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Nilsson, Fritjof, Docent
Publications (10 of 13) Show all publications
Yang, G., Nilsson, F. & Schubert, D. W. (2019). A Study of Finite Size Effects and Periodic Boundary Conditions to Simulations of a Novel Theoretical Self-Consistent Mean-Field Approach. Macromolecular Theory and Simulations, Article ID 1900023.
Open this publication in new window or tab >>A Study of Finite Size Effects and Periodic Boundary Conditions to Simulations of a Novel Theoretical Self-Consistent Mean-Field Approach
2019 (English)In: Macromolecular Theory and Simulations, ISSN 1022-1344, E-ISSN 1521-3919, article id 1900023Article in journal (Refereed) Published
Abstract [en]

In a previous work, a very promising mathematical model for predicting the electrical conductivity below the electrical percolation threshold, for both isotropic and anisotropic composites, was published by Schubert. In this work, periodic boundary condition of the simulation is utilized. The results are also compared to the previous work and other theoretical models. The truncated fibers due to finite size of the simulation volume are considered as two individual pieces so that the real aspect ratios will also be taken into consideration. A comparison is made between two groups, in which the length and the radius of the carbon fibers are changed, respectively, under certain aspect ratios. With three different sizes of the simulation volumes, the influence on the results due to the finite size effect is calculated.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2019
Keywords
conductivity, finite size effect, simulation
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-255743 (URN)10.1002/mats.201900023 (DOI)000477285900001 ()2-s2.0-85069884915 (Scopus ID)
Note

QC 20190813

Available from: 2019-08-13 Created: 2019-08-13 Last updated: 2019-10-04Bibliographically approved
Sanchez, C., Wåhlander, M., Karlsson, M. E., Quintero, D. C. M., Hillborg, H., Malmström, E. & Nilsson, F. (2019). Characterization of Reduced and Surface-Modified Graphene Oxide in Poly(Ethylene-co-Butyl Acrylate) Composites for Electrical Applications. Polymers, 11(4), Article ID 740.
Open this publication in new window or tab >>Characterization of Reduced and Surface-Modified Graphene Oxide in Poly(Ethylene-co-Butyl Acrylate) Composites for Electrical Applications
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2019 (English)In: Polymers, ISSN 2073-4360, E-ISSN 2073-4360, Vol. 11, no 4, article id 740Article in journal (Refereed) Published
Abstract [en]

Promising electrical field grading materials (FGMs) for high-voltage direct-current (HVDC) applications have been designed by dispersing reduced graphene oxide (rGO) grafted with relatively short chains of poly (n-butyl methacrylate) (PBMA) in a poly(ethylene-co-butyl acrylate) (EBA) matrix. All rGO-PBMA composites with a filler fraction above 3 vol.% exhibited a distinct non-linear resistivity with increasing electric field; and it was confirmed that the resistivity could be tailored by changing the PBMA graft length or the rGO filler fraction. A combined image analysis- and Monte-Carlo simulation strategy revealed that the addition of PBMA grafts improved the enthalpic solubility of rGO in EBA; resulting in improved particle dispersion and more controlled flake-to-flake distances. The addition of rGO and rGO-PBMAs increased the modulus of the materials up to 200% and the strain did not vary significantly as compared to that of the reference matrix for the rGO-PBMA-2 vol.% composites; indicating that the interphase between the rGO and EBA was subsequently improved. The new composites have comparable electrical properties as today's commercial FGMs; but are lighter and less brittle due to a lower filler fraction of semi-conductive particles (3 vol.% instead of 30-40 vol.%).

