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Åkerström, Paul
Publications (10 of 16) Show all publications
Lindgren, L.-E., Edberg, J., Åkerström, P. & Zhang, Z. (2019). Modeling of thermal stresses in low alloy steels. Paper presented at The 12th International Congress on Thermal Stresses June 1–5, 2019, Zhejiang University, Hangzhou, China. Journal of thermal stresses, 42(6), 725-743
Open this publication in new window or tab >>Modeling of thermal stresses in low alloy steels
2019 (English)In: Journal of thermal stresses, ISSN 0149-5739, E-ISSN 1521-074X, Vol. 42, no 6, p. 725-743Article in journal (Refereed) Published
Abstract [en]

Computing the evolution of thermal stresses accurately requires appropriate constitutive relations. This includes both the thermal and mechanical aspects, as temperature is the driver to thermal stresses. The paradigm of Integrated Computational Materials Engineering (ICME) aims at being able to quantitatively relate process-structure-property of a material. The article describes physics based models, denoted bridging elements, which are one step towards the vision of ICME. They couple material structure with heat capacity, heat conductivity, thermal and transformation strains and elastic properties for hypo-eutectoid steels. The models can account for the chemical composition of the steel and its processing, i.e. thermomechanical history, giving the evolution of the microstructure and the corresponding properties.

Place, publisher, year, edition, pages
Taylor & Francis, 2019
Keywords
Elastic properties, heat capacity, heat conductivity, thermal expansion, thermal stresses
National Category
Other Materials Engineering
Research subject
Material Mechanics
Identifiers
urn:nbn:se:ltu:diva-73488 (URN)10.1080/01495739.2019.1587329 (DOI)000468282400003 ()2-s2.0-85063905757 (Scopus ID)
Conference
The 12th International Congress on Thermal Stresses June 1–5, 2019, Zhejiang University, Hangzhou, China
Note

Konferensartikel i tidskrift

Available from: 2019-04-08 Created: 2019-04-08 Last updated: 2019-09-13Bibliographically approved
Åkerström, P. (2017). A Novel Tooling Technology for Hot Forming Processes. In: Mats Oldenburg, Braham Prakash, Kurt Steinhoff (Ed.), 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2: June 4-7 2017, Atlanta, Georgia, USA : proceedings. Paper presented at 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2, Atlanta, Georgia, 4-7 June 2017 (pp. 243-250). Warrendale, PA: Association for Iron & Steel Technology, AIST
Open this publication in new window or tab >>A Novel Tooling Technology for Hot Forming Processes
2017 (English)In: 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2: June 4-7 2017, Atlanta, Georgia, USA : proceedings / [ed] Mats Oldenburg, Braham Prakash, Kurt Steinhoff, Warrendale, PA: Association for Iron & Steel Technology, AIST , 2017, p. 243-250Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Warrendale, PA: Association for Iron & Steel Technology, AIST, 2017
Series
CHS2-series ; 6
National Category
Other Mechanical Engineering Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-64312 (URN)978-1-935117-66-7 (ISBN)
Conference
6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2, Atlanta, Georgia, 4-7 June 2017
Available from: 2017-06-21 Created: 2017-06-21 Last updated: 2017-11-24Bibliographically approved
Golling, S., Östlund, R., Bergman, G., Åkerström, P. & Oldenburg, M. (2017). Modelling of Plastic Deformation and Fracture in Hot Stamped Steel with Multi-Phase Microstructure. Paper presented at International Conference on the Technology of Plasticity, ICTP 2017, Cambridge, United Kingdom, 17-22 September 2017. Procedia Engineering, 207, 687-692
Open this publication in new window or tab >>Modelling of Plastic Deformation and Fracture in Hot Stamped Steel with Multi-Phase Microstructure
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2017 (English)In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 207, p. 687-692Article in journal (Refereed) Published
Abstract [en]

Hot stamping is an industrialized technique with the aim of improving material properties by heat treatment and forming of a component in a single production step. Within the field of hot stamping the method of tailored material properties evolved. Components with tailored material properties possess different mechanical properties in designated areas. The mechanical properties in a blank are modified by the formation of different microstructures. Martensite is a microstructure with high strength but low ductility, ferrite has lower strength but higher ductility. Using special tooling tough martensite and soft ferrite can be placed in adjacent sections in a blank. Between those sections a transition zone consisting of a mixed microstructure exists with mechanical properties between martensite and ferrite. Transition zones possess intermediate cooling rates, hence formation of bainite and composites of bainite and another phase can from.

