187Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of randomly distributed defects of different sizes on the fatigue performance of a notched member has been studied. Both the effect of the volume density of defects and the size distribution of the defects have been studied. The fatigue life and the fatigue limit distributions of a smooth or notched specimen have been estimated. Using this probabilistic approach, the fatigue notch factor as function of failure probability can be estimated. It is shown that the approach with randomly distributed defects has better predictive capabilities than classical methods. The weakest link approach can be seen as an alternative to simulation of the randomly distributed defects. The two methods have similar predictive capabilities. The stress based methods generally do not take the load ratio into account when estimating the fatigue notch factor. It is also shown that the fatigue limit estimated with defect analysis is lower than the experimental one.

  • 40.
    Kazymyrovych, Vitaliy
    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.
    Thuvander, Fredrik
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
    Local stresses and material damping in very high cycle fatigue2010Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 32, s. 1669-1674Artikkel i tidsskrift (Annet vitenskapelig)
  • 41.
    Khurshid, Mansoor
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Daeuwel, Thomas
    Barsoum, Imad
    The Petroleum Institute, United Arab Emirates.
    Root fatigue strength assessment of fillet welded tube-to-plate joints subjected to multi-axial stress state using stress based local methods2017Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 101, s. 209-223Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study the fatigue strength of fillet welded tube-to-plate joints failing at the weld root and subjected to multi-axial stress states is investigated. The fatigue test data is collected from the literature and it is assessed together with the experimental data generated in this study. Finite element analysis is used to analyze the stress state at the weld root. The fatigue strength estimation capabilities of local stress based methods such as the Principal Stress Hypothesis (PSH), von Mises Stress Hypothesis (vMH), Modified Wohler Curve Method (MWCM), and Effective Equivalent Stress Hypothesis (EESH) are compared. The applicability of modified Gough Pollard Equation (GPE) in local stress system is also assessed. It is observed that most of the proposed local stress assessment methods can estimate the fatigue strength of fillet welds subjected to multiaxial stress states with constant principal stress direction, e.g. proportional loading. In case of load histories which produce varying principal stress directions with respect to time, e.g. non-proportional loading, better estimation capability is shown by MWCM and EESH. In most of the cases of varying principal stress direction load histories, vMH and PSH fail to estimate the fatigue strength. The fatigue strength of specimens tested with combined loading is reduced in comparison to the fatigue strength of specimens tested with only internal pressure and only bending loading. Out-of-phase loading does not affect the fatigue strength significantly for the specimens in this study. However; a decrease in fatigue strength is observed for the test data for out-of-phase loading collected from the literature.

  • 42.
    Kovářík, Ondrej
    et al.
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Haušild, Petr
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Čapek, Jiří
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Medřický, Jan
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Siegl, Jan
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Mušálek, Radek
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Pala, Zdeněk
    Institute of Plasma Physics AS CR, v.v.i., Prague, Czech Republic.
    Curry, Nicholas
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avd för maskinteknik.
    Björklund, Stefan
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avd för tillverkningsprocesser.
    Resonance bending fatigue testing with simultaneous damping measurement and its application on layered coatings2016Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 82, Part 2, s. 300-309Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Abstract The use of specimen loss factor as fatigue damage indicator of Hastelloy-X substrates with different surface treatments was investigated together with other fatigue damage indicators, namely resonance frequency and crack mouth length. The tested surface treatments included grit-blasting and plasma spraying of NiCoCrAlY bond coat and yttria stabilized zirconia (YSZ) top coat. The loss factors of fatigue test specimens were measured repeatedly during the resonance bending fatigue test using the conventional free decay method. The analysis of the damping spectra, i.e. the model describing the relation of loss factor to maximum macroscopic specimen strain εyy was drafted. The model is based on the combination of defect models developed by Göken and Riehemann (2004) and classical dislocation model of Granato and LÌcke (1956). It appears, that the damping spectra can be well approximated as a combination of two defect peaks (C1 and C2) and one dislocation peak (D1). The low strain defect peak (peak C1) is sensitive to the presence of fatigue cracks. The second defect peak (peak C2) can be attributed to the remaining substrate and coating defects such as embedded grit particles, coating porosity, surface roughness and sliding in the sample clamping area. The fatigue damage detection using the C1 peak magnitude was performed and its results were related to the crack length obtained by digital image correlation (DIC) method. In the crack initiation stage I., the C1 peak height shows different behavior than the resonance frequency and therefore provides new information. The underlying processes causing C1 peak changes need to be found yet, however. In the crack growth stage II., both resonance frequency and peak height C1 correlate with the measured fatigue crack size.

