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  • 1.
    Al-Maqdasi, Zainab
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hajlane, Abdelghani
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Materials Science and Nano-engineering, Mohammed VI Polytechnic University, Benguerir, Morocco.
    Renbi, Abdelghani
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Ouarga, Ayoub
    Materials Science and Nano-engineering, Mohammed VI Polytechnic University, Benguerir, Morocco.
    Chouhan, Shailesh Singh
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Conductive Regenerated Cellulose Fibers by Electroless Plating2019In: Fibers, ISSN 2079-6439, Vol. 7, no 5, article id 38Article in journal (Refereed)
    Abstract [en]

    Continuous metallized regenerated cellulose fibers for advanced applications (e.g. multi-functional composites) are produced by electroless copper plating. Copper is successfully deposited on the surface of cellulose fibers using commercial cyanide-free electroless copper plating package commonly available for manufacturing of printed wiring boards. The deposited copper is found to enhance the thermal stability, electrical conductivity and resistance to moisture uptake of the fibers. On the other hand, involved chemistry results in altering the molecular structure of the fibers as is indicated by the degradation of their mechanical performance (tensile strength and modulus).

  • 2.
    Basso, Margherita
    et al.
    Politecnico di Milano, Department of Chemistry, Materials and Chemical Engineering “G. Natta”, Milan, Italy. Research Hub by Electrolux Professional, Pordenone, Italy.
    Piselli, Agnese
    Research Hub by Electrolux Professional, Pordenone, Italy. Politecnico di Milano, Department of Design, Milan, Italy.
    Simonato, Michele
    Research Hub by Electrolux Professional, Pordenone, Italy.
    Furlanetto, Riccardo
    Research Hub by Electrolux Professional, Pordenone, Italy.
    Pupure, Liva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    De Nardo, Luigi
    Politecnico di Milano, Department of Design, Milan. INSTM—National Interuniversity Consortium of Materials Science and Technology, Firenze, Italy.
    Effect of food chemicals and temperature on mechanical reliability of bio-based glass fibers reinforced polyamide2019In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 157, p. 140-149Article in journal (Refereed)
    Abstract [en]

    This paper presents an experimental study to assess the effects of food chemicals and temperature on the mechanical performance of glass fiber reinforced bio-based polyamide. The diffusion of food chemicals was mainly driven by thermal energy, following Arrhenius law in all tested environments. Degradation of mechanical properties and decrease in reliability were assessed, due to the plasticization of polymer matrix. Secondary but not negligible effect on flexural strength degradation is given by the different chemical interaction between polymeric chains and molecules of food chemicals. Colour change was measured and resulted to be positively correlated to diffusion.

  • 3.
    Basso, Margherita
    et al.
    Politecnico di Milano, Department of Chemistry, Materials and Chemical Engineering, Milan, Italy;The Research Hub by Electrolux Professional, Pordenone, Italy.
    Pupure, Liva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Simonato, Michele
    The Research Hub by Electrolux Professional, Pordenone, Italy.
    Furlanetto, Riccardo
    The Research Hub by Electrolux Professional, Pordenone, Italy.
    De Nardo, Luigi
    Politecnico di Milano, Department of Chemistry, Materials and Chemical Engineering, Milan, Italy;INSTM—National Interuniversity Consortium of Materials Science and Technology, Firenze, Italy.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Nonlinear creep behaviour of glass fiber reinforced polypropylene: Impact of aging on stiffness degradation2019In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 163, p. 702-709Article in journal (Refereed)
    Abstract [en]

    Nonlinear creep behavior of one commercial short glass fiber reinforced polypropylene was investigated using tensile creep tests and stiffness degradation measurements. The impact of thermal aging and following quenching was evaluated on the latter mechanical property. Experimental results were modeled applying nonlinear viscoelastic model used by Pupure et al. (2013) and developed by Lou and Schapery [1,2]. Results showed that this model can describe nonlinear behavior of short glass fiber reinforced polymer composites, where microdamage is given by debonding of fiber-matrix interfaces already at low strains, where cracks propagate and lead to tensile creep fracture.

