| 1. |
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| 2. |
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| 3. |
- Hassila Karlsson, Carl Johan, et al.
(author)
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Influence of scanning strategy on residual stresses in laser powder bed fusion manufactured alloy 718: Modeling and experiments
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Other publication (other academic/artistic)abstract
- Residual stresses are a known phenomenon in additively manufactured materials. The residual stresses increase the risk of cracks, limit in-service performance, and distort printed parts. In this work, thermo-mechanical finite element models using the hatch-by-hatch and layer-by-layer approach, and the inherent strain method has been developed and applied to predict the effects of different scanning strategies on the deflection and the residual stresses of two PBF-LB processed geometries. To account for viscoplasticty and relaxation effects, a mechanism-based material model have been implemented and used. It is shown that the hatch-by-hatch approach and inherent strain method both successfully predicted the experimentally measured deflections of the first geometry, which was printed using different scanning directions. To predict the stress field experimentally, high-energy synchrotron measurements have been used to. The thermo-mechanical models and the inherent strain method both captures the trend of experimentally measured residual stress fields, although with an overall underprediction. The predictions of the models were evaluated, and their accuracy discussed in terms of physical aspects of the Powder Bed Fusion – Laser Beam process.
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| 4. |
- Lindgren, Lars-Erik, et al.
(author)
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Thermal stresses and computational welding mechanics
- 2019
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In: Journal of thermal stresses. - : Taylor & Francis. - 0149-5739 .- 1521-074X. ; 42:1, s. 107-121
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Journal article (peer-reviewed)abstract
- Computational welding mechanics (CWM) have a strong connection to thermal stresses, as they are one of the main issues causing problems in welding. The other issue is the related welding deformations together with existing microstructure. The paper summarizes the important models related to prediction of thermal stresses and the evolution of CWM models in order to manage the large amount of ‘welds’ in additive manufacturing.
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| 5. |
- Lindwall, Johan, et al.
(author)
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Efficiency and Accuracy in Thermal Simulation of Powder Bed Fusion of Bulk Metallic Glass
- 2018
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In: JOM. - : Springer. - 1047-4838 .- 1543-1851. ; 70:8, s. 1598-1603
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Journal article (peer-reviewed)abstract
- Additive manufacturing by powder bed fusion processes can be utilized to create bulk metallic glass as the process yields considerably high cooling rates. However, there is a risk that reheated material set in layers may become devitrified, i.e., crystallize. Therefore, it is advantageous to simulate the process to fully comprehend it and design it to avoid the aforementioned risk. However, a detailed simulation is computationally demanding. It is necessary to increase the computational speed while maintaining accuracy of the computed temperature field in critical regions. The current study evaluates a few approaches based on temporal reduction to achieve this. It is found that the evaluated approaches save a lot of time and accurately predict the temperature history.
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| 6. |
- Malmelöv, Andreas, et al.
(author)
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History Reduction by Lumping for Time-Efficient Simulation of Additive Manufacturing
- 2020
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In: Metals. - : MDPI. - 2075-4701. ; 10:1
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Journal article (peer-reviewed)abstract
- Additive manufacturing is the process by which material is added layer by layer. In most cases, many layers are added, and the passes are lengthy relative to their thicknesses and widths. This makes finite element simulations of the process computationally demanding owing to the short time steps and large number of elements. The classical lumping approach in computational welding mechanics, popular in the 80s, is therefore, of renewed interest and is evaluated in this work. The method of lumping means that welds are merged. This allows fewer time steps and a coarser mesh. It was found that the computation time can be reduced considerably, with retained accuracy for the resulting temperatures and deformations. The residual stresses become, to a certain degree, smaller. The simulations were validated against a directed energy deposition (DED) experiment with alloy 625.
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| 7. |
- Malmelöv, Andreas
(author)
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History Reduction Techniques for Simulation of Additive Manufacturing and Physically based Material Modeling
- 2020
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Licentiate thesis (other academic/artistic)abstract
- In this thesis, finite element (FE) simulations of additive manufacturing (AM) and physically based material modeling are presented. AM is a process where the component is built layer-wise. The material undergoes repeated heating and cooling cycles when layers are added, which may result in undesired deformation and residual stress in the built component. The choice of process parameters and scan strategy affect the resulting residual stress. Simulations can be used to support the experimental determination of process parameters and scan strategy. AM processes often comprise many added layers, and the passes are lengthy relative to their thicknesses and widths. This makes the FE simulations computationally expensive, with many elements and time steps. In this work, AM processes have been simulated with the FE-method using a lumping technique. This technique allows fewer time steps and a coarser mesh. Thermal behavior, deformation, and residual stresses have been simulated and compared with experiments. The simulations show that, by using the lumping technique, the computational effort can be reduced significantly with retained accuracy for the resulting temperature and deformations. The residual stresses become somewhat smaller. Alloy 625 is a nickel-based superalloy used in high-temperature applications owing to the hightemperature strength. The material is difficult to manufacture by conventional machining owing to excessive tool wear and low material removal rates. Thus alloy 625 is a material appropriate for the AM technology with its near-net shape potential. An existing, physically based flow stress model has been further developed to fit the mechanisms typical for alloy 625. This model gives an accurate mechanical behavior and capture viscoplasticity, creep, and relaxation. The physically based model has been calibrated versus compression tests and validated with a stress relaxation test performed in a Gleeble 3800 machine. The predicted relaxation was in good agreement with the measured relaxation. The usage of this kind of material model is expected to improve the prediction of the material behavior during the AM process and, thereby, the overall prediction of the AM process.
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| 8. |
- Malmelöv, Andreas, et al.
(author)
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Mechanism based flow stress model for Alloy 625 and Alloy 718
- 2020
-
In: Materials. - : MDPI. - 1996-1944 .- 1996-1944. ; 13:24
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Journal article (peer-reviewed)abstract
- To predict the final geometry in thermo-mechanical processes, the use of modeling tools is of great importance. One important part of the modeling process is to describe the response correctly. A previously published mechanism-based flow stress model has been further developed and adapted for the nickel-based superalloys, alloy 625, and alloy 718. The updates include the implementation of a solid solution strengthening model and a model for high temperature plasticity. This type of material model is appropriate in simulations of manufacturing processes where the material undergoes large variations in strain rates and temperatures. The model also inherently captures stress relaxation. The flow stress model has been calibrated using compression strain rate data ranging from 0.01 to 1 s−1 with a temperature span from room temperature up to near the melting temperature. Deformation mechanism maps are also constructed which shows when the different mechanisms are dominating. After the model has been calibrated, it is validated using stress relaxation tests. From the parameter optimization, it is seen that many of the parameters are very similar for alloy 625 and alloy 718, although it is two different materials. The modeled and measured stress relaxation are in good agreement.
