Improved failure characterisation of high-strength steel using a butterfly test rig with rotation control

authored by: Eugen Stockburger, Hendrik Wester, Vithusaan Jegatheeswaran, Matthäus Dykiert, Bernd Arno Behrens
Abstract: A forming limit diagram is the standard method to describe the forming capacity of sheet materials. It predicts failure due to necking by limiting major and minor strains. For failure due to fracture, the fracture forming limit diagram is used, but fracture caused by plastic deformation at a shear-dominated stress state cannot be predicted with a conventional fracture forming limit diagram. Therefore, stress-based failure models are used as an alternative. These models are describing the fracture of sheet materials based on the failure strain and the stress state. Material-specific parameters must be determined, but a standardised procedure for the calibration of stress-based failure models is currently not established. Most test procedures show non-constant stress paths and varying stress states in the crack initiation area, which leads to uncertainties and inaccuracies for modelling. Therefore, a new test methodology was invented at the IFUM: a prior presented butterfly test rig was extended to enable an online rotation to adapt the loading angle while testing. First, butterfly tests with CP800 were performed for three fixed loading conditions. The tests were modelled numerically with boundary conditions corresponding to the tests. Based on the numerical results, the stress state as well as failure strain were identified and the stress state deviations were calculated. Afterwards, the necessary angular displacements to compensate the stress state deviations for the adaptive test rig were iteratively determined with numerical simulations using an automatised Python script. Finally, the butterfly tests were performed experimentally with the determined adaptive loading angles to identify the specimen failure and compared to the simulations for validation.
Organisation(s): Institute of Metal Forming and Metal Forming Machines
Type: Conference contribution
Pages: 737-746
No. of pages: 10
Publication date: 19.04.2023
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: General Materials Science
Electronic version(s): https://doi.org/10.21741/9781644902479-80 (Access: Open)
: Details in the research portal "Research@Leibniz University"

BibTeX

@inproceedings{7a437333dd07495d868f14e1bca5a40d,
title = "Improved failure characterisation of high-strength steel using a butterfly test rig with rotation control",
abstract = "A forming limit diagram is the standard method to describe the forming capacity of sheet materials. It predicts failure due to necking by limiting major and minor strains. For failure due to fracture, the fracture forming limit diagram is used, but fracture caused by plastic deformation at a shear-dominated stress state cannot be predicted with a conventional fracture forming limit diagram. Therefore, stress-based failure models are used as an alternative. These models are describing the fracture of sheet materials based on the failure strain and the stress state. Material-specific parameters must be determined, but a standardised procedure for the calibration of stress-based failure models is currently not established. Most test procedures show non-constant stress paths and varying stress states in the crack initiation area, which leads to uncertainties and inaccuracies for modelling. Therefore, a new test methodology was invented at the IFUM: a prior presented butterfly test rig was extended to enable an online rotation to adapt the loading angle while testing. First, butterfly tests with CP800 were performed for three fixed loading conditions. The tests were modelled numerically with boundary conditions corresponding to the tests. Based on the numerical results, the stress state as well as failure strain were identified and the stress state deviations were calculated. Afterwards, the necessary angular displacements to compensate the stress state deviations for the adaptive test rig were iteratively determined with numerical simulations using an automatised Python script. Finally, the butterfly tests were performed experimentally with the determined adaptive loading angles to identify the specimen failure and compared to the simulations for validation.",
keywords = "Butterfly Specimen, CP800, Experimental-Numerical Procedure",
author = "Eugen Stockburger and Hendrik Wester and Vithusaan Jegatheeswaran and Matth{\"a}us Dykiert and Behrens, {Bernd Arno}",
note = "Funding Information: The authors would like to thank the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) for the financial and organisational support of this project with the number 405334714. Furthermore, the authors would like to thank voestalpine Stahl GmbH for providing the material under investigation.; 26th International ESAFORM Conference on Material Forming, ESAFORM 2023 ; Conference date: 19-04-2023 Through 21-04-2023",
year = "2023",
month = apr,
day = "19",
doi = "10.21741/9781644902479-80",
language = "English",
isbn = "9781644902462",
series = "Materials Research Proceedings",
publisher = "Association of American Publishers",
pages = "737--746",
editor = "Lukasz Madej and Mateusz Sitko and Konrad Perzynsk",
booktitle = "Material Forming",
}