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Modelling of Failure in High Strength Steel Sheets
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
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: urn:nbn:se:liu:diva-77759Local ID: LIU-TEK-LIC-2012:14ISBN: 978-91-7519-895-5 OAI: oai:DiVA.org:liu-77759DiVA: diva2:528964
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
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. Failure of high strength steel sheets: Experiments and modelling
Open this publication in new window or tab >>Failure of high strength steel sheets: Experiments and modelling
2013 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 213, no 7, 1103-1117 p.Article in journal (Refereed) Published
Abstract [en]

Failure in sheet metal structures of ductile material is usually caused by one of, or a combination of, ductile fracture, shear fracture or localised instability. In this paper the failure of the high strength steel Docol 600DP and the ultra high strength steel Docol 1200M is explored. The constitutive model used in this study includes plastic anisotropy and mixed isotropic-kinematic hardening. For modelling of the ductile and shear fracture the models presented by Cockroft–Latham and Bressan–Williams have been used. The instability phenomenon is described by the constitutive law and the finite element (FE) models. For calibration of the failure models and validation of the results, an extensive experimental series has been conducted including shear tests, plane strain tests and Nakajima tests. The geometries of the Nakajima tests have been chosen so that the first quadrant of the forming limit diagram (FLD) were covered. The results are presented both in an FLD and using prediction of force–displacement response of the Nakajima test employing element erosion during the FE simulations. The classical approach for failure prediction is to compare the principal plastic strains obtained from FE simulations with experimental determined forming limit curves (FLCs). It is well known that the experimental FLC requires proportional strains to be useful. In this work failure criteria, both of the instability and fracture, are proposed which can be used also for non-proportional strain paths.

Keyword
Sheet metal failure, high strength steels, forming limits, ductile fracture, shear fracture
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-77758 (URN)10.1016/j.jmatprotec.2013.01.027 (DOI)000318325100011 ()
Available from: 2012-05-28 Created: 2012-05-28 Last updated: 2017-12-07Bibliographically approved

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Björklund, Oscar

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