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| 9. |
- Malmelöv, Andreas, et al.
(author)
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Numerical modeling and synchrotron diffraction measurements of residual stresses in laser powder bed fusion manufactured alloy 625
- 2022
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In: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 216
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Journal article (peer-reviewed)abstract
- Residual stresses in metal additive manufactured components are a well-known problem. It causes distortion of the samples when removing them from the build plate, as well as acting detrimental with regard to fatigue. The understanding of how residual stresses in a printed sample are affected by process parameters is crucial to allow manufacturers to tune their process parameters, or the design of their component, to limit the negative influence of residual stresses. In this paper, residual stresses in additive manufactured samples are simulated using a thermo-mechanical finite element model. The elasto-plastic behavior of the material is described by a mechanism-based material model that accounts for microstructural and relaxation effects. The heat source in the finite element model is calibrated by fitting the model to experimental data. The residual stress field from the finite element model is compared with experimental results attained from synchrotron X-ray diffraction measurements. The results from the model and measurement give the same trend in the residual stress field. In addition, it is shown that there is no significant difference in trend and magnitude of the resulting residual stresses for an alternation in laser power and scanning speed.
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| 10. |
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| 11. |
- Malmelöv, Andreas
(author)
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Simulation of additive manufacturing using a mechanism based plasticity model
- 2022
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Doctoral thesis (other academic/artistic)abstract
- This thesis presents finite element (FE) simulations of additive manufacturing (AM) and physically based material modeling of alloy 625 and alloy 718. In recent years, there has been an increasing interest in AM and there has been a dramatic increase in publications in the field. AM can be beneficial compared to conventional manufacturing methods in many applications. The method offers short component lead times and large design freedom with the possibility to create complex components. Alloy 625 and alloy 718 are nickel-based superalloys used in high-temperature applications owing to their high-temperature strength. The materials are difficult to manufacture by conventional machining due to rapid tool wear and low material removal rates. Thus, the alloys are appropriate for the AM technology with its near-net shape potential.Owing to the rapid heating and solidification in the AM process, residual stresses are induced in the component. This is a well-known problem and causes distortion of the samples when removing them from the build plate. The residual stresses may also deteriorate the fatigue properties. It is important for the manufacturer to understand how the choice of process parameters and scanning strategy affect the residual stresses to minimize those and improve the quality of the components. Simulation can be used as a tool while developing the process parameters and support the experimental efforts. FEM is generally the preferred method for simulation of deformations and residual stresses in AM. The simulation technique used when modeling AM has its origin from welding simulations that was performed already since the beginning of 1970. However, it is not possible in practice to simulate an AM process in the traditional way due to a large number of elements and time increments to be calculated. This is especially true for the laser-based powder bed fusion (PBF-LB) process where the process of a full-scale part may comprise many thousands of added layers, and the passes are lengthy relative to their thicknesses and widths.The aim of this thesis work is to develop FE simulation techniques that reduce the computational effort when modeling residual stresses in AM processes to enable simu-lation of full-scale parts. This has been done with thermo-mechanical FE-models using different lumping techniques e.g., lumping of layers and lumping of hatches. Lumping of layers and hatches means that several physical layers, or several physical hatches, are merged and added in one modeled layer or hatch respectively. Lumping allows fewer time steps and a coarser mesh which reduces the computational effort. An existing mechanism based flow stress model has been developed to fit the mechanisms typical for alloy 625 and alloy 718 and implemented in the FE model. Also, synchrotron X-ray diffraction was performed to measure the residual stress for comparison with the models. The stress was extracted from the diffraction data using the full Debye ring fitting method.In this work, using the lumping techniques described above, it was possible to simu-late AM processes with up to physical 1500 layers. For different process parameter sets and scan strategies, thermal behavior, deformation and residual stresses have been mod-eled and compared with experiments. Using the lumping of layer technique resulted in modeled residual stresses showing the same trend as measured stresses from synchrotron X-ray diffraction for two different process parameter sets. Utilizing lumping of hatches, the resulting deflection in a part was modeled successfully for different scanning strate-gies. In the modeling, the larger deflection was seen for the samples printed with the scanning direction parallel to the long-side which was also shown experimentally.The results in this work shows that the presented lumping approaches are promising when it comes to modeling of the deformations and residual stresses in AM. Using lumping approaches, it is also possible to simulate different scanning strategies for processes of larger parts. The description of the mechanical behavior of the material is improved, using the mechanism based material model, compared to when the flow stress was modeled with tabulated data, since it takes mechanisms as viscoplasticity and stress relaxation into account. The mechanism based model includes microstructural information as grain size and solutes and can thus more easily be combined with a microstructure model. The combination of the mechanism based material model and the use of lumping techniques is thus an advance in the development of predictive models of the AM process.
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| 12. |
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| 13. |
- Agelet de Saracibar, Carlos, et al.
(author)
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Shaped Metal Deposition Processes
- 2014
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In: Encyclopedia of Thermal Stresses. - Dordrecht : Encyclopedia of Global Archaeology/Springer Verlag. - 9789400727380 ; , s. 4347-4355
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Book chapter (peer-reviewed)abstract
- The shaped metal deposition (SMD) process is a novel manufacturing technology which is similar to the multi-pass welding used for building features such as lugs and flanges on components [1–7]. This innovative technique is of great interest due to the possibility of employing standard welding equipment without the need for extensive new investment [8, 9]. The numerical simulation of SMD processes has been one of the research topics of great interest over the last years and requires a fully coupled thermo-mechanical formulation, including phase-change phenomena defined in terms of both latent heat release and shrinkage effects [1–6]. It is shown how computational welding mechanics models can be used to model SMD for prediction of temperature evolution, transient, as well as residual stresses and distortions due to the successive welding layers deposited. Material behavior is characterized by a thermo-elasto-viscoplastic constitutive model coupled with a metallurgical model [6]. Two different materials, nickel superalloy 718 [6] and titanium Ti-6Al-4 V [7], are considered in this work. Both heat convection and heat radiation models are introduced to dissipate heat through the boundaries of the component. The in-house-developed coupled thermo-mechanical finite element (FE) software COMET [10] is used to deal with the numerical simulation, and an ad hoc activation methodology is formulated to simulate the deposition of the different layers of filler material.
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| 14. |
- Almqvist, Helena, et al.
(author)
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CETSA screening identifies known and novel thymidylate synthase inhibitors and slow intracellular activation of 5-fluorouracil
- 2016
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 7
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Journal article (peer-reviewed)abstract
- Target engagement is a critical factor for therapeutic efficacy. Assessment of compound binding to native target proteins in live cells is therefore highly desirable in all stages of drug discovery. We report here the first compound library screen based on biophysical measurements of intracellular target binding, exemplified by human thymidylate synthase (TS). The screen selected accurately for all the tested known drugs acting on TS. We also identified TS inhibitors with novel chemistry and marketed drugs that were not previously known to target TS, including the DNA methyltransferase inhibitor decitabine. By following the cellular uptake and enzymatic conversion of known drugs we correlated the appearance of active metabolites over time with intracellular target engagement. These data distinguished a much slower activation of 5-fluorouracil when compared with nucleoside-based drugs. The approach establishes efficient means to associate drug uptake and activation with target binding during drug discovery.
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| 15. |
- Andersson, Carl, et al.
(author)
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Modeling the Evolution of Grain Texture during Solidification of Laser-Based Powder Bed Fusion Manufactured Alloy 625 Using a Cellular Automata Finite Element Model
- 2023
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In: Metals. - : MDPI. - 2075-4701. ; 13:11
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Journal article (peer-reviewed)abstract
- The grain texture of the as-printed material evolves during the laser-based powder bed fusion (PBF-LB) process. The resulting mechanical properties are dependent on the obtained grain texture and the properties vary depending on the chosen process parameters such as scan velocity and laser power. A coupled 2D Cellular Automata and Finite Element model (2D CA-FE) is developed to predict the evolution of the grain texture during solidification of the nickel-based superalloy 625 produced by PBF-LB. The FE model predicts the temperature history of the build, and the CA model makes predictions of nucleation and grain growth based on the temperature history. The 2D CA-FE model captures the solidification behavior observed in PBF-LB such as competitive grain growth plus equiaxed and columnar grain growth. Three different nucleation densities for heterogeneous nucleation were studied, 1 × 1011, 3 × 1011, and 5 × 1011. It was found that the nucleation density 3 × 1011 gave the best result compared to existing EBSD data in the literature. With the selected nucleation density, the aspect ratio and grain size distribution of the simulated grain texture also agrees well with the observed textures from EBSD in the literature.
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| 16. |
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| 17. |
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| 18. |
- Babu, Bijish, et al.
(author)
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Physically based constitutive model for Ti-6Al-4V used in the simulation of manufacturing chain
- 2009
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In: Computational Plasticity X. - : International Center for Numerical Methods in Engineering (CIMNE). - 9788496736696
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Conference paper (peer-reviewed)abstract
- Simulations of manufacturing process chain involving forming, welding and heat treatment are complex because of the varying length and time scales and the range of temperatures which trigger the different associated deformation mechanisms. This paper demonstrates the use of a physically based constitutive model in simulation of a manufacturing chain.
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| 19. |
- Babu, Bijish, et al.
(author)
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Simulation of additive manufacturing of Ti-6Al-4V using a coupled physics-based flow stress and microstructure model
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Other publication (other academic/artistic)abstract
- Simulating the additive manufacturing process of Ti-6Al-4V is very complex owing to the microstructural changes and allotropic transformation occurring during its thermo-mechanical processing. The alpha-phase with a hexagonal close pack structure is present in three different forms; Widmanstatten, grain boundary, and Martensite. A metallurgical model that computes the formation and dissolution of each of these phases is used in this work. Furthermore, a physically based flow-stress model coupled with the metallurgical model is applied in the simulation of direct energy deposition additive manufacturing case.
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| 20. |
- Babu, Bijish, Tec. Lic. 1979-, et al.
(author)
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Simulation of Ti-6Al-4V Additive Manufacturing Using Coupled Physically Based Flow Stress and Metallurgical Model
- 2019
-
In: Materials. - : MDPI. - 1996-1944 .- 1996-1944. ; 12:23
-
Journal article (peer-reviewed)abstract
- Simulating the additive manufacturing process of Ti-6Al-4V is very complex due to the microstructural changes and allotropic transformation occurring during its thermomechanical processing. The α -phase with a hexagonal close pack structure is present in three different forms—Widmanstatten, grain boundary and Martensite. A metallurgical model that computes the formation and dissolution of each of these phases was used here. Furthermore, a physically based flow-stress model coupled with the metallurgical model was applied in the simulation of an additive manufacturing case using the directed energy-deposition method. The result from the metallurgical model explicitly affects the mechanical properties in the flow-stress model. Validation of the thermal and mechanical model was performed by comparing the simulation results with measurements available in the literature, which showed good agreement
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| 21. |
- Barsoum, Zuheir, et al.
(author)
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Simplified FE welding simulation of fillet welds : 3D effects on the formation residual stresses
- 2009
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In: Engineering Failure Analysis. - : Elsevier BV. - 1350-6307 .- 1873-1961. ; 16:7, s. 2281-2289
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Journal article (peer-reviewed)abstract
- In this study two- and three-dimensional finite element welding simulations have been carried out. The welded component studied is a T-type fillet weld which is frequently used in the heavy vehicle machine industry with plate thicknesses of eight and 20 mm, respectively. The software's used for the welding simulations is MSC.Marc and ANSYS. The objective is to study the formation of the residual stresses due to 3D effect of the welding process. Moreover, welding simulations using solid models and contact models in the un-fused weld roots were carried out in order to investigate the possible effect with respect to the residual stresses. Residual stress measurements were carried out using X-ray diffraction technique on the manufactured T-welded structure. The 2D residual stress predictions shows good agreement with measurements, hence the 2Dwelding simulation procedure is suitable for residual stress predictions for incorporation in further fatigue crack growth analysis from weld defects emanating from the weld toe and the un-fused root.
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| 22. |
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| 23. |
- Charles Murgau, Corinne, et al.
(author)
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Temperature and Microstructure Evolution in Gas Tungsten Arc Welding Wire Feed Additive Manufacturing of Ti-6Al-4V
- 2019
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In: Materials. - : MDPI. - 1996-1944 .- 1996-1944. ; 12:21
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Journal article (peer-reviewed)abstract
- In the present study, the gas tungsten arc welding wire feed additive manufacturing process is simulated and its final microstructure predicted by microstructural modelling, which is validated by microstructural characterization. The Finite Element Method is used to solve the temperature field and microstructural evolution during a gas tungsten arc welding wire feed additive manufacturing process. The microstructure of titanium alloy Ti-6Al-4V is computed based on the temperature evolution in a density-based approach and coupled to a model that predicts the thickness of the α lath morphology. The work presented herein includes the first coupling of the process simulation and microstructural modelling, which have been studied separately in previous work by the authors. In addition, the results from simulations are presented and validated with qualitative and quantitative microstructural analyses. The coupling of the process simulation and microstructural modeling indicate promising results, since the microstructural analysis shows good agreement with the predicted alpha lath size.
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| 24. |
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| 25. |
- Fisk, Martin, et al.
(author)
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Simulation and validation of repair welding and heat treatment of an alloy 718 plate
- 2012
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In: Finite elements in analysis and design (Print). - : Elsevier BV. - 0168-874X .- 1872-6925. ; 58, s. 66-73
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Journal article (peer-reviewed)abstract
- This paper describes simulation of repair welding and heat treatment together with measurements for validation. The possibility to replace global heat treatment with local using induction heating is evaluated with respect to obtained residual stresses. A physically based material model is used in the analyses. The result from the residual stress measurement shows that there are no significant differences between local heat treatment and global heat treatment.
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| 26. |
- Fisk, Martin, et al.
(author)
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Simulation of microstructural evolution during repair welding of an IN718 plate
- 2016
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In: Finite elements in analysis and design (Print). - : Elsevier. - 0168-874X .- 1872-6925. ; 120, s. 92-101
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Journal article (peer-reviewed)abstract
- A precipitate evolution model based on classical nucleation, growth and coarsening theory is adapted and solved using the multi-class approach for the superalloy IN718. The model accounts for dissolution of precipitates and is implemented in a finite element program. The model is used to simulate precipitate evolution in the fused zone and the adjacent heat affected zone for a welding simulation. The calculated size distribution of precipitates is used to predict Vickers hardness. The simulation model is compared with nanoindentation experiments. The agreement between simulated and measured hardness is good. (C) 2016 Elsevier B.V. All rights reserved.
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| 27. |
- Gad, Helge, et al.
(author)
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MTH1 inhibition eradicates cancer by preventing sanitation of the dNTP pool
- 2014
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In: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 508:7495, s. 215-221
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Journal article (peer-reviewed)abstract
- Cancers have dysfunctional redox regulation resulting in reactive oxygen species production, damaging both DNA and free dNTPs. The MTH1 protein sanitizes oxidized dNTP pools to prevent incorporation of damaged bases during DNA replication. Although MTH1 is non-essential in normal cells, we show that cancer cells require MTH1 activity to avoid incorporation of oxidized dNTPs, resulting in DNA damage and cell death. We validate MTH1 as an anticancer target in vivo and describe small molecules TH287 and TH588 as first-in-class nudix hydrolase family inhibitors that potently and selectively engage and inhibit the MTH1 protein in cells. Protein co-crystal structures demonstrate that the inhibitors bindin the active site of MTH1. The inhibitors cause incorporation of oxidized dNTPs in cancer cells, leading to DNA damage, cytotoxicity and therapeutic responses in patient-derived mouse xenografts. This study exemplifies the non-oncogene addiction concept for anticancer treatment and validates MTH1 as being cancer phenotypic lethal.
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| 28. |
- Herold, Nikolas, et al.
(author)
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Targeting SAMHD1 with the Vpx protein to improve cytarabine therapy for hematological malignancies
- 2017
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In: Nature Medicine. - : Springer Science and Business Media LLC. - 1078-8956 .- 1546-170X. ; 23:2, s. 256-263
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Journal article (peer-reviewed)abstract
- The cytostatic deoxycytidine analog cytarabine (ara-C) is the most active agent available against acute myelogenous leukemia (AML). Together with anthracyclines, ara-C forms the backbone of AML treatment for children and adults'. In AML, both the cytotoxicity of ara-C in vitro and the clinical response to ara-C therapy are correlated with the ability of AML blasts to accumulate the active metabolite ara-C triphosphate (ara-CTP)(2-5), which causes DNA damage through perturbation of DNA synthesis(6). Differences in expression levels of known transporters or metabolic enzymes relevant to ara-C only partially account for patient-specific differential ara-CTP accumulation in AML blasts and response to ara-C treatment(7-9). Here we demonstrate that the deoxynucleoside triphosphate (dNTP) triphosphohydrolase SAM domain and HD domain 1 (SAMHD1) promotes the detoxification of intracellular ara-CTP pools. Recombinant SAMHD1 exhibited ara-CTPase activity in vitro, and cells in which SAMHD1 expression was transiently reduced by treatment with the simian immunodeficiency virus (SIV) protein Vpx were dramatically more sensitive to ara-C-induced cytotoxicity. CRISPR-Cas9-mediated disruption of the gene encoding SAMHD1 sensitized cells to ara-C, and this sensitivity could be abrogated by ectopic expression of wild-type (WT), but not dNTPase-deficient, SAMHD1. Mouse models of AML lacking SAMHD1 were hypersensitive to ara-C, and treatment ex vivo with Vpx sensitized primary patient derived AML blasts to ara-C. Finally, we identified SAMHD1 as a risk factor in cohorts of both pediatric and adult patients with de novo AML who received ara-C treatment. Thus, SAMHD1 expression levels dictate patient sensitivity to ara-C, providing proof-of-concept that the targeting of SAMHD1 by Vpx could be an attractive therapeutic strategy for potentiating ara-C efficacy in hematological malignancies.
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| 29. |
- Karlsson, Dennis, et al.
