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  • 1.
    Afshar, R
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    van Dijk, N.P.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Bjurhager, Ingela
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Comparison of experimental testing and finite element modelling of a replica of a section of the Vasa warship to identify the behaviour of structural joints2017In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 147, p. 62-76Article in journal (Refereed)
    Abstract [en]

    Modelling in design of new support systems necessitates the joint stiffness of the existing wooden structures. In valuable structures, e.g. in cultural heritage, or structures with inaccessible joints, these stiffness values must be estimated, e.g. by testing joints in tailored replicas of the original parts. Although a simplified structure, the replica, can call for finite element (FE) modelling to capture the stiffness parameters. The first step in such a process is to compare FE predictions with experimental tests, for validation purposes. The reasons for unavoidable differences in load-displacement behaviour between model predictions and experimental test should be identified, and then possibly remedied by an improved model. Underlying causes like the complex shape of joints, geometrical uncertainties, contact mechanisms and material nonlinearity are generally too computationally expensive to be included in a full-scale model. It is therefore convenient to collect such effects in the contact penalty stiffness in the joint contact areas where stresses are high, which influences the resulting joint stiffness. A procedure for this is here illustrated for the case of the 17th century Vasa shipwreck A replica of a section of the ship has been constructed, and its joints were tested in bending-compression, in-plane shear and rotation. The FE simulations showed stiffer behaviour than the experimental results. Therefore, a normal penalty stiffness in contact surfaces of the joint were introduced, and used as a calibration parameter to account for the simplifying assumptions or indeliberate imprecision in the model, e.g. concerning boundary conditions, material properties and geometrical detail. The difference between numerical predictions and experimental results could then be significantly reduced, with a suitable normal penalty stiffness value. Once an acceptable finite element model has been obtained, it is shown how this can be used to identify stiffness values for joints in the physical structure with compensation for degradation of material properties due to aging and conservation treatment.

  • 2.
    Afshar, Reza
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Ahlgren, Anders
    Vasa museum.
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Characterization of mechanical properties of Vasa oak and their application in a full-scale numerical model for support assessment2019Conference paper (Other academic)
    Abstract [en]

    The 17th century Vasa shipwreck is a well-known object of cultural heritage. According to geodetic measurements inside and outside of the ship as well as on the support structure, the ship is sinking onto its cradle. The analysis of measurements showed the ship undergoes continued deformation with increasing strain. Previous research projects on the Vasa ship have largely been focused on the chemical degradation of the Vasa oak, which concerns the waterlogged polyethylene glycol (PEG) impregnated oak wood. The main goal was to provide understanding of the degradation mechanisms and possible remedies to mitigate the chemical decay. In this paper, a review is presented of previous research in term of characterization of mechanical properties, and effects of PEG and moisture on the mechanical behaviour of the Vasa oak. In addition, a full-scale finite-element model of the Vasa ship has been developed to assess its current and future structural behaviour, as well as a tool to design an improved support structure. The mechanical properties, defined in the model in terms of orthotropic elastic engineering constants, have been determined in previous work. Moreover, creep properties of the archaeological wood material have been and are being characterized, so that the model can be extended by extrapolation to predict future deformation. Geodetic measurements have been used for validation of the static model. The approach undertaken in this project could hopefully be useful in design strategies of improved support for other aging and deforming wood structures in cultural heritage.

  • 3.
    Afshar, Reza
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Alavyoon, Navid
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Ahlgren, Anders
    Swedish National Maritime Museums, the Vasa Museum.
    van Dijk, Nico P.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Vorobyev, Alexey
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Gamstedt, Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    A full-scale finite-element model of the Vasa ship2017In: Proceedings of ECCOMAS Thematic Conference CompWood 2017: Computational Methods in Wood Mechanics, 2017Conference paper (Refereed)
    Abstract [en]

    A full-scale model of the 17th century Vasa shipwreck has been developed to assess its current and future structural stability as well as design an improved support structure. A wireframe model, consisting of only lines, points and curves to describe the geometry of the ship, has been provided by the Vasa museum. It has been developed based on geodetic measurements using a total station. From this wireframe model, a three-dimensional (3D) model comprising solid bodies for solid-like parts (i.e. hull and keel), surfaces for the shell-like components (deck planks) and lines for beam-like constituents (deck beams) has been developed in Creo Parametric 3D software. This geometric model has been imported in finite-element software, Ansys, for further development of the stiffeners (knees, riders, stanchions, masts, etc.), adjustment of the correct location of deck beams and, finally, structural analyses of the entire ship (Figure 1). The procedure for selection of the different types of elements in the finite-element (FE) model, the definition of orthotropic material properties for the timber structure and preliminary results are discussed in this paper. Experiences drawn from this engineering project may also be useful in development of finite element models for structural assessment of other complex wooden structures in cultural heritage.

