| 1. |
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| 2. |
- Anund Vogel, Jonas, et al.
(author)
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Buildings post corona
- 2023
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In: The REHVA European HVAC Journal. - 1307-3729. ; 59:2, s. 19-21
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Journal article (pop. science, debate, etc.)abstract
- Buildings Post Corona is a Swedish collaborative research project between Chalmers, KTH Royal Institute of Technology, Lund, and Umeå Universities. The project supports the building sector in designing and maintaining sustainable buildings with a healthy and good indoor environment. The COVID-19 crisis has stressed the importance and urge of this research.The scope of the project is to develop a methodology for the operation and design of buildings with an indoor environment that meets future health and climate challenges. The project’s overall goal is to establish an interdisciplinary platform to document existing experiences and knowledge and to gain new knowledge required for good building design and operation.
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| 3. |
- Anund Vogel, Jonas, et al.
(author)
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Enbart avstånd och handhygien räcker inte
- 2023
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In: Fastighetstidningen. - 0348-5552.
-
Journal article (pop. science, debate, etc.)abstract
- I denna debattartikel lyfter sex forskare frågan att myndigheter och branschorganisationer delvis gav olika råd kring åtgärder för att begränsa risken för smittspridning inomhus. För att klara nästa pandemi krävs bättre samordning av riktlinjer kring ventilation och luftkvalitet.
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| 4. |
- Ekberg, Lars, 1962, et al.
(author)
-
Buildings Post Corona
- 2022
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In: The REHVA European HVAC Journal. - 1307-3729. ; 59:2, s. 19-21
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Journal article (other academic/artistic)abstract
- Buildings Post Corona is a Swedish collaborative research project between Chalmers, KTH Royal Institute of Technology, Lund, and Umeå Universities. The project supports the building sector in designing and maintaining sustainable buildings with a healthy and good indoor environment. The COVID-19 crisis has stressed the importance and urge of this research, which is financially supported by FORMAS (a governmental research council for sustainable development https://formas.se)
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| 5. |
- Ekberg, Lars, et al.
(author)
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Covid 19 guidance for the Swedish construction and real estate sectors : results from a survey study
- 2023
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In: The REHVA European HVAC Journal. - 1307-3729. ; 60:2, s. 18-20
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Journal article (pop. science, debate, etc.)abstract
- Buildings Post Corona is a Swedish collaborative research project between Chalmers, KTH Royal Institute of Technology, Lund, and Umeå Universities. The project intends to provide knowledge related to designing, maintaining and operating sustainable buildings with a healthy and good indoor environment.The project aims to contribute to the knowledge and processes needed for the construction and real-estate sectors to meet the needs of the post-pandemic era.In this article, the authors describe the approach in the study and its results.
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| 6. |
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| 7. |
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| 8. |
- Ghasemi, Rohollah, et al.
(author)
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Modelling and simulation of local mechanical properties of high silicon solution-strengthened ferritic compacted graphite iron
- 2017
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In: International Journal of Cast Metals Research. - : Taylor & Francis Group. - 1364-0461 .- 1743-1336. ; 30:3, s. 125-132
-
Journal article (peer-reviewed)abstract
- This study focuses on the modelling and simulation of local mechanical properties of compacted graphite iron cast at different section thicknesses and three different levels of silicon, ranging from about 3.6% up to 4.6%. The relationship between tensile properties and microstructure is investigated using microstructural analysis and statistical evaluation. Models are generated using response surface methodology, which reveal that silicon level and nodularity mainly affect tensile strength and 0.2% offset yield strength, while Young′s modulus is primarily affected by nodularity. Increase in Si content improves both the yield and tensile strength, while reduces elongation to failure. Furthermore, mechanical properties enhance substantially in thinner section due to the high nodularity. The obtained models have been implemented into a casting process simulation, which enables prediction of local mechanical properties of castings with complex geometries. Very good agreement is observed between the measured and predicted microstructures and mechanical properties, particularly for thinner sections.
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| 9. |
- Herkner, Birgitta, 1951-
(author)
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Studier av läsrelaterade språkliga förmågor i förskola och läsutveckling i grundskola
- 2022
-
Doctoral thesis (other academic/artistic)abstract
- The purpose of this doctoral thesis was to explore relationships that impact language development, and how reading ability develops during the compulsory school years. The thesis includes four studies, study I (licentiate thesis), with students from grades 2–5, from 24 classrooms (N = 428), study II examined whether the National test (NP) was able to identify students with word decoding problems from a sample of third graders from study I (n= 112). In study III a small number of students (n = 8) from Study II were followed-up to the ninth grade. The students’ and their parents’ perception of special education support is described.In Study IV the correlation between socioeconomic status (SES) and language development was examined in preschool children (N= 231) from three municipalities in the middle of Sweden. Furthermore, the language ability among these preschool boys and girls is described. Students’ language abilities are examined in these four studies, where the participants are students in preschool (N= 231), and compulsory school (N=428).The results indicated that the student’s reading profiles (the correlation between phonological decoding and reading ability) based on Simple View of Reading showed difficulties in reading ability for students in the fourth grade to a larger extent than in the third grade. National tests (NP) in Swedish for the third grade do not identify students with decoding difficulties.The students that had difficulties with decoding in the third grade also had difficulties with decoding in the ninth grade and scored low on all reading and writing tests. In interviews with parents and students, the respondents described that the students did not engage in leisure reading in their free time and that when they did, they read using their computer or their mobile phone. The respondents also described school experiences where special education support had been provided too late, and to an unsatisfactory extent. Between the fourth and sixth grade, special support was provided as reading in a small group, and between the seventh and ninth grade, special support was provided from a paraprofessional; receiving support from a special educational needs teacher was uncommon. Study IV does not indicate differences between preschool boys’ and girls’ results on tests in language abilities, letter knowledge, and rapid automatized naming. Children from areas with lower SES performed worse on the language tests than children from areas with higher SES. The results from these studies indicate the importance of early language interventions for preschool children in areas with low SES. Taken together, the studies indicate that the early identification of children with delays in language abilities is feasible in preschool, as well as the early identification of children with difficulties with decoding in primary school. The follow-up suggests that without early and effective interventions the difficulties may last for the following school years, and may affect negatively the students’ educational achievement.
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| 10. |
- Jansson, Johan, et al.
(author)
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An anisotropic non-linear material model for glass fibre reinforced plastics
- 2018
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In: Composite structures. - : Elsevier. - 0263-8223 .- 1879-1085. ; 195, s. 93-98
-
Journal article (peer-reviewed)abstract
- This paper aims to present a methodology to predict the anisotropic and non-linear behaviour of glass fibre reinforced plastics using finite element methods. A material model is implemented in order to remedy the need of multiple material definitions, and to control the local plastic behaviour as a function of the fibre orientation. Injection moulding simulations traditionally provide second order orientation tensors, which are considered together with a homogenization scheme to compute local material properties. However, in the present study, fourth order tensors are used in combination with traditional methods to provide more accurate material properties. The elastic and plastic response of the material model is optimized to fit experimental test data, until simulations and experiments overlap. The proposed material model can support design engineers in making more informed decisions, allowing them to create smarter products without the need of excessive safety factors, leading to reduced component weight and environmental impact.