(author)
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Binder jetting of the AlCoCrFeNi alloy
- 2019
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In: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 27, s. 72-79
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Journal article (peer-reviewed)abstract
- High density components of an AlCoCrFeNi alloy, often described as a high-entropy alloy, were manufactured by binder jetting followed by sintering. Thermodynamic calculations using the CALPHAD approach show that the high-entropy alloy is only stable as a single phase in a narrow temperature range below the melting point. At all other temperatures, the alloy will form a mixture of phases, including a sigma phase, which can strongly influence the mechanical properties. The phase stabilities in built AlCoCrFeNi components were investigated by comparing the as-sintered samples with the post-sintering annealed samples at temperatures between 900 °C and 1300 °C. The as-sintered material shows a dominant B2/bcc structure with additional fcc phase in the grain boundaries and sigma phase precipitating in the grain interior. Annealing experiments between 1000 °C and 1100 °C inhibit the sigma phase and only a B2/bcc phase with a fcc phase is observed. Increasing the temperature further suppresses the fcc phase in favor for the B2/bcc phases. The mechanical properties are, as expected, dependent on the annealing temperature, with the higher annealing temperature giving an increase in yield strength from 1203 MPa to 1461 MPa and fracture strength from 1996 MPa to 2272 MPa. This can be explained by a hierarchical microstructure with nano-sized precipitates at higher annealing temperatures. The results enlighten the importance of microstructure control, which can be utilized in order to tune the mechanical properties of these alloys. Furthermore, an excellent oxidation resistance was observed with oxide layers with a thickness of less than 5 μm after 20 h annealing at 1200 °C, which would be of great importance for industrial applications.
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| 30. |
- Karlsson Tiselius, Andreas, 1977-, et al.
(author)
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Bryophyte community assembly on young land uplift islands : dispersal and habitat filtering assessed using species traits
- 2019
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In: Journal of Biogeography. - : John Wiley & Sons. - 0305-0270 .- 1365-2699. ; 46:10, s. 2188-2202
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Journal article (peer-reviewed)abstract
- Aim: To assess habitat filtering and dispersal limitation in spore plant community assembly using bryophytes on recently emerged land uplift islands as study system. Location Gulf of Bothnia, northern Europe. Taxa Bryophytes, including the spore plant phyla Bryophyta (mosses) and Marchantiophyta (liverworts).Methods: The species compositions of 20 coastal land uplift islands differing in age, area, connectivity and habitat composition were recorded in the field. In addition, we compiled a list of the regional species pool (446 species) and gathered data on species traits related to habitat affiliations (substrate, light, moisture, and pH) and dispersal capacity (regional abundance, spore size, sporophyte frequency, sexual system, vegetative propagules). For the 420 species with available trait data, we used multivariate generalized linear models to compare trait effects on species occurrence probabilities on the islands.Results: Occurrence probabilities depended strongly on habitat affiliations. In addition, occurrence probabilities were lower for predominantly asexual species than for sexual species and for regionally rare than for regionally abundant species. Having specialized asexual propagules increased occurrence probabilities, but compensated only partly for the reductions in asexual species. No effect of the size of sexually produced spores was detected. Comparison of trait effects across island size and connectivity gradients revealed (a) reduced habitat filtering on larger islands and (b) decreasing negative effects of being predominantly asexual with increasing island connectivity.Conclusions: Both habitat filtering and dispersal capacities affect the community assembly of spore plants on land uplift islands. Asexual mosses and liverworts show landscape scale (<= 10 km) dispersal limitation. The weak or absent relationships between island connectivity and the effects of dispersal traits suggest that colonization is regulated mainly by habitat availability and the abundance of each species in a "regional spore rain" from which colonists are recruited.
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| 31. |
- Lindgren, Lars-Erik, et al.
(author)
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Additive manufacturing and high performance applications
- 2018
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In: Proceedings Of The 3rd International Conference On Progress In Additive Manufacturing (PRO-AM 2018). - : Pro-AM. ; , s. 214-219
-
Conference paper (peer-reviewed)abstract
- The requirement on life and robustness for aero-engine components poses obstacles to additive manufacturing. It is expected that increasing knowledge about the process and thereby its development together with adaption of existing alloys may improve this state. Simulations can contribute to understanding as well as be used in the design of process and components in order to reduce residual deformations and stresses as well as defects. Models for the latter are still not well established. The paper describes various existing approaches and also on-going developments at Luleå University of Technology that enable better descriptions in the near weld region for crack initiation.
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| 32. |
- Lindgren, Lars-Erik, et al.
(author)
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Approaches in computational welding mechanics applied to additive manufacturing : Review and outlook
- 2018
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In: Comptes rendus. Mecanique. - : Elsevier. - 1631-0721 .- 1873-7234. ; 346:11, s. 1033-1042
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Journal article (peer-reviewed)abstract
- The development of computational welding mechanics (CWM) began more than four decades ago. The approach focuses on the region outside the molten pool and is used to simulate the thermo-metallurgical-mechanical behaviour of welded components. It was applied to additive manufacturing (AM) processes when they were known as weld repair and metal deposition. The interest in the CWM approach applied to AM has increased considerably, and there are new challenges in this context regarding welding. The current state and need for developments from the perspective of the authors are summarised in this study.
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| 33. |
- Lindgren, Lars-Erik, et al.
(author)
-
Challenges in finite element simulations of chain of manufacturing processes
- 2013
-
In: Physical and numerical simulation of materials processing VII. - Durnten-Zurich : Trans Tech Publications Inc.. - 9783037857281 ; , s. 349-353
-
Conference paper (peer-reviewed)abstract
- Simulation of some, or all, steps in a manufacturing chain may be important for certain applications in order to determine the final achieved properties of the component. The paper discusses the additional challenges in this context
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| 34. |
- Lindgren, Lars-Erik, et al.