  • 4.
    Bermejo, Daniel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry.
    Kadekar, Sandeep
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry.
    Tavares da Costa, Marcus Vinicius
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Podiyan, Oommen
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Hilborn, Jöns
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Varghese, Oommen P.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry. Uppsala University, Science for Life Laboratory, SciLifeLab.
    First Aldol-Crosslinked Hyaluronic Acid Hydrogel: Fast and Hydrolytically Stable Gel with Tissue Adhesive PropertiesIn: Chemical Sciences Journal, ISSN 2150-3494Article in journal (Refereed)
    Abstract [en]

    Currently, there are limited approaches to tailor 3D scaffolds crosslinked with a stable covalent C-C bond that does not require any catalysts or initiators. We present here the first hydrogels employing aldol condensation chemistry that exhibit exceptional physicochemical properties. We investigated the aldol-crosslinking chemistry using two types of aldehyde-modified hyaluronic acid (HA) derivatives, namely; an enolizable HA-aldehyde (HA-Eal) and a non-enolizable HA-aldehyde (HA-Nal). Hydrogels formed using HA-Eal demonstrate inferior crosslinking efficiency (due to intramolecular loop formation), when compared with hydrogels formed by mixing HA-Eal and HA-NaI leading to a cross-aldol product. The change in mechanical properties as a result of crosslinking at different pH is determined using rheological measurements and is interpreted in terms of molecular weight between cross-links (Mc). The novel HA cross-aldol hydrogels demonstrate excellent hydrolytic stability and favorable mechanical properties but allow hyaluronidase mediated enzymatic degradation. Interestingly, residual aldehyde functionality within the aldol product leads to adhesion to tissue as demonstrated by bonding two bone tissues. The aldehyde functionality also permits facile post-synthetic modifications with nucleophilic reagents such as Alexa FluorTM 488. Finally, we demonstrate that the novel hydrogel is biocompatible with encapsulated stem cells that show a linear rate of expansion in our 3–6 days of study.

  • 5.
    Bermejo-Velasco, Daniel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry.
    Kadekar, Sandeep
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry.
    Tavares da Costa, Marcus Vinicius
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Oommen, Oommen P.
    Tampere Univ, Bioengn & Nanomed Lab, Fac Med & Hlth Technol, Korkeakoulunkatu 3, Tampere 33720, Finland;Tampere Univ, BioMediTech Inst, Korkeakoulunkatu 3, Tampere 33720, Finland.
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Hilborn, Jöns
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry.
    Varghese, Oommen P.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry.
    First Aldol Cross-Linked Hyaluronic Acid Hydrogel: Fast and Hydrolytically Stable Hydrogel with Tissue Adhesive Properties2019In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, no 41, p. 38232-38239Article in journal (Refereed)
    Abstract [en]

    Currently, there are limited approaches to tailor 3D scaffolds cross-linked with a stable covalent C-C bond that does not require any catalysts or initiators. We present here the first hydrogels employing aldol condensation chemistry that exhibit exceptional physicochemical properties. We investigated the aldol-cross-linking chemistry using two types of aldehyde-modified hyaluronic acid (HA) derivatives, namely, an enolizable HA-aldehyde (HA-EaI) and a non-enolizable HA-aldehyde (HA-NaI). Hydrogels formed using HA-EaI demonstrate inferior cross linking efficiency (due to intramolecular loop formation), when compared with hydrogels formed by mixing HA-EaI and HA-NaI leading to a cross-aldol product. The change in mechanical properties as a result of cross-linking at different pH values is determined using rheological measurements and is interpreted in terms of molecular weight between cross-links (Me). The novel HA cross-aldol hydrogel demonstrate excellent hydrolytic stability and favorable mechanical properties but allow hyaluronidase-mediated enzymatic degradation. Interestingly, residual aldehyde functionality within the aldol product rendered the tissue adhesive properties by bonding two bone tissues. The aldehyde functionality also facilitated facile post-synthetic modifications with nucleophilic reagents. Finally, we demonstrate that the novel hydrogel is biocompatible with encapsulated stem cells that show a linear rate of expansion in our 3-6 days of study.

  • 6.
    Bjurhager, Ingela
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Gamstedt, E. KristoferUppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Predicting creep rate in archeological wood from theVasa ship – a first appraoch2012Conference proceedings (editor) (Refereed)
  • 7.
    Bjurhager, Ingela
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Gamstedt, Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Keunecke, Daniel
    Niemz, Peter
    Berglund, Lars A.
    Mechanical performance of yew (Taxus baccata L.) from a longbow perspective2013In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 67, no 7, p. 763-770Article in journal (Refereed)
    Abstract [en]

    Yew (Taxus baccata L.) longbow was the preferred weapon in the Middle Ages until the emergence of guns. In this study, the tensile, compression, and bending properties of yew were investigated. The advantage of yew over the other species in the study was also confirmed by a simple beam model. The superior toughness of yew has the effect that a yew longbow has a higher range compared with bows made from other species. Unexpectedly, the mechanical performance of a bow made from yew is influenced by the juvenile-to-mature wood ratio rather than by the heartwood-to-sapwood ratio. A yew bow is predicted to have maximized performance at a juvenile wood content of 30-50%, and located at the concave side (the compressive side facing the bowyer). Here, the stiffness and yield stress in compression should be as high as possible.