This paper presents an approach of modelling the complete process from austenitized blank to fracture. The method presented relies on the prediction of phases formed during cooling using an austenite decomposition model. In the course of ferrite formation the carbon content in the remaining austenite increases, the carbon content in austenite influences formation of additional daughter phases. The estimated phase composition is used in a homogenization scheme to predict the hardening of the material during plastic deformation. Fracture in the different microstructural phases is predicted using the strain decomposition provided by the homogenization and a fracture criteria. The homogenization scheme and the fracture criteria use measured data from single phase microstructures, i.e. ferrite, bainite and martensite.

A heat treatment process for tensile test specimens is used to produce samples with different volume fractions of the microstructures ferrite, bainite and martensite. The pre-cut specimens are austenitized, ferrite is formed in a second furnace with lower temperature, bainite and martensite are formed by the use of a temperature controlled plane tool.

Prediction of the phase content in mixed microstructures showed good agreement with microstructural characterization and therefore results can be used as input value for the homogenization. Comparing experimental and numerical results for a variety of different mixed microstructures good agreement in the prediction of hardening and fracture is found.

It is concluded that the use of a homogenization method combined with a fracture model can be used to predict the mechanical response of mixed microstructures. The method described in the present work can be applied in the development of hot stamped components.

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Applied Mechanics Other Materials Engineering
Research subject
Solid Mechanics; Material Mechanics
Identifiers
urn:nbn:se:ltu:diva-64056 (URN)10.1016/j.proeng.2017.10.1042 (DOI)2-s2.0-85036655085 (Scopus ID)
Conference
International Conference on the Technology of Plasticity, ICTP 2017, Cambridge, United Kingdom, 17-22 September 2017
Note

Konferensartikel i tidskrift

Available from: 2017-06-15 Created: 2017-06-15 Last updated: 2017-12-19Bibliographically approved
Salomonsson, P., Oldenburg, M., Åkerström, P. & Bergman, G. (2008). Experimental and numerical evaluation of the heat transfer coefficient in press hardening (ed.). In: (Ed.), Kurt Steihoff; Mats Oldenburg; Braham Prakash (Ed.), Hot Sheet Metal Forming of High-Performance Steel: Proceedings, 1st International Conference, Kassel, Germany, October 22-24, 2008. Paper presented at International Conference on Hot Sheet Metal Forming of High-Performance Steel : 22/10/2008 - 24/10/2008 (pp. 267-274). Bad Harzburg: GRIPS media
Open this publication in new window or tab >>Experimental and numerical evaluation of the heat transfer coefficient in press hardening
2008 (English)In: Hot Sheet Metal Forming of High-Performance Steel: Proceedings, 1st International Conference, Kassel, Germany, October 22-24, 2008 / [ed] Kurt Steihoff; Mats Oldenburg; Braham Prakash, Bad Harzburg: GRIPS media , 2008, p. 267-274Conference paper, Published paper (Refereed)
Abstract [en]

When producing thin ultra high strength steel components with the press hardening process it is essential that the final component achieves desirable material properties. This applies in particular to passive automotive safety components were it is of great importance to accurately predict the final component properties early in the product development process. The transfer of heat is a key process that affects the evolution of the mechanical properties in the product and it is essential that the thermal contact conditions between the blank and tool are properly described in the forming simulations. In this study an experimental setup is developed combined with an elementary inverse simulation approach to predict the interfacial heat transfer coefficient (IHTC) when the hot blank and cold tool are in mechanical contact. Different process conditions such as contact pressure and blank material (22MnB5 and Usibor 1500P) are investigated. In the inverse simulation, a thermo-mechanical coupled simulation model is used with a thermo-elastic-plastic constitutive model including effects from changes in the microstructure during quenching. The results from simulations give the variations of the heat transfer coefficient in time for best match to experimental results. It is found that the pressure dependence for the two materials is different and the heat transfer coefficient is varying during quenching. This information together with further testing will be used as a base in a future model of the heat transfer coefficient influence at different conditions in press hardening process.