  • 43.
    Kovářík, Ondřej
    et al.
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Haušild, Petr
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Čapek, Jiří
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Medřický, Jan
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Siegl, Jan
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Mušálek, Radek
    Institute of Plasma Physics AS CR, v.v.i., Prague, Czech Republic.
    Pala, Zdeněk
    Institute of Plasma Physics AS CR, v.v.i., Prague, Czech Republic.
    Curry, Nicholas
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avd för maskinteknik.
    Björklund, Stefan
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avd för tillverkningsprocesser.
    Damping measurement during resonance fatigue test and its application for crack detection in TBC samples2016Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 82, nr Part 2, s. 300-309Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Abstract The use of specimen loss factor as fatigue damage indicator of Hastelloy-X substrates with different surface treatments was investigated together with other fatigue damage indicators, namely resonance frequency and crack mouth length. The tested surface treatments included grit-blasting and plasma spraying of NiCoCrAlY bond coat and yttria stabilized zirconia (YSZ) top coat. The loss factors of fatigue test specimens were measured repeatedly during the resonance bending fatigue test using the conventional free decay method. The analysis of the damping spectra, i.e. the model describing the relation of loss factor to maximum macroscopic specimen strain εyy was drafted. The model is based on the combination of defect models developed by Göken and Riehemann [1] and classical dislocation model of Granato and LÌcke [2]. It appears, that the damping spectra can be well approximated as a combination of two defect peaks (C1 and C2) and one dislocation peak (D1). The low strain defect peak (peak C1) is sensitive to the presence of fatigue cracks. The second defect peak (peak C2) can be attributed to the remaining substrate and coating defects such as embedded grit particles, coating porosity, surface roughness and sliding in the sample clamping area. The fatigue damage detection using the C1 peak magnitude was performed and its results were related to the crack length obtained by digital image correlation (DIC) method. In the crack initiation stage I., the C1 peak height shows different behavior than the resonance frequency and therefore provides new information. The underlying processes causing C1 peak changes need to be found yet, however. In the crack growth stage II., both resonance frequency and peak height C1 correlate with the measured fatigue crack size.

  • 44.
    Kuznecovs, Artjoms
    et al.
    Chalmers University of Technology, Sweden.
    Ringsberg, Jonas
    Chalmers University of Technology, Sweden.
    Yang, Shun Han
    Chalmers University of Technology, Sweden.
    Johnson, Erland
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Anderson, Andreas
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    A methodology for design and fatigue analysis of power cables for wave energy converters2019Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 122, s. 61-71Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The recent development of subsea power cables for various offshore marine renewable energy technologies has identified the need for new cables that have low structural stiffness properties. This type of cable is referred to as dynamic cable because of its high bending flexibility compared to static cables. The current study presents a cable design model and simulation models that were developed for the design and fatigue analysis of dynamic cables. These models were applied on a subsea dynamic power cable with a design that is suitable for a floating point-absorbing wave energy converter (WEC), where the cable must withstand cyclic loads imposed by the motions of the WEC, the waves and the ocean currents. The cable design model is presented with its detailed design and dimensioning methodology for cables with multiorder helical structures, with respect to desired (target) mechanical properties. The cable design model is verified against a verification study in the literature. A simulation model of a fatigue test rig for accelerated rotational bending is presented. The results from the numerical simulations and the subsequent fatigue analyses are compared against results from experiments using the test rig. The influence of the dynamic effects and mechanical properties on the fatigue life of the cable is discussed. This study contributes to a better understanding of the fatigue failure mechanisms of the cable, and it also highlights the importance of further development of numerical models.

  • 45.
    Leander, John
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Al-Emrani, Mohammad
    Chalmers University of Technology.
    Reliability-based fatigue assessment of steel bridges using LEFM: A sensitivity analysis2016Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 93, nr 1, s. 82-91Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The lack of an established safety format prohibits a widespread use of linear elastic fracture mechanics (LEFM) for the fatigue assessment of steel bridges. The aim of this study is to facilitate a future development of a deterministic design approach. A probabilistic sensitivity analysis has been performed to study the influence of different modeling options on the resulting time variant reliability. The analyses have been performed by the first order reliability method (FORM) together with a model correction factor. The result shows the importance of modeling the crack shape in an adequate manor and, the importance of the material parameters. Other parameters as the load sequence and the option between a linear and a bi-linear crack growth law are less important. A calculation of the omission sensitivity factors shows that the uncertainties of the material parameters in the crack growth law have the most decisive influence and, thereafter, the uncertainty of the stress intensity factor.

