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  • 201.
    Jeong, Seung Hee
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Mikrosystemteknik.
    Chen, Si
    Chalmers University of Technology.
    Huo, Jinxing
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Gravier, Laurent
    University of Applied Sciences and Arts Western Switzerland.
    Gamstedt, Erik Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Liu, Johan
    Chalmers University of Technology.
    Zhang, Shi-Li
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Zhang, Zhi-Bin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Wu, Zhigang
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Mikrosystemteknik. Huazhong Univ Sci & Technol, State Key Lab Digital Mfg Equipment & Technol, Wuhan, Peoples R China.
    Hjort, Klas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Mikrosystemteknik.
    Thermal Elastomer Composites for Soft Transducers2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    There is a need for thermal elastomer composites (TEC) which are stretchable, electrically insulating and easily processablefor soft and stretchable sensor or actuator systems as a thermal conductor or heat spreader at an interface or in a package.A novel TEC was made by embedding a gallium based liquid alloy (Galinstan) as a droplet in polydimethylsiloxane (PDMS,Elastosil RT 601) matrix with a high speed mechanical mixing process.

  • 202. Joffre, T.
    et al.
    Gamstedt, Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Passas, R.
    Dumont, P.
    Neagu, C.
    Moisture-induced deformation of wood fibres on the tracheid and cell-wall layer2011Inngår i: Proceedings of the Annual Workshop of COST Action FP0802: Hierarchical Structure and Mechanical Characterization of Wood, 2011, s. 89-90Konferansepaper (Fagfellevurdert)
  • 203.
    Joffre, Thomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Structure and Mechanical Behaviour of Wood-Fibre Composites2014Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Wood fibres have several advantages compared to man-made synthetic fibres: they have high specific stiffness, are renewable, relatively inexpensive, available in industrial quantities and biodegradable. However, to increase and diversify their utilisation, it is necessary to increase the understanding on what controls their mechanical properties.

    In this work, the hygroelastic behaviour of isolated wood fibres has been investigated using an analytical model and a finite element model based on three dimensional images obtained using synchrotron-based X-ray micro-computed tomography. It was thus possible to show how the cell wall responds to a mechanical load or a change in ambient relative humidity.

    The wood fibres were then mixed with a biopolymer aiming to produce a cost-efficient, 100% renewable composite material. The microstructure of the produced composites has been characterised using X-ray microtomography and digital image processing. It was for instance possible to measure the moisture-induced swelling of fibres embedded in a polymeric matrix. The experimental results have then been successfully compared with prediction obtained with a finite element model. The length of the fibres inside the composite has also been measured from three dimensional images, aiming to understand how each step of the processing chain is affecting the degradation of the aspect ratio of the reinforcing fibres.

    The presence of defects inside the composite has also been quantified using X-ray microtomography. The effects of the defects on the tensile strength have been predicted using an analytical model. The results have been compared with the measured tensile strength on each sample, showing that the size and orientation of the critical defect controls the tensile strength of the material.

    Finally, wood-fibre mats without any matrix material were compressed in the chamber of a microtomographic scanner. Sequential images were taken during the test. Using digital volume correlation, it was possible to calculate the local strain field inside the material. The effects of heterogeneities on the strain field have then been investigated. The applied compressive load resulted in transport of material from high to low density regions.

    Delarbeid
    1. Swelling of cellulose fibres in composite materials: Constraint effects of the surrounding matrix
    Åpne denne publikasjonen i ny fane eller vindu >>Swelling of cellulose fibres in composite materials: Constraint effects of the surrounding matrix
    Vise andre…
    2013 (engelsk)Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 74, s. 52-59Artikkel i tidsskrift (Fagfellevurdert) Published
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-188545 (URN)10.1016/j.compscitech.2012.10.006 (DOI)000314379700008 ()
    Tilgjengelig fra: 2012-10-17 Laget: 2012-12-17 Sist oppdatert: 2017-12-06bibliografisk kontrollert
    2. Modelling of the hygroelastic behaviour of normal and compression wood tracheids
    Åpne denne publikasjonen i ny fane eller vindu >>Modelling of the hygroelastic behaviour of normal and compression wood tracheids
    2014 (engelsk)Inngår i: Journal of Structural Biology, ISSN 1047-8477, E-ISSN 1095-8657, Vol. 185, nr 1, s. 89-98Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Compression wood conifer tracheids show different swelling and stiffness properties than those of usual normal wood, which has a practical function in the living plant: when a conifer shoot is moved from its vertical position, compression wood is formed in the under part of the shoot. The growth rate of the compression wood is faster than in the upper part resulting in a renewed horizontal growth. The actuating and load-carrying function of the compression wood is addressed, on the basis of its special ultrastructure and shape of the tracheids. As a first step, a quantitative model is developed to predict the difference of moisture-induced expansion and axial stiffness between normal wood and compression wood. The model is based on a state space approach using concentric cylinders with anisotropic helical structure for each cell-wall layer, whose hygroelastic properties are in turn determined by a self-consistent concentric cylinder assemblage of the constituent wood polymers. The predicted properties compare well with experimental results found in the literature. Significant differences in both stiffness and hygroexpansion are found for normal and compression wood, primarily due to the large difference in microfibril angle and lignin content. On the basis of these numerical results, some functional arguments for the reason of high microfibril angle, high lignin content and cylindrical structure of compression wood tracheids are supported.

    Emneord
    Compression wood, Reaction wood, Dimensional stability, Hygroelastic properties, Modelling
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-219205 (URN)10.1016/j.jsb.2013.10.014 (DOI)000330162300010 ()
    Tilgjengelig fra: 2014-02-25 Laget: 2014-02-24 Sist oppdatert: 2017-12-05bibliografisk kontrollert
    3. Effects of defects on the tensile strength of short-fibre composite materials
    Åpne denne publikasjonen i ny fane eller vindu >>Effects of defects on the tensile strength of short-fibre composite materials
    Vise andre…
    2014 (engelsk)Inngår i: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 75, s. 125-134Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Heterogeneous materials tend to fail at the weakest cross-section, where the presence of microstructural heterogeneities or defects controls the tensile strength. Short-fibre composites are an example of heterogeneous materials, where unwanted fibre agglomerates are likely to initiate tensile failure. In this study, the dimensions and orientation of fibre agglomerates have been analysed from three-dimensional images obtained by X-ray microtomography. The geometry of the specific agglomerate responsible for failure initiation has been identified and correlated with the strength. At the plane of fracture, a defect in the form of a large fibre agglomerate was almost inevitably found. These new experimental findings highlight a problem of some existing strength criteria, which are principally based on a rule of mixture of the strengths of constituent phases, and not on the weakest link. Only a weak correlation was found between stress concentration induced by the critical agglomerate and the strength. A strong correlation was however found between the stress intensity and the strength, which underlines the importance of the size of largest defects in formulation of improved failure criteria for short-fibre composites. The increased use of three-dimensional imaging will facilitate the quantification of dimensions of the critical flaws. 