Place, publisher, year, edition, pages
Bad Harzburg: GRIPS media, 2008
Series
GRIPS' Sparkling World of Steel, ISSN 1619-9529 ; 1
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-30735 (URN)4a5ee190-bd48-11dd-a7c4-000ea68e967b (Local ID)978-3-937057-18-7 (ISBN)4a5ee190-bd48-11dd-a7c4-000ea68e967b (Archive number)4a5ee190-bd48-11dd-a7c4-000ea68e967b (OAI)
Conference
International Conference on Hot Sheet Metal Forming of High-Performance Steel : 22/10/2008 - 24/10/2008
Note
Godkänd; 2008; 20081128 (ysko)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-25Bibliographically approved
Oldenburg, M., Åkerström, P., Bergman, G. & Salomonsson, P. (2008). Modelling of microstructure and material response in the press hardening process (ed.). In: (Ed.), Nader Asnafi (Ed.), Conference Best in Class Stamping, June 16 - 18, 2008, Olofström, Sweden: [proceedings] / IDDRG, International Deep Drawing Research Group. Paper presented at International Deep Drawing Research Group Conference : Best in Class Stamping 16/06/2008 - 18/06/2008 (pp. 463-474). Olofström: Industriellt utvecklingscentrum i Olofström AB
Open this publication in new window or tab >>Modelling of microstructure and material response in the press hardening process
2008 (English)In: Conference Best in Class Stamping, June 16 - 18, 2008, Olofström, Sweden: [proceedings] / IDDRG, International Deep Drawing Research Group / [ed] Nader Asnafi, Olofström: Industriellt utvecklingscentrum i Olofström AB , 2008, p. 463-474Conference paper, Published paper (Refereed)
Abstract [en]

The use of ultra-high strength components in automotive structures is rapidly increasing due to strong driving forces to reduce weight in order to minimise fuel consumption. This should also be accomplished with maintained or increased passenger safety. Components manufactured with the press hardening process meet most of the requirements and the market for such products is currently growing very fast. The quenching results in a material with a very high yield and tensile strength falling into the category of martensitic ultra high strength steels. Simulation of the complete press hardening process requires coupled thermo-mechanical transient analysis with the possibility to account for mechanical end thermal contact conditions between the tool and the blank. In addition, one sided or two sided contact areas may occur. Thus, large temperature variations through the thickness of the blank may be present during the process. In an earlier work, Bergman and Oldenburg formulated a thermal shell element with quadratic temperature interpolation through the thickness of the shell while there is a linear interpolation in the plane of the element. This formulation is implemented in the LS-Dyna code and is used in coupled thermomechanical analysis of hot forming processes. The modelling of the press hardening process has been developed in several steps. The model development involves e.g. determination of the flow stress, austenite decomposition modelling, constitutive modelling, experimental studies and evaluation of simulation results. The presented model accounts for the most significant phenomena occurring in the thermo-mechanical press hardening process. The mechanical response and the micro-structure evolution as well as the final material state can be predicted with good accuracy.

Place, publisher, year, edition, pages
Olofström: Industriellt utvecklingscentrum i Olofström AB, 2008
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-37120 (URN)b0503560-42c5-11dd-bfd7-000ea68e967b (Local ID)978-91-633-2948-7 (ISBN)b0503560-42c5-11dd-bfd7-000ea68e967b (Archive number)b0503560-42c5-11dd-bfd7-000ea68e967b (OAI)
Conference
International Deep Drawing Research Group Conference : Best in Class Stamping 16/06/2008 - 18/06/2008
Note

Godkänd; 2008; Bibliografisk uppgift: CD-ROM; 20080625 (ysko)

Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2019-10-10Bibliographically approved
Oldenburg, M., Åkerström, P., Bergman, G. & Salomonsson, P. (2008). Simulation of the micro structure evolution in a press hardened component (ed.). In: (Ed.), Kurt Steihoff; Mats Oldenburg; Braham Prakash (Ed.), Hot Sheet Metal Forming of High-Performance Steel: Proceedings, 1st International Conference, Kassel, Germany, October 22-24, 2008. Paper presented at International Conference on Hot Sheet Metal Forming of High-Performance Steel : 22/10/2008 - 24/10/2008 (pp. 3-13). Bad Harzburg: GRIPS media
Open this publication in new window or tab >>Simulation of the micro structure evolution in a press hardened component
2008 (English)In: Hot Sheet Metal Forming of High-Performance Steel: Proceedings, 1st International Conference, Kassel, Germany, October 22-24, 2008 / [ed] Kurt Steihoff; Mats Oldenburg; Braham Prakash, Bad Harzburg: GRIPS media , 2008, p. 3-13Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Bad Harzburg: GRIPS media, 2008
Series
GRIPS' Sparkling World of Steel, ISSN 1619-9529 ; 1
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-26977 (URN)0420f7a0-bd47-11dd-a7c4-000ea68e967b (Local ID)978-3-937057-18-7 (ISBN)0420f7a0-bd47-11dd-a7c4-000ea68e967b (Archive number)0420f7a0-bd47-11dd-a7c4-000ea68e967b (OAI)
Conference
International Conference on Hot Sheet Metal Forming of High-Performance Steel : 22/10/2008 - 24/10/2008
Note
Godkänd; 2008; Bibliografisk uppgift: Keynote; 20081128 (ysko)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-25Bibliographically approved
Åkerström, P., Bergman, G. & Oldenburg, M. (2007). Numerical implementation of a constitutive model for simulation of hot stamping (ed.). Paper presented at . Modelling and Simulation in Materials Science and Engineering, 15(2), 105-119
Open this publication in new window or tab >>Numerical implementation of a constitutive model for simulation of hot stamping
2007 (English)In: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 15, no 2, p. 105-119Article in journal (Refereed) Published
Abstract [en]

In order to increase the accuracy of numerical simulations of the hot stamping process, an accurate and robust constitutive model is crucial. During the process, a hot blank is inserted into a tool where it is continuously formed and cooled. For the steel grades often used for this purpose, the initially austenitized blank will decompose into different product phases depending on the cooling and mechanical history. As a consequence, the phase proportions change will affect both the thermal and mechanical properties of the continuously formed and cooled blank. A thermo-elastic-plastic constitutive model based on the von Mises yield criterion with associated plastic flow is implemented into the LS-Dyna finite element code. Models accounting for the austenite decomposition and transformation induced plasticity are included in the constitutive model. The implemented model results are compared with experimental dilatation results with and without externally applied forces. Further, the calculated isothermal mechanical response during the formation of a new phase is compared with the corresponding experimental response for two different temperatures.

National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-14308 (URN)10.1088/0965-0393/15/2/007 (DOI)000245828400007 ()2-s2.0-34247248310 (Scopus ID)da8b1690-c267-11db-9ea3-000ea68e967b (Local ID)da8b1690-c267-11db-9ea3-000ea68e967b (Archive number)da8b1690-c267-11db-9ea3-000ea68e967b (OAI)
Note
Validerad; 2007; 20070216 (cira)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Oldenburg, M., Åkerström, P., Bergman, G. & Salomonsson, P. (2007). Simulation and evaluation of phase transformations and mechanical response in the hot stamping process (ed.). In: (Ed.), Jose M.A.Cesar de Sa; Abel D. Santos (Ed.), Materials Processing and Design: Modeling, Simulation and Applications; NUMIFORM 2007: Proceedings of the 9th International Conference on Numerical Methods in Industrial Forming Processes. Paper presented at International Conference on Numerical Methods in Industrial Forming Processes : 17/06/2007 - 21/06/2007 (pp. 1181-1186). Melville, NY: American Institute of Physics (AIP), 908
Open this publication in new window or tab >>Simulation and evaluation of phase transformations and mechanical response in the hot stamping process
2007 (English)In: Materials Processing and Design: Modeling, Simulation and Applications; NUMIFORM 2007: Proceedings of the 9th International Conference on Numerical Methods in Industrial Forming Processes / [ed] Jose M.A.Cesar de Sa; Abel D. Santos, Melville, NY: American Institute of Physics (AIP), 2007, Vol. 908, p. 1181-1186Conference paper, Published paper (Refereed)
Abstract [en]

