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A study of high strength steels undergoing non-linear strain paths—Experiments and modelling
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.
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.
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. Vol. 211, no 1, 121-131 p.
Keyword [en]
Non-linear strain paths, Plastic anisotropy, Mixed isotropic-kinematic hardening, Shear test
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-60772DOI: 10.1016/j.jmatprotec.2010.09.004OAI: oai:DiVA.org:liu-60772DiVA: diva2:373703
Available from: 2010-12-01 Created: 2010-10-26 Last updated: 2017-12-12
In thesis
1. Modelling of Failure in High Strength Steel Sheets
Open this publication in new window or tab >>Modelling of Failure in High Strength Steel Sheets
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this theses the high strength steel Docol 600DP and the ultra high strength steel Docol 1200M are studied. Constitutive laws and failure models are calibrated and veried by the use of experiments and numerical simulations. For the constitutive equations, an eight parameter high exponent yield surface has been adopted, representing the anisotropic behaviour, and a mixed isotropic-kinematic hardening has been used to capture non-linear strain paths.

For ductile sheet metals three dierent failure phenomena have been observed: (i) ductile fracture, (ii) shear fracture, and (iii) instability with localised necking. The models for describing the dierent failure types have been chosen with an attempt to use just a few tests in addition to these used for the constitutive model. In this work the ductile and shear fracture have been prescribed by models presented by Cockroft-Latham and Bressan-Williams, respectively. The instability phenomenon is described by the constitutive law and the nite element models. The results obtained are in general in good agreement with test results.

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

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 58 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1529
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-77759 (URN)LIU-TEK-LIC-2012:14 (Local ID)978-91-7519-895-5 (ISBN)LIU-TEK-LIC-2012:14 (Archive number)LIU-TEK-LIC-2012:14 (OAI)
Presentation
2012-06-01, A39, Hus A, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2012-05-28 Created: 2012-05-28 Last updated: 2012-07-09Bibliographically approved
2. 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
3. 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
4. Ductile Failure in High Strength Steel Sheets
Open this publication in new window or tab >>Ductile Failure in High Strength Steel Sheets
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Developments in computer-aided engineering and the rapid growth of computational power have made simulation-driven process and product development efficient and useful since it enables detailed evaluation of product designs and their manufacturing processes. In the context of a sheet metal component, it is vital to predict possible failure both during its forming process and its subsequent usage. Accurate numerical models are needed in order to obtain trustworthy simulation results. Furthermore, the increasing demands imposed on improved weight-to-performance ratio for many products endorse the use of high-strength steels. These steels often show anisotropic behaviour and more complex hardening and fracturing compared to conventional steels. Consequently, demand for research on material and failure models suitable for these steels has increased.

In this work, the mechanical and fracture behaviour of two high-strength steels, Docol 600DP and Docol 1200M, have been studied under various deformation processes. Experimental results have been used both for material characterisation and for calibration of fracture criteria. One major requirement as concerns the fracture criteria studied is that they should be simple to apply in industrial applications, i.e. it should be possible to easily calibrate the fracture criteria in simple mechanical experiments and they should be efficient and accurate. Consequently, un-coupled phenomenological damage models have been the main focus throughout this work.

Detailed finite element models including accurate constitutive laws have be used to predict and capture material instabilities. Most of the fracture criteria studied are modifications of the plastic work to fracture. Ductile tensile and ductile shear types of fracture are of particular interest in sheet metal applications. For these fractures the modification of the plastic work relates to void coalescence and void collapse, respectively. Anisotropy in fracture behaviour can be captured by the introduction of a material directional function.

The dissertation consists of two parts. The first part contains theory and background. The second consists of five papers.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 60 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1579
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-105213 (URN)10.3384/diss.diva-105213 (DOI)978-91-7519-389-2 (ISBN)
Public defence
2014-04-11, C3, Hus C, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-03-13 Created: 2014-03-13 Last updated: 2014-05-27Bibliographically approved

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Larsson, RikardBjörklund, OscarNilsson, LarsgunnarSimonsson, Kjell

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