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From Blank to Fractured Component: Numerical and Experimental Results of a Laboratory Scale Component
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.ORCID iD: 0000-0001-9626-5406
Gestamp R&D, Luleå, Sweden.
Gestamp R&D, Luleå, Sweden.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.ORCID iD: 0000-0001-7074-8960
2018 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Hot stamping of boron alloyed steel has become a standard in the automotive industry for safety relevant chassis components. Hot stamping of ultra-high strength steel allows the design of complex geometries with superior mechanical properties. In the present work, a laboratory scale test component is followed up from blank to fractured component. The production process starts with a pre-cut blank, which then is austenitized, transferred to the press hardening tool, formed and quenched and ends with post-cooling to room temperature. These components are tested under tensile deformation until fracture, where force, elongation and the strain field on the components surface are measured. The strain field measurements are performed by using digital image correlation (DIC). The laboratory scale test component is evaluated using finite element modelling. The production process is modelled starting with a pre-cut austenitized blank, subsequent transfer and forming operation, and ends with post-cooling. Furthermore, the deformation and fracture under tension/bending is studied using the OPTUS damage model. The as-produced component is measured using a three dimensional scanning system. Shape deviation and thickness change are compared to in the forming simulation predicted geometry after post-cooling. A finite element investigation on the deformation and fracture under tensional/bending loading is conducted applying shape and thickness deviations in the model. The majority of industrial components undergo paint curing before they are included in an assembly. Paint baking is a heat treatment at relatively low temperatures and causes relaxation in a martensitic microstructure. The effect of paint baking on the mechanical response of the laboratory scale test component is investigated. In the present work the reliability of modelling tools from blank to fractured component is shown. The possibility is shown to predict the failure of the component, with the specific phase composition after the hot stamping process obtained from simulations. Furthermore, the influence of the paint baking process on the mechanical properties is presented.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2018. Vol. 418, article id 012008
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-71045DOI: 10.1088/1757-899X/418/1/012008ISI: 000546393900008Scopus ID: 2-s2.0-85054247283OAI: oai:DiVA.org:ltu-71045DiVA, id: diva2:1252998
Conference
International Deep Drawing Research Group 37th Annual Conference 3–7 June 2018, University of Waterloo, Waterloo, Ontario, Canada
Available from: 2018-10-03 Created: 2018-10-03 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, StefanOldenburg, Mats

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