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Failure of high strength steel sheets: 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.
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.

Place, publisher, year, edition, pages
2013. Vol. 213, no 7, 1103-1117 p.
Keyword [en]
Sheet metal failure, high strength steels, forming limits, ductile fracture, shear fracture
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-77758DOI: 10.1016/j.jmatprotec.2013.01.027ISI: 000318325100011OAI: oai:DiVA.org:liu-77758DiVA: diva2:528962
Available from: 2012-05-28 Created: 2012-05-28 Last updated: 2017-12-07Bibliographically approved
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. 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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