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| 11. |
- Jansson, Johan, et al.
(author)
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Image-based semi-multiscale finite element analysis using elastic subdomain homogenization
- 2021
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In: Meccanica (Milano. Print). - : Springer. - 0025-6455 .- 1572-9648. ; 56:11, s. 2799-2811
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Journal article (peer-reviewed)abstract
- In this paper we present a semi-multiscale methodology, where a micrograph is split into multiple independent numerical model subdomains. The purpose of this approach is to enable a controlled reduction in model fidelity at the microscale, while providing more detailed material data for component level- or more advanced finite element models. The effective anisotropic elastic properties of each subdomain are computed using periodic boundary conditions, and are subsequently mapped back to a reduced mesh of the original micrograph. Alternatively, effective isotropic properties are generated using a semi-analytical method, based on averaged Hashin–Shtrikman bounds with fractions determined via pixel summation. The chosen discretization strategy (pixelwise or partially smoothed) is shown to introduce an uncertainty in effective properties lower than 2% for the edge-case of a finite plate containing a circular hole. The methodology is applied to a aluminium alloy micrograph. It is shown that the number of elements in the aluminium model can be reduced by 99.89 % while not deviating from the reference model effective material properties by more than 0.65 % , while also retaining some of the characteristics of the stress-field. The computational time of the semi-analytical method is shown to be several orders of magnitude lower than the numerical one. © 2021, The Author(s).
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| 12. |
- Jansson, Johan
(author)
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Multiscale Constitutive Modeling of Heterogeneous Engineering Materials
- 2021
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Doctoral thesis (other academic/artistic)abstract
- This work deals with different methods used to determine heterogeneous constitutive model parameters for macro-scale finite element models, based on microstructural variations, caused by the manufacturing process. These methods could be applied to decrease modeling errors associated with the material behavior, improving the predictive capabilities of structural analyses in simulation-driven industrial product development. By providing engineers with more sophisticated tools and methods which lets them consider the complex relationships between the manufacturing process, the resulting microstructure and the final properties, manufactured components have the potential to be further optimized with respect to both weight and performance, reducing their cost and environmental impact.An empirical approach for cast components is presented in Papers I & II, where material testing is used as a basis for constitutive model parameter extraction via optimization. Linear models were created for both thermo-mechanical and thermo-physical material properties, by characterizing specimens extracted from different regions in a lamellar graphite cast iron cylinder head. These models were used to generate heterogeneous constitutive model parameters for the cylinder head, based on the solidification time as predicted by casting process simulations. The influence of several commonly made casting-specific engineering simplifications were investigated, and it was shown that non-trivial errors of a potentially large magnitude are introduced by not considering e.g. the compressive behavior of the material, residual stresses from the casting process, the temperature dependency of the material, or the process-induced heterogeneity.Paper III describes a statistical homogenization-based method, for modeling of anisotropic fiber reinforced materials. A non-linear anisotropic constitutive model was developed and implemented in commercial finite element codes, which is able to consider heterogeneous fiber orientations using only one material definition. The anisotropic elastic constitutive tensor is determined from fiber-matrix homogenization, and orientation averaging using second- and fourth order fiber orientation tensors provided by injection molding simulations. The plastic constitutive parameters are determined by optimization against experimental tensile tests using specimens with different fiber orientations. The method was demonstrated using a injection molded 50 wt.% short glass fiber reinforced plastic.A pixel/voxel-based method is presented in Papers IV (2D) & V (3D), for simple and efficient generation of reduced numerical microstructure models using imaging data as input. The input micrograph or image stack is split into subdomains, which are evaluated individually using numerical or semi-analytical homogenization. The constitutive tensor of each subdomain is mapped to a new, reduced numerical model. The purpose of this approach was to support component level analyses, by representing process-induced microstructural imperfections like e.g. porosity on the macro-scale, in a computationally efficient way. The geometrical description of the microstructure can be retrieved from experimental imaging methods like Scanning Electron Microscopy (SEM) or X-ray based Computed Tomography (CT). Alternatively, it can be approximated from phase field or manufacturing process simulations. The method was demonstrated by reducing a 2D aluminium micrograph by 99.89%, with material property errors of less than 0.5% in Paper IV. Also, in paper V by reducing a complex high-resolution 3D aluminum shrinkage porosity by 99.2%, with a material property error of approximately 1%. The method significantly reduces the complexity of building finite element models of complex microstructures, where the pre-processing step is replaced by image segmentation.
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| 13. |
- Jansson, Johan, et al.
(author)
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On the use of heterogeneous thermomechanical and thermophysical material properties in finite element analyses of cast components
- 2019
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In: Joint 5th International Conference on Advances in Solidification Processes (ICASP-5) & 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5) 17–21 June 2019, Salzburg, Austria. - : Institute of Physics Publishing (IOPP).
-
Conference paper (peer-reviewed)abstract
- Cast components generally show a heterogeneous distribution of material properties, caused by variations in the microstructure that forms during solidification. Variations caused by the casting process are not commonly considered in structural analyses, which might result in manufacturing of sub-optimised components with unexpected in-use behaviour. In this paper, we present a methodology which can be used to consider both thermomechanical and thermophysical variations using finite element analyses in cast components. The methodology is based on process simulations including microstructure modelling and correlations between microstructural features and material properties. Local material data are generated from the process simulation results, which are integrated into subsequent structural analyses. In order to demonstrate the methodology, it is applied to a cast iron cylinder head. The heterogeneous distribution of material properties in this component is investigated using experimental methods, demonstrating local variations in both mechanical and physical behaviour. In addition, the strength-differential effect on tensile and compressive behaviour of cast iron is considered in the modelling. The integrated simulation methodology presented in this work is relevant to both design engineers, production engineers as well as material scientists, in order to study and better understand how local variations in microstructure might influence the performance and behaviour of cast components under in-use conditions.
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| 14. |
- Jansson, Johan
(author)
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Process-Induced Local Material Variations in Finite Element Simulations of Cast and Fibre Reinforced Injection Moulded Components
- 2019
-
Licentiate thesis (other academic/artistic)abstract
- The purpose of this thesis is to provide an overview of the methods used in the appended papers, in order to consider heterogeneous material properties in finite element simulations by using process simulations as input. The work deals with both injection moulded and cast components, and focuses on process-induced local material variations and their effect on component performance.The influence of heterogeneous properties originating from the casting process as well as some other common simplifications, which are made in finite element analyses, are evaluated for a cast iron component. It is found that commonly neglected properties such as compressive strength, residual stresses, temperature dependency and heterogeneous properties have a non-trivial and potentially large influence on the simulation results.Lastly, a computational method for fibre reinforced plastics is presented. The methodology enables designers to consider the non-linear anisotropic properties of fibre-reinforced polymers, due to the flow-induced fibre orientation predicted by injection moulding simulations. The method allows material data assignment in each integration-point of the structural mesh. The method is demonstrated to capture the behaviour of the full range of fibre orientations simultaneously with good accuracy.
