| 1. |
- Hergens, Maria-Pia, et al.
(författare)
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Use of Scandinavian Moist Smokeless Tobacco (Snus) and the Risk of Atrial Fibrillation
- 2014
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Ingår i: Epidemiology. - 1044-3983 .- 1531-5487. ; 25:6, s. 872-876
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Snus is a smokeless tobacco product, widely used among Swedish men and increasingly so elsewhere. There is debate as to whether snus is an acceptable "harm-reduction" tobacco product. Since snus use delivers a dose of nicotine equivalent to cigarettes, and has been implicated in cardiac arrhythmia because of associations with sudden cardiovascular death, a relation with atrial fibrillation is plausible and important to investigate.METHODS:: To assess the relation between use of snus and risk of atrial fibrillation, we carried out a pooled analysis of 7 prospective Swedish cohort studies. In total, 274,882 men, recruited between 1978 and 2004, were followed via the National Patient Register for atrial fibrillation. Primary analyses were restricted to 127,907 never-smokers. Relative risks were estimated using Cox proportional hazard regression.RESULTS:: The prevalence of snus use was 25% among never-smokers. During follow-up, 3,069 cases of atrial fibrillation were identified. The pooled relative risk of atrial fibrillation was 1.07 (95% confidence interval = 0.97-1.19) in current snus users, compared with nonusers.CONCLUSION:: Findings from this large national pooling project indicate that snus use is unlikely to confer any important increase in risk of atrial fibrillation.
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| 2. |
- Jansson, Johan, et al.
(författare)
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An anisotropic non-linear material model for glass fibre reinforced plastics
- 2018
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Ingår i: Composite structures. - : Elsevier. - 0263-8223 .- 1879-1085. ; 195, s. 93-98
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Jansson, Johan, et al.
(författare)
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Image-based semi-multiscale finite element analysis using elastic subdomain homogenization
- 2021
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Ingår i: Meccanica (Milano. Print). - : Springer. - 0025-6455 .- 1572-9648. ; 56:11, s. 2799-2811
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Jansson, Johan
(författare)
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Multiscale Constitutive Modeling of Heterogeneous Engineering Materials
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 5. |
- Jansson, Johan, et al.
(författare)
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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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Ingår i: 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).
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Konferensbidrag (refereegranskat)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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| 6. |
- Jansson, Johan
(författare)
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Process-Induced Local Material Variations in Finite Element Simulations of Cast and Fibre Reinforced Injection Moulded Components
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)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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| 7. |
- Jansson, Johan, et al.
(författare)
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Simulation-driven product development of cast components with allowance for process-induced material behaviour
- 2020
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Ingår i: Journal of Computational Design and Engineering. - : Oxford University Press. - 2288-5048. ; 7:1, s. 78-85
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Tidskriftsartikel (refereegranskat)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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