Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Towards energy-based fracture modelling for crashworthiness applications
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.ORCID iD: 0000-0001-5120-6533
2024 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The automotive industry is currently adapting to progessively more stringent emission and safety regulations imposed by governmental agencies. This introduces significant design difficulties due to the conflicting nature of passenger safety in automotive manufacturing, namely that increased crashworthiness generally leads to heavier vehicles, which in turn leads to more severe crashes. Significant industry effort to introduce lightweight materials into automotive Body-in-White (BIW) design has thus been introduced in recent years to reduce curb weight while improving crashworthiness. Third generation Advanced High Strength Steels (3rd-gen AHSS) and new generations of press hardening steels (PHS) has emerged as cost-effective and natural substitutes in the safety critical crush zones of the vehicle. The limited ductility of these higher strength materials can however make them more prone to cracking, which in turn make reliable deformation behaviour difficult in a crash event. Thus, predicting cracks in the material and its resistance to further propagate them are essential in evaluating crash performance of a design. Fracture toughness measured within the frame of fracture mechanics using the Essential Work of Fracture (EWF) has shown to correlate well with AHSS crashworthiness for steel sheets, making it an interesting parameter for further study in this area. EWF is however strain rate dependent, and most available EWF testing for AHSS is still performed using quasi-static loading rates, conditions completely different from common high-speed crash scenarios. Furthermore, since full-scale testing is a costly endeavor, numerical modelling is used in Computer Aided Engineering (CAE) to test designs before proceeding with a physical prototype. To promote the use of new high strength steel grades in the industry, reliable and properly characterised material models are thus necessary. These models then need to be validated with component experiments to ensure that the models are accurate enough. This is usually done using crash box components in an axial compression or three-point bending setup because of their similarity to real structural components used in crash zones. In this work, EWF at the higher loading rates common in crash scenarios is further investigated to contribute additional data regarding strain rate dependence of fracture toughness measured within the frame of fracture mechanics for AHSS sheets. Furthermore, the crashworthiness of dynamically loaded axially compressed AHSS and PHS crash boxes are evaluated both experimentally using full-field measurements and numerically using a commercially available damage model. The high-speed photography allow for a more efficient component crashworthiness evaluation with fewer components due to the possibility to track crack initiations and their propagation during the deformation. The results from the commercial damage model show that although the prediction of the first cracks is decent, the damage evolution is not captured accurately. These results show the need for further development of economically feasible (shell) damage models that take propagation energy into account in crash simulations. This would also help promote the use of fracture toughness in the automotive industry.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2024.
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-104681ISBN: 978-91-8048-503-6 (print)ISBN: 978-91-8048-504-3 (electronic)OAI: oai:DiVA.org:ltu-104681DiVA, id: diva2:1845610
Presentation
2024-05-03, C305, Luleå University of Technology, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2024-03-19 Created: 2024-03-19 Last updated: 2024-04-12Bibliographically approved
List of papers
1. Evaluation of Crashworthiness Using High-Speed Imaging, 3D Digital Image Correlation, and Finite Element Analysis
Open this publication in new window or tab >>Evaluation of Crashworthiness Using High-Speed Imaging, 3D Digital Image Correlation, and Finite Element Analysis
2023 (English)In: Metals, E-ISSN 2075-4701, Vol. 13, no 11, article id 1834Article in journal (Refereed) Published
Abstract [en]

To promote the use of newhigh-strengthmaterials in the automotive industry, the evaluation of crashworthiness is essential, both in terms of finite element (FE) analysis aswell as validation experiments. Thiswork proposes an approach to address the crash performance through high-speed imaging combined with 3D digital image correlation (3D-DIC). By tracking the deformation of the component continuously, cracks can be identified and coupled to the load and intrusion history of the experiment. The so-called crash index (CI) and its decreasing rate (CIDR) can then be estimated using only one single (or a few) component, instead of a set of components with different levels of intrusion and crushing. Crash boxes were axially and dynamically compressed to evaluate the crashworthiness of TRIP-aided bainite ferrite steel and press-hardenable steel. Acalibrated rate-dependent constitutivemodel, and a phenomenological damage model were used to simulate the crash box testing. The absorbed energy, the plastic deformation, and the CIDR were evaluated and compared to the experimentally counterparts. When applying the proposed method to evaluate the CIDR, a good agreement was found when using CI:s reported by other authors using large sets of crash boxes. The FE analyses showed a fairly good agreement with some underestimation in terms of energy absorptions. The crack formation was overestimated resulting in too high a predicted CIDR. It is concluded that the proposed method to evaluate the crashworthiness is promising. To improve the modelling accuracy, better prediction of the crack formation is needed and the introduction of the intrinsic material property, fracture toughness, is suggested for future investigations and model improvements.

Place, publisher, year, edition, pages
MDPI, 2023
Keywords
crashworthiness, crash index, third-generation AHSS, 3D digital image correlation, high strain rate, damage modelling
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-101999 (URN)10.3390/met13111834 (DOI)001113335200001 ()2-s2.0-85177648214 (Scopus ID)
Funder
EU, Horizon 2020, FormPlanet, no. 814519
Note

Validerad;2023;Nivå 2;2023-11-01 (joosat);

Part of special issue: Mechanical Behaviors and Damage Mechanisms of Metallic Materials

CC BY 4.0 License

Available from: 2023-11-01 Created: 2023-11-01 Last updated: 2025-03-12Bibliographically approved
2. Studying the rate-dependence of Essential Work of Fracture in press hardening steels
Open this publication in new window or tab >>Studying the rate-dependence of Essential Work of Fracture in press hardening steels
Show others...
2024 (English)In: : 9th International Conference on Hot Sheet Metal Forming of High-Performance Steel, CHS2 2024 - Proceedings / [ed] Casellas D.; Hardell J., Association for Iron and Steel Technology, AISTECH , 2024, p. 47-52Conference paper, Published paper (Other academic)
Place, publisher, year, edition, pages
Association for Iron and Steel Technology, AISTECH, 2024
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-104677 (URN)10.33313/512/A0302 (DOI)2-s2.0-85197874368 (Scopus ID)
Conference
9th International Conference on Hot Sheet Metal Forming of High-Performance Steel (CHS2 2024), Nashville, USA, May 27-29, 2024
Note

Funder: EU Horizon2020 (814519);

ISBN for host publication: 978-093076730-3; 

Available from: 2024-03-19 Created: 2024-03-19 Last updated: 2025-07-04Bibliographically approved

Open Access in DiVA

fulltext(15092 kB)692 downloads
File information
File name FULLTEXT01.pdfFile size 15092 kBChecksum SHA-512
db4702cfe7af4389f88c312c97c6b954ce2686f20ce5698b36f1f1ec2effcda1fb43c04a5bed1e6599d5994ffa66b457e317e4e98d15f00225daa54d365cd8f8
Type fulltextMimetype application/pdf

Authority records

Jonsson, Simon

Search in DiVA

By author/editor
Jonsson, Simon
By organisation
Solid Mechanics
Applied Mechanics

Search outside of DiVA

GoogleGoogle Scholar
Total: 693 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 423 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf