| 1. |
- Bödeker, Felix, et al.
(författare)
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A novel FFT-based homogenization scheme for cohesive zones
- 2022
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Ingår i: Procedia Structural Integrity. - : Elsevier. - 2452-3216. ; 42, s. 490-497
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Tidskriftsartikel (refereegranskat)abstract
- Cohesive Zone Models with finite thickness are widely used for the fracture mechanical modeling of layers of material, e.g., adhesives. Within this approach, the whole layer is modeled as a Cohesive Zone. Moreover, computational homogenization techniques are crucial for the development of advanced engineering materials, which are often heterogeneous. Compared to the classical Finite Element Method (FEM), computationally more efficient solvers based on the Fast Fourier Transform (FFT) are expected to reduce the computational effort needed for the homogenization. Originated from an existing method for the computational homogenization of Cohesive Zones using FEM, a novel FFT-based homogenization scheme for Cohesive Zone Models was developed. Our implementation of the FFT solver uses the Barzilai-Borwein scheme and a non-local ductile damage model for the fracture behavior. Finally, the method is applied to the core material of HybrixTM metal sandwich plates, and the good agreement with experimental results in opening mode I is shown.
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| 2. |
- Bödeker, Felix, et al.
(författare)
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An FFT-based homogenization scheme for cohesive zones with an application to adhesives and the core material of thin metal sandwich plates
- 2024
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Ingår i: Theoretical and applied fracture mechanics (Print). - : Elsevier. - 0167-8442 .- 1872-7638. ; 129
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Tidskriftsartikel (refereegranskat)abstract
- Cohesive Zone Models with finite thickness are widely used for the fracture mechanical modeling of material layers, e.g., adhesive layers. Within this approach, the whole layer is modeled as a cohesive zone. Moreover, computational homogenization techniques are crucial for the development of advanced engineering materials, which are often heterogeneous. Compared to the commonly used Finite Element Method (FEM), solvers based on the Fast Fourier Transform (FFT) are expected to reduce the computational effort needed for the homogenization. Originated from an existing method for the computational homogenization of cohesive zones using FEM, a novel FFT-based homogenization scheme for cohesive zone models is presented. Our implementation of the FFT solver uses a displacement-based Barzilai–Borwein scheme and a non-local ductile damage model for the fracture behavior. Finally, the practical application of the method is discussed using an adhesive layer and the core material of HybrixTM metal sandwich plates as examples.
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| 3. |
- Gabrielson, Per, et al.
(författare)
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Evaluation of material models and element types for sheet metal formning of titanium
- 2007
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Ingår i: Forming the future : innovations in sheet metal forming : proceedings of IDDRG 2007, Győr, Hungary, 21-23 May, 2007. ; , s. 109-116
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Konferensbidrag (refereegranskat)abstract
- In the last decades, the growing competitiveness of the market has continuously driven the forming companies to highly optimize their products regarding offered performance at minimum cost. In order to achieve better products, studies where conducted with different material models when simulating the forming process of titanium. The material is often used in heat exchanger applications. Titanium has a HCP structure which results in high anisotropy in rolled sheet metal. It is of importance to be able to simulate the sheet metal forming process of titanium in a more precise way both regarding formability and springback. In this work different material models for titanium where used and evaluated against experimental work in special test module tools (TMT). The evaluation is made by comparing results of simulations with pressed test parts in titanium. This paper describes FE-analysis of springback using the YLD 2000 model compared to the anisotropic-viscoplastic material model. Different element types were also analysed. It has been shown that material model YLD 2000 and elements with through thickness stretch gives the most accurate results in the performed simulations.