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
field grading nanocomposites, non-linear resistivity, reduced graphene oxide (rGO), HVDC, SI-ATRP surface modification
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-252652 (URN)10.3390/polym11040740 (DOI)000467312900169 ()31022914 (PubMedID)2-s2.0-85065904341 (Scopus ID)
Note

QC 20190610

Available from: 2019-06-10 Created: 2019-06-10 Last updated: 2019-06-10Bibliographically approved
Nilsson, F., Moyassari, A., Bautista, A., Castro, A., Arbeloa, I., Jarn, M., . . . Johansson, K. (2019). Modelling anti-icing of railway overhead catenary wires by resistive heating. International Journal of Heat and Mass Transfer, 143, Article ID 118505.
Open this publication in new window or tab >>Modelling anti-icing of railway overhead catenary wires by resistive heating
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2019 (English)In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 143, article id 118505Article in journal (Refereed) Published
Abstract [en]

Aggregation of ice on electrical cables and apparatus can cause severe equipment malfunction and is thus considered as a serious problem, especially in arctic climate zones. In particular, cable damage caused by ice accumulation on railway catenary wires is in wintertime a common origin for delayed trains in the northern parts of Europe. This study examines how resistive heating can be used for preventing formation of ice on metallic, non-insulated electrical cables. The heat equation and the Navier Stokes equations were solved simultaneously with FEM in 3D in order to predict the cable temperature as function of external temperature, applied voltage, wind speed, wind direction, and heating time. An analytical expression for the heat transfer coefficient was derived from the FEM simulations and it was concluded that the influence of wind direction can typically be neglected. Experimental validation measurements were performed on Kanthal cables in a climate chamber, giving temperature increase results in good agreement with the simulation predictions. The resistive heating efficiency, i.e. the ratio between applied electrical energy and resulting thermal energy, was found to be approximately 68% in this particular study.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
Keywords
Ice-prevention, Resistive heating, FEM, Kanthal, Railway overhead lines
National Category
Engineering and Technology
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-261935 (URN)10.1016/j.ijheatmasstransfer.2019.118505 (DOI)000487564400031 ()2-s2.0-85070233997 (Scopus ID)
Note

QC 20191015

Available from: 2019-10-15 Created: 2019-10-15 Last updated: 2019-11-26Bibliographically approved
Qu, M., Nilsson, F. & Schubert, D. W. (2019). Novel definition of the synergistic effect between carbon nanotubes and carbon black for electrical conductivity. Nanotechnology, 30(24), Article ID 245703.
Open this publication in new window or tab >>Novel definition of the synergistic effect between carbon nanotubes and carbon black for electrical conductivity
2019 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 30, no 24, article id 245703Article in journal (Refereed) Published
Abstract [en]

Anisotropic ternary composites comprising poly(methy-methacrylate) (PMMA), carbon black (CB), and carbon nanotubes (CNTs) were extruded using a capillary rheometer and the electrical conductivities of the composites were measured and presented in a detailed contour plot covering a large range of filler fractions (up to 30 vol% CNTs, 20 vol% CB). A recent generic conductivity model for ternary composites was successfully validated using the conductivity measurements. When analyzing the conductivity measurements using four traditional definitions of 'synergy' between two conductive fillers, no clear synergetic effect was observed between CB and CNT. Also, when all the conductivity data for ternary CNT/CB composites from the existing literature was carefully gathered and analyzed, the number of confirmed occurrences of strong and convincing CNT/CB synergies was surprisingly low. Finally, a novel definition of synergy based on the physical aspect, in particular, its maximum, the 'synergasm', was defined in order to obtain a more precise instrument for revealing regions of potential synergy.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2019
Keywords
carbon nanotubes, carbon black, electrical properties, synergistic effect
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-249840 (URN)10.1088/1361-6528/ab0bec (DOI)000462890900001 ()30822767 (PubMedID)2-s2.0-85064144640 (Scopus ID)
Note

QC 20190502

Available from: 2019-05-02 Created: 2019-05-02 Last updated: 2019-05-02Bibliographically approved
Holder, S., Hedenqvist, M. S. & Nilsson, F. (2019). Understanding and modelling the diffusion process of low molecular weight substances in polyethylene pipes. Water Research, 301-309
Open this publication in new window or tab >>Understanding and modelling the diffusion process of low molecular weight substances in polyethylene pipes
2019 (English)In: Water Research, ISSN 0043-1354, E-ISSN 1879-2448, p. 301-309Article in journal (Refereed) Published
Abstract [en]