  • 8.
    Bjurhager, Ingela
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Halonen, Helena
    Wallenberg Wood Science Center, KTH, Stockholm.
    Lindfors, Eva-Lisa
    Innventia AB, Stockholm.
    Iversen, Tommy
    Wallenberg Wood Science Center, KTH, Stockholm.
    Almkvist, Gunnar
    Dept of Chemistry, SLU, Uppsala.
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Berglund, Lars A.
    Wallenberg Wood Science Center, KTH, Stockholm.
    State of Degradation in Archeological Oak from the 17th Century Vasa Ship: Substantial Strength Loss Correlates with Reduction in (Holo)Cellulose Molecular Weight2012In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 13, no 8, p. 2521-2527Article in journal (Refereed)
    Abstract [en]

    In 1628, the Swedish warship Vasa capsized on her maiden voyage and sank in the Stockholm harbor. The ship was recovered in 1961 and, after polyethylene glycol (PEG) impregnation, it was displayed in the Vasa museum. Chemical investigations of the Vasa were undertaken in 2000, and extensive holocellulose degradation was reported at numerous locations in the hull. We have now studied the longitudinal tensile strength of Vasa oak as a function of distance from the surface. The PEG-content, wood density, and cellulose microfibril angle were determined. The molar mass distribution of holocellulose was determined as well as the acid and iron content. A good correlation was found between the tensile strength of the Vasa oak and the average molecular weight of the holocellulose, where the load bearing cellulose microfibril is the critical constituent The mean, tensile strength is reduced by approximately 40%, and the most affected areas show a reduction of up to 80%. A methodology is,, developed where variations in density, cellulose microfibril angle, and PEG content are taken into account, so that. cell wall effects can be evaluated in wood samples with different rate of impregnation and morphologies.

  • 9.
    Bjurhager, Ingela
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Vorobyev, AlexeyUppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.van Dijk, NicoUppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.Gamstedt, E. KristoferUppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.Ahlgren, AndersOlofsson, Magnus
    Investigation of time-dependent deformation of wood from the warship Vasa2013Conference proceedings (editor) (Refereed)
  • 10.
    Chinga-Carrasco, Gary
    et al.
    Paper and Fibre Research Institute (PFI), Norway.
    Miettinen, Arttu
    Department of Physics, University of Jyväskylä, Finland.
    Luengo Hendriks, Cris L.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Centre for Image Analysis. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Kataja, Markku
    Department of Physics, University of Jyväskylä, Finland.
    Structural Characterisation of Kraft Pulp Fibres and Their Nanofibrillated Materials for Biodegradable Composite Applications2011In: Nanocomposites and Polymers with Analytical Methods / [ed] Cuppoletti, John, InTech , 2011, p. 243-260Chapter in book (Refereed)
  • 11.
    Duanmu, Jie
    et al.
    Functional Materials Center, Laboratory of Polymer Technology, Åbo Akademi University, Åbo, Finland.
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Pranovich, Andrey
    Laboratory of Wood and Paper Chemistry, Åbo Akademi University, Åbo, Finland.
    Rosling, Ari
    Functional Materials Center, Laboratory of Polymer Technology, Åbo Akademi University, Åbo, Finland.
    Allyloxy-modified starch with low degree of substitution for fiber reinforced thermoset starch composites2011In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 71, no 4, p. 520-527Article in journal (Refereed)
    Abstract [en]

    In the present work dough moulding compound premixes of allyl glycidyl ether modified (AGE)-potato starch, (DS) = 0.2, has been prepared and tested for its fiber reinforced composite properties. The AGE-starch was hydrolyzed with a-amylase under neutral condition for 6 h at 45 degrees C for improved process ability. The grafting and hydrolytic scission was confirmed by nuclear magnetic resonance (NMR) and size exclusion chromatography (SEC), respectively. Homogeneous composite premixes of AGE-starch, wood fibers, various amount of glycerol and ethylene glycol dimethacrylate were successfully mixed with a Brabender-kneader at 55 degrees C and cured by compression molding at 150 degrees C using 2 wt% of dibenzoyl peroxide. Adding 5 wt% of glycerol did not reduce the ultimate strength of the composites: 10% glycerol reduced the strength from 60 MPa to 40 MPa, and 16% glycerol to 14 MPa. The results with 5 wt% glycerol are comparable with earlier achieved results. The water absorption rate increased with increased glycerol content and the mechanical strength of the composites was lost completely when the moisture uptake reached 15 wt%.

