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| 9. |
- Berggren, Cathrine, et al.
(author)
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Att utvärdera och använda resultaten – vilka avtryck ger bibliotekens utvärderingar i samhället?
- 2013
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Conference paper (pop. science, debate, etc.)abstract
- Det har blivit allt viktigare för biblioteken att kunna visa på sin betydelse i samhället. Mätetal och utvärderingar är nödvändiga instrument för att kunna jämföra satsningar på biblioteken med satsningar på andra områden. Men finns det en synergi mellan mätetalen och verksamhetens planer och mål? Hur mäter vi måluppfyllese i biblioteksverksamheten? Finns det kvalitetsindikatorer som vi har gemensamma oavsett bibliotekstyp? Hur kan biblioteksstatistiken användas? Vad gör bibliotekens utvärderingar för avtryck i beslutsprocessen? Vad gör bibliotekens utvärderingar för avtryck i samhället?För att svara på frågorna ovan har expertgruppen påbörjat ett arbete med att kartlägga hur svenska bibliotek arbetar med utvärdering. I det arbetet har vi bland annat sett vikten av ett gemensamt språk mellan bibliotekstyperna i arbetet med utvärderingar och kvalitetsutveckling. Gruppen kommer att under år 2014 publicera ett utvärderingsverktyg för bibliotek. Där kan bibliotek finna vägledning och stöd i valet av utvärderingsmetod, i genomförandet och i nyttjandet av utvärderingars resultat i syfte att utveckla och synliggöra biblioteksverksamheten.I det här papret presenterar vi syftet med vårt arbete och den metod vi har använt samt mer ingående berättar om hur vi har tänkt kring det verktyg som vi i slutet av papret ger en beskrivning av – ett verktyg som går under namnet "Utvärderingshjälpen".Vid konferensen kommer vi att presentera hur en årscykel kan se ut vid ett bibliotek som väljer att använda sig av utvärderingsarbete och systematiskt kvalitetsutveckling i nära relation till måluppfyllelse och till dialog med beslutsfattare samt omgivande samhälle. Vi presenterar också hur "Utvärderingshjälpen" skall kunna användas som stöd i det arbetet.
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| 11. |
- Blixt, Kevin, et al.
(author)
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Evaluation of grain boundary energy, structure and stiffness from phase field crystal simulations
- 2021
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In: Modelling and Simulation in Materials Science and Engineering. - 0965-0393. ; 30:1
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Journal article (peer-reviewed)abstract
- A two-mode phase field crystal (PFC) model is employed to investigate the equilibrium configurations of a range of grain boundaries in fcc-structured materials. A total of 80 different symmetrical tilt grain boundaries are evaluated by PFC simulations in 3D and the results are shown to agree well with data taken from the literature, both regarding the variation of grain boundary energy and also in terms of the resulting grain boundary structures. This verification complements existing PFC studies which are almost exclusively focused either on grain boundaries found in 2D systems or in bcc lattices in 3D. The present work facilitates application of PFC in the analysis of grain boundary mechanics in an extended range of materials, in particular such mechanics that take place at extended time scales not tractable for molecular dynamics (MD) simulations. In addition to the verification of predicted grain boundary energies and structures, wavelet transforms of the density field are used in the present work to obtain phase fields from which it is possible to identify grain boundary fluctuations that provide the means to evaluate grain boundary stiffness based on the capillarity fluctuation method. It is discussed how PFC provides benefits compared to alternative methods, such as MD simulations, for this type of investigations.
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| 12. |
- Blixt, Kevin, et al.
(author)
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Grain boundary and particle interaction: Enveloping and pass-through mechanisms studied by 3D phase field crystal simulations
- 2022
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In: Materials & Design. - : Elsevier BV. - 0261-3069 .- 0264-1275. ; 220
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Journal article (peer-reviewed)abstract
- Grain boundary interaction with second-phase particles having different degrees of coherency is investigated using the phase field crystal (PFC) method. Both the enveloping and pass-through mechanisms are studied with regards to grain boundary pressure, passage time and interface evolution. It is found that coherent particles exert a stronger retardation effect on grain boundaries compared to incoherent particles, with regards to both pressure and time, but also that this benefit is limited to a small range of misfit values. The simulations also show that the mobility is not a constant during particle passage, as commonly assumed, which means that grain boundary pressure cannot easily be extracted from the grain boundary velocity. Furthermore, the complex evolution of the pass-through mechanism and the transient behavior for intermediate coherencies is also investigated. The highest drag force is found to occur at the switching point between enveloping and pass-through. As part of the study, the advantages of using PFC for this type of analyses are also highlighted.
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| 13. |
- Blixt, Kevin Hult, et al.
(author)
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Grain boundary stiffness based on phase field crystal simulations
- 2022
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In: Materials Letters. - : Elsevier BV. - 0167-577X. ; 318
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Journal article (peer-reviewed)abstract
- Phase field crystal modeling with wavelet filtering is shown to be an attractive replacement for molecular dynamics simulations when evaluating grain boundary stiffness by the capillary fluctuation method. Obstacles such as iterative equilibration of grain boundary structures and repeated reconstruction of the grain boundary over extended simulations can be avoided.
