| 1. |
- Barlo, Alexander, et al.
(författare)
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A Study of the Boundary Conditions in the ISO-16630 Hole Expansion Test
- 2022
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Ingår i: IOP Conference Series. - : IOP Publishing. - 1757-8981 .- 1757-899X. ; 1238
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Tidskriftsartikel (refereegranskat)abstract
- As new and more advanced sheet metal materials are introduced to the market, more accurate techniques for determination of failure limits are needed. One area that needs attention is edge formability, where the ISO-16630 standardized Hole Expansion Test currently is used to express this through the Hole Expansion Ratio. Over the years, this standard has been criticized for producing a large scatter in repeated tests. This paper investigates a new setup for the Hole Expansion Test which introduces draw beads into the setup to ensure sufficient restraining of the specimen during the test in an effort to reduced the scatter. In total 62 tests of a DP800 steel alloy were executed, but a large scatter in the results were still seen. It was therefore concluded that a lack of restraining force in the Hole Expansion Test was not the primary cause of the reported scatter seen in other tests.
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| 2. |
- Barlo, A, et al.
(författare)
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Proposal of a New Tool for Pre-Straining Operations of Sheet Metals and an Initial Investigation of CR4 Mild Steel Formability
- 2023
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Ingår i: IOP Conference Series: Materials Science and Engineering. - 1757-899X. ; 1284
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Tidskriftsartikel (refereegranskat)abstract
- With the increased focus on reducing carbon emissions in the automotive industry, more advanced materials are introduced to reduce the vehicle weight, and more complex component geometries are designed to both satisfy customer demands and to optimize the vehicle aerodynamically. With the increase in component complexity, the strain paths produced during the forming operation of car body components often display a highly non-linear behavior which makes the task of failure prediction during the manufacturing feasibility studies more difficult. Therefore, CAE engineers need better capabilities to predict failure induced by strain path nonlinearity. This study proposes a new tool designed for creating bi-linear strain paths, by performing a pre-strain of a sheet large enough to cut out Nakajima specimens to perform the post-straining in any direction. From five pre-straining tests the tool present a stable pre-straining operation with a uniform strain field in a radius of 100 [mm] from the centre, corresponding to the region of interest of a Nakajima specimen. From the five pre-strained samples, different Nakajima specimens are cut transverse and longitudinal to the rolling direction and a failure prediction approach in an alternative, path independent evaluation space was used to predict the onset of necking with promising results.
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| 3. |
- Odenberger, Eva-Lis, et al.
(författare)
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Thermo-mechanical Material Characterization and Stretch-bend Forming of AA6016
- 2018
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Ingår i: IOP Conference Series. - : Institute of Physics (IOP). - 1757-8981 .- 1757-899X. ; 418
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Tidskriftsartikel (refereegranskat)abstract
- Lightweight design has become increasingly in focus for the manufacturing industry. Global environmental challenges, goals and legislations imply that lighter and sustainable products are imperative to remain competitive. One example is stamped products made of aluminum alloys which are of interest to the automotive industry, where lightweight designs are essential. In order to increase formability and to produce more complex geometries in stamped aluminum components there is a need to develop hot forming techniques. The Finite Element Method (FEM) has enabled important advances in the study and design of competitive manufacturing procedures for metal parts. Predicting the final geometry of a component is a complex task, especially if the forming procedure occurs at elevated temperatures. This work presents selected results from thermo-mechanical material testing procedures, FE-analyses and forming validation tests in AA6016 material. The material tests are used to determine the thermo-mechanical anisotropic properties, strain rate sensitivity and formability (Forming Limit Curves, FLC) at temperatures up to 490°C. Stretch-bending tests are performed to compare predicted results with experimental observations such as punch force, strain levels, thinning, forming temperatures, springback and failure. It was found that the heat-treatment and forming at elevated temperatures substantially increased formability and that measured responses could in general be predicted if care was taken to model the initial blank temperatures, heat transfer and thermo-mechanical material properties. The room temperature case confirms the importance of considering anisotropy.
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| 4. |
- Pérez Caro, Lluís, 1985-, et al.
(författare)
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Calibration of a damage and fracture model for alloy 718
- 2016
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Ingår i: Advancements in Theoretical and Applied Plasticity. - Fulton, Maryland 20759-0591, USA : NEAT PRESS. - 9780991165476 ; , s. 223-225
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 5. |
- Pérez Caro, Lluís, 1985-, et al.
(författare)
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Cold and Hot Forming Procedures for Alloy 718
- 2019
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Ingår i: Proceedings of the Processing and fabrication of advanced materials - XXVII. - : Jönköping University. ; , s. 118-124
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Konferensbidrag (refereegranskat)abstract
- Since the past few decades, superalloys have had an important role in the reduction of fuel consumption and carbon dioxide emissions for the transportation sector due to major concerns about climate change and more restrictive environmental laws. Advanced manufacturing methods in nickel-based superalloy aero-engine components allow lightweight designs with a reduced product cost and weight while increasing the efficiency of the engine. However, the prediction of the final geometry of a hot-formed part remains a challenge. In this work, a double-curved sheet-metal component in alloy 718 is studied. The material is characterized at 20°C and 900°C. The predicted shape deviation of the part when considering the anisotropic Barlat Yld2000-2D material model with data at both temperatures is discussed. The effect of including data from stress-relaxation tests at 900°C on the simulated springback is assessed. A hot-forming test is performed at around 900°C to validate the FE simulations regarding springback, strain levels, forming temperatures, and press forces. The results show the significance in considering the input data at high temperatures along with the stress-relaxation behaviour at different strain levels to accurately predict the final geometry of the component.