  • 12. Duanmu, Jie
    et al.
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Rosling, Ari
    Bulk composites from microfibrillated cellulose-reinforced thermoset starch made from enzymatically degraded allyl glycidyl ether-modified starch2012In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 46, no 25, p. 3201-3209Article in journal (Refereed)
    Abstract [en]

    Microfibrillated cellulose consists of nanoscale bundles of elementary microfibrils prepared, e.g. by the defibrillation of delignified wood pulp fibres in high-pressure homogenizers. In this study, microfibrillated cellulose was used to reinforce a thermoset starch plastic. The starch was modified with allyl glycidyl ether with a degree of substitution of 1.3, which was further hydrolyzed with alpha-amylase for 18 h yielding significantly improved processing properties. Dry premixes of all constituents were prepared by a stepwise drying process before sample manufacturing. The composite was cured by ethylene glycol dimethacrylate initiated with benzoyl peroxide during compression moulding at 150 degrees C. Scanning electron microscopy revealed some degree of porosity in the samples, where the dispersed microfibrillated cellulose network was detectable. Microfibrillated cellulose, even in relatively small additions (2 wt%, 5 wt% and 10 wt%), resulted in composites with rather good hygromechanical properties. The ultimate strength increased with microfibrillated cellulose content and reached values of comparable composites with 40 wt% softwood fibre. Importantly, the dimensional stability in water was much improved compared to similar composites reinforced with substantially larger weight fractions of softwood fibres.

  • 13. Fayet, P.
    et al.
    Neagu, R. C.
    Gamstedt, Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Mechnics-driven design optimized barrier films2015In: Proceedings of the AIMCAL Web Coating and Handling Conference, 2015, p. 10-Conference paper (Refereed)
  • 14.
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Moisture induced softening and swelling of natural cellulose fibres in composite applications2016In: 37th Riso International Symposium on Materials Science, 2016, article id 012003Conference paper (Refereed)
    Abstract [en]

    Composites based on natural cellulose fibres are susceptible to moisture. The fibres as well as the composite will inevitably soften and swell as moisture is absorbed. The intention of the present paper is to shed some light on the mechanisms behind softening and swelling. Also references to modelling work are made, to predict the moisture-induced dimensional stability. Characterisation techniques and models of such kind can be useful in choosing suitable fibres for improved moisture resistance, and identifying the main controlling parameters which affect the engineering consequences of moisture absorption. Understanding of the mechanisms and the main contributions to swelling can rationalise materials development. The examples shown in this review attempt to show the benefits by experimental mechanics and modelling in development of moisture resistant cellulose composites.

  • 15.
    Gamstedt, E. Kristofer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Afshar, Reza
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Ahlgren, Anders
    Swedish National Maritime Museums, the Vasa Museum, Stockholm, Sweden.
    Preserving the Vasa ship: Research and development of a new support structure2018Conference paper (Other academic)
  • 16.
    Gamstedt, E. Kristofer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Bader, T.K.Borst, K.
    Mixed numerical-experimental methods in woodmicromechanics2012Conference proceedings (editor) (Refereed)
  • 17.
    Gamstedt, E. Kristofer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Joffre, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Berthold, F.
    Monitoring of fibre length degradation during processing of short-fibre composites by use of X-ray computed tomography2013In: Proceedings of the 34th Risø International Symposium on Materials Science: Processing of fibre composites - Challenges for maximum materials performanc, Roskilde, Denmark: Technical University of Denmark , 2013Conference paper (Refereed)
  • 18.
    Gamstedt, E. Kristofer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Sandell, Robert
    Berthold, Fredrik
    Pettersson, Torbjörn
    Characterization of interfacial stress transfer ability of particulate cellulose composite materials2011In: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 43, no 11, p. 693-704Article in journal (Refereed)
    Abstract [en]

    Composites with cellulose reinforcements are steadily gaining increased use. The stress transfer ability between reinforcement and polymer matrix has a strong influence on mechanical properties like strength and fracture toughness. This work presents a method to assess the stress transfer ability between cellulose and polymer matrix from a model material with cellulose spheres embedded in a polymer matrix. Such a material show smaller variability compared with composites based on natural cellulose fibres, and is less cumbersome than single fibre tests with regard to interfacial characterization. Measured elastic moduli of particulate composites is compared with predicted values from a micromechanical model based on a composite sphere assembly in a self-consistent scheme with only a spring constant of an imperfect interface as fitting parameter expressed in Pa/m. This interface parameter is identified through inverse modelling and used to quantify stress-transfer ability of cellulose/polylactide and cellulose/polystyrene composite interfaces. A higher degree of interfacial interaction was found for the former. This ranking was corroborated by adhesive force measurements using a micrometre sized cellulose sphere attached to the end of a cantilever in an atomic force microscope. With the model microstructure of a cellulose-sphere composite, an interfacial efficiency parameter can be backed out from stiffness measurements to be used in e.g. ranking of different fibre surface treatments and choice of matrix in the development of stronger natural-fibre composites.

  • 19.
    Gamstedt, E. Kristofer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Ståhlberg, MartinBjurhager, IngelaAhlgren, AndersOlofsson, Magnus
    From creep characterization of Vasa oak towards design strategies of an improved support structure for the ship2011Conference proceedings (editor) (Refereed)
  • 20.
    Gamstedt, E. Kristofer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Sun, Fengzhen
    Department of Mechanical Engineering, Imperial College London, UK.
    Polymer physics in nanoscale cutting: Opportunities for improved control in nano-manufacturing?2018Conference paper (Refereed)
    Abstract [en]

    Nano-scale manufacturing imposes demands on prediction of cutting processes on small scales. Specifically for applications that include optical functions, means to control the process parameter to produce high quality and damage-free surfaces are of importance. Control through empirical testing may be time-consuming and costly. Predictive modelling schemes based on the underlying physical mechanisms could potentially be more generally applicable in manufacturing. The understanding of polymer physics and mechanics on sub-micrometre scale is emerging, and slowly but increasingly transferred from a fundamental research field to useful engineering applications. Nanoscale cutting of metals has been studied more and is better understood than that of polymers. For polymers, there are generally more complex interactions between deformation rates, temperature change and material transitions. These effects need to be included in physical models describing the cutting processes in polymers. Furthermore, the mechanical behaviour of polymers may be quite different on the nanoscale compared with macroscale. The material properties are frequently known to be size-dependent. This calls for development of experimental methods to characterize the material properties on the nanoscale, to be used in predictive modelling.

