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History Reduction Techniques for Simulation of Additive Manufacturing and Physically based Material Modeling
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.ORCID iD: 0000-0002-2592-9073
2020 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, finite element (FE) simulations of additive manufacturing (AM) and physically based material modeling are presented. AM is a process where the component is built layer-wise. The material undergoes repeated heating and cooling cycles when layers are added, which may result in undesired deformation and residual stress in the built component. The choice of process parameters and scan strategy affect the resulting residual stress. Simulations can be used to support the experimental determination of process parameters and scan strategy. AM processes often comprise many added layers, and the passes are lengthy relative to their thicknesses and widths. This makes the FE simulations computationally expensive, with many elements and time steps. In this work, AM processes have been simulated with the FE-method using a lumping technique. This technique allows fewer time steps and a coarser mesh. Thermal behavior, deformation, and residual stresses have been simulated and compared with experiments. The simulations show that, by using the lumping technique, the computational effort can be reduced significantly with retained accuracy for the resulting temperature and deformations. The residual stresses become somewhat smaller. Alloy 625 is a nickel-based superalloy used in high-temperature applications owing to the hightemperature strength. The material is difficult to manufacture by conventional machining owing to excessive tool wear and low material removal rates. Thus alloy 625 is a material appropriate for the AM technology with its near-net shape potential. An existing, physically based flow stress model has been further developed to fit the mechanisms typical for alloy 625. This model gives an accurate mechanical behavior and capture viscoplasticity, creep, and relaxation. The physically based model has been calibrated versus compression tests and validated with a stress relaxation test performed in a Gleeble 3800 machine. The predicted relaxation was in good agreement with the measured relaxation. The usage of this kind of material model is expected to improve the prediction of the material behavior during the AM process and, thereby, the overall prediction of the AM process.

Place, publisher, year, edition, pages
Luleå tekniska universitet, 2020.
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-78579ISBN: 978-91-7790-591-2 (print)ISBN: 978-91-7790-592-9 (electronic)OAI: oai:DiVA.org:ltu-78579DiVA, id: diva2:1425505
Presentation
2020-06-16, E231, Luleå Tekniska Universitet, 97187, Luleå, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research , GMT14-0048Available from: 2020-04-21 Created: 2020-04-21 Last updated: 2020-05-19Bibliographically approved
List of papers
1. History Reduction by Lumping for Time-Efficient Simulation of Additive Manufacturing
Open this publication in new window or tab >>History Reduction by Lumping for Time-Efficient Simulation of Additive Manufacturing
2020 (English)In: Metals, ISSN 2075-4701, Vol. 10, no 1, article id 58Article in journal (Refereed) Published
Abstract [en]

Additive manufacturing is the process by which material is added layer by layer. In most cases, many layers are added, and the passes are lengthy relative to their thicknesses and widths. This makes finite element simulations of the process computationally demanding owing to the short time steps and large number of elements. The classical lumping approach in computational welding mechanics, popular in the 80s, is therefore, of renewed interest and is evaluated in this work. The method of lumping means that welds are merged. This allows fewer time steps and a coarser mesh. It was found that the computation time can be reduced considerably, with retained accuracy for the resulting temperatures and deformations. The residual stresses become, to a certain degree, smaller. The simulations were validated against a directed energy deposition (DED) experiment with alloy 625.

Place, publisher, year, edition, pages
MDPI, 2020
Keywords
finite element, thermo-mechanical analysis, additive manufacturing, alloy 625
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-77958 (URN)10.3390/met10010058 (DOI)000516827800058 ()2-s2.0-85077642374 (Scopus ID)
Funder
Swedish Foundation for Strategic Research , GMT14-0048
Note

Validerad;2020;Nivå 2;2020-04-01 (alebob)

Available from: 2020-03-04 Created: 2020-03-04 Last updated: 2020-04-21Bibliographically approved
2. Mechanism based flow stress model for Alloy 625 and Alloy 718
Open this publication in new window or tab >>Mechanism based flow stress model for Alloy 625 and Alloy 718
(English)Manuscript (preprint) (Other academic)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:ltu:diva-78575 (URN)
Funder
Swedish Foundation for Strategic Research , GMT14-0048
Available from: 2020-04-20 Created: 2020-04-20 Last updated: 2020-04-21
3. Efficiency and Accuracy in Thermal Simulation of Powder Bed Fusion of Bulk Metallic Glass
Open this publication in new window or tab >>Efficiency and Accuracy in Thermal Simulation of Powder Bed Fusion of Bulk Metallic Glass
2018 (English)In: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 70, no 8, p. 1598-1603Article in journal (Refereed) Published
Abstract [en]

Additive manufacturing by powder bed fusion processes can be utilized to create bulk metallic glass as the process yields considerably high cooling rates. However, there is a risk that reheated material set in layers may become devitrified, i.e., crystallize. Therefore, it is advantageous to simulate the process to fully comprehend it and design it to avoid the aforementioned risk. However, a detailed simulation is computationally demanding. It is necessary to increase the computational speed while maintaining accuracy of the computed temperature field in critical regions. The current study evaluates a few approaches based on temporal reduction to achieve this. It is found that the evaluated approaches save a lot of time and accurately predict the temperature history.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Other Materials Engineering
Research subject
Material Mechanics
Identifiers
urn:nbn:se:ltu:diva-68768 (URN)10.1007/s11837-018-2919-8 (DOI)000440845900039 ()
Note

Validerad;2018;Nivå 2;2018-08-07 (rokbeg)

Available from: 2018-05-17 Created: 2018-05-17 Last updated: 2020-04-21Bibliographically approved

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Malmelöv, Andreas

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