  • 4.
    Hajlane, Abdelghani
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Laboratory of Organometallic and Macromolecular Chemistry-Composite Materials, Faculty of Sciences and Technologies, Cadi Ayyad University, Marrakech. Department of Materials Science and Nano-engineering, Mohammed VI Polytechnic University, Ben Guerir, Morocco.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kaddami, Hamid
    Laboratory of Organometallic and Macromolecular Chemistry-Composite Materials, Faculty of Sciences and Techniques, Cadi Ayyad University.
    Cellulose nanocrystal deposition onto regenerated cellulose fibres: effect on moisture absorption and fibre–matrix adhesion2018In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 25, no 3, p. 1783-1793Article in journal (Refereed)
    Abstract [en]

    The effect of treatment of regenerated cellulose fibres by cellulose nanocrystals on the moisture absorption of the fibres as well as on fibre–epoxy resin adhesion has been investigated. Nanocrystals were deposited on the fibres using γ-methacryloxypropyltrimethoxysilane (MPS) as coupling agent. Water absorption tests performed on fibres showed that, at 64% relative humidity, treatment by the coupling agent decreased the water uptake by a factor of two compared with untreated fibres, whereas deposition of cellulose nanocrystals (CNC) on fibres treated with MPS (FMMPS) did not further increase the water absorption despite the hydrophilic character of the CNC. This result was confirmed by monitoring fibre swelling using contact angle measurements. Indeed, it was found that FMMPS presented the same contact angle with glycerol before and after CNC deposition, being higher than that obtained for untreated fibres. The tensile strength and stiffness of fibres were not affected by moisture after either treatment, but nanocrystal deposition enhanced the fibre–epoxy resin adhesion, as revealed by results of pull-out tests performed on fibre bundles at 64% relative humidity.

  • 5.
    Gong, Guan
    et al.
    Swerea SICOMP AB, Piteå, Sweden.
    Nyström, Birgitha
    Swerea SICOMP AB, Piteå, Sweden.
    Sandlund, Erik
    Swerea SICOMP AB, Piteå, Sweden.
    Eklund, Daniel
    Swerea SICOMP AB, Piteå, Sweden.
    Noël, Maxime
    Swerea SICOMP AB, Piteå, Sweden.
    Westerlund, Robert
    Swerea SICOMP AB, Piteå, Sweden.
    Stenberg, Sofia
    Swerea SICOMP AB, Piteå, Sweden.
    Pupure, Liva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Swerea SICOMP AB, Piteå, Sweden.
    Pupurs, Andrejs
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Swerea SICOMP AB, Piteå, Sweden.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Development of Electrophoretic Deposition Prototype for Continuous Production of Carbon Nanotube-Modified Carbon Fiber Fabrics Used in High-Performance Multifunctional Composites2018In: Fibers, ISSN 2079-6439, Vol. 6, no 4, article id 71Article in journal (Refereed)
    Abstract [en]

    An electrophoretic deposition (EPD) prototype was developed aiming at the continuous production of carbon nanotube (CNT) deposited carbon fiber fabric. Such multi-scale reinforcement was used to manufacture carbon fiber-reinforced polymer (CFRP) composites. The overall objective was to improve the mechanical performance and functionalities of CFRP composites. In the current study, the design concept and practical limit of the continuous EPD prototype, as well as the flexural strength and interlaminar shear strength, were the focus. Initial mechanical tests showed that the flexural stiffness and strength of composites with the developed reinforcement were significantly reduced with respect to the composites with pristine reinforcement. However, optical microscopy study revealed that geometrical imperfections, such as waviness and misalignment, had been introduced into the reinforcement fibers and/or bundles when being pulled through the EPD bath, collected on a roll, and dried. These defects are likely to partly or completely shadow any enhancement of the mechanical properties due to the CNT deposit. In order to eliminate the effect of the discovered defects, the pristine reinforcement was subjected to the same EPD treatment, but without the addition of CNT in the EPD bath. When compared with such water-treated reinforcement, the CNT-deposited reinforcement clearly showed a positive effect on the flexural properties and interlaminar shear strength of the composites. It was also discovered that CNTs agglomerate with time under the electric field due to the change of ionic density, which is possibly due to the electrolysis of water (for carboxylated CNT aqueous suspension without surfactant) or the deposition of ionic surfactant along with CNT deposition (for non-functionalized CNT aqueous suspension with surfactant). Currently, this sets time limits for the continuous deposition.