Peroxides are widely used as crosslinkers in polyethylene (PE) drinking water pipes. Cross-linked polyethylene (PEX) has better mechanical properties than PE, but peroxide decomposition by-products can migrate from PEX water pipes into the drinking water unless sufficient preventive actions are undertaken. This work systematically examines the migration of tert-Butyl methyl ether (MTBE), a dominating crosslinking by-product from PEX water pipes, into tap water by utilizing both experimental techniques and finite element (FEM) diffusion modeling. The effects of pipe geometry, tap water temperature (23–80 °C), boundary conditions (air or water interface) and degasing (at 180 °C) were considered. The MTBE diffusivity increased strongly with increasing temperature and it was concluded that a desired water quality can be achieved with proper degasing of the PEX pipes. As the FEM simulations were in excellent agreement with the experimental results, the model can accurately predict the MTBE concentration as a function of time, water temperature and PEX pipe geometry, and enable the pipe manufacturers to aid in ensuring desirable drinking water quality.

Place, publisher, year, edition, pages
Elsevier Ltd, 2019
Keywords
Crosslinked polyethylene, Diffusion coefficient, Diffusion model, Drinking water, PEX pipes, Polymers, Diffusion, Oxidation, Peroxides, Phase interfaces, Polyethylenes, Temperature, Water pipelines, Water piping systems, Water quality, Drinking water pipes, Experimental techniques, Increasing temperatures, Low molecular weight, Peroxide decomposition, Tert-butyl methyl ethers, Potable water, deionized water, peroxide, polyethylene, polymer, tap water, tert butyl methyl ether, byproduct, decomposition, molecular analysis, MTBE, pipe, plastic, pollution incidence, water temperature, Article, biodegradation, concentration (parameter), cross linking, diffusivity, finite element analysis, heat treatment, mass fragmentography, molecular weight, priority journal, process model, simulation
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-252470 (URN)10.1016/j.watres.2019.03.084 (DOI)000468253500030 ()2-s2.0-85063760634 (Scopus ID)
Note

QC 20190715

Available from: 2019-07-15 Created: 2019-07-15 Last updated: 2019-07-15Bibliographically approved
Yang, G., Nilsson, F. & Schubert, D. W. (2019). Universal and anisotropic simulation platform for the study of electrical properties of conductive polymer composites. In: AIP Conference Proceedings: . Paper presented at 2017 Europe/Africa Regional Conference of the Polymer Processing Society (PPS), Dresden, Germany, 27 June 2017 through 29 June 2017. American Institute of Physics (AIP), 2055, Article ID 050012.
Open this publication in new window or tab >>Universal and anisotropic simulation platform for the study of electrical properties of conductive polymer composites
2019 (English)In: AIP Conference Proceedings, American Institute of Physics (AIP), 2019, Vol. 2055, article id 050012Conference paper, Published paper (Refereed)
Abstract [en]

In order to carry out a study on the synergistic relationship of variables which could affect the electrical properties of CPC, a universal and anisotropic platform of simulation, containing three simulation modules are explored. The simulation modules are: finite element modelling (FEM), percolation threshold modeling (PTM) and electrical networks modelling (ENM).

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2019
Series
AIP Conference Proceedings, ISSN 0094-243X ; 2055
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-244275 (URN)10.1063/1.5084831 (DOI)000464909300030 ()2-s2.0-85061092063 (Scopus ID)9780735417830 (ISBN)
Conference
2017 Europe/Africa Regional Conference of the Polymer Processing Society (PPS), Dresden, Germany, 27 June 2017 through 29 June 2017
Note