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| 14. |
- Blixt, Kevin H., et al.
(author)
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Phase field crystal modeling of grain boundary structures in diamond cubic systems
- 2024
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In: Physical Review Materials. - 2475-9953. ; 8:3
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Journal article (peer-reviewed)abstract
- Phase field crystal (PFC) modeling has proved to be a versatile numerical tool in the analysis of crystalline microstructures. Most often, however, the focus is put on bulk crystal behavior, while crystal defects such as grain boundaries (GBs) are less explored. This is, in particular, the case for crystal structures beyond fcc and bcc. In this work, the possibilities and challenges in adopting PFC to diamond cubic (DC) crystal structures is investigated. Three different PFC models are considered for this purpose. One of them was published previously, and two are modifications proposed in the present work. The models are compared in terms of both DC phase stabilization and their ability to provide relevant GB structures. The models employ combinations of two- and three-point correlations, and the addition of a three-point correlation is found to be required for stabilization of the expected DC GB structures. It is concluded that although each of the models has limitations in terms of the GB structures which can be stabilized and performance in terms of phase stability, key PFC components for successful modeling of DC structures can be identified.
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| 16. |
- Edsjö, Anders, et al.
(author)
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Differences in early and late responses between neurotrophin-stimulated trkA- and trkC-transfected SH-SY5Y neuroblastoma cells
- 2001
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In: Cell Growth & Differentiation. - 1044-9523. ; 12:1, s. 39-50
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Journal article (peer-reviewed)abstract
- Despite their sympathetic neuroblast origin, highly malignant neuroblastoma tumors and derived cell lines have no or low expression of the neurotrophin receptor genes, trkA and trkC. Expression of exogenous trkA in neuroblastoma cells restores their ability to differentiate in response to nerve growth factor (NGF). Here we show that stable expression of trkC in SH-SY5Y neuroblastoma cells resulted in morphological and biochemical differentiation upon treatment with neurotrophin-3 (NT-3). To some extent, trkA- and trkC-transfected SH-SY5Y (SH-SY5Y/trkA and SH-SY5Y/trkC) cells resembled one another in terms of early signaling events and neuronal marker gene expression, but important differences were observed. Although induced Erk 1/2 and Akt/PKB phosphorylation was stronger in NT-3-stimulated SH-Y5Y/trkC cells, activation of the immediate-early genes tested was more prominent in NGF-treated SH-SY5Y/ trkA cells. In particular, c-fos was not induced in the SH-SY5Y/trkC cells. There were also phenotypic differences. The concentrations of norepinephrine, the major sympathetic neurotransmitter, and growth cone-located synaptophysin, a neurosecretory granule protein, were increased in NGF-treated SH-SY5Y/trkA but not in NT-3-treated SH-SY5Y/trkC cells. Our data suggest that NT-3/p145trkC and NGF/p140trkA signaling differ in some aspects in neuroblasoma cells, and that this may explain the phenotypic differences seen in the long-term neurotrophin-treated cells.
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| 18. |
- Englund, Gunilla, et al.
(author)
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Association between the number of coadministered P-glycoprotein inhibitors and serum digoxin levels in patients on therapeutic drug monitoring
- 2004
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In: BMC Medicine. - : BioMed Central (BMC). - 1741-7015. ; 2:1
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Journal article (peer-reviewed)abstract
- BackgroundThe ABC transporter P-glycoprotein (P-gp) is recognized as a site for drug-drug interactions and provides a mechanistic explanation for clinically relevant pharmacokinetic interactions with digoxin. The question of whether several P-gp inhibitors may have additive effects has not yet been addressed.MethodsWe evaluated the effects on serum concentrations of digoxin (S-digoxin) in 618 patients undergoing therapeutic drug monitoring. P-gp inhibitors were classified as Class I, with a known effect on digoxin kinetics, or Class II, showing inhibition in vitro but no documented effect on digoxin kinetics in humans. Mean S-digoxin values were compared between groups of patients with different numbers of coadministered P-gp inhibitors by a univariate and a multivariate model, including the potential covariates age, sex, digoxin dose and total number of prescribed drugs.ResultsA large proportion (47%) of the digoxin patients undergoing therapeutic drug monitoring had one or more P-gp inhibitor prescribed. In both univariate and multivariate analysis, S-digoxin increased in a stepwise fashion according to the number of coadministered P-gp inhibitors (all P values < 0.01 compared with no P-gp inhibitor). In multivariate analysis, S-digoxin levels were 1.26 ± 0.04, 1.51 ± 0.05, 1.59 ± 0.08 and 2.00 ± 0.25 nmol/L for zero, one, two and three P-gp inhibitors, respectively. The results were even more pronounced when we analyzed only Class I P-gp inhibitors (1.65 ± 0.07 for one and 1.83 ± 0.07 nmol/L for two).ConclusionsPolypharmacy may lead to multiple drug-drug interactions at the same site, in this case P-gp. The S-digoxin levels increased in a stepwise fashion with an increasing number of coadministered P-gp inhibitors in patients taking P-gp inhibitors and digoxin concomitantly. As coadministration of digoxin and P-gp inhibitors is common, it is important to increase awareness about P-gp interactions among prescribing clinicians.