  • 6.
    Tsampas, Spyros
    et al.
    Swerea SICOMP AB, Mölndal.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Development of novel high Tg polyimide-based composites: Part II: Mechanical characterisation2018In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 52, no 2, p. 261-274Article in journal (Refereed)
    Abstract [en]

    In this study, the mechanical performance assessment of a newly developed carbon fibre-reinforced polyimide composite system T650/NEXIMID® MHT-R is presented. This system was subjected to a series of mechanical tests at ambient and elevated temperature (320℃) to determine basic material properties. Moreover, an additional test was conducted, using a T650/NEXIMID® MHT-R laminate in which the fibre sizing was thermally removed prior to laminate manufacturing, to investigate the effect of fibre treatment on mechanical performance. The experimental results indicated that the T650/NEXIMID® MHT-R composites along with exceptionally high Tg (360–420℃) exhibited competitive mechanical properties to other commercially available polyimide and epoxy-based systems. At elevated temperature, the fibre-dominated properties were not affected whilst the properties defined by matrix and fibre/matrix interface were degraded by approximately 20–30%. Finally, the fibre sizing removal did not affect the tensile and compressive strength, however, the shear strength obtained from short-beam shear test was deteriorated by approximately 15%. to serve as baseline for further studies.

  • 7.
    Al-Ramahi, Nawres
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Institute of Technology, Middle Technical University, Baghdad.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Swerea SICOMP AB.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fem analysis of stresses in adhesive single-lap joints with non-linear materials under thermo-mechanical loading2018In: ECCM18, 2018Conference paper (Refereed)
    Abstract [en]

    This study presents comprehensive numerical stress analysis in the adhesive layer of a single-lap joint subjected to various loading scenarios (mechanical and thermal loading). For this purpose numerical model (finite element method) with novel displacement coupling conditions able to correctly represent monoclinic materials (off-axis layers of composite laminates) has been developed. This model includes nonlinear material model and geometrical nonlinearity is also accounted for. The effect of thermal residual stresses (in adhesive) is analysed for various methods of manufacturing of single lap joint. The sequences of application of thermal and mechanical loads for the analysis of the thermal residual stresses in joints are proposed. It is shown that the most common approach used in many studies of linear superposition of thermal and mechanical stresses works well only for linear materials and produces wrong results if material is non-linear. The present study demonstrates suitable method to apply combined thermal and mechanical loads to get accurate stress distributions. Based on the analysis of these stress distributions the conclusions concerning the effect of the thermal residual stresses on peel and shear stress concentrations are made. The comparison between effect of thermal stresses in case of the one-step and two-step joint manufacturing techniques is made.

  • 8.
    Al-Ramahi, Nawres
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Institute of Technology / Baghdad, Middle Technical University, Baghdad, Iraq.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Swerea SICOMP AB, Piteå, Sweden.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Investigation of end and edge effects on results of numerical simulation of single lap adhesive joint with non-linear materials2018In: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 87, p. 191-204Article in journal (Refereed)
    Abstract [en]

    This paper presents systematic numerical study of stresses in the adhesive of a single-lap joint with the objective to improve understanding of the main material and geometrical parameters determining performance of adhesive joints. For this purpose a 3D model as well as 2D model, optimized with respect to the computational efficiency by use of novel displacement coupling conditions able to correctly represent monoclinic materials (off-axis layers of composite laminates), are employed. The model accounts for non-linearity of materials (adherend and adhesive) as well as geometrical non-linearity. The parameters of geometry of the joint are normalized with respect to the dimensions of adhesive (e.g. thickness) thus making analysis of results more general and applicable to wide range of different joints. Optimal geometry of the single-lap joint allowing to separate edge effect from end effects is selected based on results of the parametric analysis by using peel and shear stress distributions in the adhesive layer as a criterion. Three different types of single lap joint with similar and dissimilar (hybrid) materials are considered in this study: a) metal-metal; b) composite-composite; c) composite-metal. In case of composite laminates, four lay-ups are evaluated: uni-directional ([08]T and [908]T) and quasi-isotropic laminates ([0/45/90/-45]S and [90/45/0/-45]S). The influence of the abovementioned parameters on peel and shear stress distributions in the adhesive layer is examined carefully and mechanical parameters governing the stress concentrations in the joint have been identified, this dependence can be described by simple but accurate fitting function. The effect of the used material model (linear vs non-linear) on results is also demonstrated.

