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Calibration of a damage and fracture model for alloy 718
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials. Forming group OSAS, Industrial Development Centre in Olofström AB, Vällaregatan 30, Olofström.ORCID iD: 0000-0002-1432-444X
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.ORCID iD: 0000-0001-9626-5406
DYNAmore Nordic AB, Linköping.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials. Forming group OSAS, Industrial Development Centre in Olofström AB, Vällaregatan 30, Olofström.
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2016 (English)In: Advancements in Theoretical and Applied Plasticity: Proceedings of PLASTICITY ’16: The Twenty Second International Symposium on Plasticity and its Current Applications / [ed] Akhtar S. Khan, Fulton, Maryland 20759-0591, USA: NEAT PRESS , 2016, p. 223-225Conference paper, Published paper (Refereed)
Abstract [en]

Nickel-based superalloys are primarily used in the hot sections of aircraft engines because they can maintain their mechanical properties and chemical stabilities at high temperatures under severe corrosive environments i.e. for a long time. In order to simulate forming procedures in Alloy 718 sheets, the GISSMO damage and failure model is coupled with both isotropic von Mises and anisotropic Barlat YLD2000 material models in the finite element code LS-DYNA. In this study, the calibration of the GISSMO model for forming simulations at room temperature is discussed. The calibration requires failure strains for different stress states as a function of triaxiality, which are obtained by testing six different specimen geometries up to fracture. Numerical predictions will be compared with experimental observations from forming tests.

Place, publisher, year, edition, pages
Fulton, Maryland 20759-0591, USA: NEAT PRESS , 2016. p. 223-225
Keywords [en]
damage, fracture, nickel-based superalloys, Alloy 718, forming, GISSMO
National Category
Metallurgy and Metallic Materials Applied Mechanics
Research subject
Solid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-62818ISBN: 978-0-9911654-7-6 (electronic)OAI: oai:DiVA.org:ltu-62818DiVA, id: diva2:1087053
Conference
22nd International Symposium on Plasticity and Its Current Applications, (Plasticity 2016), Kona, Hawaii, January 3-9, 2016
Projects
NFFP6 - Virtuell processkedja för plåtformade flygmotorstrukturer i superlegeringar – Validering och demonstrator
Funder
VINNOVA, 2013-01173Available from: 2017-04-05 Created: 2017-04-05 Last updated: 2019-10-04Bibliographically approved
In thesis
1. Modelling of Forming and Welding in Alloy 718
Open this publication in new window or tab >>Modelling of Forming and Welding in Alloy 718
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The reduction of fuel consumption and carbon dioxide emissions are currently a key factor for the aviation industry due to major concerns about climate change and more restrictive environmental laws. One way to reduce both fuel consumption and CO2 emissions is by significantly decreasing the vehicle’s weight while increasing engine's efficiency. In order to meet these requirements, the European aero engine industry is continuously focusing on alternative manufacturing methods for load carrying structures in advanced materials, such as titanium and nickel-based superalloys. Alternatively to traditional large-scale single castings, new manufacturing methods involve sheet metal parts, small castings and forgings assembled by welding. These new manufacturing methods allow more flexible designs in which each part is made of the most suitable material state, leading to several advantages such as reduction of product cost and weight while increasing engine's efficiency. Nickel-based superalloys are widely used in the aero engine industry, typically constituting up to 50% of the total weight of the aircraft engine. Due to their excellent material properties at high temperatures in severe corrosive environments, these superalloys are employed most extensively in the hot sections of gas turbine engines for both military and civil aircrafts with running temperatures up to 650°C.

In this thesis, a manufacturing process chain including forming and welding in the nickelbased superalloy 718 is studied. The main focus in the work lies on determining the thermomechanical properties, modelling and simulation of cold forming, study forming limits based on Nakazima tests for forming limit curves (FLC) and applying a damage and failure criterion. The work also comprises a brief study on hot forming. Finally, modelling of a subsequent welding procedure is included where residual stresses from the forming simulation are used to predict shape distortions due to the welding procedure. The results are compared with experimental observations.