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| 19. |
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| 20. |
- Ericsson, Anders, et al.
(author)
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Modeling of nucleation and growth in glass-forming alloys using a combination of classical and phase-field theory
- 2019
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In: Computational materials science. - : Elsevier. - 0927-0256 .- 1879-0801. ; 165, s. 167-179
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Journal article (peer-reviewed)abstract
- For metallic glasses, it is of vital importance to understand the glass formation properties and to be able to predict the crystallization process in the supercooled liquid. In the present work, we model the process of nucleation and growth using a combination of classical nucleation and phase-field theory. A diffusion coupled phase-field model is used to evaluate the work of formation and the growth behavior of the critical nucleus. The results are combined with classical nucleation and JMAK theory in order to estimate the glass forming ability of the compositions Cu64Zr36, Cu10Zr7 and CuZr2 in terms of TTT-diagrams and critical cooling rates. It is found that the work of formation of the critical nucleus from the phase-field theory agrees with the classical theory when the critical size is larger than the width of the solid-liquid interface. At smaller critical sizes, the work of formation deviates approximately linearly between the two theories. Furthermore, it is shown that the growth behavior from the phase-field simulations agree with analytical expressions of the growth rate from the classical theory.
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| 24. |
- Haglund, Lena, et al.
(author)
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Practice models in Swedish psychiatric occupational therapy
- 2000
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In: Scandinavian Journal of Occupational Therapy. - : Informa UK Limited. - 1103-8128 .- 1651-2014. ; 7:3, s. 107-113
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Journal article (peer-reviewed)abstract
- In clinical settings, occupational therapists need models both from their own field, occupational therapy, and from other fields in order to offer the clients adequate treatment. It is unknown which theoretical approaches and practice models influence Swedish occupational therapists' daily work. In this study a questionnaire (n=334) was used to investigate approaches and models used in Swedish psychiatric care service and in psychiatric occupational therapy service. The results showed that the psychosocial approach influenced both psychiatric care and psychiatric occupational therapy most. The most frequently used practice model was the Model of Human Occupation. However, 75% of the respondents did not identify theoretical thinking based on models from their own field behind their actions. Many practitioners seemed to use knowledge developed by other disciplines more often. Years of clinical experience in the profession or education did not seem to have any impact on the ability to identify the practice models that were used. The results indicate that education in occupational therapy must emphasize knowledge in its own field more than has been done up to now.
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| 26. |
- Hallberg, Håkan, et al.
(author)
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A biological or a synthetic mesh in immediate breast reconstruction? A cohort-study of long-term Health related Quality of Life (HrQoL)
- 2019
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In: European Journal of Surgical Oncology. - : Elsevier BV. - 0748-7983 .- 1532-2157. ; 45:10, s. 1812-1816
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Journal article (peer-reviewed)abstract
- Objectives: Meshes/matrices are commonly used in immediate breast reconstruction. There are few studies comparing biological and synthetic meshes and it is unknown what type of mesh gives the best long-term results. The aim of this study was to compare long-term health-related quality of life (HrQoL) and patient satisfaction in implant-based immediate breast reconstruction with a biological mesh (Surgisis ® ) with that of patients reconstructed with a synthetic mesh (TIGR ® Matrix Surgical Mesh). Material and methods: Both cohorts were prospectively included and consecutively operated. Clinical data was collected. HrQoL was evaluated with EuroQoL-5 dimension – 3 levels questionnaire (EQ-5D-3L) and the Hospital Anxiety and Depression Scale (HADS) and the Breast-Q. Results and conclusion: Seventy-one patients were operated on in the biological group and 49 in the synthetic group. The response rates were 75 and 84 per cent, respectively. Mean follow-up time was 74 months and 23 months, respectively. There were no statistical differences in satisfaction and quality of life between the two groups. Complications and radiation seem to lead to a lower satisfaction. Our findings could indicate that biological and synthetic meshes give an equal long-term result as regards patients’ perceived quality of life.
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| 27. |
- Hallberg, Håkan, et al.
(author)
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A constitutive model for the flow stress behavior and microstructure evolution in aluminum alloys under hot working conditions - with application to AA6099
- 2019
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In: Applied Mathematical Modelling. - : Elsevier BV. - 0307-904X. ; 81, s. 253-262
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Journal article (peer-reviewed)abstract
- A constitutive model for aluminum alloys under hot working conditions is proposed. The elastic-viscoplastic model is implemented in a finite strain continuum mechanical framework. The model accounts for the interplay between dynamic recovery and recrystallization during hot working of aluminum alloys and central aspects of microstructure evolution such as grain/subgrain size and dislocation density. The proposed model is generic in the sense that it can be used for arbitrary aluminum alloys, but in order to demonstrate its capabilities, the model is calibrated to a newly developed AA6099 alloy in the present study. The model is thoroughly discussed and details on the numerical implementation as well as on the calibration of the model against experimental data are provided.