  • 9.
    Pupure, Liva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Swerea SICOMP, Piteå.
    Berthold, Fredrik
    Rise Bioeconomy/Innventia AB, Stockholm.
    Miettinen, Arttu
    Department of Physics, University of Jyväskylä.
    Mechanical properties of natural fiber composites produced using dynamic sheet former2018In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280Article in journal (Refereed)
    Abstract [en]

    Composites formed from wood fibers and man-made cellulosic fibers in PLA (polylactic acid) matrix, manufactured using sheet forming technique and hot pressing, are studied. The composites have very low density (due to high porosity) and rather good elastic modulus and tensile strength. As expected, these properties for the four types of wood fiber composites studied here improve with increasing weight fraction of fibers, even if porosity is also increasing. On the contrary, for man-made cellulosic fiber composites with circular fiber cross-section, the increasing fiber weight fraction (accompanied by increasing void content) has detrimental effect on stiffness and strength. The differences in behavior are discussed attributing them to fiber/ fiber interaction in wood fiber composites which does not happen in man-made fiber composites, and by rather weak fiber/matrix interface for man-made fibers leading to macro-crack formation in large porosity regions.

  • 10.
    Pupure, Liva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Methodology for macro-modeling of bio-based composites with inelastic constituents2018In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 163, p. 41-48Article in journal (Refereed)
    Abstract [en]

    Methodology for development of a macro-scale model (with strain as an input) for Regenerated Cellulose fiber (RCF) composites with highly non-linear (viscoelastic (VE) and viscoplastic (VP)) constituents is presented and demonstrated. The VE is described by Schapery's models and Zapas' model is used for VP. For a purely VE constituent the model can be identified from stress relaxation in constant strain tests. In the presence of VP the constant strain test does not render VE stress relaxation functions, because part of the applied strain is VP and the VE strain is changing. As an alternative creep and strain recovery tests are suggested to find the plasticity law and also the nonlinear creep compliances to identify the VE model where stress is an input. The incremental form of this model is then inverted and used to simulate the VE relaxation tests and the simulated relaxation functions are used to identify the VE model with VE strain as an input.

    Models for constituents are used in micromechanics simulations of the composite behavior in arbitrary ramps including the composite VE relaxation test. Using the latter, a macro-model is developed and its validity and accuracy are demonstrated.

  • 11.
    Suñer Moreno, Silvia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Gowland, N.
    Institute of Medical and Biological Engineering, University of Leeds.
    Craven, R.
    Institute of Medical and Biological Engineering, University of Leeds.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tripper, J.L.
    Institute of Medical and Biological Engineering, University of Leeds.
    Ultrahigh molecular weight polyethylene/graphene oxide nanocomposites: wear characterization and biological response to wear particles2018In: Journal of Biomedical Materials Research. Part B - Applied biomaterials, ISSN 1552-4973, E-ISSN 1552-4981, Vol. 106, no 1, p. 183-190Article in journal (Refereed)
    Abstract [en]

    In the field of total joint replacements, polymer nanocomposites are being investigated as alternatives to ultrahigh molecular weight polyethylene (UHMWPE) for acetabular cup bearings. The objective of this study was to investigate the wear performance and biocompatibility of UHMWPE/graphene oxide (GO) nanocomposites. This study revealed that low concentrations of GO nanoparticles (0.5 wt %) do not significantly alter the wear performance of UHMWPE. In contrast, the addition of higher concentrations (2 wt %) led to a significant reduction in wear. In terms of biocompatibility, UHMWPE/GO wear particles did not show any adverse effects on L929 fibroblast and PBMNC viability at any of the concentrations tested over time. Moreover, the addition of GO to a UHMWPE matrix did not significantly affect the inflammatory response to wear particles. Further work is required to optimize the manufacturing processes to improve the mechanical properties of the nanocomposites and additional biocompatibility testing should be performed to understand the potential clinical application of these materials

  • 12.
    Al-Maqdasi, Zainab
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gong, Guan
    Swerea SICOMP AB, Piteå.
    Nyström, Birgitha
    Swerea SICOMP AB, Piteå.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wood Fiber Composites With Added Multi-Functionality2018Conference paper (Refereed)
    Abstract [en]

