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Improved Material Models for High Strength Steel
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
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 [en]
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: urn:nbn:se:liu:diva-80744Local ID: LIU-TEK-LIC-2011:14ISBN: 978-91-7393-205-9 (print)OAI: oai:DiVA.org:liu-80744DiVA: diva2:548088
Supervisors
Available from: 2012-08-29 Created: 2012-08-29 Last updated: 2012-08-31Bibliographically approved
List of papers
1. A study of high strength steels undergoing non-linear strain paths—Experiments and modelling
Open this publication in new window or tab >>A study of high strength steels undergoing non-linear strain paths—Experiments and modelling
2011 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 211, no 1, 121-131 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents an evaluation of the constitutive behaviour, including plastic anisotropy and mixed isotropic-kinematic hardening of two high strength steels, Docol 600DP and Docol 1200M, during strain path changes. A series of tensile and shear tests was performed on both virgin and pre-strained materials. The initial anisotropy and work hardening parameters were obtained from tensile tests, shear tests and a bulge test of the virgin material, whereas the kinematic hardening parameters were identified by comparing numerical predictions to experimental results related to the pre-strained materials. Numerical predictions using the obtained parameters agree well with the experimental results, both in the case of proportional, and under non-proportional strain paths.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
Non-linear strain paths, Plastic anisotropy, Mixed isotropic-kinematic hardening, Shear test
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-60772 (URN)10.1016/j.jmatprotec.2010.09.004 (DOI)
Available from: 2010-12-01 Created: 2010-10-26 Last updated: 2017-12-12
2. On the modelling of strain ageing in a metastable austenitic stainless steel
Open this publication in new window or tab >>On the modelling of strain ageing in a metastable austenitic stainless steel
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
Keyword
Plastic anisotropy; Isotropic-distortional hardening; Portevin-Le Chatelier effect; Dynamic strain ageing; Static strain ageing; Martensitic transformation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-73731 (URN)10.1016/j.jmatprotec.2011.08.003 (DOI)000297893000008 ()
Available from: 2012-01-12 Created: 2012-01-12 Last updated: 2017-12-08

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