QC 20190219

Available from: 2019-02-19 Created: 2019-02-19 Last updated: 2019-07-23Bibliographically approved
Nakamura, K., Ankyu, S., Nilsson, F., Kanno, T., Niwano, Y., von Steyern, P. V. & Örtengren, U. (2018). Critical considerations on load-to-failure test for monolithic zirconia molar crowns. Journal of The Mechanical Behavior of Biomedical Materials, 87, 180-189
Open this publication in new window or tab >>Critical considerations on load-to-failure test for monolithic zirconia molar crowns
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2018 (English)In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 87, p. 180-189Article in journal (Refereed) Published
Abstract [en]

Application of monolithic zirconia crowns (MZCs) with reduced thickness to the molar region has been proposed, but potential complications have yet to be fully evaluated in laboratory tests. The present study aimed to develop a clinically relevant load-to-failure test in combination with fatigue treatments involving thermal and mechanical cycling (TC and MC) to evaluate the fracture resistance of molar MZCs. MZCs with a minimal thickness of 0.5 mm were bonded to dies made of resin-based composite (RBC), epoxy resin (EP), or polyoxymethylene-copolymer (POM-C). The samples were either untreated (UT) or subjected to TC (5-55 degrees C for 1 x 10(5) cycles) and MC (300 N for 2.4 x 10(6) cycles). The stress generated by TC and MC was simulated by finite element modeling. The load-to-failure test was performed using an inverse V-shaped two-plane indenter and was followed by fractographic analysis. The median values of fracture load for MZC/RBC and MZC/EP in the TC group were significantly lower than those in the UT group. MC also decreased the median value of fracture load for MZC/RBC significantly, but not that for MZC/EP and MZC/POM-C. Fractography revealed that the fracture started in the cervical area in all groups, which is similar to clinically failed crowns. The simulation confirmed stress concentration at the cervical area in both TC and MC groups. The present study suggests that the load-to-failure test using a two-plane indenter could induce clinically relevant fracture of MZCs, the vulnerability of the MZCs depends largely on the die material employed, and MZCs are more likely to be damaged by thermal fatigue than mechanical fatigue.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Monolithic zirconia crowns, Fractography, Fracture resistance, Thermal fatigue, Mechanical fatigue, CAD/CAM, Finite element modeling
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-237088 (URN)10.1016/j.jmbbm.2018.07.034 (DOI)000446286000021 ()30077077 (PubMedID)2-s2.0-85050811130 (Scopus ID)
Note

QC 20181024

Available from: 2018-10-24 Created: 2018-10-24 Last updated: 2018-10-24Bibliographically approved
Qu, M., Nilsson, F. & Schubert, D. W. (2018). Effect of filler orientation on the electrical conductivity of carbon Fiber/PMMA composites. Fibers, 6(1), Article ID 3.
Open this publication in new window or tab >>Effect of filler orientation on the electrical conductivity of carbon Fiber/PMMA composites
2018 (English)In: Fibers, ISSN 2079-6439, Vol. 6, no 1, article id 3Article in journal (Refereed) Published
Abstract [en]

The electrical conductivity of extruded carbon fiber (CF)/Polymethylmethacrylate (PMMA) composites with controlled CF aspect ratio and filler fractions ranging from 0 to 50 vol. % has been investigated and analyzed. The composites were extruded through a capillary rheometer, utilizing either 1-mm or 3-mm diameter extrusion dies, resulting in cylindrical composite filaments of two different diameters. Since the average CF orientation becomes more aligned with the extrusion flow when the diameter of the extrusion dies decreases, the relationship between conductivity and average fiber orientation could therefore be examined. The room temperature conductivities of the extruded filaments as a function of CF fractions were fitted to theMcLachlan general effective medium (GEM) equation and the percolation thresholds were determined to 20.0 ± 2.5 vol. % and 32.0 ± 5.9 vol. % for the 3-mm (with CFs oriented less) and 1-mm(with CFs orientedmore) filaments, respectively. It turned out that the oriented CFs in the composite shift the percolation threshold to a higher value, however, the conductivity above the percolation threshold is higher for composites with oriented CFs. A novel approach based on the Balberg excluded volume theory was proposed to explain this counterintuitive phenomenon. 