    Emneord
    Strength, Agglomeration, X-ray microtomography, Composite materials
    HSV kategori
    Forskningsprogram
    Teknisk fysik med inriktning mot hållfasthetslära
    Identifikatorer
    urn:nbn:se:uu:diva-229212 (URN)10.1016/j.mechmat.2014.04.003 (DOI)000337983300011 ()
    Tilgjengelig fra: 2014-08-05 Laget: 2014-08-05 Sist oppdatert: 2017-12-05bibliografisk kontrollert
    4. X-ray micro-computed tomography investigation of fibre length degradation during the processing steps of short-fibre composites
    Åpne denne publikasjonen i ny fane eller vindu >>X-ray micro-computed tomography investigation of fibre length degradation during the processing steps of short-fibre composites
    2014 (engelsk)Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 105, s. 127-133Artikkel i tidsskrift (Fagfellevurdert) Published
    Emneord
    Polymer-matrix composites (PMCs), . Microstructures, Injection moulding, X-ray tomography
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-229209 (URN)10.1016/j.compscitech.2014.10.011 (DOI)000346943400016 ()
    Tilgjengelig fra: 2014-08-05 Laget: 2014-08-05 Sist oppdatert: 2017-12-05bibliografisk kontrollert
    5. A method to measure moisture induced swelling properties of a single wood cell
    Åpne denne publikasjonen i ny fane eller vindu >>A method to measure moisture induced swelling properties of a single wood cell
    Vise andre…
    2016 (engelsk)Inngår i: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 56, s. 723-733Artikkel i tidsskrift (Fagfellevurdert) Published
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-229210 (URN)10.1007/s11340-015-0119-9 (DOI)000375727600005 ()
    Eksternt samarbeid:
    Prosjekter
    eSSENCE
    Tilgjengelig fra: 2016-01-05 Laget: 2014-08-05 Sist oppdatert: 2017-12-05bibliografisk kontrollert
    6. A 3D in-situ investigation of the deformation in compressive loading in the thickness direction of cellulose fiber mats
    Åpne denne publikasjonen i ny fane eller vindu >>A 3D in-situ investigation of the deformation in compressive loading in the thickness direction of cellulose fiber mats
    Vise andre…
    2015 (engelsk)Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 22, nr 5, s. 2993-3001Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Fiber mat materials based on cellulose natural fibers combines a useful set of properties, including renewability, stiffness, strength and dielectric insulation, etc. The dominant in-plane fiber orientation ensures the in-plane performance, at the expense of reduced out-of-plane behavior, which has not been studied as extensively as the in-plane behavior. Quantitative use of X-ray micro-computed tomography and strain analyses under in-situ loading open up possibilities to identify key mechanisms responsible for deformation. In the present investigation, focus is placed on the out-of-plane deformation under compressive loading of thick, high density paper, known as pressboard. The samples were compressed in the chamber of a microtomographic scanner. 3D images were captured before and after the loading the sample. From sequential 3D images, the strain field inside the material was calculated using digital volume correlation. Two different test pieces were tested, namely unpolished and surface polished ones. The first principal strain component of the strain tensor showed a significant correlation with the density variation in the material, in particular on the top and bottom surfaces of unpolished samples. The manufacturing-induced grooves generate inhomogeneities in the microstructure of the surface, thus creating high strain concentration zones which give a sensible contribution to the overall compliance of the unpolished material. More generally, the results reveal that, on the micrometer scale, high density fiber pressboard behaves as a porous material rather than a low density fiber network.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-229211 (URN)10.1007/s10570-015-0727-7 (DOI)000361002000011 ()
    Forskningsfinansiär
    Swedish Research Council
    Tilgjengelig fra: 2014-08-05 Laget: 2014-08-05 Sist oppdatert: 2017-12-05
  • 204.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Ando, Edwardo
    University of Grenoble Alpes, France.
    Dumont, Pierre
    Université de Lyon, INSA Lyon, France.
    Ferguson, Stephen
    ETH Zurich, Switzerland.
    Persson, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Isaksson, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Deformation field estimation in compressed human trabecular bone using synchrotron X-ray tomography2016Konferansepaper (Annet vitenskapelig)
  • 205.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Chen, Song
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Isaksson, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Microscopic strain fields at crack tips in porous materials analyzed by a gradient-enhanced elasticity theory2016Inngår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 168, s. 160-173Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The microstructural influence on the strain field at opening mode crack tips in porous materials, and especially its practical implication for understanding macroscopic failure, i.e. on a scale above, is investigated. Theoretical subscale microstrain fields are approximated using a gradient-enhanced elasticity theory and compared to microstrain fields computed in discrete high-resolution finite element microstructural models having varying pore densities but similar macroscopic geometry and boundary conditions as the theoretical gradient-enhanced model. The numerical elastic microstrain and microstress fields are non-singular in strong contrast to the singular macroscopic fields in classical linear elastic fracture theories. Experimentally approximated microstrain fields, estimated with a digital image correlation algorithm on images obtained in X-ray computational tomography fracture tests on a small wood specimen, are used to contrast the.numerical analyses. A key observation is that an internal length parameter, used in the gradient-enhanced model, seems to be linked to the average pore diameter, allowing for direct bridging between scales.

