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Post necking characterisation for sheet metal materials using full field measurement
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.ORCID iD: 0000-0001-9626-5406
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.ORCID iD: 0000-0002-7514-0513
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.ORCID iD: 0000-0001-7074-8960
Number of Authors: 42016 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 238, p. 315-324Article in journal (Refereed) Published
Abstract [en]

precise prediction of the post-necking behaviour of materials is needed to increase the precision of computer simulations with large deformations. Applications in which this need is encountered include crash, forming, and failure simulations. By using an optical full-field measurement of the localised deformation field, an effective and computationally fast method is presented to determine the relationship between true stress and true plastic strain, including post-necking behaviour. The presented stepwise modelling method is used to characterise heat-treated boron steel using thin sheet metal specimens. These results are validated with the results determined by a method based on inverse modelling. It can be concluded that the stepwise modelling method is considerably faster than the compared inverse modelling method. The method is also suitable for effectively determining element size dependency due to regularisation of the hardening behaviour needed for finite element analysis with strain localisation, e.g., for crash simulations

Place, publisher, year, edition, pages
2016. Vol. 238, p. 315-324
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-7653DOI: 10.1016/j.jmatprotec.2016.07.036ISI: 000383291500035Scopus ID: 2-s2.0-84979761844Local ID: 60ea60e7-bbdb-410a-ad81-db321eb80b2cOAI: oai:DiVA.org:ltu-7653DiVA, id: diva2:980543
Note

Validerad; 2016; Nivå 2; 20160816 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
In thesis
1. Material Characterization for Modelling of Sheet Metal Deformation and Failure
Open this publication in new window or tab >>Material Characterization for Modelling of Sheet Metal Deformation and Failure
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Weight reduction is one possibility to reduce fuel consumption and emission of transportation vehicles. Sheet metals are often used in automotive and aerospace applications and therefore the weight reduction achieved by reducing the sheet metals thickness is an important contribution to weight reduction. Increasing the strength of sheet metal materials gives the opportunity to reduce the total weight while maintaining safety. To prove a maintained safety for parts with a decreased weight Finite Element (FE) simulations are commonly used. This leads to a high demand on the simulation precision of sheet metals, where an accurate prediction of the post-necking behaviour of materials is needed. Improved FE simulations are reducing time and costs during the development processes. 

One application to improve the strength of sheet metals in the automotive industry is the usage of ultra high strength steels, which has constantly increased in usage during the last decades. The development of the press hardening process, where sheet metal blanks are formed and quenched simultaneously, brings new design opportunities. Using press hardening tools with zones that uses different cooling rates sheet metal parts can be produced with tailored properties, to improve their performance. Simulating materials based on the microstructure demands high precision on the plasticity modelling for high strain values. 

In this thesis work a method to characterize the elasto plastic post necking behaviour of sheet metal materials, the Stepwise Modelling Method (SMM), is presented. The method uses full field measurements of the deformation field on the surface of tensile specimen. The hardening relation is modelled as a piecewise linear in a step by step procedure. The linear hardening parameter is adapted to reduce the residual between experimental and calculated tensile forces. The SMM is used to characterize the post necking behaviour of a ferritic boron steel and the results are compared with the commonly used inverse modelling method. It is shown that the stepwise modelling method characterizes the true stress, true plastic strain relation in an effective and computational efficient way. Furthermore, the SMM is used to characterize the stress state evolution during tensile testing, which is an important factor for failure and fracture modelling. This method is shown in an aerospace application for the nickel based super alloy Alloy 718. 

The results shows that the stepwise modelling method is an effective and efficient alternative method to characterize the deformation and failure of sheet metals. Based on the results of this method plasticity and fracture models can be characterized in future work.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2017
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Materials Engineering Mechanical Engineering Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-62477 (URN)978-91-7583-845-8 (ISBN)978-91-7583-846-5 (ISBN)
Presentation
2017-05-12, E231, Luleå University of Technology, Luleå, 10:00 (English)
Available from: 2017-03-15 Created: 2017-03-13 Last updated: 2017-11-24Bibliographically approved

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Marth, StefanHäggblad, Hans-åkeOldenburg, MatsÖstlund, Rickard

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