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| 28. |
- Hallberg, Håkan, et al.
(author)
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A constitutive model for the formation of martensite in austenitic steels under large strain plasticity
- 2007
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In: International Journal of Plasticity. - : Elsevier BV. - 0749-6419. ; 23:7, s. 1213-1239
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Journal article (peer-reviewed)abstract
- A constitutive model for diffusionless phase transitions in elastoplastic materials undergoing large deformations is developed. The model takes basic thermodynamic relations as its starting point and the phase transition is treated through an internal variable (the phase fractions) approach. The usual yield potential is used together with a transformation potential to describe the evolution of the new phase. A numerical implementation of the model is presented, along with the derivation of a consistent algorithmic tangent modulus. Simulations based on the presented model are shown to agree well with experimental findings. The proposed model provides a robust tool suitable for large-scale simulations of phase transformations in austenitic steels undergoingz extensive deformations, as is demonstrated in simulations of the necking of a bar under tensile loading and also in simulations of a cup deep-drawing process.
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| 29. |
- Hallberg, Håkan
(author)
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A modified level set approach to 2D modeling of dynamic recrystallization
- 2013
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In: Modelling and Simulation in Materials Science and Engineering. - : IOP Publishing. - 0965-0393 .- 1361-651X. ; 21:8
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Journal article (peer-reviewed)abstract
- The macroscopic properties of metallic materials depend on the state of the grain microstructure. Recrystallization acts as one of the most important mechanisms in the evolution of the microstructure and hence also of the macroscopic properties. This paper presents a mesoscale model of microstructure evolution due to recrystallization, based on a level set formulation employed in a finite element setting. The use of level sets to represent grains and grain boundaries in polycrystal microstructures is a relatively recent development in computational materials science and the present contribution suggests new methodologies such as interface reconstruction, allowing for example boundary conditions to be prescribed along grain boundary interfaces and distinct localization and representation of grain boundary junctions. Polycrystal plasticity is modeled by considering the evolution of dislocation density in the individual crystals. The influence of grain boundaries on dislocation accumulation is captured in the model, causing the formation of dislocation density gradients within the grains. The model is used in simulations of dynamic recrystallization, taking pure copper as example material. It is shown that the proposed model captures the salient features of dynamic recrystallization during thermomechanical materials processing.
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| 30. |
- Hallberg, Håkan
(author)
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A Note on the Kelvin Effect in 100Cr6 Steel with Application to Identification of the Elastoplastic Limit
- 2012
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In: ISRN Thermodynamics. - : Hindawi Limited. - 2090-5203 .- 2090-5211. ; 2012
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Journal article (peer-reviewed)abstract
- Experimental and analytical results are presented regarding the temperature evolution in 100Cr6 steel under uniaxial loading. Differently heat-treated conditions of the material are studied at different strain rates. In the annealed state, the materials exhibits a pronounced initial yield stress as it passes from the elastic region to the plastic through discontinuous yielding. In contrast, the quenched and tempered material yields continuously. The focus of the paper is on the temperature decrease during elastic deformation that precedes the more pronounced heating due to inelastic dissipation once the elastoplastic limit stress is surpassed. The applicability of the maximum temperature decrease in the elastic regime as a replacement for the commonly used 0.2%-strain measure to define the elastoplastic limit is discussed. For 100Cr6 steel, the 0.2%-strain measure is found, in some cases, to overestimate the initial yield stress by 50 MPa. The drop in temperature corresponding to the shift from elastic to inelastic material behavior is experimentally determined and compared to predictions by the Kelvin formula which in the current study give a maximum 50% error.
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| 31. |
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| 32. |
- Hallberg, Håkan
(author)
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Approaches to Modeling of Recrystallization
- 2011
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In: Metals. - : MDPI AG. - 2075-4701. ; 1:1, s. 16-48
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Journal article (other academic/artistic)abstract
- Control of the material microstructure in terms of the grain size is a key component in tailoring material properties of metals and alloys and in creating functionally graded materials. To exert this control, reliable and efficient modeling and simulation of the recrystallization process whereby the grain size evolves is vital. The present contribution is a review paper, summarizing the current status of various approaches to modeling grain refinement due to recrystallization. The underlying mechanisms of recrystallization are briefly recollected and different simulation methods are discussed. Analytical and empirical models, continuum mechanical models and discrete methods as well as phase field, vertex and level set models of recrystallization will be considered. Such numerical methods have been reviewed previously, but with the present focus on recrystallization modeling and with a rapidly increasing amount of related publications, an updated review is called for. Advantages and disadvantages of the different methods are discussed in terms of applicability, underlying assumptions, physical relevance, implementation issues and computational efficiency.
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| 33. |
- Hallberg, Håkan, et al.