(author)
-
Modelling additive manufacturing of superalloys
- 2019
-
In: Procedia Manufacturing. - : Elsevier. - 2351-9789. ; 35, s. 252-258
-
Journal article (peer-reviewed)abstract
- There exist several variants of Additive Manufacturing (AM) applicable for metals and alloys. The two main groups are Directed Energy Deposition (DED) and Powder Bed Fusion (PBF). AM has advantages and disadvantages when compared to more traditional manufacturing methods. The best candidate products are those with complex shape and small series and particularly individualized product. Repair welding is often individualized as defects may occur at various instances in a component. This method was used before it became categorized as AM and in most cases, it is a DED process. PBF processes are more useful for smaller items and can give a finer surface. Both DED and PBF products require subsequent surface finishing for high performance components and sometimes there is also a need for post heat treatment. Modelling of AM as well as eventual post-processes can be of use in order to improve product quality, reducing costs and material waste. The paper describes the use of the finite element method to simulate these processes with focus on superalloys.
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| 35. |
- Lindgren, Lars-Erik, et al.
(author)
-
Simulation of additive manufacturing using coupled constitutive and microstructure models
- 2016
-
In: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 12:Part B, s. 144-158
-
Journal article (peer-reviewed)abstract
- The paper describes the application of modeling approaches used in Computational Welding Mechanics (CWM) applicable for simulating Additive Manufacturing (AM). It focuses on the approximation of the behavior in the process zone and the behavior of the solid material, particularly in the context of changing microstructure. Two examples are shown, one for the precipitation hardening Alloy 718 and one for Ti-6Al-4V. The latter alloy is subject to phase changes due to the thermal cycling
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| 36. |
- Lindgren, Lars-Erik, et al.
(author)
-
Thermo-Mechanics and Microstructure Evolution in Manufacturing Simulations
- 2013
-
In: Journal of thermal stresses. - : Taylor & Francis. - 0149-5739 .- 1521-074X. ; 36:6, s. 564-588
-
Journal article (peer-reviewed)abstract
- Thermal stresses and deformations are present and important for many manufacturing processes. Their effect depends strongly on the material behavior. The finite element method has been applied successfully for manufacturing simulations. There are numerical challenges in some cases due to large deformations, strong non-linearities etc. However, the most challenging aspect is the modeling of the material behavior. This requires in many cases coupled constitutive and microstructure models.
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| 37. |
- Lindwall, Johan, et al.
(author)
-
Boundary conditions for simulation of powder bed fusion for metallic glass formation: Measurements and calibrations
- 2019
-
In: II International Conference on Simulation for Additive Manufacturing. ; , s. 51-59
-
Conference paper (other academic/artistic)abstract
- A finite element model for prediction of the temperature field in the powder bed fusion process is presented and compared to measurements. Accurate temperature predictions at the base plate are essential to accurately predict the formation of crystals in a metallic glass forming material. The temperature measurements were performed by equipping the base plate with thermocouples during manufacturing of a cylinder with the glass forming alloy AMZ4. Boundary conditions for heat losses through the base plate/machine contact interfaces was calibrated to fit the measurements. Additional heat losses was used to account for radiation at the top surface and conduction through the powder bed. An interface boundary condition based on conservation of heat flux was examined to match the heat flow to the machine structure and the temperature predictions was satisfying. Still, temperature predictions with a constant heat transfer coefficient matched the measurements within 1.5oC during the entire building process of about 9 hours.
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| 38. |
- Lindwall, Johan
(author)
-
Modelling of Bulk Metallic Glass formation in Powder Bed Fusion
- 2019
-
Licentiate thesis (other academic/artistic)abstract
- This thesis discusses a model for simulation of the Powder Bed Fusion (PBF) process of metallic powder with the capability to become amorphous. The temperature field in the PBF process is predicted by a three-dimensional thermal finite element model in three dimensions using a layer-by-layer approach, meaning that the scanning strategy of the moving laser spot is consolidated into a single heat source acting on the entire layer momentarily. This temporal reduction enables simulations of large domains and many layers while it becomes less computational demanding compared to a detailed transient model that incorporates a scanning sequence. Predictions of the amorphous and crys- talline phase fractions are performed with a phase model coupled to the temperature field simulation. The phase model is based on differential scanning calorimetry measure- ments and optimized to fit continuous heating transformation into a crystalline state of an amorphous sample. The simulations are performed on the commercial available glass forming alloy AMZ4.Bulk Metallic Glass (BMG) have an amorphous structure and possesses desirable me- chanical, magnetic and corrosion properties such as high yield stress, low magnetic losses and high corrosion resistance. Glass forming alloy has the potential to become amorphous provided that the solidification rate is rapid enough to avoid crystallization. However, traditional manufacturing techniques, such as casting, limits the cooling rates and size of components due to limited heat conduction in the bulk. With Additive Manufacturing (AM) on the other hand, it is possible to produce BMG’s as the melt pool is very small and solidification can be achieved very rapid to bypass crystallization. Yet, crystals may form by devitrification (crystal formation upon heating of the amorphous phase) because of thermal cycling in previous layers. Simulation of the process will aid the understanding of glass formation during AM and the development of process parameters to control the level of devitrification.
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| 39. |
- Lindwall, Johan
(author)
-
Modelling of laser-based powder bed fusion for bulk metallic glass formation
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- The work presented in this thesis aims to develop a modelling approach to predict crystalline phase evolution in bulk metallic glass during additive manufacturing with laser-based powder bed fusion (PBF-LB). Metallic glasses are non-crystalline metallic materials that generally possess exceptional properties because of its amorphous struc-ture. Manufacturing of metallic glass is possible by rapid cooling of a liquid metal alloy. The required cooling rates to avoid crystallisation generally limits traditional manufac-turing techniques to small/thin samples. The desirable properties of metallic glasses motivate manufacturing of larger samples. PBF-LB is one promising method by which bulk metallic glass potentially can be produced without size limitation. Cooling rates in this process are generally several orders of magnitude higher than critical cooling rates to bypass crystallisation in glass forming alloys. Crystalline structures may still evolve within the solid material because of thermal cycling during the manufacturing process. Numerical simulation can assist development of process for bulk metallic glass formation by predicting the phase evolution. Simulations can also help to increase the understand-ing of where and when crystalline structures develop with respect to process parameters and scanning strategy. Simulation of bulk metallic glass formation during PBF-LB is a challenge. The thermodynamic and kinetic properties of the material and the large variations in time and length scales in the process makes accurate simulations difficult. This thesis address these challenges by developing a modelling approach for simulation of the temperature history and crystalline phase evolution. The objective is to assist the development of process parameters for bulk metallic glass formation. The approach includes finite element modelling to compute the temperature history in the heat affected zone. The modelling includes approximations of the energy input and approaches to sim-ulate the large variations in time and length scales associated with PBF-LB. Computed temperature histories acts as input in calculations of the crystalline phase evolution in the metallic glass. The phase transformation modelling approach includes a modified isothermal model and classical nucleation and growth theory. The result is a coupled thermal and phase transformation model that can predict the trend in crystalline phase evolution in a bulk metallic glass with respect to the process parameters. The predictions show very good agreement to experimental estimates of the crystalline volume fraction. Comparison of simulations makes it possible to evaluate the process parameters in terms of crystalline size distribution. The model is a powerful tool that help the development and fine tuning of process parameters to produce bulk metallic glass.