  • 206.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Girlanda, Orlando
    Forsberg, Fredrik
    Sahlén, Fredrik
    Sjödahl, Mikael
    Gamstedt, E. Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    A 3D in-situ investigation of the deformation in compressive loading in the thickness direction of cellulose fiber mats2015Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 22, nr 5, s. 2993-3001Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fiber mat materials based on cellulose natural fibers combines a useful set of properties, including renewability, stiffness, strength and dielectric insulation, etc. The dominant in-plane fiber orientation ensures the in-plane performance, at the expense of reduced out-of-plane behavior, which has not been studied as extensively as the in-plane behavior. Quantitative use of X-ray micro-computed tomography and strain analyses under in-situ loading open up possibilities to identify key mechanisms responsible for deformation. In the present investigation, focus is placed on the out-of-plane deformation under compressive loading of thick, high density paper, known as pressboard. The samples were compressed in the chamber of a microtomographic scanner. 3D images were captured before and after the loading the sample. From sequential 3D images, the strain field inside the material was calculated using digital volume correlation. Two different test pieces were tested, namely unpolished and surface polished ones. The first principal strain component of the strain tensor showed a significant correlation with the density variation in the material, in particular on the top and bottom surfaces of unpolished samples. The manufacturing-induced grooves generate inhomogeneities in the microstructure of the surface, thus creating high strain concentration zones which give a sensible contribution to the overall compliance of the unpolished material. More generally, the results reveal that, on the micrometer scale, high density fiber pressboard behaves as a porous material rather than a low density fiber network.

  • 207.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Isaksson, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Dumont, Pierre J. J.
    Rolland du Roscoat, Sabine
    Sticko, Simon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för beräkningsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Orgéas, Laurent
    Gamstedt, E. Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    A method to measure moisture induced swelling properties of a single wood cell2016Inngår i: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 56, s. 723-733Artikkel i tidsskrift (Fagfellevurdert)
  • 208.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Isaksson, PerUppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.Latil, P.Dumont, P.Gamstedt, KristoferUppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Identification of hygroelastic properties of the woodcell wall from 3D images obtained by X-ray synchrotron microtomography2012Konferanseproceedings (Fagfellevurdert)
  • 209.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Isaksson, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Procter, Philip
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Persson, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Deformations in trabecular bone during pull-out of screw implants2016Konferansepaper (Annet vitenskapelig)
  • 210.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Isaksson, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Procter, Philip
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Persson, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Trabecular deformations during screw pull-out: a micro-CT study of lapine bone2017Inngår i: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 16, nr 4, s. 1349-1359Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mechanical fixation of endosseous implants, such as screws, in trabecular bone is challenging because of the complex porous microstructure. Development of new screw designs to improve fracture fixation, especially in high-porosity osteoporotic bone, requires a profound understanding of how the structural system implant/trabeculae interacts when it is subjected to mechanical load. In this study, pull-out tests of screw implants were performed. Screws were first inserted into the trabecular bone of rabbit femurs and then pulled out from the bone inside a computational tomography scanner. The tests were interrupted at certain load steps to acquire 3D images. The images were then analysed with a digital volume correlation technique to estimate deformation and strain fields inside the bone during the tests. The results indicate that the highest shear strains are concentrated between the inner and outer thread diameter, whereas compressive strains are found at larger distances from the screw. Tensile strains were somewhat smaller. Strain concentrations and the location of trabecular failures provide experimental information that could be used in the development of new screw designs and/or to validate numerical simulations.

  • 211.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Miettinen, A.Berthold, F.Kataja, M.Gamstedt, E. KristoferUppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    X-ray micro-computed tomography investigation of agglomeration and fibre length degradation through the processing chain of wood fibre composite2013Konferanseproceedings (Fagfellevurdert)
  • 212.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Miettinen, A.Isaksson, PerUppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.Wemersson, E.Gamstedt, E. KristoferUppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Effects of fibre agglomeration on strength of wood-fibre composites2012Konferanseproceedings (Fagfellevurdert)
  • 213.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Miettinen, Arttu
    Berthold, Fredrik
    Gamstedt, E. Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    X-ray micro-computed tomography investigation of fibre length degradation during the processing steps of short-fibre composites2014Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 105, s. 127-133Artikkel i tidsskrift (Fagfellevurdert)
  • 214.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Miettinen, Arttu
    Wernersson, Erik L. G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för visuell information och interaktion. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Bildanalys och människa-datorinteraktion.
    Isaksson, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Gamstedt, E. Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Effects of defects on the tensile strength of short-fibre composite materials2014Inngår i: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 75, s. 125-134Artikkel i tidsskrift (Fagfellevurdert)
  • 215.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Miettinen, Arttu
    Wernersson, Erik L. G.
    Isaksson, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Gamstedt, Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Effects of defects on the tensile strength of short-fibre composite materials2014Inngår i: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 75, s. 125-134Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Heterogeneous materials tend to fail at the weakest cross-section, where the presence of microstructural heterogeneities or defects controls the tensile strength. Short-fibre composites are an example of heterogeneous materials, where unwanted fibre agglomerates are likely to initiate tensile failure. In this study, the dimensions and orientation of fibre agglomerates have been analysed from three-dimensional images obtained by X-ray microtomography. The geometry of the specific agglomerate responsible for failure initiation has been identified and correlated with the strength. At the plane of fracture, a defect in the form of a large fibre agglomerate was almost inevitably found. These new experimental findings highlight a problem of some existing strength criteria, which are principally based on a rule of mixture of the strengths of constituent phases, and not on the weakest link. Only a weak correlation was found between stress concentration induced by the critical agglomerate and the strength. A strong correlation was however found between the stress intensity and the strength, which underlines the importance of the size of largest defects in formulation of improved failure criteria for short-fibre composites. The increased use of three-dimensional imaging will facilitate the quantification of dimensions of the critical flaws. 

  • 216.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Neagu, R. Cristian
    Bardage, Stig L.
    Gamstedt, Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Modelling of the hygroelastic behaviour of normal and compression wood tracheids2014Inngår i: Journal of Structural Biology, ISSN 1047-8477, E-ISSN 1095-8657, Vol. 185, nr 1, s. 89-98Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Compression wood conifer tracheids show different swelling and stiffness properties than those of usual normal wood, which has a practical function in the living plant: when a conifer shoot is moved from its vertical position, compression wood is formed in the under part of the shoot. The growth rate of the compression wood is faster than in the upper part resulting in a renewed horizontal growth. The actuating and load-carrying function of the compression wood is addressed, on the basis of its special ultrastructure and shape of the tracheids. As a first step, a quantitative model is developed to predict the difference of moisture-induced expansion and axial stiffness between normal wood and compression wood. The model is based on a state space approach using concentric cylinders with anisotropic helical structure for each cell-wall layer, whose hygroelastic properties are in turn determined by a self-consistent concentric cylinder assemblage of the constituent wood polymers. The predicted properties compare well with experimental results found in the literature. Significant differences in both stiffness and hygroexpansion are found for normal and compression wood, primarily due to the large difference in microfibril angle and lignin content. On the basis of these numerical results, some functional arguments for the reason of high microfibril angle, high lignin content and cylindrical structure of compression wood tracheids are supported.

