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Stepwise modelling method for post necking characterisation of anisotropic sheet metal
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.ORCID iD: 0000-0001-9626-5406
Nagoya Institute of Technology, Japan.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.ORCID iD: 0000-0001-5218-396X
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.ORCID iD: 0000-0002-7514-0513
2021 (English)In: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 29, no 8, article id 085001Article in journal (Refereed) Published
Abstract [en]

Modelling and simulation are important tools during design and development processes. For accurate predictions of, e.g. manufacturing processes or final product performance, reliable material data is needed. Usually, the applied material models are calibrated by utilising direct methods such as conventional uniaxial tensile/compression tests but also inverse methods are occasionally applied. Recently, an effective inverse method, the stepwise modelling method (SMM), was presented. By using SMM, the flow stress from initial yielding, beyond necking to final fracture, can be determined. However, the method is developed for sheet materials having isotropic von Mises hardening. In this paper the SMM is extended for post necking characterisation of anisotropic sheet metals using the Barlat yield 2000 criterion. The novel method was applied to analyse the post necking plasticity of the widely used aluminium alloy AA6016 in T4 condition and the aluminium alloy AA5754 in H111 condition. The latter alloy has reported to show serrated yielding, also known as the Portevin–Le Chatelier effect. The obtained flow stress curves agree well with the curves form conventional uniaxial tensile tests up to the point of necking and show credible post necking predictions to final fracture. Furthermore, SMM showed that it could handle the effect of serrated yielding for AA5754-H111. Hence, the novel approach can be used to characterise the post necking hardening of a variety of anisotropic sheet metals and thereby contributes to efficient and reliable material model calibration.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2021. Vol. 29, no 8, article id 085001
Keywords [en]
Anisotropy, Post necking, Barlat Yield 2000, Stepwise Modelling Method, SMM, AA6016 T4, AA5754 H111
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-87207DOI: 10.1088/1361-651X/ac2797ISI: 000702062400001Scopus ID: 2-s2.0-85117469314OAI: oai:DiVA.org:ltu-87207DiVA, id: diva2:1597059
Funder
EU, Horizon 2020, 814517Vinnova, 2019-02639
Note

Validerad;2021;Nivå 2;2021-10-01 (alebob)

Available from: 2021-09-24 Created: 2021-09-24 Last updated: 2023-09-05Bibliographically approved
In thesis
1. An Approach on Material Model Calibration for Modelling of Sheet Metal Deformation and Failure
Open this publication in new window or tab >>An Approach on Material Model Calibration for Modelling of Sheet Metal Deformation and Failure
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Sheet metals are often used in automotive and aerospace applications for safety-relevant components. Weight reduction is one possibility to reduce fuel consumption or increase the payload capacity and therewith reduce the carbondioxide emission of these trans-portation vehicles. The weight reduction can be achieved by using new sheet metal alloys and thereby reducing the sheet metals thickness. Advanced material process-ing technologies like for example the press hardening process to manufacture ultra high strength steels (UHSS) are an important contribution to weight reduction. Furthermore, the usage of many different sheet metal materials and grades, like the new generation of advanced high strength steels (AHSS) and aluminium alloys will replace further low strength steel components.To challenge the balance between safety and weight reduction, while maintaining safety, reliable and efficient engineering tools are needed. Finite Element (FE) simulations are commonly used to prove a maintained safety for parts with a decreased sheet thickness and weight. This leads to a high demand on the simulation precision of sheet metals, where an accurate prediction of the failure behaviour and the post-necking hardening of materials is needed. Therefore, an approach on material model calibration for modelling of sheet metal deformation and failure is developed. The ability for companies to predict the performance envelop of all these new sheet metal alloys and components is of great importance for the metal manufacturer as well as for the automotive industry.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 relation 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 com-putational 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 mod-elling. This method is shown in an aerospace application for the nickel based super alloy Alloy 718. A study on simulating the whole comments lifespan from blank to fractured component is presented by producing a laboratory scale UHSS-component and testing it until fracture. The component performance simulation is based on results obtained by SMM for paint baked fully hardened boron steel. To enable the post necking characterization of anisotropic sheet metals like aluminium alloys an updated SMM version based on an anisotropic plasticity model is presented and evaluated for the aluminium alloys AA6016 and AA5754. Finally, the fracture behaviour of an automotive 6000 series alu-minium alloy in different directions is presented. In this study a GISSMO failure model is calibrated based on full field measurements under different stress states and evaluated on a multi triaxiality tensile specimen.The results shown in this thesis are that the presented 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 calibrated and used for advanced forming and component performance simulations. This can lead to reduce time and costs during the development processes of new materials and products.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2021
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-87209 (URN)978-91-7790-930-9 (ISBN)978-91-7790-931-6 (ISBN)
Public defence
2021-11-23, E632, Luleå, 14:00 (English)
Opponent
Supervisors
Available from: 2021-09-27 Created: 2021-09-24 Last updated: 2023-09-05Bibliographically approved

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Marth, StefanKajberg, JörgenHäggblad, Hans-Åke

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