Endre søk
Begrens søket
1 - 7 of 7
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.
    Draxler, Joar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Modeling and Simulation of Weld Hot Cracking2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Several alloy systems are susceptible to weld hot cracking. Weld hot cracking occurs by fracture of liquid films, normally grain boundary liquid films, at the late stage of the solidification of the weld. The cracks can be small and therefore difficult to detect by nondestructive test methods. If hot cracks are not repaired, they can act as sites for initiation of fatigue and stress corrosion cracking, which in turn can lead to catastrophic failure in critical applications such as aerospace engines and nuclear power plants. Therefore, it is of highest importance to design weld processes so that hot cracking can be avoided. Here, numerical simulation can be a powerful tool for optimizing weld speed, heat input, weld path geometry, weld path sequences, weld fixturing, etc., such that the risk for hot cracking can be minimized. In this thesis, we propose a modeling approach for simulating weld hot cracking in sheet metals with low welding speeds and fully penetrating welds. These conditions are assumed to give rise to isolated grain boundary liquid films (GBLFs) whose crack susceptibility can be analyzed using one-dimensional models. The work is divided into four journal papers. The three first papers treat hot cracking that occurs in the fusion zone of the weld while the last paper treats hot cracking in the partially melted zone of the weld. The main content of the four papers are summarized below. In paper A, a pore-based crack criterion for hot cracking has been developed. This criterion states that cracking occurs in a GBLF if the liquid pressure in the film goes below a fracture pressure. The fracture pressure is determined from a pore model as the liquid pressure that is required to balance the surface tension of an axisymmetric pore in a liquid film located between two parallel plates at a given critical pore radius. The fracture pressure depends on the surface tension, the spacing between the parallel plates and the gas concentration in the liquid. In order to evaluate the above pore-based crack criterion in a GBLF the liquid pressure in the film most be known. In paper B, a one-dimensional GBLF pressure model for a columnar dendritic microstructure has been developed. This model is based on a combination of Poiseuille parallel plate flow and Darcy porous flow. Flow induced by mechanical straining of the GBLF is accounted for by a macroscopic mechanical strain field that is localized to the GBLF by a temperature dependent length scale. In paper C, a computational welding mechanics model for a Varestraint test is developed. The model is used to calibrate the crack criterion in paper A and the pressure model in paper B. It is then used to test the crack criterion in Varestraint tests with different augmented strains. Calculated crack locations, orientations, and widths are shown to correlate well to the experimental Varestraint tests. vii Finally, in paper D, a segregation model for predicting the thickness of eutectic bands has been developed. The thickness of eutectic bands affects the degree of liquation in partially melted zone, and therefore is an important factor for hot cracking in this region of the weld.

  • 2.
    Draxler, Joar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Edberg, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Andersson, J.
    University West, Trollhättan, Sweden.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Modeling and simulation of weld solidification cracking part I: A pore-based crack criterion2019Inngår i: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 63, nr 5, s. 1489-1502Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several advanced alloy systems are susceptible to weld solidification cracking. One example is nickel-based superalloys, which are commonly used in critical applications such as aerospace engines and nuclear power plants. Weld solidification cracking is often expensive to repair and, if not repaired, can lead to catastrophic failure. This study, presented in three papers, presents an approach for simulating weld solidification cracking applicable to large-scale components. The results from finite element simulation of welding are post-processed and combined with models of metallurgy, as well as the behavior of the liquid film between the grain boundaries, in order to estimate the risk of crack initiation. The first paper in this study describes the crack criterion for crack initiation in a grain boundary liquid film. The second paper describes the model for computing the pressure and the thickness of the grain boundary liquid film, which are required to evaluate the crack criterion in paper 1. The third and final paper describes the application of the model to Varestraint tests of alloy 718. The derived model can fairly well predict crack locations, crack orientations, and crack widths for the Varestraint tests. The importance of liquid permeability and strain localization for the predicted crack susceptibility in Varestraint tests is shown.

  • 3.
    Draxler, Joar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Edberg, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Andersson, J.
    University West, Trollhättan, Sweden.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Modeling and simulation of weld solidification cracking part II: A model for estimation of grain boundary liquid pressure in a columnar dendritic microstructure2019Inngår i: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 63, nr 5, s. 1503-1519Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several advanced alloy systems are susceptible to weld solidification cracking. One example is nickel-based superalloys, which are commonly used in critical applications such as aerospace engines and nuclear power plants. Weld solidification cracking is often expensive to repair, and if not repaired, can lead to catastrophic failure. This study, presented in three papers, presents an approach for simulating weld solidification cracking applicable to large-scale components. The results from finite element simulation of welding are post-processed and combined with models of metallurgy, as well as the behavior of the liquid film between the grain boundaries, in order to estimate the risk of crack initiation. The first paper in this study describes the crack criterion for crack initiation in a grain boundary liquid film. The second paper describes the model for computing the pressure and the thickness of the grain boundary liquid film, which are required to evaluate the crack criterion in paper 1. The third and final paper describes the application of the model to Varestraint tests of Alloy 718. The derived model can fairly well predict crack locations, crack orientations, and crack widths for the Varestraint tests. The importance of liquid permeability and strain localization for the predicted crack susceptibility in Varestraint tests is shown.

  • 4.
    Draxler, Joar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Edberg, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Andersson, J.
    University West, Trollhättan, Sweden.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Modeling and simulation of weld solidification cracking part III: Simulation of solidification cracking in Varestraint tests of alloy 7182019Inngår i: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 63, nr 6, s. 1883-1901Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several advanced alloy systems are susceptible to weld solidification cracking. One example is nickel-based superalloys, which are commonly used in critical applications such as aerospace engines and nuclear power plants. Weld solidification cracking is often expensive to repair, and if not repaired, can lead to catastrophic failure. This study, presented in three papers, presents an approach for simulating weld solidification cracking applicable to large-scale components. The results from finite element simulation of welding are post-processed and combined with models of metallurgy, as well as the behavior of the liquid film between the grain boundaries, in order to estimate the risk of crack initiation. The first paper in this study describes the crack criterion for crack initiation in a grain boundary liquid film. The second paper describes the model required to compute the pressure and thickness of the liquid film required in the crack criterion. The third and final paper describes the application of the model to Varestraint tests of alloy 718. The derived model can fairly well predict crack locations, crack orientations, and crack widths for the Varestraint tests. The importance of liquid permeability and strain localization for the predicted crack susceptibility in Varestraint tests is shown.

  • 5.
    Draxler, Joar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Edberg, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Andersson, Joel
    University West.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Simulation of weld solidifiation cracking in varestraint tests of alloy 7182019Inngår i: / [ed] C. Sommitsch, Gratz, 2019, Vol. 12, s. 485-504Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Several nickel-based superalloys are susceptible to weld solidification cracking. Numerical simulation can be a powerful tool for optimizing the welding process such that solidification cracking can be avoided. In order to simulate the cracking, a crack model inspired by the RDG model is proposed. The model is based on a crack criterion that estimates the likelihood for a preexisting pore in a grain boundary liquid film to form a crack. The criterion depends on the thickness and the liquid pressure in the grain boundary liquid film, as well as the surface tension of the pore. The thickness of the liquid film is computed from the macroscopic mechanical strain field of an FE model with a double ellipsoidal heat source. A temperature-dependent length scale is used to partition the macroscopic strain to the liquid film. The liquid pressure in the film is evaluated using a combination of Poiseuille parallel plate flow and Darcy’s law for porous flows. The Poiseuille flow is used for the part of the grain boundary liquid film that extends into the region with liquid fraction less than 0.1, while Darcy’s law is used for the rest of the liquid film that extends into the regions with liquid fraction greater than 0.1. The proposed model was calibrated and evaluated in Varestraint tests of Alloy 718. Crack location, width, and orientation were all accurately predicted by the model.

  • 6.
    Draxler, Joar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Edberg, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Åkerström, Paul
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Andersson, Joel
    University West.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A Numerical Model for Simulating the Effect of Strain Rate on Eutectic Band ThicknessInngår i: Artikkel i tidsskrift (Fagfellevurdert)
  • 7.
    Lindgren, Lars-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lundbäck, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Fisk, Martin
    Malmö University, Malmö, Sweden.
    Draxler, Joar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Modelling additive manufacturing of superalloys2019Inngår i: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 35, s. 252-258Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    There exist several variants of Additive Manufacturing (AM) applicable for metals and alloys. The two main groups are Directed Energy Deposition (DED) and Powder Bed Fusion (PBF). AM has advantages and disadvantages when compared to more traditional manufacturing methods. The best candidate products are those with complex shape and small series and particularly individualized product. Repair welding is often individualized as defects may occur at various instances in a component. This method was used before it became categorized as AM and in most cases, it is a DED process. PBF processes are more useful for smaller items and can give a finer surface. Both DED and PBF products require subsequent surface finishing for high performance components and sometimes there is also a need for post heat treatment. Modelling of AM as well as eventual post-processes can be of use in order to improve product quality, reducing costs and material waste. The paper describes the use of the finite element method to simulate these processes with focus on superalloys.

1 - 7 of 7
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