  • 217.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Procter, Philip
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Brown, Chris
    Brunel University London.
    Isaksson, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Persson, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Mechanical testing in uCT and synchrotron scanners for an increased understanding of the role of bone microstructure on fracture processes and in fracture treatments2015Konferansepaper (Annet vitenskapelig)
  • 218.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Segerholm, Kristoffer
    SP Technical Research Institute of Sweden, Sustainable Built Environment & KTH, Div. of Building Materials.
    Persson, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Bardage, Stig L.
    SP Technical Research Institute of Sweden, Sustainable Built Environment.
    Luengo Hendriks, Cris L.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för visuell information och interaktion. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Bildanalys och människa-datorinteraktion.
    Isaksson, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Characterization of interfacial stress transfer ability in acetylation-treated wood fibre composites using X-ray microtomography2017Inngår i: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 95, s. 43-49Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The properties of the fibre/matrix interface contribute to stiffness, strength and fracture behaviour of fibre-reinforced composites. In cellulosic composites, the limited affinity between the hydrophilic fibres and the hydrophobic thermoplastic matrix remains a challenge, and the reinforcing capability ofthe fibres is hence not fully utilized. A direct characterisation of the stress transfer ability through pull-out tests on single fibres is extremely cumbersome due to the small dimension of the wood fibres. Here a novel approach is proposed:the length distribution ofthe fibres sticking out ofthe matrix atthe fracture surface is approximated using X-ray microtomography and is used as an estimate of the adhesion between the fibres and the matrix. When a crack grows in the material, the fibres will either break or be pulled-out of the matrix depending on their adhesion to the matrix: good adhesion between the fibres and the matrix should result in more fibre breakage and less pull-out of the fibres than poor adhesion. The effect of acetylation on the adhesion between the wood fibres and the PLA matrix was evaluated at different moisture contents using the proposed method. By using an acetylation treatment of the fibres it was possible to improve the strength of the composite samples soaked in the water by more than 30%.

  • 219.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Segerholm, Kristoffer
    SP Technical Research Institute of Sweden, Sustainable Built Environment & KTH, Div. of Building Materials.
    Persson, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Luengo Hendriks, Chris
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för visuell information och interaktion. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Bildanalys och människa-datorinteraktion.
    Bardage, Stig L.
    SP Technical Research Institute of Sweden, Sustainable Built Environment.
    Isaksson, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    A combined computational and experimental X-ray CT multiscale study of stable, slowly growing cracks in wood-fibre based composite materials2016Konferansepaper (Annet vitenskapelig)
  • 220.
    Joffre, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Wernersson, Erik L. G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för visuell information och interaktion. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Bildanalys och människa-datorinteraktion.
    Miettinen, Arttu
    Luengo Hendriks, Cris L.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för visuell information och interaktion. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Bildanalys och människa-datorinteraktion.
    Gamstedt, E. Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Swelling of cellulose fibres in composite materials: Constraint effects of the surrounding matrix2013Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 74, s. 52-59Artikkel i tidsskrift (Fagfellevurdert)
  • 221.
    Johannesson, Simon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik, Byggteknik.
    Förskolor med passivhusteknik: En utredning av passiva förskolor2013Independent thesis Basic level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [en]

    As a result of directives from EU, with the ambition to reach environmetal goals, The German organisation Passivhaus Institut has defined a passive house. A passive house is a building that is very energy efficient and makes a small impact on the environment. The energy from the inhabitants as well as the appliances & fixtures in the building should equal the energy that is required to heat the building. A Swedish version of the passive house definition has been defined, taking into account the climate conditions and the difference in building regulations.

    This thesis is a request from Skanska on how it can improve and develop an ongoing passive house project, involving an infant school. The intention of this thesis is to identify difficulties & display potential development areas for infant schools.

    The method of research conducted is as follows: interviews of clients, ventilation consultant, consultant for heating system and an energy calculation consultant, an inspection of the infant shcool in process, investigation of completed infant schools and a study of relevant literature.

    From this research it was found that it is difficult for infant schools to pass the criteria for passive houses. The conclusion of this thesis provide several guidelines on how to improve the outcome of existing projects & the steps needed to be taken for future development in this area.

  • 222.
    Johansson, Emil
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik, Byggteknik.
    Granskning av Solibri Model Checker - En Svenskanpassning: Jämförelse av två egenkontrollsystem2013Independent thesis Basic level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [en]

    The building industry are currently going through a huge alteration. The introduction of BIM (Building Information Modeling). Which also implements a lot of new ways of solving problems that building modeling can cause. This report is written for Uppsala University in cooperation with Temagruppen in Uppsala. However, it contains a comparison between two different systems that checks building models. Temagruppen invested in a new Swedish adaptation of a software called Solibri Model Checker. This Software controlling the availability in building models, it also introduces a new way of interaction between different instances during a building project. The definition of the report is availability in public buildings. A building model has been designed in Revit, then imported to Solibri Model Checker who controls the availability and creates a report of certain design fault. Interviews are given to get a look into how the work with availability controls currently works at Temagurppuen. This results in a discussion of benefits and disadvantages

    of the two different methods. The result finally shows that certain work can be more effectively done with Solibri Model Checker. But availability contains more than just disabled impairment. Visual- and cognitive impairment can’t still be controlled by just a computer software. 

  • 223.
    Johansson, Emil
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Utsläpp och lagring av koldioxid: En jämförelse mellan två byggnadsstommar2019Independent thesis Basic level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [en]

    Impacts from climate change are affecting all life on earth and the building sector is a great contributor of greenhouse gases. A transformation of the building sector is one part of the solution to limit impacts from human-driven climate change. In Sweden approximately one fifth of all emissions of carbon dioxide comes from the building sector. In this report a comparison of emissions of greenhouse gases and storage of carbon dioxide has been done for two different building systems of a house with three floors and 12 apartments.