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| 4. |
- Govik, Alexander
(författare)
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Finite Element Analysis of Sheet Metal Assemblies : Prediction of Product Performance Considering the Manufacturing Process
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns the development of methodologies to be used to simulate complete manufacturing chains of sheet components and the study of how different mechanical properties propagate and influence succeeding component performance.Since sheet metal assemblies are a major constituent of a wide range of products it is vital to develop methodologies that enable detailed evaluation of assembly designs and manufacturing processes. The manufacturing process influences several key aspects of a sheet metal assembly, aspects such as shape fulfilment, variation and risk of material failure.Developments in computer-aided engineering and computational resources have made simulation-based process and product development efficient and useful since it allows for detailed, rapid evaluation of the capabilities and qualities of both process and product. Simulations of individual manufacturing processes are useful, but greater benefits can be gained by studying the complete sequence of a product's manufacturing processes. This enables evaluation of the entire manufacturing process chain, as well as the final product. Moreover, the accuracy of each individual manufacturing process simulation is improved by establishing appropriate initial conditions, including inherited material properties.In this thesis, a methodology of sequentially simulating each step in the manufacturing process of a sheet metal assembly is presented. The methodology is thoroughly studied using different application examples with experimental validation. The importance of information transfer between all simulation steps is also studied. Furthermore, the methodology is used as the foundation of a new approach to investigate the variation of mechanical properties in a sheet metal assembly. The multi-stage manufacturing process of the assembly is segmented, and stochastic analyses of each stage is performed and coupled to the succeeding stage in order to predict the assembly's final variation in properties.Two additional studies are presented where the methodology of chaining manufacturing processes is utilised. The influence of the dual phase microstructure on non-linear strain recovery is investigated using a micromechanical approach that considers the annealing process chain. It is vital to understand the non-linear strain recovery in order to improve springback prediction. In addition, the prediction of fracture in a dual phase steel subjected to non-linear straining is studied by simulating the manufacturing chain and subsequent stretch test of a sheet metal component.
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| 5. |
- Govik, Alexander, et al.
(författare)
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Finite element simulation of the manufacturing process chain of a sheet metal assembly
- 2012
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Ingår i: Journal of Materials Processing Technology. - : Elsevier. - 0924-0136 .- 1873-4774. ; 212:7, s. 1453-1462
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Tidskriftsartikel (refereegranskat)abstract
- An increasing number of components in automotive structures are today made from advanced high strength steel (AHSS). Since AHSS demonstrates more severe springback behaviour than ordinary mild steels, it requires more efforts to meet the design specification of the stamped parts. Consequently, the physical fine tuning of the die design and the stamping process can be time consuming. The trial-and-error development process may be shortened by replacing most of the physical try-outs with finite element (FE) simulations of the forming process, including the springback behaviour. Still it can be hard to identify when a stamped part will lead to an acceptable assembly with respect to the geometry and the residual stress state. In part since the assembling process itself will distort the components. To resolve this matter it is here proposed to extend the FE-simulation of the stamping process, to also include the first level sub-assembly stage. In this study a methodology of sequentially simulating each step in the manufacturing process of an assembly is proposed. Each step of the proposed methodology is described, and a validation of the prediction capabilities is performed by comparing with a physically manufactured assembly. The assembly is composed of three sheet metal components made from DP600 steel which are joined by spot welding. The components are designed to exhibit severe springback behaviour in order to put both the forming and subsequent assembling simulations to the test. The work presented here demonstrates that by using virtual prototyping it is possible to predict the final shape of an assembled structure.
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| 6. |
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| 7. |
- Govik, Alexander, et al.
(författare)
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Simulation of the forming and assembling process of sheet metal assembly
- 2011
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Ingår i: Swedish Production Symposium, SPS11.
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Konferensbidrag (refereegranskat)abstract
- A sheet metal assembly must meet functional, manufacturing, and sometimes also esthetical requirements. The properties of the assembly are to a large extent affected by the manufacturing process, i.e. the forming processes of the sheet metal components and the subsequent assembling sub-processes. It is of a great industrial interest to be able to predict the properties of the assembly at an early design stage.This paper presents a methodology, based on Finite Element simulations, which makes it possible to accurately predict the properties of a sheet metal assembly. Each forming process of the individual components is simulated, and all properties affected by the forming process are included in the subsequent simulations of the assembling process. Thus, this methodology makes it possible to optimize both the functional properties of the assembly and also its manufacturing process considering all mechanical effects introduced by the individual manufacturing processes.A case study of a semi-industrial assembly has been conducted and the simulation results agree well to experimental data.