(author)
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Benefits and risks with acellular dermal matrix (ADM) and mesh support in immediate breast reconstruction: a systematic review and meta-analysis
- 2018
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In: Journal of Plastic Surgery and Hand Surgery. - 2000-656X .- 2000-6764. ; 52:3, s. 130-147
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Journal article (peer-reviewed)abstract
- In modern implant-based immediate breast reconstruction, it has become common to use biological acellular dermal and synthetic matrices in combination with a tissue expander or an implant. The aim of this systematic review was to examine differences in recurrence of cancer, impact on oncological treatment, health related quality of life, complications and aesthetic outcome between matrix and no matrix in immediate breast reconstruction. Systematic searches, data extraction and assessment of methodological quality were performed according to predetermined criteria. Fifty-one studies were eligible and included in the review. The certainty of evidence for overall complication rate and implant loss is low (GRADE ⊕⊕□ □). The certainty of evidence for delay of adjuvant treatment, implant loss, infection, capsular contraction and aesthetic outcome is very low (GRADE ⊕□ □ □). No study reported data on recurrence of cancer or health related quality of life. In conclusion, there is a lack of high quality studies that compare the use of matrix with no matrix in immediate breast reconstruction. Specifically, there are no data on risk of recurrence of cancer, delay of adjuvant treatment and Health related quality of life (HRQoL). In addition, there is a risk of bias in many studies. It is often unclear what complications have been included and how they have been diagnosed, and how and when capsular contracture and aesthetic outcome have been evaluated. Controlled trials that further analyse the impact of radiotherapy, type of matrix and type of procedure (one or two stages) are necessary.
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| 34. |
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| 35. |
- Hallberg, Håkan, et al.
(author)
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Complications, long-term outcome and quality of life following Surgisis® and muscle-covered implants in immediate breast reconstruction: a case-control study with a 6-year follow-up
- 2019
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In: European Journal of Plastic Surgery. - : Springer Science and Business Media LLC. - 0930-343X .- 1435-0130. ; 42:1, s. 33-42
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Journal article (peer-reviewed)abstract
- © 2018, The Author(s). Background: Matrices are now commonly used in breast reconstruction, but the scientific evidence is still scares. The main aim was to compare complications and the need for corrections in immediate breast reconstruction with the porcine-derived Surgisis®with the traditional muscle-covered technique. The secondary aim was to compare long-term quality of life and satisfaction. Methods: All consecutive patients who had their breast reconstructed with a Surgisis®or muscle-covered tissue expander/implant were included. Patients were followed clinically and with BREAST-Q. Results: During the study period, 116 reconstructions (71 patients) were operated in the Surgisis®group and 132 reconstructions (90 patients) in the control group. The median follow-up time was 74months (min 43–max 162). The total early complication rate was 37% in the Surgisis®group and 27% in the control group. There were no differences in implant loss (p = 0.68) or total number of complications (p = 0.24) between the two groups. Risk factors for complications were mainly patient characteristics and the use of a tissue expander. There was a slightly higher capsular contracture frequency in the Surgisis®patients (4.2% vs. 2.5%). The need for corrections and patient satisfaction and quality of life were similar in the two groups. Conclusions: The use of Surgisis®in implant-based reconstruction seems to result in an acceptable total early complication rate. The rate might be higher in tissue expander-based reconstruction. Risk factors are mainly patient characteristics. The capsular contracture rate and need for corrections, as well as patient satisfaction and quality of life, are similar in the Surgisis®patients and muscle-covered controls. Level of evidence: III.
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| 36. |
- Hallberg, Håkan, et al.
(author)
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Crack tip transformation zones in austenitic stainless steel
- 2012
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In: Engineering Fracture Mechanics. - : Elsevier BV. - 1873-7315 .- 0013-7944. ; 79, s. 266-280
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Journal article (peer-reviewed)abstract
- Crack tip conditions in SUS 304 austenitic stainless steel are studied using a constitutive model in which the martensitic phase transformation is an integral part. The phase transformation occurring in the crack tip region gives rise to fracture toughening of the material whereby the resistance against crack initiation, as well as the macroscopic material response are strongly altered by the presence of a martensitic phase. The constitutive model employed herein permits studying the transformation zones under different isothermal conditions. Local crack tip conditions and related plastic deformation is confirmed to depend strongly on the varying extent of the martensitic phase transformation at different temperatures. The shape and size of the plastic and transformation zones in the neighborhood of the crack tip are obtained from numerical simulations, as well as derived analytically.
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| 37. |
- Hallberg, Håkan, et al.
(author)
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Crystal plasticity modeling of microstructure influence on fatigue crack initiation in extruded Al6082-T6 with surface irregularities
- 2018
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In: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 111, s. 16-32
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Journal article (peer-reviewed)abstract
- The influence of surface roughness and microstructure heterogeneities in the vicinity of macroscopic stress concentrations are investigated by crystal plasticity simulations. It is shown that in the extruded Al6082-T6 alloy under consideration, twin grain boundaries and other highly misoriented grain interfaces, which constitute significant barriers to plastic slip, provide internal domains in the material where initiation of fatigue damage is more likely to occur than at the stress concentrations which are due to the surface roughness. In addition, the microstructure influence on the appearance of stress gradients is found to be significant. Further, the present study indicates that frequently used fatigue initiation parameters (FIP) such as the locally accumulated plastic strain or stored energy may be insufficient to identify fatigue crack initiation. Such parameters should be complemented or replaced by other FIP which take additional characteristics of the microstructure into account. This is exemplified in the present study by employing two additional FIPs, based on a modified Fatemi-Socie critical-plane parameter and on the Dang Van criterion, respectively.