    In the result it appears that emissions from the wooden building is near 0 carbon dioxide equivalent (9 000 kg CDE) when the storage of carbon dioxide in wooden products are considered. The value for the concrete building is almost 20 times higher, 164 000 kilogram CDE. Comparisons of each construction like exterior walls, interior walls and floors show that emissions of greenhouse gases from the concrete building are bigger for each part. Also when the captured carbon dioxide in wooden products is not considered. Floors in both buildings stand for most of the greenhouse gas emissions. For all wooden products the captured carbon is about ten times higher than the emissions of CDE in productions of the products. These values could be interpreted that wooden buildings have potential to work as efficient carbon storage.

  • 224.
    Johansson, Louise
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik, Byggteknik.
    Att planera bort störningar: Verktyg för smartare tidplanering inom grundläggning2014Independent thesis Basic level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Detta är ett examensarbete skrivet i samarbete med Skanska Grundläggning Syd med syftet att utreda hur deras planeringsarbete ser ut idag och vad som eventuellt kan göras bättre.

    Ett tidigare examensarbete har skrivits på avdelningen som undersökte produktiviteten ute på arbetsplatserna. I detta arbete var slutsatsen att produktionen stod still ca 40 % av arbetsdagen på grund av problem med maskiner eller leveranser, onödiga förflyttningar och att andra entreprenörer stod i vägen med mera. Målet med mitt arbete har varit att bygga vidare på detta och se om bättre planering kan bidra till att minska olika typer av produktionsstörningar.

    Underlaget till rapporten består av observationsstudier där arbetet på tre olika arbetsplatser följts samt av intervjuer med arbetsledare och andra personer som varit delaktiga i planeringsprocessen. Där noterades att en noggrann planering inte alltid görs, trots att det ofta finns krav på detta från beställaren. Tecken på detta syns bland annat på tidplanen och arbetsplatsdispositionsplanen som ofta är alltför odetaljerade. Resultatet blir att de kanske inte stämmer helt och är mycket svåra att följa upp. En effekt blir också att det är väldigt svårt att kommunicera hur stort utrymme entreprenören behöver och till när, vilket naturligtvis lätt leder till att de andra entreprenörerna på plats står i vägen eller inte har hunnit förbereda marken. Det uppstår också svårigheter hos leverantören av pålarna om inte projektet kan ge en tillräcklig framförhållning, vilket självklart ger problem med leveranser.

    De slutsatser som har dragits av undersökningarna är att arbetena behöver planeras mer noggrant och på ett sätt som går att kommunicera till andra. En rekommendation är att tidplanen görs visuellt genom markera etapper på en pålplan. En sådan visuell tidplan kan också användas som underlag för att diskutera dispositionen av arbetsytan och vilka ytor man behöver tillgång till. Utöver detta föreslås att en uppföljning görs av produktiviteten varje dag. En tredje rekommendation är att en checklista för planeringsstadiet tas fram, så att man inte behöver upprepa samma misstag som gjorts tidigare. När planeringen görs noggrant, erfarenheter sparas och kommunikationen på arbetsplatsen är öppen och tydlig så finns stora möjligheter till en trevligare arbetsmiljö och ett lönsamt projekt för alla inblandade.

  • 225.
    Johansson, Pontus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik, Byggteknik.
    Hisskärna av skalväggar i höga byggnader: Ett alternativ till den platsgjutna kärnan2013Independent thesis Basic level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [en]

    A common way to stabilize high rise buildings is to use an elevator core built of concrete. Today, we use to build these elevator cores of in-situ concrete. Precast concrete twin wall (double wall) is a semi-finished product that has become more common in recent years. This diploma work studies how the twin wall works out as structural elements in an elevator core. The work also shows some possible ways of designing twin walls and highlights some important parts of the design that will be vital to the stability of the building.

        The result shows that it is important to think through where the element joints should be placed. The reason why this placement is important, is partly because of the stability of the structure and partly because the elements has to be mounted in a convenient way. The result also shows that it is more difficult to place the reinforcement in the twin walls than in an in-situ concrete wall. The consequence of this is that twin walls may need more space than an in-situ concrete wall to achieve the same load capacity.

  • 226.
    Joneby, Annika
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik, Byggteknik.
    Jonsson Norling, Sarah
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik, Byggteknik.
    Infästning och montering av fasadskivor: En utvärdering av lämpliga metoder2014Independent thesis Basic level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Enstegstätade putsade fasader har använts mycket vid byggproduktion av bostäder de senaste årtiondena. Efter att många av byggnaderna drabbats av fuktskador rekommenderas det istället att man bygger tvåstegstätade ventilerade fasader. Detta är enkelt att utföra med möjlighet till stor variation genom att använda fasadskivor.

    Tillsammans med Uppsala Universitet har uppdragsgivare till detta examensarbete varit NCC i Uppsala. Syftet med arbetet är att vara till framtida hjälp för projekteringsledare, inköpare och platschefer i valet av infästningssystem till projekt med fasadskivor. Projektet som studeras för att inhämta kunskap är Kvarntornen i Uppsala, en elvavåningsbyggnad med fasad av aluminiumskivor. I projektet används NCCs typyttervägg; en utfackningsvägg med träreglar.

    Examensarbetet har bestått av intervjuer med personer som arbetar/har arbetat med fasadskivor och dess infästning, till exempel leverantörer och personer från tidigare projekt på NCC. De faktorer som står i fokus för examensarbetet är materialåtgång, arbetsmiljö och kostnad för att undersöka vilka alternativ för infästningssystem och byggnadsställningar som är möjliga att använda vid projekt Kvarntornen.

    Resultatet visar att det är mest lönsamt att använda sig av ett system som består av horisontella profiler som fästs i utfackningsväggens reglar och sedan vertikal läkt som fästs i profilerna där infästning av fasadskivorna kan ske. Är det istället en yttervägg av betong finns fler alternativ för infästningsmetod. Som ställning rekommenderas att använda en arbetsplattform i form av klätterställning. Där det inte är möjligt att använda klätterställning på Kvarntornen är det enda rimliga alternativet att använda en hängställning.

    Slutsatsen av examensarbetet är en projekteringsanvisning för framtida projekt där man väljer att använda fasadskivor i kombination med utfackningsvägg.