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| 15. |
- Jansson, Johan, et al.
(author)
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Simulation-driven product development of cast components with allowance for process-induced material behaviour
- 2020
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In: Journal of Computational Design and Engineering. - : Oxford University Press. - 2288-5048. ; 7:1, s. 78-85
-
Journal article (peer-reviewed)abstract
- This paper presents a methodology that can be used to consider local variations in thermomechanical and thermophysical material properties, residual stresses, and strength-differential effects in finite element analyses of cast components. The methodology is based on applying process simulations and structural analyses together with experimentally established, or already available literature data, in order to describe element-specific material variations. A cast-iron cylinder head was used in order to evaluate the influence of several simplifications that are commonly performed in computer aided engineering. It is shown that non-trivial errors of a potentially large magnitude are introduced by not considering residual stresses, compressive behaviour, temperature dependence, and process-induced material property variations. By providing design engineers with tools that allow them to consider the complex relationships between these aspects early in the development phase, cast components have the potential to be further optimized with respect to both weight and performance.
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| 16. |
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| 17. |
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| 18. |
- Johannesson, Mats, et al.
(author)
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Att skapa optimerad längd för kollektivtrafikkörfält och kostnadseffektiva kollektivtrafiklösningar genom datadriven innovation
- 2024
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In: Sammanställning av referat från Transportforum 2024. - Linköping : Statens väg- och transportforskningsinstitut. ; , s. 130-131
-
Conference paper (other academic/artistic)abstract
- Södertälje har i ett samarbetsprojekt med region Stockholm och Nobina formulerat höga ambitioner för framtidens kollektivtrafik. Målet är över 80 % nöjda kunder, en halverad restid inom tätorten och att kollektivtrafikens marknadsandel ökar till 30%. En viktig del i kommunens arbete är att utveckla en BRT-linje genom Södertälje. Linjen infördes i december 2022 och under 2023 beviljades stadsmiljöavtal för framkomlighetsåtgärder för linjen. Kritiskt för projektet har varit att möjliggöra genomförandet av åtgärderna utan att det ska påverka bussens framkomlighet under byggtiden. I underlagen för ansökan användes innovativa teknikstöd för att analysera optimal längd för kollektivtrafikkörfälten och därmed kunde en effektivare utformning säkerställas som minskade anläggningskostnaden avsevärt.I syfte att minska framkomlighetsproblem för BRT-busslinjen i högtrafik föreslogs separata kollektivtrafikkörfält längs en relativt lång sträcka. Detta innebar att vägen behövde breddas från ett till två körfält i vardera riktning, en omfattande och kostsam framkomlighetsåtgärd. För att få en tydligare uppfattning om köbildningens omfattning valde Södertälje kommun att göra en analys av framkomlighetsproblematiken utifrån busstrafikens kördata. Som analysunderlag användes högupplöst och bearbetad GPS-data från tusentals fordon som illustrerar körvägen indelad i sekvenser på 25 meter. Tack vare att realtidsinsamlingen snabbt skapar ett stort dataunderlag var det möjligt att säkerställa ett gott kvantitativt dataset, trots att endast 1,5–2 månaders realtidsdata hade hunnit samlas in sedan linjens införande. Utifrån denna data analyserades den så kallade restidsspridningen, som syftar på att det tar olika lång tid att köra samma sträcka och avgång under olika dagar. Restidsspridningen beskriver på så sätt hur robust en körtid är. Genom att utgå ifrån restidsspridningen var det möjligt att på 25-metersnivå utläsa precis var och hur ofta kollektivtrafiken upplevde framkomlighetsproblem och därmed anpassa längder för kollektivtrafikkörfälten.Med GPS-data som underlag blev det tydligt att det var ytterst få turer som hade behov av ett så långt kollektivtrafikkörfält som hade föreslagits, kollektivtrafikkörfältet var helt enkelt onödigt långt. Analysen utgjorde på så sätt ett bra diskussionsunderlag och skapade en förståelse för behovet av ett kollektivtrafikkörfält under olika tidpunkter. Utifrån det kunde Södertälje kommun göra en bedömning för optimal längd på kollektivtrafikkörfältet.
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| 19. |
- Karnevi, Emelie, et al.
(author)
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Translational study reveals a two-faced role of RBM3 in pancreatic cancer and suggests its potential value as a biomarker for improved patient stratification
- 2018
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In: Oncotarget. - : Impact Journals LLC. - 1949-2553. ; 9:5, s. 6188-6200
-
Journal article (peer-reviewed)abstract
- Periampullary adenocarcinoma, including pancreatic cancer, is a heterogeneous group of tumors with dismal prognosis, partially due to lack of reliable targetable and predictive biomarkers. RNA-binding motif protein 3 (RBM3) has previously been shown to be an independent prognostic and predictive biomarker in several types of cancer. Herein, we examined the prognostic value of RBM3 in periampullary adenocarcinoma, as well as the effects following RBM3 suppression in pancreatic cancer cells in vitro. RBM3 mRNA levels were examined in 176 pancreatic cancer patients from The Cancer Genome Atlas. Immunohistochemical expression of RBM3 was analyzed in tissue microarrays with primary tumors and paired lymph node metastases from 175 consecutive patients with resected periampullary adenocarcinoma. Pancreatic cancer cells were transfected with anti-RBM3 siRNA in vitro and the influence on cell viability following chemotherapy, transwell migration and invasion was assessed. The results demonstrated that high mRNA-levels of RBM3 were significantly associated with a reduced overall survival (p = 0.026). RBM3 protein expression was significantly higher in lymph node metastases than in primary tumors (p = 0.005). High RBM3 protein expression was an independent predictive factor for the effect of adjuvant chemotherapy and an independent negative prognostic factor in untreated patients (p for interaction = 0.003). After siRNA suppression of RBM3 in vitro, pancreatic cancer cells displayed reduced migration and invasion compared to control, as well as a significantly increased resistance to chemotherapy. In conclusion, the strong indication of a positive response predictive effect of RBM3 expression in pancreatic cancer may be highly relevant in the clinical setting and merits further validation.
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| 20. |
- Kasvayee, Keivan Amiri, 1986-, et al.