  • 46.
    Leander, John
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Aygül, Mustafa
    Chalmers University of Technology.
    Norlin, Bert
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Refined fatigue assessment of joints with welded in-plane attachments by LEFM2013Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 56, s. 25-32Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The fatigue life of joints with welded in-plane gusset plates is studied. The purpose is to suggest a descriptive detail category to be used in assessment of existing structures. Linear elastic fracture mechanics is used together with fictitious initial crack depths to predict the fatigue life. By calibrating the fictitious crack depths to real fatigue tests and simulating new test results, fatigue strengths dependent on the dimensions of the joint have been derived. The results show that a decreasing length and thickness of the gusset give decreasing stress intensity and higher fatigue strength. A numerical example is presented showing the merit of the proposed strengths in fatigue life.

  • 47.
    Leidermark, Daniel
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan. Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    A combined critical plane and critical distance approach for predicting fatigue crack initiation in notched single-crystal superalloy components2011Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 33, nr 10, s. 1351-1359Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The fatigue crack initiation in notched single-crystal components of material MD2 is investigated and analysed. A critical plane approach in combination with a critical distance method has been adopted, in which the total shear strain ranges on the discrete crystallographic slip planes are evaluated. To determine the critical distance two approaches were evaluated, a mean value approach and a cycle dependent approach. Furthermore, a Coffin-Manson type of expression (derived from the results of a set of 12 smooth specimens) is used to predict the number of cycles to fatigue crack initiation. The numerical procedure is applied to a series of experiments, in which notched single-crystal components were exposed to uniaxial cyclic loading in the nominal [001] crystal direction at 500 degrees C with R(epsilon) = 0. A good correlation between the experimental results and the simulated results was found.

  • 48. Linder, Jan
    et al.
    Axelsson, Markus
    Nilsson, Henrik
    The influence of porosity on the fatigue life for sand and permanent mould cast aluminium2006Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 28, nr 12, s. 1752-1758Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The automotive industry always strives to achieve light weight components to reduce fuel consumption and to meet environmental requirements. One way to obtain weight reduction is to replace steel components with components made of aluminium or other light weight materials. Aluminium has good corrosion properties and a high strength to weight ratio which makes it favourable in many applications. The increased use of aluminium castings in the automotive industry does also imply that the need for design data for aluminium, increases. Especially for castings, the influence of casting defects are always an issue. For this reason fatigue properties for as-cast sand and permanent mould specimens with different contents of porosity have been studied. Sand cast and permanent mould cast aluminium specimens of two different geometries were fatigue tested in cyclic bending at R= -1. Prior to fatigue test specimens were examined by X-ray and sorted into three quality groups depending on the porosity level. The aim of this work was to investigate the fatigue life for sand cast and permanent mould cast AlSi10Mg with different amounts of porosity. An additional aim was to predict the largest defect contained in a specified volume of a component, by using a statistical analysis of extreme values, and relate it to the fatigue life. The results showed that fatigue strength for a smooth specimen geometry decreases by up to 15% with increased porosity. For specimens with a notched geometry, no influence of porosity on the fatigue strength was found. This is believed to be due to a much smaller volume subject to high stress than for specimens with low stress concentration.

  • 49. Linder, Jan
    et al.
    Melander, Åke
    Fatigue strength of spot welded stainless sheet steels exposed to 3% NaCl solution1998Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 20, nr 5, s. 383-388Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fatigue properties of spot welded stainless sheets steels have been investigated in a 3% NaCl solution and, for comparison, also in air at ambient temperature. Corrosion fatigue tests have been conducted both for one austenitic Stainless steel type AISI304, and for one duplex (similar to 50% austenite, 50% ferrite) stainless steel SAF2304. For the duplex steel, the effect of preexposure of unloaded specimens to a 3%NaCl solution before corrosion fatigue testing was also investigated. Corrosion fatigue strength in 3% NaCl for the stainless steels investigated was found to be reduced by approximately 30-40% compared to fatigue strength in air. Preexposure of unloaded specimens prior to fatigue testing was shown not to reduce fatigue strength further.

  • 50. MackAldener, M.
    et al.
    Olsson, Mårten
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Tooth Interior Fatigue Fracture - computational and material aspects2001Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 23, nr 4, s. 329-340Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The hypothesis of the gear failure mode Tooth Interior Fatigue Fracture (TIFF), i.e. a fatigue crack is initiated in the interior of the tooth, is analysed by numerical simulations using FEM and the critical plane fatigue initiation criterion according to Findley. The residual stress profile in the gear is simulated and calibrated versus a neutron diffraction residual stress measurement. Fatigue properties are determined experimentally and are taken to vary with depth in the numerical analysis. In addition, the effect of shot peening is included. The analysis shows that a TIFF-crack is initiated approximately mid-height of the tooth and slightly below the case-core boundary. Furthermore, the analysis shows that TIFF is more pronounced in idlers than in single stage gears.

12 1 - 50 of 90
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