  • 227.
    Jonsson, Henrik
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaci.
    Öhman-Mägi, Caroline
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Alderborn, Göran
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaci.
    Isaksson, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Frenning, Göran
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaci.
    Crack nucleation and propagation in microcrystalline-cellulose based granules subject to uniaxial and triaxial load2019Inngår i: International Journal of Pharmaceutics, ISSN 0378-5173, E-ISSN 1873-3476, Vol. 559, s. 130-137Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cracking patterns in four kinds of granules, based on the common pharmaceutical excipient microcrystalline cellulose (MCC) and subject to compressive load, were examined. The initial pore structure and the location of initial failure under uniaxial compression were assessed using X-ray micro-computed tomography, whereas contact force development and onset of cracking under more complex compressive load were examined using a triaxial testing apparatus. Smoothed particle hydrodynamics (SPH) simulations were employed for numerical analysis of the stress distributions prior to cracking. For granules subject to uniaxial compression, initial cracking always occurred along the meridian and the precise location of the crack depended on the pore structure. Likewise, for granules subject to triaxial compression, the fracture plane of the primary crack was generally parallel to the dominant loading direction. The occurrence of cracking was highly dependent on the triaxiality ratio, i.e. the ratio between the punch displacements in the secondary and dominant loading directions. Compressive stresses in the lateral directions, induced by triaxial compression, prevented crack opening and fragmentation of the granule, something that could be verified by simulations. These results provide corroboration as well as further insights into previously observed differences between confined and unconfined compression of granular media.

  • 228.
    Jonsson, Åsa
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Skarsgård, Grim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Synchrotron tomography of pressboard during in-situ compression loading: Construction of compression rig, image acquisition procedure and methods for image processing2015Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    Pressboard, a high density cellulose-based material used for insulation in high voltage power transformers, exhibits stress relaxation during compressive loading. Investigating the micro-mechanical mechanisms responsible for the relaxation can lead to modifications of the production process to control the behaviour of the material. This investigation can be done using Synchrotron X-ray micro Computed Tomography which provides sufficient temporal and spatial resolutions to capture the stress relaxation process. In the present thesis, a compression rig for in-situ mechanical loading during X-ray micro Computed Tomography was designed and constructed. Local tomography scans with sub-micrometre resolution were obtained at the TOMCAT beamline at the Swiss Light Source, Paul Scherrer Institut, Switzerland. Several fibre segmentation techniques are analysed, together with Optical Flow and Digital Volume Correlation (DVC), methods used for estimating displacement, strain and velocity vector fields. Suitability of the tested methods is evaluated, and it is found that segmentation of individual fibres in a cellulose material of such a high density is probably not possible using currently available segmentation techniques. The movements during relaxation are measurable at the used resolution, and can be estimated using Optical Flow. Further work into correction of image shift due to rig movement between scans, as well as image artefact reduction should allow for measurement and comparisons of displacement during relaxation as well as DVC-computed strain measurements during compression, recreating earlier results.

  • 229.
    Jordebo, Robin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik, Byggteknik.
    Samverkan inom anläggningsbranschen: En studie om arbetsformens framgångsfaktorer2019Independent thesis Basic level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [en]

    For over 20 years Collaborative project has been used extensively in major construction projects. The aim of this study, together with Birka Markbyggnad AB, has been to investigate the success factors, risks, pros and cons with a focus on contract forms and leadership. This study will then be used by Birka in order to increase competence and also estimate employee demeanor towards the project model within Skanska.

    This study has mainly been carried out as a qualitative study. Initially, information has been gathered through literature, followed by an interview study of five people, as well as a quantitative questionnaire from employees’ experiences of collaborative projects. The conclusion of this study shows that the construction industry has many different perceptions and models of what collaborative project actually entails. With the new ISO 44001 standard, the hope is to clarify the project model.  The survey also shows that leaderships typically differs in a collaborative project in the form of more reserved management decree. 

    In general, literature shows that the model has no direct advantages nor disadvantages, while the interview study advocates a turnkey contract in collaboration. The conclusion is: a proper contract and a clear cooperation model is the way to a long-term sustainable and profitable collaborative project where the best end product is achieved.

  • 230.
    Josefsson, Gabriella
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Elasticity of Cellulose Nanofibril Materials2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The demand for renewable load-carrying materials is increasing with increasing environmental awareness. Alternative sources for materials manufacturing and design have to be investigated in order to replace the non-biodegradable materials. The work presented in this thesis investigates structure-property relations of such renewable materials based on cellulose nanofibrils. Cellulose is the most abundant polymer on earth and exists in both ordered and disordered phases, where the ordered crystalline cellulose shows excellent mechanical properties. The celluloses nanofibril is composed of partly crystalline cellulose where the stiff crystal regions, or crystallites, are orientated in the axial direction of the fibrils. The cellulose nanofibrils have a high aspect ratio, i.e. length to diameter ratio, with a diameter of less than 100 nm and a length of some micrometres. In the presented work, different properties of the cellulose nanofibril were studied, e.g. elastic properties, structure, and its potential as a reinforcement constituent. The properties and behaviour of the fibrils were studied with respect to different length scales, from the internal structure of the cellulose nanofibril, based on molecular dynamic simulations, to the macroscopic properties of cellulose nanofibril based materials. Films and composite materials with in-plane randomly oriented fibrils were produced. Properties of the cellulose nanofibril based materials, such as stiffness, thickness variation, and fibril orientation distribution, were investigated, from which the effective elastic properties of the fibrils were determined. The studies showed that a typical softwood based cellulose nanofibril has an axial stiffness of around 65 GPa. The properties of the cellulose nanofibril based materials are highly affected by the dispersion and orientation of the fibrils. To use the full potential of the stiff fibrils, well dispersed and oriented fibrils are essential. The orientation distribution of fibrils in hydrogels subjected to a strain was therefore investigated. The study showed that the cellulose nanofibrils have high ability to align, where the alignment increased with increased applied strain.

    Delarbeid
    1. Prediction of elastic properties of nanofibrillated cellulose from micromechanical modeling and nano-structure characterization by transmission electron microscopy
    Åpne denne publikasjonen i ny fane eller vindu >>Prediction of elastic properties of nanofibrillated cellulose from micromechanical modeling and nano-structure characterization by transmission electron microscopy
    Vise andre…
    2013 (engelsk)Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 20, nr 2, s. 761-770Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Cellulose-based materials have a great potential in terms of mechanical performance, since crystalline cellulose is known to have excellent stiffness along the main axis. This potential is not completely fulfilled in structural wood materials and in composite materials, due to structural inhomogeneities, misalignment, voids etc. on several length scales. This study investigates the difference in stiffness of nanofibrillated cellulose (NFC) compared to that of cellulose crystallites, based on nanostructural characterization, image analysis and micromechanical modeling. Nanofibrillated cellulose is believed to be composed of a distribution of crystallites in an amorphous matrix, and it is assumed to represent the distribution of the crystalline allomorph I-beta. To predict the elastic properties of NFC, a micromechanical model based on a Mori-Tanaka approach and self-consistent scheme was used. The input data, i.e. orientation distribution, aspect ratio and volume fraction of these crystalline regions, were estimated from image analysis of transmission electron micrographs. The model predicts a ca. 56 % loss of stiffness of NFC compared to that of cellulose crystals along the main axis.