(author)
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Characterization and modeling of the mechanical behavior of high silicon ductile iron
- 2017
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In: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 708, s. 159-170
-
Journal article (peer-reviewed)abstract
- This paper investigates the effect of the solidification conditions and silicon content on the mechanical properties of ductile iron and presents empirical models for predicting the tensile behavior based on the microstructural characterizations. Two ductile iron grades of GJS-500-7 and GJS-500-14 were cast with silicon content of 2.36% and 3.71%, respectively. The cast geometry consisted of six plates with different thicknesses that provided different cooling rates during the solidification. Microstructure analysis, tensile and hardness tests were performed on the as-cast material. Tensile behavior was characterized by the Ludwigson equation. The tensile fracture surfaces were analyzed to quantify the fraction of porosity. The results showed that graphite content, graphite nodule count, ferrite fraction and yield strength were increased by increasing the silicon content. A higher silicon content resulted in lower work hardening exponent and strength coefficient on the Ludwigson equation. The results for 0.2% offset yield and the Ludwigson equation parameters were modeled based on microstructural characteristics, with influence of silicon content as the main contributing factor. The models were implemented into a casting process simulation to enable prediction of microstructure-based tensile behavior. A good agreement was obtained between measured and simulated tensile behavior, validating the predictions of simulation in cast components with similar microstructural characteristics.
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| 21. |
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| 22. |
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| 23. |
- Klawonn, Isabell, et al.
(author)
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Cell-specific nitrogen- and carbon-fixation of cyanobacteria in a temperate marine system (Baltic Sea)
- 2016
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In: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920 .- 1758-2229. ; 18:12, s. 4596-4609
-
Journal article (peer-reviewed)abstract
- We analysed N2- and carbon (C) fixation in individual cells of Baltic Sea cyanobacteria by combining stable isotope incubations with secondary ion mass spectrometry (SIMS). Specific growth rates based on N2- and C-fixation were higher for cells of Dolichospermum spp. than for Aphanizomenon sp. and Nodularia spumigena. The cyanobacterial biomass, however, was dominated by Aphanizomenon sp., which contributed most to total N2-fixation in surface waters of the Northern Baltic Proper. N2-fixation by Pseudanabaena sp. and colonial picocyanobacteria was not detectable. N2-fixation by Aphanizomenon sp., Dolichospermum spp. and N. spumigena populations summed up to total N2-fixation, thus these genera appeared as sole diazotrophs within the Baltic Sea's euphotic zone, while their mean contribution to total C-fixation was 21%. Intriguingly, cell-specific N2-fixation was 8-fold higher at a coastal station compared to an offshore station, revealing coastal zones as habitats with substantial N2-fixation. At the coastal station, the cell-specific C- to N2-fixation ratio was below the cellular C:N ratio, i.e., N2 was assimilated in excess to C-fixation, whereas the C- to N2-fixation ratio exceeded the C:N ratio in offshore sampled diazotrophs. Our findings highlight SIMS as a powerful tool not only for qualitative but also for quantitative N2-fixation assays in aquatic environments.
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| 24. |
- Kvande, Lise, 1967-, et al.
(author)
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Concept learning and reasoning in social studies education (COURSE) : Session 160: How do values transform when history culture change?
- 2021
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Conference paper (other academic/artistic)abstract
- How do values transform when history culture change? In addition, is it possible to discern such a development in an ongoing classroom student-teacher discourse? In this presentation, I try to address these questions through two intertwined issues: first as a theoretical concept interpretation and then as a presentation of some empirical findings. The observed classroom data was collected the years around 2010, which I argue, could be seen as a somehow unnoticed turning point in a national history culture development, at least in Sweden. The theoretical part of the presentation consists of an analysis of “third order” concepts in regard to history didactics and with some comparisons with social science didactics. In history education third order concepts has been perceived as distinctive both from “first order” concepts (like Renaissance, 9 th of April or Boston Tea Party) and from “second order” concepts (like cause & consequence, historical evidence or similarity & differences), but there are still some uncertainties regarding in what way. While second order concepts are rather well known in research on history teaching, there are few enquiries on the value loaded third order concepts (like "historical hatred”, “historical identity” or “historical proudness”). Third order concepts correspond furthermore with value aspects in first order concepts like “revolution” or “democracy”. Of these reasons, I claim third order concepts to be an important issue to explore in speech-acts in schools. The empirical data consists of a bulk of utterances on history
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| 25. |
- Levlin, Maria, 1971-
(author)
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Lässvårigheter, språklig förmåga och skolresultat i tidiga skolår : en undersökning av 44 elever i årskurs 2 till 3
- 2014
-
Doctoral thesis (other academic/artistic)abstract
- I skolverkets rapporter framkommer att ca 15-20 % av eleverna inte klarar nationella proven i grundskolan. Varje år går även alltför många elever ut grundskolan utan behörighet till något av de nationella gymnasieprogrammen. Det finns ett behov av mer kunskap om vilka elever som riskerar att inte nå målen för att underlätta tidig identifiering. Läsförmåga och språkförståelse är några av de faktorer som i tidigare studier visat sig påverka utfallet i skolresultat. I den här studien undersöks hur lässvårigheter i tidiga skolår relaterar till språkförståelse, samt hur lässvårigheter och variationer i språkförståelsen påverkar skolresultaten i nationella proven i åk 3. I studien deltog 44 elever med positivt utfall i en screening av läsförståelse, avkodning och stavning i åk 2. Svag läsförståelse i åk 2 innebar en större risk för språkförståelsesvårigheter i åk 3. Elever med enbart avkodnings- eller stavningssvårigheter i åk 2 hade däremot en god språkförståelse i åk 3. Språkförståelsen visade i sin tur signifikanta samband med utfallet i läsförståelse i ämnesprovet i svenska och med 5 av 6 delprov i matematik i nationella proven i åk 3. En viktig implikation blir att inkludera även språkförståelse i arbetet med elever som har läsförståelsesvårigheter. Studiens resultat indikerar att det inte räcker med en bättre avkodningsförmåga för att uppnå en god läsförståelse. Det krävs även insatser för att främja ordförråd, grammatisk kompetens och förståelsestrategier på diskursnivå. En hög andel av eleverna som inte fick godkänt i delproven i svenska respektive matematik i åk 3 var identifierade i screeningen redan i åk 2. Det här indikerar att det är möjligt att använda en screening av läsförmågan i åk 2 för att identifiera vilka elever som riskerar att inte klara läroplanens mål. Samtidigt var det många elever med svag läs- och stavningsförmåga i åk 2 som ändå klarade nationella proven. Den här studiens resultat indikerar att det framförallt är eleverna med läsförståelsesvårigheter som riskerar att inte klara nationella proven, medan eleverna med enbart avkodnings- eller stavningssvårigheter klarar nationella proven betydligt bättre. Det behövs däremot fortsatta longitudinella studier för att klargöra i vilken mån de elever som klarade de nationella proven i åk 3 trots lässvårigheter även kommer att klara nationella prov och läroplanens mål på längre sikt.
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| 26. |
- Löndahl, Jakob, et al.