    In this work, we have used an ultramicrotome, normally intended for preparation of ultrathin samples for transmission electron microscopy, instrumented with piezoelectric transducers to measure the cutting forces on sections down to about 50 nm thickness of thermoplastic PMMA. With this equipment, it was possible to investigate the effects of cutting speed and cutting thickness on the formation of surface damage in a well-controlled and reproducible manner. Using atomic force microscopy, the surface damage was identified as shear yield bands triggered by adiabatic heating. A suitable physical model including these observed phenomena made it possible to link the processing conditions with the onset of damage formation, i.e. the transition between a high-quality transparent surface and a damaged uneven surface. A finite element model was developed to predict the formation of the undesired shear bands. From an engineering perspective, such an approach could be potentially useful in improved manufacturing control. The present example supports the idea that material mechanics can be integrated in nanoscale manufacturing. In the future, it is not unlikely that instrumented nanomachining will provide on-line feedback through physical predictive models to adjust the processing parameters (forces, speed, etc.) to maintain a sufficiently high product quality at the highest production rate.

  • 21.
    Gamstedt, Kristofer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Bader, Thomas K.
    de Borst, Karin
    Mixed numerical-experimental methods in wood micromechanics2013In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 47, no 1, p. 183-202Article in journal (Refereed)
    Abstract [en]

    Mixed numerical-experimental methods are increasingly used in various disciplines in materials science, recently also in wood micromechanics. Having a relatively irregular microstructure, direct interpretation of mechanical tests is not always possible since structurally specific properties are quantified rather than general material properties. The advent of combined numerical-experimental methods unlocks possibilities for a more accurate experimental characterization. A number of examples of mixed methods pertaining to both emerging experimental techniques and physical phenomena are presented: nano-indentation, moisture transport, digital-image correlation, dimensional instability and fracture of wood-based materials. Successful examples from other classes of materials are also presented, in an attempt to provide some ideas potentially useful in wood mechanics. Some general pit-falls in parameter estimation from experimental results are also outlined.

  • 22.
    Gamstedt, Kristofer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Bommier, Florian
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Madsen, B.
    Estimation of axial stiffness of plant fibres from compaction of non-woven mats2014In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 25, no 3, p. 035601-Article in journal (Refereed)
    Abstract [en]

    Plant fibres are known to show a large variability in stiffness, which makes it time-consuming to experimentally characterize this property by conventional tensile testing. In this work, an alternative method is used, where the average fibre stiffness is back-calculated from compaction tests of in-plane randomly oriented fibre mats. The model by Toll is used to relate the load-displacement curve from the test to the Young modulus of the fibre, taking into account the natural variability in fibre cross section. Several tests have been performed on hemp fibre mats and compared with results from single-fibre tensile testing. The average back-calculated Young's modulus of the fibres was 45 GPa, whereas the average value from tensile testing ranged from 30 to 60 GPa. The straightforward compaction test can be useful in ranking of fibre stiffness, provided that the mat is composed of well-separated fibres and not of twisted yarns.

  • 23.
    Gamstedt, Kristofer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Vorobyev, A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    van Dijk, N.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Bjurhager, Ingela
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Hassel, Ivon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Multiscale approach from micromechanics up towards creeping wood structures2014In: MS046A in Proceedings of the 11th Word Congress on Computational Mechanics (WCCM XI) and the 5th Europen Conference on Computational mechanics (ECCM V), 2014Conference paper (Refereed)
  • 24. Girlanda, O
    et al.
    Sahlen, F
    Joffre, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Gamstedt, Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Schmidt, L
    Forsberg, F
    Sjödahl, M
    Analysis of the micromechanical deformation in pressboard performed by X-ray microtomography2015In: 2015 IEEE Electrical Insulation Conference (EIC), 2015, p. 89-92Conference paper (Refereed)
    Abstract [en]

    A large number of electrical insulation components are produced in paper-based materials. Paper combines good insulating properties with the necessary mechanical and chemical stability. Paper consists of a system of fibers binding to each other creating a strong network. The presence of large open pores allows for impregnability of the material but also causes mechanical weakness in particular in the out-of-plane direction of the material. This aspect is important for pressboard components, where the resistance to compression stress is relevant for e.g. transformer windings. It is therefore relevant to understand the mechanisms that underlay the out-of-plane deformation of pressboard. In order to get a clear picture of the deformation patterns within the material, X-ray micro-computed tomography was used. Pressboard test pieces were subjected to in-situ out-of-plane compressive loading. 3D images of the sample could be captured before, during and after the loading sequence. Image analysis allowed for the definition of strain fields. The results revealed a strong correlation between the density variation within the sample and the strain calculated from the 3D images.