    Graphene nanoplatelets (GNPs) are used to enhance the mechanical properties and functionality of wood plastic composite (WPC) targeting applications such as de-icing or anti-icing and fast thermal diffusivity. The GNPs are integrated into neat polymer using a masterbatch containing functionalized graphene by melt compounding through a twin-screw extruder without the use of any coupling agent or compatibilizer. The same manufacturing process (melt compounding) but with the use of compatibilizer is employed to produce WPC with nano-doped matrix. The effect of different GNP loadings (up to 15 wt.%) on morphology, crystallinity, mechanical and thermal conductivity of the nanocomposites and the WPCs was investigated. It was found that both strength and modulus of nanocomposites, in tension and bending, were increased with the addition of GNPs. With the aid of MAPE compatibilizer WPCs show higher flexural strength and modulus than neat polymer. GNP has marginal effect on the flexural stress but further increases flexural modulus of WPC. The preliminary results related to the thermal conductivity of studied materials indicate that the incorporation of GNP may be beneficial for faster and more uniform heat distribution in WPC.

  • 13.
    Joffe, Roberts
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Swerea SICOMP.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjögren, Anders
    Lund University.
    Characterization of defects in polymer composites used in medical devices by means of x-ray microtomography2017In: 3rd International Conference on Tomography of Materials and Structures (ICTMS2017), 2017Conference paper (Refereed)
    Abstract [en]

    This paper presents a study on micro-structural characterization of carbon fibre-reinforced plastics used inmedical devices. The focus of the investigation is on determination of void content in the materials, since voids act asdefects and will affect the service life of the composites/devices. The results show that x-ray microtomography is anaccurate and powerful technique to identify defects in composites, and it is of great value in quality control.

  • 14.
    Hajlane, Abdelghani
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kaddami, Hamid
    Laboratory of Organometallic and Macromolecular Chemistry-Composite Materials, Faculty of Sciences and Techniques, Cadi Ayyad University.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Chemical modification of regenerated cellulose fibres by cellulose nano-crystals: Towards hierarchical structure for structural composites reinforcement2017In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 100, p. 41-50Article in journal (Refereed)
    Abstract [en]

    A simple and innovative new route, with less negative impact on the environment, for depositing and hope-grafting cellulose nano-crystals onto the surface of regenerated cellulose fibres (Cordenka 700 Super 3), using γ-methacryloxypropyltrimethoxysilane as coupling agent, is presented. Hierarchical cellulosic structure involving micro-scale fibres and nano-scale cellulose crystal network was created as verified by the scanning electron microscopy. The fibres were initially oxidised by optimized concentration of cerium ammonium nitrate to generate radicals on the cellulose backbone in order to polymerize the coupling agent at the surface. Infrared spectroscopy and scanning electron microscopy confirmed the chemical polymerisation of MPS onto regenerated cellulose fibres without enabling to show the chemical bonding between silane and nano-crystals. However, tensile test which was performed to study the impact of different treatments on mechanical properties of regenerated cellulose fibres, revealed that the modification by silane decreased the stiffness and strength of fibres (22% and 10% decrease, respectively) while the strain at failure was increased. These changes were attributed to the treatment conditions which may have induced the disorder and the misalignment of the structure of cellulose fibres (e.g. axial orientation of molecular chains and crystalline phase of the fibre has been reduced). This assumption is supported by the results from successive loading-unloading test of the fibre bundle. However, after depositing cellulose nano-crystals onto the fibre’s surface, the stiffness was recovered (20% increase in comparison to MPS treated fibres) while the strength and strain at failure remained at the same order of magnitude as for fibres treated only by the coupling agent.

  • 15.
    Ansari, Farhan
    et al.
    Department of Fiber and Polymer Technology, KTH Royal Institute of Technology.
    Granda, Luis A.
    Laboratory of Paper Engineering and Polymer Materials (LEPAMAP) Group, Department of Chemical Engineering, University of Girona.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Berglund, Lars A.
    Department of Fiber and Polymer Technology, KTH Royal Institute of Technology.
    Vilaseca, Fabiola
    Department of Fiber and Polymer Technology, KTH Royal Institute of Technology.
    Experimental evaluation of anisotropy in injection molded polypropylene/wood fiber biocomposites2017In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 96, p. 147-154Article in journal (Refereed)
    Abstract [en]