(author)
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Physical and biological properties of bioaerosol
- 2014
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In: Bioaerosol Detection Technologies. - 9781441955814 ; , s. 33-48
-
Book chapter (peer-reviewed)abstract
- Bioaerosols include bacterial cells and spores, viruses, pollen, fungi, algae, detritus, allergens and cell fragments. Bioaerosol particles are usually a small fraction of all aerosol particles in our surroundings, but their impact can be critical. They are a means for transmission of disease, they cause allergic reactions and they have effects on the global climate, ecology and biodiversity. This chapter provides an overview of the main types of bioaerosol particles, their sources, transport and sinks, and their potential effects on health and atmosphere.
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| 27. |
- Malakizadi, Amir, 1983, et al.
(author)
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Effects of workpiece microstructure, mechanical properties and machining conditions on tool wear when milling compacted graphite iron
- 2018
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In: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 410-411, s. 190-201
-
Journal article (peer-reviewed)abstract
- The aim of the present study was to investigate the tool performance when machining compacted graphite iron (CGI) alloys. A comparison was made between solid solution strengthened CGI including various amounts of silicon (Si-CGI) and the pearlitic-ferritic CGI as a reference material. The emphasis was on examining the influence of microstructure and mechanical properties of the material on tool wear in face milling process. Machining experiments were performed on the engine-like test pieces comprised of solid solution strengthened CGI with three different silicon contents and the reference CGI alloy. The results showed up-to 50% lower flank wear when machining Si-CGI alloys, although with comparable hardness and tensile properties. In-depth analysis of the worn tool surfaces showed that the abrasion and adhesion were the dominant wear mechanisms for all investigated alloys. However, the better tool performance when machining Si-CGI alloys was mainly due to a lower amount of abrasive carbo-nitride particles and the suppression of pearlite formation in the investigated solid solution strengthened alloys.
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| 28. |
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| 29. |
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| 30. |
- Myers-Smith, Isla H., et al.
(author)
-
Complexity revealed in the greening of the Arctic
- 2020
-
In: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-678X .- 1758-6798. ; 10:2, s. 106-117
-
Journal article (peer-reviewed)abstract
- As the Arctic warms, vegetation is responding, and satellite measures indicate widespread greening at high latitudes. This ‘greening of the Arctic’ is among the world’s most important large-scale ecological responses to global climate change. However, a consensus is emerging that the underlying causes and future dynamics of so-called Arctic greening and browning trends are more complex, variable and inherently scale-dependent than previously thought. Here we summarize the complexities of observing and interpreting high-latitude greening to identify priorities for future research. Incorporating satellite and proximal remote sensing with in-situ data, while accounting for uncertainties and scale issues, will advance the study of past, present and future Arctic vegetation change.
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| 31. |
- Olofsson, Jakob, et al.
(author)
-
A methodology for microstructure-based structural optimization of cast and injection moulded parts using knowledge-based design automation
- 2017
-
In: Advances in Engineering Software. - : Elsevier. - 0965-9978 .- 1873-5339. ; 109, s. 44-52
-
Journal article (peer-reviewed)abstract
- The local material behaviour of cast metal and injection moulded parts is highly related to the geometrical design of the part as well as to a large number of process parameters. In order to use structural optimization methods to find the geometry that gives the best possible performance, both the geometry and the effect of the production process on the local material behaviour thus has to be considered. In this work, a multidisciplinary methodology to consider local microstructure-based material behaviour in optimizations of the design of engineering structures is presented. By adopting a knowledge based industrial product realisation perspective combined with a previously presented simulation strategy for microstructure-based material behaviour in Finite Element Analyses (FEA), the methodology integrates Computer Aided Design (CAD), casting and injection moulding simulations, FEA, design automation and a multi-objective optimization scheme into a novel structural optimization method for cast metal and injection moulded polymeric parts. The different concepts and modules in the methodology are described, their implementation into a prototype software is outlined, and the application and relevance of the methodology is discussed.
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| 32. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
Casting and stress-strain simulations of a cast ductile iron component using microstructure based mechanical behavior
- 2012
-
In: IOP Conference Series: Materials Science and Engineering, Volume 33. - London : IOP Publishing.
-
Conference paper (peer-reviewed)abstract
- The industrial demand for increased component performance with concurrent reductions in component weight, development times and verifications using physical prototypes drives the need to use the full potential of casting and Finite Element Method (FEM) simulations to correctly predict the mechanical behavior of cast components in service. The mechanical behavior of the component is determined by the casting process, and factors as component geometry and casting process parameters are known to affect solidification and microstructure formation throughout the component and cause local variations in mechanical behavior as well as residual stresses. Though residual stresses are known to be an important factor in the mechanical behavior of the component, the importance of local mechanical behavior is not well established and the material is typically considered homogeneous throughout the component. This paper deals with the influence of solidification and solid state transformation on microstructure formation and the effect of local microstructure variations on the mechanical behavior of the cast component in service. The current work aims to investigate the coupling between simulation of solidification, microstructure and local variations in mechanical behavior and stress-strain simulation. This is done by performing several simulations of a ductile iron component using a recently developed simulation strategy, a closed chain of simulations for cast components, able to predict and describe the local variations in not only elastic but also plastic behavior throughout the component by using microstructural parameters determined by simulations of microstructural evolution in the component during the casting process. In addition the residual stresses are considered. The results show that the FEM simulation results are significantly affected by including microstructure based mechanical behavior. When the applied load is low and the component is subjected to stress levels well below the yield strength of the material, the residual stresses highly affects the simulation results while the effect of local material behavior is low. As the applied load increases and the stress level in the component approaches and passes the yield strength, the effect of residual stresses diminishes while the effect of local mechanical behavior increases. In particular the predicted strain level is heavily affected by the use of local mechanical behavior. It is proposed that it is important to include both local mechanical behavior and residual stresses in stress-strain simulations to predict the true mechanical behavior of the component.
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| 33. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
Characterisation and investigation of local variations in mechanical behaviour in cast aluminium using gradient solidification, Digital Image Correlation and finite element simulation
- 2014
-
In: Materials & Design. - : Elsevier. - 0261-3069. ; 56, s. 755-762
-
Journal article (peer-reviewed)abstract
- Due to design and process-related factors, there are local variations in the microstructure and mechanical behaviour of cast components. This work establishes a Digital Image Correlation (DIC) based method for characterisation and investigation of the effects of such local variations on the behaviour of a high pressure, die cast (HPDC) aluminium alloy. Plastic behaviour is studied using gradient solidified samples and characterisation models for the parameters of the Hollomon equation are developed, based on microstructural refinement. Samples with controlled microstructural variations are produced and the observed DIC strain field is compared with Finite Element Method (FEM) simulation results. The results show that the DIC based method can be applied to characterise local mechanical behaviour with high accuracy. The microstructural variations are observed to cause a redistribution of strain during tensile loading. This redistribution of strain can be predicted in the FEM simulation by incorporating local mechanical behaviour using the developed characterization model. A homogeneous FEM simulation is unable to predict the observed behaviour. The results motivate the application of a previously proposed simulation strategy, which is able to predict and incorporate local variations in mechanical behaviour into FEM simulations already in the design process for cast components.
