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Predicting Sheared Edge Characteristics of High Strength Steels
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.ORCID iD: 0000-0002-0764-5667
2022 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

An efficient way of reducing CO2 emissions from the transportation sector is to reduce the vehicle weights, i.e. lightweighting. A common strategy for lightweighting of vehicles is to replace the steels used to build structural parts of the vehicle, usually manufactured by metallic sheets, with stronger, advanced high strength steel (AHSS) grades. Using stronger steel grades enables down-gauging while the structural integrity of the parts remain unchanged. However, the increase in strength of AHSS typically comes with a loss of ductility, affecting their forming properties. A common AHSS manufacturing defect is edge cracking occurring when a sheared edge (damaged by the shearing operation) is bent or stretched. It is known in the sheet metal forming industry that the shear cutting process introduces damage, in terms of micro-cracks and notches, to sheared edges from which edge cracks can grow. Conventional forming analyses do not include the effects from sheared edge damage and therefore can not predict edge cracking during forming. Numerical modelling of the shear cutting process can aid the understanding of sheared edge damage and how it affects the AHSS edge cracking phenomena.

This thesis presents experimental and numerical methods for calibration of acommercial damage- and failure model, intended for shear cutting simulations. Crack initiation and propagation govern the shear cutting process of AHSS sheets. Therefore, a commercial numerical damage- and failure model was studied regarding its ability to predict shear edge damage. The investigation shows that the damage and failure model has limitations concerning prediction of crack initiation, thus concluding that modelling of processes including formation of cracks using the said damage- and failure model risks to generate erroneous results. This phenomena was also seen in modelling of shear cutting, where the crack-driven fracture process following burnish formation was delayed. Through sensitivity analysis of uncalibrated areas on the failure locus could accurate correlation between numerical and experimental cut edge morphology be obtained. Such results show that additional calibration experiments are necessary, but also the need for development of stress-state dependent failure modelling of AHSS that includes the effect from cracks.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2022.
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-93322ISBN: 978-91-8048-157-1 (print)ISBN: 978-91-8048-158-8 (electronic)OAI: oai:DiVA.org:ltu-93322DiVA, id: diva2:1699964
Presentation
2022-11-25, C305, Luleå tekniska universitet, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2022-09-29 Created: 2022-09-29 Last updated: 2023-09-05Bibliographically approved
List of papers
1. Stating failure modelling limitations of high strength sheets: Implications to sheet metal forming
Open this publication in new window or tab >>Stating failure modelling limitations of high strength sheets: Implications to sheet metal forming
2021 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 14, no 24, article id 7821Article in journal (Refereed) Published
Abstract [en]

This article discusses the fracture modelling accuracy of strain-driven ductile fracture models when introducing damage of high strength sheet steel. Numerical modelling of well-known fracture mechanical tests was conducted using a failure and damage model to control damage and fracture evolution. A thorough validation of the simulation results was conducted against results from laboratory testing. Such validations show that the damage and failure model is suited for modelling of material failure and fracture evolution of specimens without damage. However, pre-damaged specimens show less correlation as the damage and failure model over-predicts the displacement at crack initiation with an average of 28%. Consequently, the results in this article show the need for an extension of the damage and failure model that accounts for the fracture mechanisms at the crack tip. Such extension would aid in the improvement of fracture mechanical testing procedures and the modelling of high strength sheet metal manufacturing, as several sheet manufacturing processes are defined by material fracture.

Place, publisher, year, edition, pages
MDPI, 2021
Keywords
Advanced high strength Steel, Crack tips, Fracture testing, High strength steel, Metal forming, Sheet metal, Advanced high strength steel, Complex-phase steels, Damage and failure, Damage modelling, Failure modelling, Fracture model, GISSMO, High strength sheets, Material fracture, Sheet metal forming, Ductile fracture
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-88595 (URN)10.3390/ma14247821 (DOI)000738368600001 ()34947415 (PubMedID)2-s2.0-85121359847 (Scopus ID)
Note

Validerad;2022;Nivå 2;2022-01-01 (johcin)

Available from: 2021-12-30 Created: 2021-12-30 Last updated: 2023-09-05Bibliographically approved
2. A numerical approach for predicting cut edge morphology in high strength sheets
Open this publication in new window or tab >>A numerical approach for predicting cut edge morphology in high strength sheets
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-93321 (URN)
Available from: 2022-09-29 Created: 2022-09-29 Last updated: 2023-09-05

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Sandin, Olle

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