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| 38. |
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| 39. |
- Hallberg, Håkan, et al.
(author)
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Evaluation of Nanoscale Deformation Fields from Phase Field Crystal Simulations
- 2022
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In: Metals. - : MDPI AG. - 2075-4701. ; 12:10
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Journal article (peer-reviewed)abstract
- Different methods for evaluation of displacement and strain fields based on phase field crystal (PFC) simulations are shown. Methods originally devised for molecular dynamics (MD) simulations or analysis of high-resolution microscopy images are adapted to a PFC setting, providing access to displacement and strain fields for systems of discrete atoms, such as in MD, as well as to continuous deformation fields. The latter being achieved by geometrical phase analysis. As part of the study, the application of prescribed non-affine deformations in a 3D structural PFC (XPFC) setting is demonstrated as well as an efficient numerical scheme for evaluation of PFC phase diagrams, such as, for example, those required to stabilize solid/liquid coexistence. The present study provides an expanded toolbox for using PFC simulations as a versatile numerical method in the analysis of material behavior at the atomic scale.
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| 40. |
- Hallberg, Håkan
(author)
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Influence of anisotropic grain boundary properties on the evolution of grain boundary character distribution during grain growth - a 2D level set study
- 2014
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In: Modelling and Simulation in Materials Science and Engineering. - : IOP Publishing. - 0965-0393 .- 1361-651X. ; 22:8
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Journal article (peer-reviewed)abstract
- The present study elaborates on a 2D level set model of polycrystal microstructures that was recently established by adding the influence of anisotropic grain boundary energy and mobility on microstructure evolution. The new model is used to trace the evolution of grain boundary character distribution during grain growth. The employed level set formulation conveniently allows the grain boundary characteristics to be quantified in terms of coincidence site lattice (CSL) type per unit of grain boundary length, providing a measure of the distribution of such boundaries. In the model, both the mobility and energy of the grain boundaries are allowed to vary with misorientation. In addition, the influence of initial polycrystal texture is studied by comparing results obtained from a polycrystal with random initial texture against results from a polycrystal that initially has a cube texture. It is shown that the proposed level set formulation can readily incorporate anisotropic grain boundary properties and the simulation results further show that anisotropic grain boundary properties only have a minor influence on the evolution of CSL boundary distribution during grain growth. As anisotropic boundary properties are considered, the most prominent changes in the CSL distributions are an increase of general low-angle Σ1 boundaries as well as a more stable presence of Σ3 boundaries. The observations also hold for the case of an initially cube-textured polycrystal. The presence of this kind of texture has little influence over the evolution of the CSL distribution. Taking into consideration the anisotropy of grain boundary properties, grain growth alone does not seem to be sufficient to promote any significantly increased overall presence of CSL boundaries.
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| 41. |
- Hallberg, Håkan, et al.
(author)
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Influence of Microstructure and Surface Roughness on Fatigue Initiation in Extruded Aluminum
- 2018
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Conference paper (peer-reviewed)abstract
- Comprehensive experimental data on the fatigue properties of extruded Al6082-T6 is used together with crystal plasticity simulations to investigate the microstructure and surface roughness influence on fatigue initiation. Thesurface roughness of the specimens used in the experiments was mapped with White Light Interferometry (WLI) and the location of the fatigue initiation sites was identified and characterized in each sample. With surface geometries based on the WLI scans, densely meshed non-linear FE models were used to identify the locations of the highest macroscopic stress concentrations. A somewhat surprising outcome of the experimental study is that the majority of fatigue failures were initiated at surface irregularities that did not correspond to the most significant macroscopic stress concentration. Since the depths of the surface irregularities are comparable to microstructure features - such as the grain size - the present study explores to what extent microstructure variations can be acause for the observed material behavior. The numerical investigation is performed by using crystal plasticity simulations and simulation models which are based on the actual surface geometries and material microstructuresencountered in the experiments. Grain structure and texture are taken into account and the simulations reveal that variations in the microstructure can indeed make initiation of fatigue more likely to occur near surface notches thathave macroscopic stress concentrations lower than maximum. Different frequently employed fatigue initiation parameters (FIP) are investigated and it is shown that a FIP based on a modified Fatemi-Socie criterion adds valuable information on local slip activity. The predictions obtained by using this criterion are to some extentconflicting with the results based on other FIPs, for example based on accumulated plastic strain or stored energy.A key observation is that macroscopic stress concentrations alone are insufficient and crystal plasticity simulations provide a competent additional tool in analyzing fatigue initiation mechanisms in polycrystalline samples. Not only the magnitude of stress concentrations, but also the stress gradients near surface irregularities appear as important aspects to consider when analyzing fatigue initiation. In addition, highly misoriented grain interfaces, which constitute significant barriers to plastic slip, provide internal domains in the material where initiation of fatiguedamage appears more likely to occur than at the stress concentrations that are due to the surface roughness. The present investigation clearly highlights the importance of considering the influence of microstructure heterogeneities on fatigue properties in polycrystals.