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| 34. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
Closed chain simulations of a cast aluminium component - Incorporating casting process simulation and local material characterization into stress-strain simulations
- 2014
-
In: ISIJ International. - Tokyo, Japan : The Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 54:2, s. 259-265
-
Journal article (peer-reviewed)abstract
- The coupling between simulations of solidification, microstructure and local mechanical behaviour and simulation of stress-strain behaviour is studied by applying a recently developed simulation strategy to a high pressure die cast aluminium component. In the simulation strategy, named a closed chain of simulations for cast components, the mechanical behaviour throughout the component is determined locally by a casting process simulation. The entire casting process, including mould filling and solidification, is simulated to predict the formation of microstructure and residual stresses throughout the component, and material characterization models are applied to relate microstructural features to local elastic and plastic mechanical material behaviour. The local material behaviour is incorporated into a finite element method (FEM) stress-strain simulation of a realistic load case of the component in service.In the current contribution the influences of local variations in mechanical behaviour and residual stresses on the component behaviour are investigated. The simulation results for local microstructure and mechanical behaviour are compared to experimental results, and the predicted local mechanical behaviour is incorporated on an element level into the FEM simulation. The numerical effect of the variations in mechanical behaviour is quantified by comparing the results achieved using local behaviour and homogeneous behaviour. The influence of residual stresses predicted by the casting process simulation on the component behaviour is also studied.The casting process simulation is found to accurately predict the local variations in microstructure throughout the component, and the local variations in mechanical behaviour are well described. The numerical results show that casting process simulation and modelling of microstructure formation, material behaviour and residual stresses are important contributions to correctly predict the behaviour of a cast aluminium component in service. This motivates the use of the proposed simulation strategy, and show the importance of incorporating materials science and casting process simulations into structural analyses of cast components. It is discussed that integration of these areas, e.g. using the closed chain of simulations, is important in order to increase the accuracy of FEM simulations and the product development efficiency in the future.
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| 35. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
Effect of Austempering on Plastic Behavior of Some Austempered Ductile Iron Alloys
- 2011
-
In: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 42:13, s. 3999-4007
-
Journal article (peer-reviewed)abstract
- A numerical description relating microstructure to elastic and plastic deformation behavior would make it possible to simulate the mechanical behavior of complex cast components with tailored material properties. Limited work and data have however been published regarding the connection between microstructure and plastic behavior of austempered ductile irons (ADI). In the current work the effects of austempering temperature and austempering time on the strength coefficient and the strain hardening exponent of the Hollomon equation have been investigated for two ADI alloys. The results show that the plastic behavior is highly dependent on the combination of austempering temperature and austempering time. It was found that as the austempering temperature increases both the strength coefficient and the strain hardening exponent initially decrease, but after reaching a minimum at the critical austempering temperature they show a plateau or an increase. The effect of the austempering time on the plastic behavior depends on the austempering temperature. At low austempering temperatures the strength coefficient and the strain hardening exponent decrease with increased austempering time, whereas at higher austempering temperatures they show little time dependence. These relations are explained by the microstructural transformations that take place during the austempering heat treatment.
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| 36. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
Incorporating predicted local mechanical behaviour of cast components into finite element simulations
- 2012
-
In: Materials & Design. - : Elsevier. - 0261-3069. ; 34, s. 494-500
-
Journal article (peer-reviewed)abstract
- A software which enables the incorporation of local variations in both elastic and plastic mechanical behaviour predicted by a casting process simulation into a Finite Element Method (FEM) simulation is presented. The software uses a piecewise linearization of the Hollomon or the Ludwigson equation to characterise plastic mechanical behaviour of the material on an element level throughout a component. The accuracy obtained in the linearization is investigated, and the performance of the software is studied using different input parameters. The applicability of the software is verified and demonstrated on a ductile iron component, and a simulation strategy for cast components denoted a closed chain of simulations for cast components is discussed.
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| 37. |
- Olofsson, Jakob, 1980-
(author)
-
Integrated fatigue life predictions of aluminium castings using simulated local microstructure and defects
- 2023
-
In: IOP Conference Series. - : Institute of Physics (IOP). - 1757-8981 .- 1757-899X. ; 1281:1
-
Journal article (peer-reviewed)abstract
- In this work, an integrated simulation approach previously developed for static FE analyses is extended to microstructure- and defect-based fatigue life assessments of castings. The approach, the closed chain of simulations for cast components, combines casting process simulation with microstructure modelling and local material characterisation to generate heterogeneous material data for FE analysis and fatigue life assessment. The method is demonstrated on a High-Pressure Die Cast aluminium component. Areas with a high risk of defects are identified based on the simulated solidification conditions, and heterogeneous material data for the fatigue life analysis is generated. Fatigue testing has been performed with different levels of porosities to quantify the effect of defects on the element-specific Wöhler curves. Pore characteristics are assessed using 2D X-ray, fracture surface analysis and Kitagawa diagram. The results highlight the importance of taking the risk of defect formation into consideration when designing industrial aluminium castings subjected to fatigue loads.
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| 38. |
- Olofsson, Jakob, 1980-
(author)
-
Local microstructure-based material performance and damage in design and finite element simulations of cast components
- 2018
-
In: Journal of Computational Design and Engineering. - : Elsevier. - 2288-4300 .- 2288-5048. ; 5:4, s. 419-426
-
Journal article (peer-reviewed)abstract
- A novel approach to incorporate local microstructure-based material performance into finite element method (FEM) simulations of cast components is presented. By adopting perspectives from natural designs as dinosaur skulls and trees, the discipline-wide approach enables accurate prediction of damage in structures based on a heterogeneous distribution of sub-scale features. It is shown that heterogeneous damage tolerance dictates the performance and failure of cast aluminum, and simulations are compared with experimental results of heterogeneous tensile samples using digital image correlation (DIC). The numerical application of the approach in the industrial product realization process of an industrial casting is demonstrated, and the applicability of the approach to understand the behavior and failure of natural as well as synthetic structures is discussed.