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| 40. |
- Lindwall, Johan, et al.
(author)
-
Simulation of phase evolution in a Zr-based glass forming alloy during multiple laser remelting
- 2022
-
In: Journal of Materials Research and Technology. - : Elsevier. - 2238-7854 .- 2214-0697. ; 16, s. 1165-1178
-
Journal article (peer-reviewed)abstract
- Additive manufacturing by laser-based powder bed fusion is a promising technique for bulk metallic glass production. But, reheating by deposition of subsequent layers may cause local crystallisation of the alloy. To investigate the crystalline phase evolution during laser scanning of a Zr-based metallic glass-forming alloy, a simulation strategy based on the finite element method and the classical nucleation theory has been developed and compared with experimental results from multiple laser remelting of a single-track. Multiple laser remelting of a single-track demonstrates the crystallisation behaviour by the influence of thermal history in the reheated material. Scanning electron microscopy and transmission electron microscopy reveals the crystalline phase evolution in the heat affected zone after each laser scan. A trend can be observed where repeated remelting results in an increased crystalline volume fraction with larger crystals in the heat affected zone, both in simulation and experiment. A gradient of cluster number density and mean radius can also be predicted by the model, with good correlation to the experiments. Prediction of crystallisation, as presented in this work, can be a useful tool to aid the development of process parameters during additive manufacturing for bulk metallic glass formation.
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| 41. |
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| 42. |
- Lindwall, Johan, et al.
(author)
-
Thermal simulation and phase modeling of bulk metallic glass in the powder bed fusion process
- 2019
-
In: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 27, s. 345-352
-
Journal article (peer-reviewed)abstract
- One of the major challenges with the powder bed fusion process (PBF) and formation of bulk metallic glass (BMG) is the development of process parameters for a stable process and a defect-free component. The focus of this study is to predict formation of a crystalline phase in the glass forming alloy AMZ4 during PBF. The approach combines a thermal finite element model for prediction of the temperature field and a phase model for prediction of crystallization and devitrification. The challenge to simulate the complexity of the heat source has been addressed by utilizing temporal reduction in a layer-by-layer fashion by a simplified heat source model. The heat source model considers the laser power, penetration depth and hatch spacing and is represented by a volumetric heat density equation in one dimension. The phase model is developed and calibrated to DSC measurements at varying heating rates. It can predict the formation of crystalline phase during the non-isothermal process. Results indicate that a critical location for devitrification is located a few layers beneath the top surface. The peak is four layers down where the crystalline volume fraction reaches 4.8% when 50 layers are built.
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| 43. |
- Lindwall, Johan, et al.
(author)
-
Virtual Development of Process Parameters for Bulk Metallic Glass Formation in Laser-Based Powder Bed Fusion
- 2022
-
In: Materials. - : MDPI. - 1996-1944 .- 1996-1944. ; 15:2
-
Journal article (peer-reviewed)abstract
- The development of process parameters and scanning strategies for bulk metallic glass formation during additive manufacturing is time-consuming and costly. It typically involves trials with varying settings and destructive testing to evaluate the final phase structure of the experimental samples. In this study, we present an alternative method by modelling to predict the influence of the process parameters on the crystalline phase evolution during laser-based powder bed fusion (PBF-LB). The methodology is demonstrated by performing simulations, varying the following parameters: laser power, hatch spacing and hatch length. The results are compared in terms of crystalline volume fraction, crystal number density and mean crystal radius after scanning five consecutive layers. The result from the simulation shows an identical trend for the predicted crystalline phase fraction compared to the experimental estimates. It is shown that a low laser power, large hatch spacing and long hatch lengths are beneficial for glass formation during PBF-LB. The absolute values show an offset though, over-predicted by the numerical model. The method can indicate favourable parameter settings and be a complementary tool in the development of scanning strategies and processing parameters for additive manufacturing of bulk metallic glass.
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| 44. |
- Llona-Minguez, Sabin, et al.
(author)
-
Discovery of the First Potent and Selective Inhibitors of Human dCTP Pyrophosphatase 1
- 2016
-
In: Journal of Medicinal Chemistry. - : American Chemical Society (ACS). - 0022-2623 .- 1520-4804. ; 59:3, s. 1140-1148
-
Journal article (peer-reviewed)abstract
- The dCTPase pyrophosphatase 1 (dCTPase) regulates the intracellular nucleotide pool through hydrolytic degradation of canonical and noncanonical nucleotide triphosphates (dNTPs). dCTPase is highly expressed in multiple carcinomas and is associated with cancer cell sternness. Here we report on the development of the first potent and selective dCTPase inhibitors that enhance the cytotoxic effect of cytidine analogues in leukemia cells. Boronate 30 displays a promising in vitro ADME profile, including plasma and mouse microsomal half-lives, aqueous solubility, cell permeability and CYP inhibition, deeming it a suitable compound for in vivo studies.
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| 45. |
- Llona-Minguez, Sabin, et al.
(author)
-
Identification of Triazolothiadiazoles as Potent Inhibitors of the dCTP Pyrophosphatase 1
- 2017
-
In: Journal of Medicinal Chemistry. - : American Chemical Society (ACS). - 0022-2623 .- 1520-4804. ; 60:5, s. 2148-2154
-
Journal article (peer-reviewed)abstract
- The dCTP pyrophosphatase 1 (dCTPase) is involved in the regulation of the cellular dNTP pool and has been linked to cancer progression. Here we report on the discovery of a series of 3,6-disubstituted triazolothiadiazoles as potent dCTPase inhibitors. Compounds 16 and 18 display good correlation between enzymatic inhibition and target engagement, together with efficacy in a cellular synergy model, deeming them as a promising starting point for hit -to-lead development.