  • 25.
    Hassel, Ivon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Afshar, R
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Vorobyev, A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Bommier, F
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Gamstedt, K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Towards determination of local and overall displacements of the Vasa ship structure: Effect of its mechanical connections2014Conference paper (Refereed)
    Abstract [en]

    The warship Vasa from the 17th century must be preserved for the future generations. There are many concerns currently being addressed by ongoing research efforts. The support structure is one of them, which needs to be re-designed. In order to do this, the local and overall deformation of the Ship’s structure must be identified. The earlier impregnation of PEG on the Vasa material is causing the material to creep significantly more than oak without PEG, resulting in an increasing deformation of the ship. In addition to this, the effect of the mechanical connections of the ship needs to be considered. Experimental tests were performed on a 1:1 scale replica of a representative section of the Vasa ship. Different load cases were applied in order to represent the current situation of the vessel’s connections. Linear displacement gauges as well as non-contacting image correlation systems were used as measurement methods to analyze the behaviour of the test sample. A validated computer model, using finite element method (FEM) simulations, with Vasa-material properties will be used to calculate the stiffness coefficients, which will be included in a simplified full-computer model of the entire vessel. Based on the latter, the overall and local displacements will be obtained. This is a necessary input in a full numerical model of the ship to optimize a new support structure.

  • 26. Hirsch, J.-M.
    et al.
    Gamstedt, KristoferUppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.Sörensen, J.Rännar, L.-E.Carlbom, I.
    Virtual planning of reconstructions, production ofindividualized implants and transfer of the plan to the operating room incraniomaxillofacial surgery2012Conference proceedings (editor) (Refereed)
  • 27.
    Huo, Jinxing
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Dérand, Per
    Department of Oral and Maxillofacial Surgery, Skåne University Hospital.
    Rännar, Lars-Erik
    Sports Tech Research Centre, Mid Sweden University.
    Hirsch, Jan-Michaél
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Oral and Maxillofacial Surgery.
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Failure location predictoin by finite element analysis for an additive manufactured mandible implant2015In: Medical Engineering and Physics, ISSN 1350-4533, E-ISSN 1873-4030, Vol. 37, no 9, p. 862-869Article in journal (Refereed)
    Abstract [en]

    In order to reconstruct a patient with a bone defect in the mandible, a porous scaffold attached to a plate, both in a titanium alloy, was designed and manufactured using additive manufacturing. Regrettably, the implant fractured in vivo several months after surgery. The aim of this study was to investigate the failure of the implant and show a way of predicting the mechanical properties of the implant before surgery. All computed tomography data of the patient were preprocessed to remove metallic artefacts with metal deletion technique before mandible geometry reconstruction. The three-dimensional geometry of the patient's mandible was also reconstructed, and the implant was fixed to the bone model with screws in Mimics medical imaging software. A finite element model was established from the assembly of the mandible and the implant to study stresses developed during mastication. The stress distribution in the load-bearing plate was computed, and the location of main stress concentration in the plate was determined. Comparison between the fracture region and the location of the stress concentration shows that finite element analysis could serve as a tool for optimizing the design of mandible implants.

  • 28.
    Huo, Jinxing
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Hirsch, Jan-Michaél
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Oral and Maxillofacial Surgery.
    Deránd, Per
    Lund University.
    Rännar, Lars-Erik
    Mittuniversitetet.
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Finite Element Investigation of the In - Vivo Failure of a Titanium Alloy HumanJaw Implant2014Conference paper (Refereed)
    Abstract [en]

    In order to reconstruct a patient with a bone defect in the right lower jaw, a scaffold attached to a reconstruction plate, both in a titanium alloy, was designed and manufactured using three-dimensional printing technique. Regrettably the implant fractured in situ several months after surgery. This paper is orientated to investigate the reason for the implant’s failure and provide a way of predicting the mechanical properties of the implant before surgery. Preoperative, postoperative and implant-break computed tomography data of the patient were provided by the responsible surgeon. Metallic artifacts introduced by previous dental implants were removed with metallic deletion technique software beforehand. Three-dimensional volume of the patient’s jaw was thereafter reconstructed with trabecular bone removed based on the cleaned computed tomography data. The implant, screws and jaw were assembled together and meshed with triangular elements in Mimics 16.0. The assembly was imported into in-house software with surface mesh converted to linear tetrahedral mesh. Simulations were implemented under simplified but suitable loading conditions with the assumption that jaw was a linear elastic and homogeneous material. The stress distribution on the implant plate was calculated and the location of stress concentration on the plate was determined and then verified by the clinical data of the patient. This validated model could serve in the future as a tool for optimizing the design of jaw implants.