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| 39. |
- Olofsson, Jakob, 1980-
(author)
-
Microstructure-based Mechanical Behaviour in Structural Analyses of Cast Components
- 2012
-
Licentiate thesis (other academic/artistic)abstract
- In the process of developing cast iron and cast aluminium components, the co-operation between product development and production is important. On the engineering level, this co-operation is limited already in the product development phase e.g. by the lack of established methods to consider the mechanical behaviour of the completed component.This thesis aims to increase the possibilities for co-operation in the product realisation process between product development and production by enabling the use of predicted local mechanical behaviour in structural analyses of cast components. A literature review on existing simulation methods and a work on characterization of mechanical behaviour from microstructural features are performed to identify important knowledge gaps. A simulation strategy is formulated that is able to predict local mechanical behaviour throughout the entire component and incorporate the behaviour into a Finite Element Method (FEM) simulation of the structural behaviour of the component. In the simulation strategy, the component specific microstructure-based mechanical behaviour is predicted using a casting process simulation. A computer program is developed to create FEM material definitions that capture the local variations in mechanical behaviour throughout the component.The relevance of the simulation strategy is demonstrated for a ductile iron component. It is found that the local variations in mechanical behaviour result in a stress-strain distribution in the component that a homogeneous material description fails to express. Residual stresses affect the mechanical behaviour at low loads. At higher loads, however, the accuracy of the simulation is determined by the local variations in mechanical behaviour. Using a material reduction technique, the local mechanical behaviour can be incorporated without increasing the FEM simulation time.
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| 40. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
Modelling and simulations of ductile iron solidification-induced variations in mechanical behaviour on component and microstructural level
- 2015
-
In: MCWASP XIV. - London : Institute of Physics Publishing (IOPP). ; , s. 1-8, s. 1-8
-
Conference paper (peer-reviewed)abstract
- The mechanical behaviour and performance of a ductile iron component is highly dependent on the local variations in solidification conditions during the casting process. Here we show a framework which combine a previously developed closed chain of simulations for cast components with a micro-scale Finite Element Method (FEM) simulation of the behaviour and performance of the microstructure. A casting process simulation, including modelling of solidification and mechanical material characterization, provides the basis for a macro-scale FEM analysis of the component. A critical region is identified to which the micro-scale FEM simulation of a representative microstructure, generated using X-ray tomography, is applied. The mechanical behaviour of the different microstructural phases are determined using a surrogate model based optimisation routine and experimental data. It is discussed that the approach enables a link between solidification- and microstructure-models and simulations of as well component as microstructural behaviour, and can contribute with new understanding regarding the behaviour and performance of different microstructural phases and morphologies in industrial ductile iron components in service.
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| 41. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
Multidisciplinary shape optimization of ductile iron castings by considering local microstructure and material behaviour
- 2018
-
In: Structural and multidisciplinary optimization (Print). - : Springer. - 1615-147X .- 1615-1488. ; 57:5, s. 1889-1903
-
Journal article (peer-reviewed)abstract
- During the casting process and solidification of ductile iron castings, a heterogeneous microstructure is formed throughout the casting. This distribution is strongly influenced by the item geometry and the process related factors, as chemical composition and local solidification conditions. Geometrical changes to the geometry of the casting thus alters the local mechanical behavior and properties, as well as the distribution of stresses and strains when the casting is subjected to load. In order to find an optimal geometry, e.g. with reduced weight and increased load-bearing capacity, this interdependency between geometry and local material behavior needs to be considered and integrated into the optimization method. In this contribution, recent developments in the multidisciplinary integration of casting process simulation, solidification and microstructure modelling, microstructure-based material characterization, finite element structural analyses with local material behavior and structural optimization techniques are presented and discussed. The effect and relevance of considering the local material behavior in shape optimization of ductile iron castings is discussed and evidenced by an industrial application. It is shown that by adopting a multidisciplinary optimization approach by integration of casting simulation and local material behavior into shape optimization, the potential of the casting process to obtain components with high performance and reliability can be enabled and utilized.
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| 42. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
Multidisciplinary shape optimization of ductile iron castings byconsidering local microstructure and material behaviour
- 2017
-
In: WCSMO12, 12th World Congress of Structural and Multidisciplinary Optimisation. - : Technische Universität. ; , s. 82-, s. 82-
-
Conference paper (peer-reviewed)abstract
- During the casting process and solidification of ductile iron castings, a heterogeneous microstructure is formed throughout the casting. This distribution is highly controlled by process related factors, as chemical composition, local solidification conditions, and the geometry of the casting. Geometrical changes to the geometry of the casting thus alters the local mechanical behaviour, as well as the distribution of stresses and strains when the casting is subjected to load. In order to find an optimal geometry, e.g. with reduced weight and increased load-bearing capacity, this interdependency between geometry and local material behaviour needs to be considered and integrated into the optimization method. In this contribution, recent developments in the multidisciplinary integration of casting process simulation, solidification and microstructure modelling, microstructure-based material characterization, Finite Element Analyses (FEA) with local material behaviour and structural optimization techniques are presented and discussed. The effect and relevance of considering the local material behaviour in shape optimization of ductile iron castings is discussed and evidenced by an industrial application. It is shown that by adopting a multidisciplinary optimization approach by integration of casting simulation and local material behaviour into shape optimization, the potential of the casting process to obtain components with high performance and reliability can be enabled and utilized.
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| 43. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
On revealing hidden entrainment damage during in situ tensile testing of cast aluminum alloy components
- 2024
-
In: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 208
-
Journal article (peer-reviewed)abstract
- Tensile tests have been conducted on die-cast coupons of an Al-Si-Cu alloy, which have been found to contain no pores via X-ray inspection. Due to the digital image correlation used during tensile testing, either single or multiple strain concentrations have been detected and subsequently characterized. In all cases, oxide films have been found on fracture surfaces at the site of the strain concentrations. The analysis of a crack away from the fracture surface has also shown it to be an oxide bifilm. These results pour doubt on the effectiveness of quality assurance practices employed in industry.
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| 44. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
On the effects of defects and imperfections on tensile toughness of a secondary aluminium alloy
- 2019
-
In: SHAPE CASTING:7th International Symposium CelebratingProf. John Campbell’s 80th Birthday. - Cham : Springer International Publishing. - 9783030060336 - 9783030060343 ; , s. 131-141
-
Conference paper (peer-reviewed)abstract
- In order to design and produce high-quality castings with reliable performance, the effect of the melt handling and melt quality during different processing stages needs to be understood and controlled, and numerical methods to provide correct input data to structural analyses of castings enabled. This paper aims to investigate tensile properties, in particular tensile toughness, of a secondary high-pressure die casting (HPDC) aluminium alloy with different levels of defects and imperfections. The melt, which was transported in liquid state from the smelter to the foundry, has been sampled after different holding times by casting into Y-blocks. Tensile testing was performed, and the levels of defects and imperfections were characterized using measurements of porosity, bifilm index, density index, sludge factor and the amount of iron-rich intermetallics. Two different quality indices have been evaluated, and a method to apply the results in simulations of damage in a casting, containing defects, subjected to load is demonstrated.
