University of Oulu

Aki-Petteri Pokka, Anna-Maija Arola, Antti Kaijalainen, Vili Kesti and Jari Larkiola, « Strain distribution during air bending of ultra-high strength steels », ESAFORM 2021 [Online], Online since 30 March 2021, connection on 19 April 2021. URL :

Strain distribution during air bending of ultra-high strength steels

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Author: Pokka, Aki-Petteri1; Arola, Anna-Maija1; Kaijalainen, Antti1;
Organizations: 1University of Oulu, Materials and Mechanical Engineering, P.O. Box 4200 FI-90014 University of Oulu, Finland
2SSAB Europe, Rautaruukintie 115, 92101 Raahe, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 0.8 MB)
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Language: English
Published: ESAFORM, 2021
Publish Date: 2021-04-19


Air bending is a widely used method for forming ultra-high strength steels (UHSS). However, the limited formability of UHSS poses some challenges for the bending process in the form of strain localisation, surface defects, punch detachment (multi-breakage) and pseudo-polygonal “nut-like” shape of the bend. In this study, the bendability of three UHSS grades (700, 900 and 1100 MPa) is investigated with 3-point bending tests, utilising Digital Image Correlation (DIC) for measuring the strain distributions on the outer curvature. The differences in the extent of multi-breakage and the bend shapes are also studied, and these observations are correlated with the findings from the bending force and strain measurements. The differences between the investigated UHSS grades are significant. The 900 MPa grade produces more localised strain distributions and pronounced multi-breakage compared to the other grades, along with a more polygonal “nut-like” geometry. The reasons and effects of the multi-breakage phenomenon, as well as the causes for the observed differences in the behaviour of the materials are discussed in this paper. The presented results and the measurement data provide more information about the behaviour of the investigated materials in bending, and can be used for improving bending simulation, numerical models, and workshop instructions.

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ISBN: 978-2-87019-003-6
ISBN Print: 978-2-87019-002-9
Pages: 1 - 7
DOI: 10.25518/esaform21.2509
Host publication: ESAFORM 2021 proceedings
Conference: International Conference on Material Forming
Type of Publication: A4 Article in conference proceedings
Field of Science: 216 Materials engineering
Copyright information: © 2021 The Authors. This article is published under the terms and conditions of the CC-BY License (