  • 29.
    Huo, Jinxing
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Rojas, RamiroKTH Royal Institute of Technology.Bohlin, JanUppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.Hilborn, JönsUppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.Gamstedt, E. KristoferUppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Parametric analysis of stiffness properties of coupled helical coils for implant application2013Conference proceedings (editor) (Refereed)
  • 30.
    Huo, Jinxing
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Rojas, Ramiro
    Bohlin, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry.
    Hilborn, Jöns
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry.
    Gamstedt, E Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Parametric elastic analysis of coupled helical coils for tubular implant applications: Experimental characterization and numerical analysis2014In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 29, p. 462-469Article in journal (Refereed)
    Abstract [en]

    Coupled helical coils show promising mechanical behavior to be used as tubular organ constructs, e.g., in trachea or urethra. They are potentially easy to manufacture by filament winding of biocompatible and resorbable polymers, and could be tailored for suitable mechanical properties. In this study, coupled helical coils were manufactured by filament winding of melt-extruded polycaprolactone, which was reported to demonstrate desired in vivo degradation speed matching tissue regeneration rate. The tensile and bending stiffness was characterized for a set of couple helical coils with different geometric designs, with right-handed and left-handed polymer helices fused together in joints where the filaments cross. The Young's modulus of unidirectional polycaprolactone filaments was characterized, and used as input together with the structural parameters of the coupled coils in finite element simulations of tensile loading and three-point bending of the coils. A favorable comparison of the numerical and experimental results was found, which paves way for use of the proposed numerical approach in stiffness design under reversible elastic conditions of filament wound tubular constructs.

  • 31.
    Huo, Jinxing
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics. Sandvik Min & Rock Technol, R&D Dept Min Tools, SE-81181 Sandviken, Sweden.
    van Dijk, Nico P.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Elastic properties of rhombic mesh structures based on computational homogenisation2018In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 172, p. 66-75Article in journal (Refereed)
    Abstract [en]

    Flat mesh structures are used in a wide variety of applications. In particular, meshes with a rhombic unit cell are frequently employed due to their simplicity and relative ease of manufacture. This paper studies the in-plane elastic properties of such a structure as a function of the geometrical parameters by means of homogenisation techniques. We compare predicted elastic in-plane properties (i) including only bending mode of the struts, cf. Gibson-Ashby model, (ii) including both bending and stretching modes of the struts, obtained by homogenisation using beam elements and (iii) by homogenisation using beam-spring elements accounting additionally for strut joint deformation, and (iv) numerical results of elastic properties obtained by homogenisation using solid elements. The expressions of the predicted elastic properties are presented in analytical form. The homogenised elastic properties accounting for both bending and stretching matches very well with those from the model including only bending. The axial deformation of struts thus has negligible impact on the overall elastic behaviour. The complex deformation in the strut joint was also captured in the homogenised using beam-spring elements, and the results agree better with the solid element results. It is concluded that a finite-element-based homogenisation approach could serve as a straightforward analytical method to obtain elastic properties of mesh structures. This approach automatically includes all deformation mechanisms as opposed to the classical unit cell analyses of bending beams.

  • 32.
    Jeong, Seung Hee
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Chen, Si
    Chalmers, Dept Microtechnol & Nanosci MC2, SE-41296 Gothenburg, Sweden..
    Huo, Jinxing
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Gamstedt, Erik Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Liu, Johan
    Chalmers, Dept Microtechnol & Nanosci MC2, SE-41296 Gothenburg, Sweden..
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Zhi-Bin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Wu, Zhigang
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Mechanically Stretchable and Electrically Insulating Thermal Elastomer Composite by Liquid Alloy Droplet Embedment2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 18257Article in journal (Refereed)
    Abstract [en]

    Stretchable electronics and soft robotics have shown unsurpassed features, inheriting remarkable functions from stretchable and soft materials. Electrically conductive and mechanically stretchable materials based on composites have been widely studied for stretchable electronics as electrical conductors using various combinations of materials. However, thermally tunable and stretchable materials, which have high potential in soft and stretchable thermal devices as interface or packaging materials, have not been sufficiently studied. Here, a mechanically stretchable and electrically insulating thermal elastomer composite is demonstrated, which can be easily processed for device fabrication. A liquid alloy is embedded as liquid droplet fillers in an elastomer matrix to achieve softness and stretchability. This new elastomer composite is expected useful to enhance thermal response or efficiency of soft and stretchable thermal devices or systems. The thermal elastomer composites demonstrate advantages such as thermal interface and packaging layers with thermal shrink films in transient and steady-state cases and a stretchable temperature sensor.

  • 33.
    Jeong, Seung Hee
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Chen, Si
    Chalmers University of Technology.
    Huo, Jinxing
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Gravier, Laurent
    University of Applied Sciences and Arts Western Switzerland.
    Gamstedt, Erik Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Liu, Johan
    Chalmers University of Technology.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Zhi-Bin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Wu, Zhigang
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology. Huazhong Univ Sci & Technol, State Key Lab Digital Mfg Equipment & Technol, Wuhan, Peoples R China.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thermal Elastomer Composites for Soft Transducers2015Conference paper (Refereed)
    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.