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| 42. |
- Hallberg, Håkan
(author)
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Influence of process parameters on grain refinement in AA1050 aluminum during cold rolling
- 2013
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In: International Journal of Mechanical Sciences. - : Elsevier BV. - 1879-2162 .- 0020-7403. ; 66, s. 260-272
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Journal article (peer-reviewed)abstract
- The microstructure evolution during cold rolling of commercial purity AA1050 aluminum is investigated through numerical simulations. A finite strain elasto-viscoplastic constitutive model is employed, where the dislocation density and average grain size are taken as variables characterizing the deformed microstructure. Grain size evolution due to dynamic recrystallization is considered and the microstructure quantities are allowed to influence the macroscopic material behavior in terms of the flow stress and deformation-rate dependence. The effects of such process parameters as rolling friction, thickness reduction in each rolling pass and amount of rolling asymmetry are discussed. The results indicate that grain refinement due to dynamic recrystallization is most significantly affected by the amount of thickness reduction in each pass and the level of rolling friction and to a lesser extent by the asymmetry of the rolling process. An increasing degree of asymmetry will, however, reduce the variations in grain size through the sheet thickness and leave the material more homogeneously recrystallized.
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| 43. |
- Hallberg, Håkan, et al.
(author)
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Investigation of microstructure evolution during self-annealing in thin Cu films by combining mesoscale level set and ab initio modeling
- 2016
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In: Journal of the Mechanics and Physics of Solids. - : Elsevier BV. - 1873-4782 .- 0022-5096. ; 90, s. 160-178
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Journal article (peer-reviewed)abstract
- Microstructure evolution in thin Cu films during room temperature self-annealing is investigated by means of a mesoscale level set model. The model is formulated such that the relative, or collective, influence of anisotropic grain boundary energy, mobility and heterogeneously distributed stored energy can be investigated. Density functional theory (DFT) calculations are performed in the present work to provide the variation of grain boundary energy for different grain boundary configurations. The stability of the predominant (111) fiber texture in the as-deposited state is studied as well as the stability of some special low-Σ grain boundaries. Further, the numerical model allows tracing of the grain size distribution and occurrence of abnormal grain growth during self-annealing. It is found that abnormal grain growth depends mainly on the presence of stored energy variations, whereas anisotropic grain boundary energy or mobility is insufficient to trigger any abnormal growth in the model. However, texture dependent grain boundary properties, mobility in particular, contribute to an increased content of low-Σ boundaries in the annealed microstructure. The increased presence of such boundaries is also promoted by stored energy variations. In addition, if the stored energy variations are sufficient the coexisting (111) and (001) texture components in the as-deposited state will evolve into a (001) dominated texture during annealing. Further, it is found that whereas stored energy variations promote the stability of the (001) texture component, anisotropic grain boundary energy and mobility tend to work the other way and stabilize the (111) component at the expense of (001) grains.
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| 44. |
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| 45. |
- Hallberg, Håkan
(author)
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Mesh-Based Immediate Breast Reconstruction. Complicantions and long-term results
- 2019
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Doctoral thesis (other academic/artistic)abstract
- There are few high-quality studies evaluating use of meshes in implant-based immediate breast reconstruction (IBR). This thesis analyzed current evidence of matrices and compared outcomes from the use of biological or synthetic meshes and traditional muscle-covered implants. The comparisons examined short- and long-term complications and corrections, predictors of complications, and patient satisfaction and quality of life (QOL). Manuscript I describes a systematic review and meta-analysis specifically assessing differences in outcomes between reconstructions with and without matrices. Manuscript II presents the results of reconstruction using a synthetic mesh [TIGR®; n = 49 patients (65 breasts)]. Manuscript III compares reconstruction outcomes using a biological mesh [Surgisis®; n = 71 (116 breasts)] with those from a traditional muscle-covered technique (n = 90; 132 breasts) regarding complications and health-related QOL. Manuscript IV compared outcomes from use of either a synthetic mesh (TIGR®; n = 41) or a biological mesh (Surgisis®; n = 53) regarding long-term patient satisfaction and health-related QOL. All patients were followed between 17 and 162 months. Meta-analysis revealed a possible increased risk of infection upon use of an acelullar dermal matrix (ADM), but not with synthetic meshes. The result must be interpreted with caution due to severe limitations in the included studies. Additionally, the results suggested that IBR with a synthetic mesh can be performed with a relatively low complication rate. The overall complication rate was higher using biological mesh as compared to muscle-covered implants; however, no significant difference was noted in implant loss rates between the groups. Predictors of complications were mainly patient-related, although high complication rates were associated with the use of tissue expanders, especially in patients with a history of irradiation. Furthermore, long-term patient satisfaction and QOL were similar when using a synthetic, biologic or no mesh, except for complications that affected patient satisfaction with the outcome. Our findings suggest that biological and synthetic meshes provide similar long-term quality of life.
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| 46. |
- Hallberg, Håkan, et al.