    Emneord
    Nanofibrillated cellulose, Elastic properties, Micromechanics, Modelling, Transmission electron microscopy
    HSV kategori
    Forskningsprogram
    Teknisk fysik med inriktning mot tillämpad mekanik
    Identifikatorer
    urn:nbn:se:uu:diva-197625 (URN)10.1007/s10570-013-9868-8 (DOI)000315480400017 ()
    Tilgjengelig fra: 2013-04-03 Laget: 2013-04-02 Sist oppdatert: 2017-12-06bibliografisk kontrollert
    2. Stiffness contribution of cellulose nanofibrils to composite materials
    Åpne denne publikasjonen i ny fane eller vindu >>Stiffness contribution of cellulose nanofibrils to composite materials
    2014 (engelsk)Inngår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 51, nr 5, s. 945-953Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Nanocomposites, reinforced by different types of cellulose fibrils, have gained increased interest the last years due to the promising mechanical properties. There is a lack of knowledge about the mechanical properties of the cellulose fibrils, and their contribution to the often claimed potential of the impressive mechanical performance of the nanocomposites. This paper investigates the contribution from different types of cellulose nanofibril to the overall elastic properties of composites. A multiscale model is proposed, that allows back-calculation of the elastic properties of the fibril from the macroscopic elastic properties of the composites. The different types of fibrils used were nanofibrillated cellulose from wood, bacterial cellulose nano-whiskers and microcrystalline cellulose. Based on the overall properties of the composite with an unaged polylactide matrix, the effective longitudinal Young's modulus of the fibrils was estimated to 65 GPa for the nanofibrillated cellulose, 61 GPa for the nano whiskers and only 38 GPa for the microcrystalline cellulose. The ranking and absolute values are in accordance with other studies on nanoscale morphology and stiffness estimates. Electron microscopy revealed that in the melt-processed cellulose nanofibril reinforced thermoplastics, the fibrils tended to agglomerate and form micrometer scale platelets, effectively forming a microcomposite and not a nanocomposite. This dispersion effect has to be addressed when developing models describing the structure-property relations for cellulose nanofibril composites.

    Emneord
    Nanocomposite, Cellulose nanofibrils, Elastic properties, Multiscale modeling, Inverse modeling
    HSV kategori
    Forskningsprogram
    Teknisk fysik med inriktning mot tillämpad mekanik
    Identifikatorer
    urn:nbn:se:uu:diva-220777 (URN)10.1016/j.ijsolstr.2013.11.018 (DOI)000331158400004 ()
    Tilgjengelig fra: 2014-03-24 Laget: 2014-03-20 Sist oppdatert: 2017-12-05bibliografisk kontrollert
    3. Elastic models coupling the cellulose nanofibril to the macroscopic film level
    Åpne denne publikasjonen i ny fane eller vindu >>Elastic models coupling the cellulose nanofibril to the macroscopic film level
    2015 (engelsk)Inngår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 5, nr 71, s. 58091-58099Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The mechanical behaviour of cellulose nanofibrils is typically characterized by casting thin films and performing tensile tests on strips cut from these films. When comparing the stiffness of different films, the stiffness of the nanofibrils is only qualitatively and indirectly compared. This study provides some schemes based on various models of fibre networks, or laminated films, which can be used to assess the inherent stiffness of the nanofibrils from the stiffness of the films. Films of cellulose nanofibrils from different raw materials were manufactured and the elastic properties were measured. The expressions relating the nanofibril stiffness and the film stiffness were compared for the presented models. A model based on classical laminate theory showed the best balance between simplicity and adequacy of the underlying assumptions among the presented models. Using this model, the contributing nanofibril stiffness was found to range from 20 to 27 GPa. The nanofibril stiffness was also calculated from mechanical properties of nanofibril films found in the literature and compared with measurements from independent test methods of nanofibril stiffness. All stiffness values were found to be comparable and within the same order of magnitude.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-240247 (URN)10.1039/c5ra04016g (DOI)000357805500100 ()
    Tilgjengelig fra: 2015-01-06 Laget: 2015-01-06 Sist oppdatert: 2017-12-05bibliografisk kontrollert
    4. Nanorobotic Testing to Assess the Stiffness Properties of Nanopaper
    Åpne denne publikasjonen i ny fane eller vindu >>Nanorobotic Testing to Assess the Stiffness Properties of Nanopaper
    Vise andre…
    2014 (engelsk)Inngår i: IEEE Transactions on robotics, ISSN 1552-3098, E-ISSN 1941-0468, Vol. 30, nr 1, s. 115-119Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    This paper deals with the nanorobotic and nondestructive assessment of the stiffness properties of nanopaper made of microfibrillated cellulose. Back-calculations of the Young's modulus show the agreement of the newly found results with conventional tensile testing results, therewith proving nanorobotics as a reasonable complement for conventional testing.

    Emneord
    Automatic testing, bending testing, elastic properties, materials testing, mechanical properties, mechanical testing, microfibrillated cellulose, nanorobotics, scanning electron microscopy (SEM), tensile testing
    HSV kategori
    Forskningsprogram
    Teknisk fysik med inriktning mot tillämpad mekanik
    Identifikatorer
    urn:nbn:se:uu:diva-221005 (URN)10.1109/TRO.2013.2283409 (DOI)000331301900013 ()
    Tilgjengelig fra: 2014-03-25 Laget: 2014-03-24 Sist oppdatert: 2017-12-05bibliografisk kontrollert
    5. Thickness variability of cellulose nanofibril films: Measurement and implications for mechanical characterization
    Åpne denne publikasjonen i ny fane eller vindu >>Thickness variability of cellulose nanofibril films: Measurement and implications for mechanical characterization
    (engelsk)Artikkel i tidsskrift (Annet vitenskapelig) Submitted
    Abstract [en]