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| 46. |
- Lundbäck, Andreas
(author)
-
CAD support for heat input in a FE [finite element] model
- 2002
-
In: Mathematical Modelling of Weld Phenomena 6. - : Maney Publishing (for The Institute of Materials, Minerals and Mining). - 1902653564 ; , s. 1113-1121
-
Conference paper (peer-reviewed)abstract
- A method using CAD is presented for simplifying the problem of defining the heat input in finite element based welding simulations. The CAD system is used to define the weld path geometrically; this information is then used in the finite element analysis. Examples of the method's use are presented.
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| 47. |
- Lundbäck, Andreas
(author)
-
Finite element modelling and simulation of welding of aerospace components
- 2003
-
Licentiate thesis (other academic/artistic)abstract
- Fusion welding is one of the most used methods for joining metals. This method has largely been developed by experiments, i.e. trial and error. The problem of distortion and residual stresses of a structure in and around a welded joint is important to control. This is especially important in the aerospace industry where the components are expensive and safety and quality are important issues. The safety requirements and the high costs of performing experiments to find different manufacturing routes is the motivation to increase the use of simulations in design of component as well as its manufacturing. Thus, in the case of welding, one can evaluate the effect of different fixtures, welding parameters etc on the deformation of the component. Then it is possible to optimise a chain of manufacturing processes as, for example, the welding residual stresses will affect the deformations during a subsequent heat treatment. The aim of the work presented in this thesis is to develop an efficient and reliable method and tool for simulation of the welding process using the Finite Element Method. The simulation tool will then be used when designing and planning the manufacturing of a component, so that introduction of new components can be made with as little disturbance as possible. In the same time the developed tool will be suitable for the task to perform an optimal design for manufacturing. Whilst this development will also be valuable in predicting the component's subsequent in-service behaviour, the key target is to ensure that designs are created which are readily manufactured. If this understanding is captured and made available to designers, true design for manufacture will result. This will lead to right first time product introduction and minimal ongoing manufacturing costs as process capability will be understood and designed into the component. When creating a numerical model, the aim is to implement the physical behaviour of the process into the computer model. However, it may be necessary to compromise between accuracy of the model and the required computational time. Different types of simplifications of the problem and more efficient computation methods are discussed. Methods for alleviating the modelling, and in particular the creation of the weld path, of complex geometries is presented. Simulations and experiments have been carried out on simple geometries in order to validate the models.
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| 48. |
- Lundbäck, Andreas, et al.
(author)
-
Finite Element Simulation to Support Sustainable Production by Additive Manufacturing
- 2016
-
In: Procedia Manufacturing. - : Elsevier BV. - 2351-9789. ; 7, s. 127-130
-
Journal article (peer-reviewed)abstract
- Additive manufacturing (AM) has been identified as a disruptive manufacturing process having the potential to provide a number of sustainability advantages. Functional products with high added value and a high degree of customization can be produced. AM is particularly suited for industries in which mass customization, light weighting of parts and shortening of the supply chain are valuable. Its applications can typically be found in fields such as the medical, dental, and aerospace industries. One of the advantages with AM is that little or no scrap is generated during the process. The additive nature of the process is less wasteful than traditional subtractive methods of production. The capability to optimize the geometry to create lightweight components can reduce the material use in manufacturing. One of the challenges is for designers to start using the power of AM. To support the designers and manufacturing, there is a need for computational models to predicting the final shape, deformations and residual stresses. This paper summarizes the advantages of AM in a sustainability perspective. Some examples of application of simulation models for AM are also given.
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| 49. |
- Lundbäck, Anna-Karin, et al.
(author)
-
Assembly of Kch, a putative potassium channel from Escherichia coli
- 2009
-
In: Journal of Structural Biology. - : Elsevier BV. - 1047-8477 .- 1095-8657. ; 168:2, s. 288-293
-
Journal article (peer-reviewed)abstract
- Attempts to explore the structure and function of Kch, a putative potassium channel of Escherichia coli have yielded varying results; potassium-associated functions have been found in vivo but not in vitro. Here the kch gene is shown to produce two proteins, full-length Kch and the large C-terminal cytosolic domain (the RCK domain). Further, these two proteins are associated at the initial stages of purification. Previous structural studies of full-length Kch claim that the isolated protein forms large aggregates that are not suitable for analysis. The results presented here show that the purified protein sample, although heterogeneous, has one major population with a mass of about 400 kDa, implying the presence of two Kch tetramers in a complex form. A three dimensional reconstruction at 25 angstrom based on electron microscopy data from negatively stained particles, revealed a 210 angstrom long and 95 angstrom wide complex in which the two tetrameric Kch units are linked by their RCK domains, giving rise to a large central ring of density. The formation of this dimer of tetramers on expression or during purification, may explain why attempts to reconstitute Kch into liposomes for activity measurements have failed.
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| 50. |
- Lundbäck, Andreas, et al.
(author)
-
Modeling and Experimental Measurement with Synchrotron Radiation of Residual Stresses in Laser Metal Deposited Ti-6Al-4V
- 2016
-
In: Proceedings of the 13th World Conference on Titanium. - Hoboken, NJ, USA : John Wiley & Sons, Inc.. - 9781119293668 - 9781119296126 ; , s. 1279-1282
-
Conference paper (peer-reviewed)abstract
- There are many challenges in producing aerospace components by additive manufacturing (AM). One of them is to keep the residual stresses and deformations to a minimum. Another one is to achieve the desired material properties in the final component. A computer model can be of great assistance when trying to reduce the negative effects of the manufacturing process. In this work a finite element model is used to predict the thermo-mechanical response during the AM-process. This work features a physically based plasticity model coupled with a microstructure evolution model for the titanium alloy Ti -6Al-4V. Residual stresses in AM components were measured non-destructively using high-energy synchrotron X-ray diffraction on beam line ID15A at the ESRF, Grenoble. The results are compared with FE model predictions of residual stresses. During the process, temperatures and deformations was continuously measured. The measured and computed thermal history agrees well. The result with respect to the deformations agrees well qualitatively. Meaning that the change in deformation in each sequence is well predicted but there is a systematic error that is summing so that the quantitative agreement is lost.
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