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On the modelling of strain ageing in a metastable austenitic stainless steel
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
2012 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 212, no 1, 46-58 p.Article in journal (Refereed) Published
Abstract [en]

The plastic hardening of metastable austenitic stainless steel is partly governed by martensitic transformation, the occurrence of serrated plastic flow, and plastic strain ageing phenomena. In this paper an elasto-viscoplastic material model with isotropic distortional plastic hardening is developed. The model accounts for static and dynamic strain ageing as well as the martensitic transformation. An experimental programme has been conducted in order to fit the model parameters to an austenitic stainless steel within the EN 1.4310 standard. The identification of the dynamic strain ageing was based on so called jump tests, where a sudden strain rate increase was shown to result in an instantaneous positive strain rate sensitivity followed by negative steady state strain rate sensitivity. Furthermore, the static strain ageing was identified by unloading tensile test specimens at specified plastic strains and then reloading these specimens after different periods of time. The observed material behaviour in the test situations can be predicted by the developed model. Lastly, the model was validated by predicting the force-displacement relation of the material in a shear test: the prediction agrees well with experimental results.

Place, publisher, year, edition, pages
Elsevier , 2012. Vol. 212, no 1, 46-58 p.
Keyword [en]
Plastic anisotropy; Isotropic-distortional hardening; Portevin-Le Chatelier effect; Dynamic strain ageing; Static strain ageing; Martensitic transformation
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-73731DOI: 10.1016/j.jmatprotec.2011.08.003ISI: 000297893000008OAI: oai:DiVA.org:liu-73731DiVA: diva2:476412
Available from: 2012-01-12 Created: 2012-01-12 Last updated: 2017-12-08
In thesis
1. Improved Material Models for High Strength Steel
Open this publication in new window or tab >>Improved Material Models for High Strength Steel
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The mechanical behaviour of the three advanced high strength steel grades, Docol 600DP, Docol 1200M and HyTens 1000, has been experimentally investigated under various types of deformation, and material models have been developed, which account for the experimentally observed behaviour.

Two extensive experimental programmes have been conducted in this work. In the first, the dual phase Docol 600DP steel and martensitic Docol 1200M steel were subjected to deformations both under linear and non-linear strain paths. Regular test specimens were made both from virgin materials, i.e. as received, and from materials pre-strained in various directions. The plastic strain hardening, as well as plastic anisotropy and its evolution during deformation of the two materials, were evaluated and modelled with a phenomenological model.

In the second experimental program, the austenitic stainless HyTens 1000 steel was subjected to deformations under various proportional strain paths and strain rates. It was shown experimentally that the material is sensitive both to dynamic and static strain ageing. A phenomenological model accounting for these effects was developed, calibrated, implemented in a Finite Element software and, finally,validated.

Both direct methods and inverse analyses were used in order to calibrate the parameters in the material models. The agreement between the  numerical and experimental results are in general very good.

This thesis is divided into two main parts. The background, theoretical framework and mechanical experiments are presented in the rst part. In the second part, two papers are appended.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2011. 45 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1475
Keyword
Plastic anisotropy, non-linear strain paths, mixed isotropic-kinematic hardening, isotropic-distortional hardening, dynamic strain ageing, static strain ageing, marten- sitic transformation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-80744 (URN)LIU-TEK-LIC-2011:14 (Local ID)978-91-7393-205-9 (ISBN)LIU-TEK-LIC-2011:14 (Archive number)LIU-TEK-LIC-2011:14 (OAI)
Supervisors
Available from: 2012-08-29 Created: 2012-08-29 Last updated: 2012-08-31Bibliographically approved
2. On Material Modelling of High Strength Steel Sheets
Open this publication in new window or tab >>On Material Modelling of High Strength Steel Sheets
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The work done in this thesis aims at developing and improving material models for use in industrial applications.

The mechanical behaviour of three advanced high strength steel grades, Docol 600DP, Docol 1200M and HyTens 1000, has been experimentally investigated under various types of deformation, and material models of their behaviour have been developed. The origins of all these material models are experimental findings from physical tests on the materials.

Sheet metal forming is an important industrial process and is used to produce a wide range of products. The continuously increasing demand on the weight to performance ratio of many products promotes the use of advanced high strength steel. In order to take full advantage of such steel, most product development is done by means of computer aided engineering, CAE. In advanced product development, the use of simulation based design, SBD, is continuously increasing. With SBD, the functionality of a product, as well as its manufacturing process, can be analysed and optimised with a minimum of physical prototype testing. Accurate numerical tools are absolutely necessary with this methodology, and the model of the material behaviour is one important aspect of such tools.

This thesis consists of an introduction followed by five appended papers. In the first paper, the dual phase Docol 600DP steel and the martensitic Docol 1200M steel were subjected to deformations, both under linear and non-linear strain paths. Plastic anisotropy and hardening were evaluated and modelled using both virgin materials, i.e. as received, and materials which were pre-strained in various material directions.

In the second paper, the austenitic stainless steel HyTens 1000 was subjected to deformations under various proportional strain paths and strain rates. It was experimentally shown that this material is sensitive both to dynamic and static strain ageing. A constitutive model accounting for these effects was developed, calibrated, implemented in a Finite Element software and, finally, validated on physical test data.

The third paper concerns the material dispersions in batches of Docol 600DP. A material model was calibrated to a number of material batches of the same steel grade. The paper provides a statistical analysis of the resulting material parameters.

The fourth paper deals with a simple modelling of distortional hardening. This type of hardening is able to represent the variation of plastic anisotropy during deformation. This is not the case with a regular isotropic hardening, where the anisotropy is fixed during deformation.

The strain rate effect is an important phenomenon, which often needs to be considered in a material model. In the fifth paper, the strain rate effects in Docol 600DP are investigated and modelled. Furthermore, the strain rate effect on strain localisation is discussed.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 59 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1478
Keyword
material modelling
National Category
Applied Mechanics
Identifiers
urn:nbn:se:liu:diva-80115 (URN)978-91-7519-791-3 (ISBN)
Public defence
2012-10-26, C3, Hus C, Campus Valla, Linköpings Universitet, Linköping, 10:15 (Swedish)
Opponent
Supervisors
Projects
SFS ProViking Super Light Steel Structures
Available from: 2012-09-25 Created: 2012-08-21 Last updated: 2012-09-25Bibliographically approved

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