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| 6. |
- Pérez Caro, Lluís, 1985-
(författare)
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Modelling Aspects in Forming and Welding of Nickel-Base Superalloys
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 7. |
- Pérez Caro, Lluís, 1985-
(författare)
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Modelling of Forming and Welding in Alloy 718
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 8. |
- Pérez Caro, Lluís, 1985-, et al.
(författare)
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Prediction of shape distortions during forming and welding of a double-curved strip geometry in alloy 718
- 2020
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Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer. - 0268-3768 .- 1433-3015. ; 107:7-8, s. 2967-2981
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Tidskriftsartikel (refereegranskat)abstract
- The finite element method (FEM) has considerably contributed to the development of advanced manufacturing methods for metal structures. The prediction of the final shape of a component is of great interest to the manufacturing industry. The level of demand may increase due to multistage processes. Therefore, including all steps of the manufacturing chain in the simulations is a key to being successful. This has been done for a long time in the stamping industry, which involves sequences of forming, trimming, and springback. However, more complex manufacturing procedures that include assembling of formed parts with forgings and castings via welding have been modelled with simplifications, resulting in a reduced prediction accuracy. In the present study, a double-curved part manufactured from alloy 718 is formed at 20 °C and laser-welded using the bead-on-plate procedure. The coupling of different manufacturing analyses, including cold forming, trimming, result mapping, welding, cooling, and springback, is achieved using LS-DYNA. Additionally, the effect of adding a damage and failure model in the forming simulation is studied. The results of the forming analysis are used as inputs for the material model *MAT_CWM in the welding simulation. The anisotropic thermomechanical properties of alloy 718 are determined at temperatures up to 1000 °C. Encouraging agreement is found between the model predictions and the results of forming and welding tests. The findings underscore the importance of including the material history and accurate process conditions along the manufacturing chain to both the prediction accuracy of shape distortions, and to the potential of the industry.
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| 9. |
- Pérez Caro, Lluís, 1985-, et al.
(författare)
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Shape prediction of a hot formed component in nickel-base superalloys
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Current manufacturing processes of advanced aero engine components in nickel-base superalloys are performed at approximately 950 °C, with varying holding times, to reduce the amount of residual stresses, and thereby shape deviations, over the part. The aim of such procedures is to obtain the final geometry of the component within tolerance and avoid costly tryouts, which can be unfavorable to the competitiveness of the aerospace industry. In addition, a reduction in the forming temperature or holding time may significantly reduce the energy consumption and carbon dioxide (CO2) emissions while increasing the ecological sustainability of the process. In this work, the numerical study of a hot forming procedure of a double-curved component in Haynes® 282® is presented. The influence of the forming temperature and holding time on the predicted amount of springback at different stages of the hot forming procedure is assessed. The resulting shape distortions are compared with identical FE analyses in alloy 718 at 870 °C available in literature. The anisotropic properties of the material are determined at temperatures ranging from 20 to 1000 °C. A qualitative analysis of the different types of serrations present in the hardening curves between 300 and 900 °C is included in the study. Microstructural observations of selected specimens are correlated to the material-characterization tests. The thermo-mechanical data is used as input to the novel version of the Barlat Yld2000-2D material model in LS-DYNA. The results show that forming of Haynes® 282® at 870 °C produces high shape distortions over the part with values beyond the sheet thickness, in contrast to the response of alloy 718. A comparison of the stress-relaxation rate with available data in literature for alloy 718 at 870 °C reveals that Haynes® 282® relaxes about 50% slower than alloy 718, whereas reasonably analogous at 950 °C. An increase in the forming temperature to 950 °C significantly reduces the amount of springback. Therefore, it can be concluded that forming of Haynes® 282® requires a higher temperature than reported for alloy 718 to reach similar amount of springback. The presented studies indicate that the use of advanced anisotropic models together with the thermo-mechanical properties and stress-relaxation behavior of the material is of utmost importance to accurately predict the final geometry of lightweight components of interest to the aerospace industry.
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| 10. |
- Pérez Caro, Lluís, 1985-, et al.
(författare)
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Springback prediction and validation in hot forming of a double-curved component in alloy 718
- 2021
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Ingår i: International Journal of Material Forming. - : Springer-Verlag Italia s.r.l.. - 1960-6206 .- 1960-6214. ; 14:6, s. 1355-1373
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Tidskriftsartikel (refereegranskat)abstract
- The demands associated with the production of advanced parts made of nickel-base superalloys are continuously increasing to meet the requirements of current environmental laws. The use of lightweight components in load-carrying aero-engine structures has the potential to significantly reduce fuel consumption and greenhouse gas emissions. Furthermore, the competitiveness of the aero-engine industry can benefit from reduced production costs and shorter development times while minimizing costly try-outs and increasing the efficiency of engines. The manufacturing process of aero-engine parts in superalloys at temperatures close to 950 °C produces reduced stamping force, residual stresses, and springback compared to traditional forming procedures occurring at room temperature. In this work, a hot forming procedure of a double-curved component in alloy 718 is studied. The mechanical properties of the material are determined between 20 and 1000 °C. The presence and nature of serrations in the stress–strain curves are assessed. The novel version of the anisotropic Barlat Yld2000-2D material model, which allows the input of thermo-mechanical data, is used in LS-DYNA to model the behaviour of the material at high temperatures. The effect of considering the stress-relaxation data on the predicted shape distortions is evaluated. The results show the importance of considering the thermo-mechanical anisotropic properties and stress-relaxation behaviour of the material to predict the final geometry of the component with high accuracy. The implementation of advanced material models in the finite element (FE) analyses, along with precise process conditions, is vital to produce lightweight components in advanced materials of interest to the aerospace industry.
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