University of Oulu

A Kaijalainen et al 2022 IOP Conf. Ser.: Mater. Sci. Eng. 1270 012080

Effect of surface roughness on strain distribution during bending

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Author: Kaijalainen, A1; Pokka, A-P1; Jaskari, M2;
Organizations: 1Materials and Mechanical Engineering, Centre for Advanced Steels Research, University of Oulu, Pentti Kaiteran katu 1, 90570 Oulu, Finland
2Kerttu Saalasti Institute, University of Oulu, Pajatie 5, 85500 Nivala, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.3 MB)
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Language: English
Published: IOP Publishing, 2022
Publish Date: 2023-01-13


The limited formability of ultra-high strength steels (UHSS) poses some challenges for the bending process in the form of strain localisation, surface defects and pseudo-polygonal “nut-like” shape of the bend. Bendability is well known to be affected by surface quality, and especially shot blasting. Therefore, in this study, the effect of surface roughness on bendability of UHSS grade is investigated with 3-point bending tests, utilising Digital Image Correlation (DIC) for measuring the strain distributions on the outer curvature. Investigated bending samples of 4 mm thick commercial martensitic were tested in different surface conditions: As-rolled (with scale), “lightly” shot blasted (SB I), “roughly” shot blasted (SB II), dry electropolished (As-rolled P) and a combination of “rough” shot blasting and dry electropolishing (SB II P). Shot blasting increased the surface roughness and subsurface hardness. Utilizing a commercial dry electropolishing process reduced the surface roughness, although this also had major effect on the hardness. Bending results showed that coarser surface roughness decreased the bending capacity, i.e. reduced maximum bending angle and critical strain. A strong correlation between surface roughness (with Rv: the maximum valley depth below the mean surface) and critical bending angle was found, likewise with the subsurface hardness and critical bending angle.

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Series: IOP conference series. Materials science and engineering
ISSN: 1757-8981
ISSN-E: 1757-899X
ISSN-L: 1757-8981
Volume: 1270
Issue: 1
Article number: 012080
DOI: 10.1088/1757-899x/1270/1/012080
Host publication: The 19th International Conference on Metal Forming (MF 2022) 11/09/2022 - 14/09/2022 Online
Conference: International Conference on Metal Forming
Type of Publication: A4 Article in conference proceedings
Field of Science: 216 Materials engineering
Funding: Financial assistance of the Business Finland, projects ISA – Intelligent Steel Applications and FOSSA– Fossil-Free Steel Applications, are acknowledged.
Copyright information: Published under licence by IOP Publishing Ltd. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.