    To investigate the properties of different types of cellulose nanofibrils (CNFs), films are often produced. CNF films are easy to manufacture and relatively straightforward to characterize. Accurate measurements of the tensile properties of the films are often performed from which the mechanical properties of the films are determined. However, accurate measurment of the film thickness is often neglected which is an important property when defining the elastic modulus and strength of a CNF film. Many papers dealing with CNF films measure the film thickness with a micrometer screw gauge. The thicknesses that are measured in such way are the maximum thicknesses resulting in a significant error when determine mechanical properties of films with a high variability of local thickness, such as unsmooth CNF films. In this paper, the statistical distribution of CNF film thickness has been investigated by scanning electron microscopy of film cross-sections. Scale factors are proposed to relate the average thickness to the maximum thickness over a cross-section segment for films of different CNFs. Such scale factors are applicable to estimate the strength and stiffness, which are usally underestimated when using thickness measurements undertaken with a micrometer screw gauge. The maximum thickness, measured with a micrometer screw gauge, was as much as 95% higher than the average thickness. This effect is significant for films that show uneven surfaces resulting from inefficient CNF fibrillation. For chemical pretreatment and several passes through the homogenizer in the CNF manufacturing process, the effect is considerably smaller, but not negligible in characterization of mechanical properties. For further investigation of the thickness distribution, various three-parametric distributions with a lower bound and an upper tail all gave a fitting approximation to the experimental data.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-240248 (URN)
    Tilgjengelig fra: 2015-01-06 Laget: 2015-01-06 Sist oppdatert: 2015-03-09
    6. Fibril orientation redistribution induced by stretching of cellulose nanofibril hydrogels
    Åpne denne publikasjonen i ny fane eller vindu >>Fibril orientation redistribution induced by stretching of cellulose nanofibril hydrogels
    2015 (engelsk)Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, nr 21, artikkel-id 214311Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The mechanical performance of materials reinforced by cellulose nanofibrils is highly affected by the orientation of these fibrils. This paper investigates the nanofibril orientation distribution of films of partly oriented cellulose nanofibrils. Stripes of hydrogel films were subjected to different amount of strain and, after drying, examined with X-ray diffraction to obtain the orientation of the nanofibrils in the films, caused by the stretching. The cellulose nanofibrils had initially a random in-plane orientation in the hydrogel films and the strain was applied to the films before the nanofibrils bond tightly together, which occurs during drying. The stretching resulted in a reorientation of the nanofibrils in the films, with monotonically increasing orientation towards the load direction with increasing strain. Estimation of nanofibril reorientation by X-ray diffraction enables quantitative comparison of the stretch-induced orientation ability of different cellulose nanofibril systems. The reorientation of nanofibrils as a consequence of an applied strain is also predicted by a geometrical model of deformation of nanofibril hydrogels. Conversely, in high-strain cold-drawing of wet cellulose nanofibril materials, the enhanced orientation is promoted by slipping of the effectively stiff fibrils.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-240249 (URN)10.1063/1.4922038 (DOI)000355925600038 ()
    Tilgjengelig fra: 2015-01-06 Laget: 2015-01-06 Sist oppdatert: 2017-12-05bibliografisk kontrollert
  • 231.
    Josefsson, Gabriella
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Ahvenainen, Patrik
    Department of Physics, University of Helsinki, Helsinki, Finland.
    Ezekiel Mushic, Ngesa
    Department of Fibre and Polymer Technology and Wallenberg Wood Science Centre, Royal Institute of Technology (KTH).
    Gamstedt, Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Fibril orientation redistribution induced by stretching of cellulose nanofibril hydrogels2015Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, nr 21, artikkel-id 214311Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mechanical performance of materials reinforced by cellulose nanofibrils is highly affected by the orientation of these fibrils. This paper investigates the nanofibril orientation distribution of films of partly oriented cellulose nanofibrils. Stripes of hydrogel films were subjected to different amount of strain and, after drying, examined with X-ray diffraction to obtain the orientation of the nanofibrils in the films, caused by the stretching. The cellulose nanofibrils had initially a random in-plane orientation in the hydrogel films and the strain was applied to the films before the nanofibrils bond tightly together, which occurs during drying. The stretching resulted in a reorientation of the nanofibrils in the films, with monotonically increasing orientation towards the load direction with increasing strain. Estimation of nanofibril reorientation by X-ray diffraction enables quantitative comparison of the stretch-induced orientation ability of different cellulose nanofibril systems. The reorientation of nanofibrils as a consequence of an applied strain is also predicted by a geometrical model of deformation of nanofibril hydrogels. Conversely, in high-strain cold-drawing of wet cellulose nanofibril materials, the enhanced orientation is promoted by slipping of the effectively stiff fibrils.

  • 232.
    Josefsson, Gabriella
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Berthold, F.Gamstedt, E. KristoferUppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Estimation of the elastic properties of cellulose nanofibrils from the elastic properties of biobased nanocomposites2013Konferanseproceedings (Fagfellevurdert)
  • 233.
    Josefsson, Gabriella
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Berthold, Fredrik
    Gamstedt, Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Stiffness contribution of cellulose nanofibrils to composite materials2014Inngår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 51, nr 5, s. 945-953Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nanocomposites, reinforced by different types of cellulose fibrils, have gained increased interest the last years due to the promising mechanical properties. There is a lack of knowledge about the mechanical properties of the cellulose fibrils, and their contribution to the often claimed potential of the impressive mechanical performance of the nanocomposites. This paper investigates the contribution from different types of cellulose nanofibril to the overall elastic properties of composites. A multiscale model is proposed, that allows back-calculation of the elastic properties of the fibril from the macroscopic elastic properties of the composites. The different types of fibrils used were nanofibrillated cellulose from wood, bacterial cellulose nano-whiskers and microcrystalline cellulose. Based on the overall properties of the composite with an unaged polylactide matrix, the effective longitudinal Young's modulus of the fibrils was estimated to 65 GPa for the nanofibrillated cellulose, 61 GPa for the nano whiskers and only 38 GPa for the microcrystalline cellulose. The ranking and absolute values are in accordance with other studies on nanoscale morphology and stiffness estimates. Electron microscopy revealed that in the melt-processed cellulose nanofibril reinforced thermoplastics, the fibrils tended to agglomerate and form micrometer scale platelets, effectively forming a microcomposite and not a nanocomposite. This dispersion effect has to be addressed when developing models describing the structure-property relations for cellulose nanofibril composites.

  • 234.
    Josefsson, Gabriella