(author)
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Mesoscale modeling of dislocation density gradients and microstructure evolution
- 2012
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In: ; , s. 211-214
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Conference paper (peer-reviewed)abstract
- The presence of grain boundaries in the microstructure of metallic materials causes heterogeneous distributions of dislocation density. In the present contribution, the evolution of dislocation density is viewed as a reaction-diffusion system, involving mobile and immobile dislocations. Gradient effects are introduced by making the immobilization of dislocations sensitive to presence of grain boundaries. The model provides a macroscopic yield stress behavior of Hall-Petch type, without explicitly incorporating a yield stress dependence on the grains size. In addition, the model is employed in a cellular automaton algorithm, allowing a polycrystalline microstructure to evolve due to dynamic recrystallization, confirming that the introduced gradients provide important additions to recrystallization modeling.
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| 47. |
- Hallberg, Håkan, et al.
(author)
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Mesoscale modeling of microstructure evolution influenced by dislocation density gradients
- 2013
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Conference paper (peer-reviewed)abstract
- The presence of grain boundaries in the microstructure of metallic materials has a major influence on the material behavior and not least on macroscopic material properties. The grain boundaries pose obstacles to slip deformation by preventing dislocation motion, resulting in localized dislocation storage and heterogeneous deformation fields within the grains. In the present contribution, the development of heterogeneous dislocation density distributions is approached on the mesoscale by modeling the evolution of distributions of mobile and immobile dislocations in a reaction-diffusion system. A polycrystal model is formulated in a combined finite difference/cellular automaton algorithm and gradient effects are introduced by making the immobilization of dislocations sensitive to the presence of grain boundaries. The result is an efficient hybrid algorithm for mesoscale modeling of the evolution of grain microstructures, influenced by dislocation density gradients. The model provides a homogenized macroscopic yield stress behavior of Hall-Petch type, without explicitly incorporating a yield stress dependence on the grains size. In addition, being employed in a cellular automaton setting, the model conveniently allows simulations of polycrystalline microstructures, evolving due to dynamic recrystallization, confirming that the introduced gradients provide important additions to recrystallization modeling.
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| 48. |
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| 49. |
- Hallberg, Håkan, et al.
(author)
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Microstructure and Property Modifications of Cold Rolled IF Steel by Local Laser Annealing
- 2017
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In: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - : Springer Science and Business Media LLC. - 1073-5623. ; 48:10, s. 4786-4802
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Journal article (peer-reviewed)abstract
- Laser annealing experiments are performed on cold rolled IF steel whereby highly localized microstructure and property modification are achieved. The microstructure is seen to develop by strongly heterogeneous recrystallization to provide steep gradients, across the submillimeter scale, of grain size and crystallographic texture. Hardness mapping by microindentation is used to reveal the corresponding gradients in macroscopic properties. A 2D level set model of the microstructure development is established as a tool to further optimize the method and to investigate, for example, the development of grain size variations due to the strong and transient thermal gradient. Particular focus is given to the evolution of the beneficial γ-fiber texture during laser annealing. The simulations indicate that the influence of selective growth based on anisotropic grain boundary properties only has a minor effect on texture evolution compared to heterogeneous stored energy, temperature variations, and nucleation conditions. It is also shown that although the α-fiber has an initial frequency advantage, the higher probability of γ-nucleation, in combination with a higher stored energy driving force in this fiber, promotes a stronger presence of the γ-fiber as also observed in experiments.
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| 50. |
- Hallberg, Håkan, et al.
(author)
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Microstructure evolution during dynamic discontinuous recrystallization in particle-containing Cu
- 2014
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In: Computational Materials Science. - : Elsevier BV. - 0927-0256. ; 84, s. 327-338
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Journal article (peer-reviewed)abstract
- Control of the grain size in a material is vital in many engineering applications. Evolving through recrystallization, the grain size is strongly influenced by the presence of impurity particles. These particles exert drag forces on migrating grain boundaries and prevent grain boundary motion by pinning of the boundaries. Taking copper as example material, the present work establishes a novel simulation model where dynamic discontinuous recrystallization is influenced by particle drag. The recrystallization kinetics are established on a microlevel and the simulations are performed using a 3D cellular automaton algorithm with probabilistic cell state switches. By this approach, computational efficiency is combined with high temporal and spatial resolution of the microstructure evolution. The simulate d microstructure changes are in good agreement with experimental findings and the recrystallization kinetics are shown to comply with classical Kolmogorov/Johnson/Mehl/Avrami (KJMA) theory. In addition, through homogenization, the macroscopic flow stress behavior is studied and is also shown to exhibit the expected transition from single-peak stable flow into serrated multiple-peak flow as the processing temperature is increased. Influence of changed initial grain sizes is studied and, in compliance with experimental data, an increased initial grain size stabilizes the flow stress behavior whereas the opposite trend is found for reduced initial grain sizes. Introducing impurity particles in the simulations, the progression of recrystallization is retarded and optimum values of the particle dispersion level are identified at different temperatures, allowing minimization of the recrystallized grain size during thermomechanical processing of the material.
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