  • 34. Joffre, T.
    et al.
    Gamstedt, Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Passas, R.
    Dumont, P.
    Neagu, C.
    Moisture-induced deformation of wood fibres on the tracheid and cell-wall layer2011In: Proceedings of the Annual Workshop of COST Action FP0802: Hierarchical Structure and Mechanical Characterization of Wood, 2011, p. 89-90Conference paper (Refereed)
  • 35.
    Joffre, Thomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Girlanda, Orlando
    Forsberg, Fredrik
    Sahlén, Fredrik
    Sjödahl, Mikael
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    A 3D in-situ investigation of the deformation in compressive loading in the thickness direction of cellulose fiber mats2015In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 22, no 5, p. 2993-3001Article in journal (Refereed)
    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.

  • 36.
    Joffre, Thomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Isaksson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Dumont, Pierre J. J.
    Rolland du Roscoat, Sabine
    Sticko, Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Orgéas, Laurent
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    A method to measure moisture induced swelling properties of a single wood cell2016In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 56, p. 723-733Article in journal (Refereed)
  • 37.
    Joffre, Thomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Isaksson, PerUppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.Latil, P.Dumont, P.Gamstedt, KristoferUppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Identification of hygroelastic properties of the woodcell wall from 3D images obtained by X-ray synchrotron microtomography2012Conference proceedings (editor) (Refereed)
  • 38.
    Joffre, Thomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Miettinen, A.Berthold, F.Kataja, M.Gamstedt, E. KristoferUppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    X-ray micro-computed tomography investigation of agglomeration and fibre length degradation through the processing chain of wood fibre composite2013Conference proceedings (editor) (Refereed)
  • 39.
    Joffre, Thomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Miettinen, A.Isaksson, PerUppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.Wemersson, E.Gamstedt, E. KristoferUppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Effects of fibre agglomeration on strength of wood-fibre composites2012Conference proceedings (editor) (Refereed)
  • 40.
    Joffre, Thomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Miettinen, Arttu
    Berthold, Fredrik
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    X-ray micro-computed tomography investigation of fibre length degradation during the processing steps of short-fibre composites2014In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 105, p. 127-133Article in journal (Refereed)
  • 41.
    Joffre, Thomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Miettinen, Arttu
    Wernersson, Erik L. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Visual Information and Interaction. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    Isaksson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Effects of defects on the tensile strength of short-fibre composite materials2014In: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 75, p. 125-134Article in journal (Refereed)
  • 42.
    Joffre, Thomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Miettinen, Arttu
    Wernersson, Erik L. G.
    Isaksson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Gamstedt, Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Effects of defects on the tensile strength of short-fibre composite materials2014In: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 75, p. 125-134Article in journal (Refereed)
    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. 

  • 43.
    Joffre, Thomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Neagu, R. Cristian
    Bardage, Stig L.
    Gamstedt, Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Modelling of the hygroelastic behaviour of normal and compression wood tracheids2014In: Journal of Structural Biology, ISSN 1047-8477, E-ISSN 1095-8657, Vol. 185, no 1, p. 89-98Article in journal (Refereed)
    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.

  • 44.
    Joffre, Thomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wernersson, Erik L. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Visual Information and Interaction. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    Miettinen, Arttu
    Luengo Hendriks, Cris L.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Visual Information and Interaction. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Swelling of cellulose fibres in composite materials: Constraint effects of the surrounding matrix2013In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 74, p. 52-59Article in journal (Refereed)
  • 45.
    Josefsson, Gabriella
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    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 University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Fibril orientation redistribution induced by stretching of cellulose nanofibril hydrogels2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 21, article id 214311Article in journal (Refereed)
    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.

  • 46.
    Josefsson, Gabriella
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Berthold, F.Gamstedt, E. KristoferUppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Estimation of the elastic properties of cellulose nanofibrils from the elastic properties of biobased nanocomposites2013Conference proceedings (editor) (Refereed)
  • 47.
    Josefsson, Gabriella
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Berthold, Fredrik
    Gamstedt, Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Stiffness contribution of cellulose nanofibrils to composite materials2014In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 51, no 5, p. 945-953Article in journal (Refereed)
    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.

  • 48.
    Josefsson, Gabriella
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Chinga-Carrasco, Gary
    Paper and Fiber Research Institute (PFI AS), Trondheim, Norway.
    Gamstedt, Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Elastic models coupling the cellulose nanofibril to the macroscopic film level2015In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 5, no 71, p. 58091-58099Article in journal (Refereed)
    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.

  • 49.
    Josefsson, Gabriella
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Gamstedt, E. KristoferUppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.Berthold, F.Chinga-Carrasco, G.
    Bio-based composites of polylactic acid reinforcedwith nanofibrillated cellulose, nanowhisekers and microcrystalline cellulose:Estimation of the elastic properties of the fillers from elastic properties ofthe composites2012Conference proceedings (editor) (Refereed)
  • 50.
    Josefsson, Gabriella
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Gamstedt, E. KristoferUppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.Tanem, B.S.Li, Y.Vullum, P.E.
    Prediction of elastic properties of wood cellulosenanofibrils from ultrastructure using a self-consistent Mori-Tanaka model2012Conference proceedings (editor) (Refereed)
12 1 - 50 of 97
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