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| 8. |
- Govik, Alexander
(författare)
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Simulation of the Manufacturing Process of Sheet Metal Assemblies
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increased complexity of products and narrow lead times for product development have intensified the use of virtual prototyping, also called simulation-based design. The simulation of each individual manufacturing process is an important part of product development, However it is also necessary to study the complete sequences of manufacturing processes. By studying the complete sequence, the properties of the entire manufacturing process and the final product can be evaluated. The quality of the results from each individual process simulation is improved by supplying initial conditions that closer match the reality. Thus, greater benefits can be gained from using simulation as a tool within process and product development. In this thesis the manufacturing process chain of a sheet metal assembly is studied. A methodology of sequentially simulating each step in the manufacturing process of the assembly is proposed. Each step of the proposed methodology is described, and a validation of the prediction capabilities is performed by comparisons with results from a physically manufactured assembly. Furthermore a simulation based sensitivity study is performed in order to investigate the influence of the forming history on the predictions of the assembly properties. In the study, several simulations of the assembly stage are performed in which different types of forming histories are retained from the forming stage. This study demonstrates that it is possible to predict the final shape of an assembled structure by using virtual prototyping. It is found that the most influential factor from the forming stage is the residual stress state. Especially for components with a more complex geometry in which large residual stresses can be retained. It is also shown that it is important for the quality of the prediction to retain as much information as possible from the previous manufacturing steps. The proposed simulation procedure is a useful tool during product development phases in order to evaluate the properties of both the manufacturing processes and of the final assembly.
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| 9. |
- Govik, Alexander, et al.
(författare)
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Stochastic analysis of a sheet metal assembly considering its manufacturing process
- 2014
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In order to accurately predict the mechanical properties of a sheet metal assembly it has been shown important to account for how the geometry and material properties are affected by the manufacturing process. It is also of a great interest to predict the variations of important responses, and how these variations depend on the manufacturing process.In this study, the variation of properties during the multi-stage manufacturing process of a sheet metal assembly is evaluated and the variability of a response due to loading is studied. A methodology to investigate how variations evolve during the assembling process is presented. The multi-stage assembling process is virtually segmented, such that stochastic analyses of each process stage are performed and coupled to succeeding stages in order to predict the variation in properties of the final assembly. The methodology is applied to an industrial assembly and experimental validations have been conducted. The prediction of the geometry of the final assembly is in good agreement with the experimental results, while the prediction of the variation of this geometry is in fair agreement.
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| 10. |
- Govik, Alexander, et al.
(författare)
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The effects of forming history on sheet metal assembly
- 2014
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Ingår i: International Journal of Material Forming. - : Springer. - 1960-6206 .- 1960-6214. ; 7:3, s. 305-316
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Tidskriftsartikel (refereegranskat)abstract
- As demand for faster product development increases, physical prototypes are replaced by virtual prototypes. By using finite element simulations to evaluate the functional behaviour of the product as well as its manufacturing process, more design alternatives can be evaluated while a considerably smaller number of physical prototypes are needed. As sheet metal assemblies are common in a wide range of products, reliable methods for predicting their properties are necessary. By sequentially simulating the complete manufacturing process chain of an assembly, early predictions concerning the geometry and material properties of the assembly can be made.In this study a simulation-based sensitivity study is performed in order to investigate the influence of the forming history on the predictions of assembly properties. In the study, several simulations of the assembly stage are performed in which different types of forming histories are retained from the forming stage. The simulations of the assembly stage will range from a case with linear elastic conditions without forming history, to a case with the full forming history state and consistent material modelling throughout all simulations. It is found that the residual stress state is the most influential history variable from the forming stage. Especially for more complex geometries in which large residual stresses can be retained.
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