The cold forming procedure of a double-curved component made of alloy 718 is studied using FE-analyses and forming tests. The same geometry was used to produce a hot forming tool. During forming tests at room temperature, micro cracks and open cracks were observed in the draw bead regions, not indicated when formability is assessed using a forming limit curve (FLC). Standard material models such as von Mises or Barlat Yld2000-2D were not capable of accurately predict the behaviour of the material after the point of diffuse necking, making the prediction of damage and failure during forming a challenge. The GISSMO damage model was therefore calibrated and used to predict material failure in forming of alloy 718. Tensile, plane strain, shear and biaxial tests at room temperature are performed up to fracture and continuously evaluated using Digital Image Correlation (DIC) by ARAMIS™. In this work, the GISSMO damage model is coupled with the anisotropic Barlat Yld2000-2D material model for forming simulations in alloy 718 at room temperature using LS-DYNA. Numerical predictions are able to accurately predict failure on the same regions as observed during the experimental forming tests. Comparisons of the distribution of damage on one of the draw beads between simulations and damage measurements by acoustic emission indicate that higher damage values correspond to bigger micro cracks. Numerical FE-predictions of the cold forming and subsequent welding procedure shows that the welding procedure further increases the shape distortions. This was found to agree with experimental observations.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2017
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keywords
Forming, welding, Alloy 718, damage, GISSMO, failure
National Category
Applied Mechanics Metallurgy and Metallic Materials
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-62901 (URN)978-91-7583-870-0 (ISBN)978-91-7583-871-7 (ISBN)
Presentation
2017-06-16, E231, Luleå, 13:00 (English)
Supervisors
Projects
Virtuell processkedja för plåtformade flygmotorstrukturer i superlegeringar – Validering och demonstrator
Funder
VINNOVA, 2013-01173
Available from: 2017-04-06 Created: 2017-04-05 Last updated: 2017-11-24Bibliographically approved
2. Modelling Aspects in Forming and Welding of Nickel-Base Superalloys
Open this publication in new window or tab >>Modelling Aspects in Forming and Welding of Nickel-Base Superalloys
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The reduction of fuel consumption and carbon dioxide emissions are currently a key factor for the aviation industry because of major concerns about climate change and more restrictive environmental laws. One way to reduce both fuel consumption and CO2 emissions is by significantly decreasing the weight of vehicles while increasing the efficiency of the engine. To meet these requirements, the European aero-engine industry is continuously focusing on improved engine designs and alternative manufacturing methods for load-carrying structures in advanced materials, such as titanium and nickel-base superalloys. These new manufacturing methods involve sheet-metal parts, small castings, and forgings assembled using welding, enabling flexible designs where each part is made of the most suitable materials and states, with advantages such as reduced product cost, lower weight, and increased engine efficiency.

In this thesis, a manufacturing process chain including forming and welding in two nickel-base superalloys, alloy 718 and Haynes® 282®, is studied. The aim of this work is to determine which aspects within the material and process are the most relevant to accurately predict the amount of shape distortions that occur along the manufacturing chain. The effect of the forming temperature on the predicted springback is included. The results are compared with experimental cold and hot forming tests with a subsequent welding procedure. During forming of a double-curved component in alloy 718 at room temperature, open fractures are observed in the drawbead regions, which could not be predicted while evaluating the formability of the material based on Nakazima tests and forming limit curves (FLC). The generalised incremental stress-state dependent damage model (GISSMO) is calibrated and coupled with the anisotropic Barlat Yld2000-2D material model to accurately predict material failure during forming using LS-DYNA. The mechanical properties of alloy 718 are determined via uniaxial tensile, plane strain, shear, and biaxial tests at 20 °C. The deformations are continuously evaluated using the digital image correlation (DIC) system ARAMIS™. Numerical predictions are able to accurately predict failure on the same regions as observed during the experimental forming tests. Comparisons of the distribution of damage on one of the drawbeads, between simulations and damage measurements by acoustic emission, indicate that higher damage values correspond to bigger micro cracks. The history from the sheet-metal forming procedure, i.e. residual stresses, strains, element thickness, and geometry, is used as the input for the FE analysis of a subsequent welding procedure of a strip geometry in alloy 718 and Haynes® 282®. A comprehensive characterization of the elasto-plastic properties of both alloys between 20 and 1000 °C is included. Other temperature-dependent properties are extracted from JMatPro-v9 for the corresponding specific batches. The results from the simulations show that the welding procedure further increases the shape distortions over the part. Encouraging agreement was found between the model predictions and the results of forming and welding tests in alloy 718. The findings underscore the importance of including the material history and accurate process conditions along the manufacturing chain to both the prediction accuracy of accumulated shape distortions, and to the potential for the industry.

The work also comprises hot forming of the double-curved component in alloy 718 and Haynes® 282®. The presence and nature of serrations due to the dynamic strain aging (DSA) phenomenon between 300 and 800 °C is studied. Microstructural observations are consistent with the behaviour of the material at the different temperatures tested. The residual stresses obtained from the hot forming simulations are transformed based on the stress-relaxation tests performed at high temperatures ranging from 700 to 1000 °C. The results show the importance of using the novel modelling approach combining the anisotropic Barlat Yld2000-2D material model with the thermo-mechanical properties and stress-relaxation behaviour of the material to predict the final geometry of the component with high accuracy. A welding simulation of a bi-metallic strip geometry obtained from the hot formed double-curved component is performed numerically. The effect of the two superalloys on the shape distortions over the part is discussed.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2019
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords
alloy 718, Haynes 282, cold forming, hot forming, material characterization, GISSMO, welding, heat treatment, manufacturing chain, springback, shape distortions, dynamic strain aging, DSA, microstructure
National Category
Metallurgy and Metallic Materials Manufacturing, Surface and Joining Technology
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-76243 (URN)978-91-7790-460-1 (ISBN)978-91-7790-461-8 (ISBN)
Public defence
2019-11-29, Föreläsningssal E231, Luleå, 09:00 (English)
Opponent
Supervisors
Projects
Virtual process chain for superalloy sheet metal aero engine structures - Validation and demonstrator (NFFP6)Validation of a fabrication procedure for bi-metallic aero engine components in superalloys (NFFP7)
Funder
Vinnova, 2013-01173 and 2017-04849
Available from: 2019-10-04 Created: 2019-10-04 Last updated: 2019-10-04Bibliographically approved

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