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| 45. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
Revealing and simulating the effect of hidden damage on local and full-field deformation behaviour of cast aluminium
- 2023
-
In: IOP Conference Series. - : Institute of Physics (IOP). - 1757-8981 .- 1757-899X. ; 1281:1
-
Journal article (peer-reviewed)abstract
- Pores have been the main focus of quality assurance in castings. Latest research has shown that in aluminium castings pores can form only if there is existing entrainment damage, i.e., pores are merely the visible parts of the entrainment damage, and usually invisible damage is much more extensive. However, its effect on deformation behaviour has not been previously established or observed in-situ. This work applies 2D Digital Image Correlation (DIC) to an in-situ full-field stress-strain analysis of tensile samples with a non-conventional heterogeneous stress distribution. The observations reveal that the effect of hidden damage extends far beyond its impact on fracture behaviour and is responsible for initiating local strain concentrations during deformation. By extracting local stress-strain data, FE simulations have been performed to mimic the effect of local hidden damage on the heterogeneous stress-strain field. SEM and FIB-SEM analysis has been applied to investigate the cause for the strain concentrations. The combined results show that hidden damage in the form of oxide films is not only responsible for premature fracture, but also affects the deformation behaviour of tensile samples by introducing dispersed strain concentrations.
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| 46. |
- Olofsson, Jakob, 1980-
(author)
-
Simulation of mechanical behaviour of cast aluminium components
- 2012
-
In: International Journal of Cast Metals Research. - : Taylor & Francis. - 1364-0461 .- 1743-1336. ; 25:6, s. 319-327
-
Research review (peer-reviewed)abstract
- A literature review on methods to consider the mechanical behaviour of cast aluminium alloys in finite element method (FEM) simulations of cast aluminium components has been performed. The mechanical behaviour is related to several microstructural parameters achieved during the casting process. Three different methods to consider these microstructural parameters are introduced. One method predicts the mechanical behaviour of the component using casting process simulation software. The other two methods implement numerical models for the mechanical behaviour of cast aluminium into the FEM simulation. Applications of the methods are shown, including combinations with statistical methods and geometry optimisation methods. The methods are compared, and their different strengths and drawbacks are discussed.
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| 47. |
- Olofsson, Jakob, 1980-
(author)
-
Simulation of Microstructure-based Mechanical Behaviour of Cast Components
- 2014
-
Doctoral thesis (other academic/artistic)abstract
- In the process of developing cast iron and cast aluminium components, a high level of co-operation between product development and production is of great importance. From an engineering standpoint, this co-operation is limited early in the product development phase by e.g. a lack of established methods for the consideration of local variations in the mechanical behaviour of a finished component.This thesis aims to increase the possibilities for co-operation between product development and production during the product realisation process by introducing and studying the use of predicted local mechanical behaviour in structural analyses of cast components. A literature review of existing simulation methods and a work on characterisation of mechanical behaviour from microstructural features have been performed to identify important knowledge gaps. A simulation strategy has been formulated which is able to predict local mechanical behaviour throughout the entire component, and to incorporate this into a Finite Element Method (FEM) simulation of the structural behaviour of the component. In the simulation strategy, componentspecific microstructure-based mechanical behaviour is predicted using a casting process simulation. A computer program was developed to create FEM material definitions which capture the local variations in mechanical behaviour throughout the component. Using a material reduction technique, the local mechanical behaviour can be incorporated without increasing the FEM simulation time.The relevance of the simulation strategy was experimentally verified on cast aluminium samples, where the strain field was observed using Digital Image Correlation (DIC). It was found that the local variations in mechanical behaviour cause a stress-strain distribution that deviates from that predicted by a homogeneous material description, indicating the importance of calculating with and including such variations in material behaviour in FEM simulations. Numerical investigations demonstrate the strategy’s relevance for predicting the behaviour of cast aluminium and ductile iron components.
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| 48. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
The effects of local variations in mechanical behaviour – Numerical investigation of a ductile iron component
- 2013
-
In: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197 .- 0261-3069. ; 43, s. 264-271
-
Journal article (peer-reviewed)abstract
- The effects of incorporating local mechanical behaviour into a structural analysis of a cast ductile iron component are investigated. A recently presented simulation strategy, the closed chain of simulations for cast components, is applied to incorporate local behaviour predicted by a casting process simulation into a Finite Element Method (FEM) structural analysis, and the effects of the strategy on predicted component behaviour and simulation time are evaluated. The results are compared to using a homogeneous material description. A material reduction method is investigated, and the effects of material reduction and number of linearization points are evaluated.The results show that local mechanical behaviour may significantly affect the predicted behaviour of the component, and a homogeneous material description fails to express the stress-strain distribution caused by the local variations in mechanical behaviour in the component. The material reduction method is able to accurately describe this effect while only slightly increasing the simulation time. It is proposed that local variations in mechanical behaviour are important to consider in structural analyses of the mechanical behaviour of ductile iron components.
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| 49. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
The multi-scale closed chain of simulations – incorporating local variations in microstructure into finite element simulations
- 2016
-
In: TMS 2015 144th Annual Meeting & Exhibition. - Cham : Springer International Publishers, Switzerland. - 9783319486086 - 9783319481272 ; , s. 1057-1064
-
Conference paper (peer-reviewed)abstract
- Numerical simulations of component behavior and performance is critical to develop optimized and robust load-bearing components. The reliability of these simulations depend on the description of the components material behavior, which for e.g. cast and polymeric materials exhibit component specific local variations depending on geometry and manufacturing parameters. Here an extension of a previously presented strategy, the closed chain of simulations for cast components, to predict and incorporate local material data into Finite Element Method (FEM) simulations on multiple scales is shown. Manufacturing process simulation, solidification modelling, material characterization and representative volume elements (RVE) provides the basis for a microstructure-based FEM analysis of component behavior and a simulation of the mechanical behavior of the local microstructure in a critical region. It is discussed that the strategy is applicable not only to cast materials but also to injection molded polymeric materials, and enables a common integrated computational microstructure-based approach to optimized components.
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| 50. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
Three-dimensional study of nodule clustering and heterogeneous strain localization for tailored material properties in ductile iron
- 2019
-
In: Joint 5th International Conference on Advances in Solidification Processes (ICASP-5) & 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5) 17–21 June 2019, Salzburg, Austria. - : Institute of Physics Publishing (IOPP).
-
Conference paper (peer-reviewed)abstract
- Tailored heterogeneous distributions of microstructural features enable extraordinary material performance in biological and physiological structures such as trees, the aortic arch, human teeth and dinosaur skulls. In ductile iron, a heterogeneous distribution in size and morphology of graphite nodules and variations of the fractions of ferrite and pearlite are created during solidification, and varies as a function of parameters such as local cooling rate, segregation and flow. In the current work, the size distribution as well as the orientation and relation between graphite nodules is obtained by a three-dimensional reconstruction of a ductile iron microstructure from X-ray tomography. The effect of the nodule morphology and clustering on the localization of plastic strains is studied numerically using finite element analysis of the reconstructed microstructure. Real castings have a variation in geometry, solidification conditions and are subjected to variations in loads. A framework for optimized geometry and solidification conditions in order to design and deliver castings with tailored local material performance is proposed.
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