When producing thin ultra high strength steel components with the hot stamping process it is essential that the final component achieves desirable material properties. This applies in particular to passive automotive safety components. Often the desirable microstructure consists of a mix of martensite and bainite. Therefore, it is of great importance to accurately predict the final microstructure of the component early in the product development process. In this work a model to predict the austenite decomposition into ferrite, pearlite, bainite and martensite during arbitrary cooling paths for thin sheet boron steel is used. The decomposition model is based on Kirkaldy's rate equations and later modifications by Li et al. The modified model accounts for the effect from the added boron. The model is implemented as part of a material subroutine in the Finite Element Program LS-DYNA 970. Both the simulated volume fractions of micro-constituents and hardness profiles show good agreement with the corresponding experimental observations. The phase proportions affect both the thermal and the mechanical properties during the process of continuous cooling and deformation of the material. A thermo-elastic-plastic constitutive model including effects from changes in the microstructure as well as transformation plasticity is implemented in the LS-DYNA code. The material model is used in combination with a thermal shell formulation with quadratic temperature interpolation in the thickness direction to simulate the complete process of simultaneous forming and quenching of sheet metal components. The implemented model is used in coupled thermo-mechanical analysis of the hot stamping process and evaluated by comparing the results from hot stamping experiments. The results from simulations such as local thickness variations, hardness distribution and spring-back in the component show good agreement with experimental results.

Place, publisher, year, edition, pages
Melville, NY: American Institute of Physics (AIP), 2007
Series
A I P Conference Proceedings Series, ISSN 0094-243X ; 908
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-32259 (URN)10.1063/1.2740970 (DOI)000246933500185 ()2-s2.0-34547551801 (Scopus ID)6b0a25b0-6bfc-11dc-89fb-000ea68e967b (Local ID)978-0-7354-0415-1 (ISBN)6b0a25b0-6bfc-11dc-89fb-000ea68e967b (Archive number)6b0a25b0-6bfc-11dc-89fb-000ea68e967b (OAI)
Conference
International Conference on Numerical Methods in Industrial Forming Processes : 17/06/2007 - 21/06/2007
Note

Validerad; 2007; 20070926 (pafi)

Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2019-06-04Bibliographically approved
Åkerström, P., Bergman, G., Oldenburg, M. & Salomonsson, P. (2007). Utveckling av mikrostruktur och mekanisk respons vid presshärdning (ed.). In: (Ed.), Niklas Davidsson; Elianne Wassvik (Ed.), Svenska Mekanikdagar 2007: Program och abstracts. Paper presented at Svenska Mekanikdagar 2007 : 13/06/2007 - 15/06/2007 (pp. 98). Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Utveckling av mikrostruktur och mekanisk respons vid presshärdning
2007 (Swedish)In: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, p. 98-Conference paper, Meeting abstract (Other academic)
Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2007
Series
Research report / Luleå University of Technology, ISSN 1402-1528 ; 2007:10
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-29422 (URN)2e4fc0f0-5c50-11dc-a955-000ea68e967b (Local ID)2e4fc0f0-5c50-11dc-a955-000ea68e967b (Archive number)2e4fc0f0-5c50-11dc-a955-000ea68e967b (OAI)
Conference
Svenska Mekanikdagar 2007 : 13/06/2007 - 15/06/2007
Note
Godkänd; 2007; 20070906 (ysko)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-25Bibliographically approved
Åkerström, P. & Oldenburg, M. (2006). Austenite decomposition during press hardening of a boron steel: computer simulation and test (ed.). Paper presented at . Journal of Materials Processing Technology, 174(1-3), 399-406
Open this publication in new window or tab >>Austenite decomposition during press hardening of a boron steel: computer simulation and test
2006 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 174, no 1-3, p. 399-406Article in journal (Refereed) Published
Abstract [en]

In this work a model to predict the austenite decomposition into ferrite, pearlite, bainite and martensite during arbitrary cooling paths for thin sheet boron steel is used. The model is based on Kirkaldy's rate equations. The basic rate equations has been modified to account for the austenite stabilization effect from the added boron. The model is implemented as part of a material subroutine in the Finite Element Program LS-DYNA 970. Both the obtained simulated volume fractions microconstituents and hardness profiles shows promising agreement to the corresponding experimental observations.

National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-10811 (URN)10.1016/j.jmatprotec.2006.02.013 (DOI)000237817700053 ()2-s2.0-33646189261 (Scopus ID)9ad4b020-9c23-11db-8975-000ea68e967b (Local ID)9ad4b020-9c23-11db-8975-000ea68e967b (Archive number)9ad4b020-9c23-11db-8975-000ea68e967b (OAI)
Note
Validerad; 2006; 20070103 (evan)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
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