Place, publisher, year, edition, pages
MDPI Multidisciplinary Digital Publishing Institute, 2018
Keywords
Carbon fibers, Conductivity, Extrusion, Orientation
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-227414 (URN)10.3390/fib6010003 (DOI)000428507900003 ()2-s2.0-85042261367 (Scopus ID)
Note

Export Date: 9 May 2018; Article; Correspondence Address: Qu, M.; Institute of Polymer Materials, Friedrich-Alexander-University Erlangen-Nuremberg, Martensstr. 7, Germany; email: muchao.qu@fau.de. QC 20180529

Available from: 2018-05-29 Created: 2018-05-29 Last updated: 2018-06-19Bibliographically approved
Yang, G., Schubert, D. W., Qu, M. & Nilsson, F. (2018). Novel Theoretical Self-Consistent Mean-Field Approach to Describe the Conductivity of Carbon Fiber-Filled Thermoplastics: PART II. Validation by Computer Simulation. Macromolecular Theory and Simulations, 27(4), Article ID 1700105.
Open this publication in new window or tab >>Novel Theoretical Self-Consistent Mean-Field Approach to Describe the Conductivity of Carbon Fiber-Filled Thermoplastics: PART II. Validation by Computer Simulation
2018 (English)In: Macromolecular Theory and Simulations, ISSN 1022-1344, E-ISSN 1521-3919, Vol. 27, no 4, article id 1700105Article in journal (Refereed) Published
Abstract [en]

The electrical conductivity of polymeric fiber composites is generally strongly dependent on the constituent conductivities, the fiber filler fraction, the fiber aspect ratio, and on the orientation of the fibers. Even though electrically conductive polymer composites are emerging materials of high scientific and commercial interest, accurate mathematical models for describing such materials are rare. A very promising mathematical model for predicting the electrical conductivity below the electrical percolation threshold, for both isotropic and anisotropic composites, is however recently published by Schubert. The shortcomings of that study are that the model includes so far only one predicted parameter and that it is not sufficiently validated. In the current study, finite element modeling is used to successfully validate the model of Schubert for isotropic fiber composites and to accurately determine the predicted parameter. These theoretical predictions are finally compared with experimental conductivity data for isotropic carbon fiber/poly(methyl methacrylate) (PMMA) composites with fiber filler fractions in the range 0-12 vol% and fiber aspect ratios from 5 to 30. The model forecasts, without any adjustable parameters, are satisfactory close to the experimental data.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2018
Keywords
computer simulation, electrical conductivity, finite element modeling, polymeric fiber composites
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-232785 (URN)10.1002/mats.201700105 (DOI)000438727100002 ()2-s2.0-85046433103 (Scopus ID)
Note

QC 20180806

Available from: 2018-08-06 Created: 2018-08-06 Last updated: 2018-08-06Bibliographically approved
Ozeren, H. D., Nilsson, F., Olsson, R. & Hedenqvist, M. S. (2018). Prediction of plasticization mechanisms for biobased plastics through a combined experimental and molecular dynamics simulations approach. Paper presented at 256th National Meeting and Exposition of the American-Chemical-Society (ACS) - Nanoscience, Nanotechnology and Beyond, AUG 19-23, 2018, Boston, MA. Abstract of Papers of the American Chemical Society, 256
Open this publication in new window or tab >>Prediction of plasticization mechanisms for biobased plastics through a combined experimental and molecular dynamics simulations approach
2018 (English)In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 256Article in journal, Meeting abstract (Other academic) Published
Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2018
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-238553 (URN)000447609105036 ()
Conference
256th National Meeting and Exposition of the American-Chemical-Society (ACS) - Nanoscience, Nanotechnology and Beyond, AUG 19-23, 2018, Boston, MA
Note

QC 20181105

Available from: 2018-11-05 Created: 2018-11-05 Last updated: 2018-11-05Bibliographically approved
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