    Although the anisotropy of wood fibers is reasonably well established, the anisotropy of injection molded wood fiber composites is not well understood. This work focuses on chemo-thermomechanical pulp (CTMP) reinforced polypropylene (PP) composites. A kinetic mixer (Gelimat) is used for compounding CTMP/PP composites, followed by injection molding. Effects from processing induced orientation on mechanical properties are investigated. For this purpose, a film gate mold was designed to inject composites in the shape of plates so that specimens in different directions to the flow could be evaluated in tensile tests. Observations from tensile tests were complemented by performing flexural tests (in different directions) on discs cut from the injected plates. SEM was used to qualitatively observe the fiber orientation in the composites. At high fiber content, both modulus and tensile strength could differ by as much as 40% along the flow and transverse to the flow. The fiber orientation was strongly increased at the highest fiber content, as concluded from theoretical analysis.

  • 16.
    Joffe, Roberts
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pupure, Liva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Berthold, Fredrik
    Innventia AB.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Micro-structure and Mechanical Properties in PLA Reinforced with Cellulosic Fiber Sheets Made by Wet Forming Method2017In: 8th International Conference on Composites Testing and Model Identification: CompTest2017 / [ed] S.V . Lomov, L. Gorbatikh, Y. Swolfs, 2017Conference paper (Refereed)
    Abstract [en]

    The current paper presents results of study of composites produced by compression moulding of sheets of comingled PLA and reinforcing fibers. The dynamic sheet former is employed to produce fiber mats (with the PLA in the form of fibers) which are consolidated into composite plates by using hot press. This processing route ensures that initial length of the fibers is preserved during the manufacturing and preferential fiber orientation is achieved. However, the internal structure of the composites in question is very complex and somewhat unpredictable, which complicates design of these materials. The main objectives of this paper are application and validation of micro-mechanical models on composites produced within this study as well as direct (experimental) and indirect (back-calculation) identification of input parameters to be used in the modelling. The main input parameters considered in this study are fiber orientation and porosity. The estimation of these parameters is done through micro–computed tomography but also by using micro-mechanical expressions in combination with experimental results (e.g. composite density, stiffness). The input parameters identified by different approaches are compared, then these parameters are used in the micro-mechanical models to predict stiffness of composites with different types of fibers and various fiber contents.

  • 17.
    Al-Ramahi, Nawres
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Model for numerical simulation and parametric analysis of composite adhesive joints under thermo-mechanical loading2017In: ICCS20: Proceedings : 20th International Conference on Composite Structures / [ed] Antonio J.M. Ferreira, W. Larbi, J.F. Deu, F. Tornabene, N. Fantuzzi, Paris: Società Editrice Esculapio, 2017 , 2017, , p. 662p. 234-Conference paper (Refereed)
    Abstract [en]

    Abstract: The current investigation focuses on development and verification of a modelfor numerical simulation of performance of adhesive joints under tensile loading. Differentcombination of materials in joints is considered: metal-metal, composite-composite andcomposite-metal. The objective of this paper is to present simulation results of joints usingan accurate finite element model including non-linear behaviour and large deformation.Moreover, several loading scenarios are analysed, including simultaneous application oftemperature and mechanical load. Not only the effect of temperature on mechanicalperformance of materials (adhesive as well as adherents) is analysed but also built up ofresidual thermal stresses during the manufacturing of joints are taken into account. Thisapproach is demonstrated by simulation of tensile tests of joints at several temperatures.Two scenarios of application of temperature and mechanical load using large deformationtheory are considered: 1) the thermal and mechanical loads are applied simultaneously (theproperties of the materials are adjusted accordingly to their performance at differenttemperatures); 2) temperature is applied on specimen which is not macroscopicallyconstrained and the obtained stress distribution is used as initial state for the nextsimulation of mechanical loaded joint. The influence of edge effects (due to limited widthof the joint) on the stress distribution within the joint are studied. In order to eliminatethese effects the periodic boundary conditions (BC) are used in the numerical model.These BC are adjusted to optimize numerical model and obtain efficient calculation routinefor analysis of stresses within interior part of the structure. The validity of these BCs isevaluated and verified by analysing number of case studies. The comparison between full3D FEM model and simplified 2D model is carried out. The resulting stress distributions inthe overlap region of joints are presented for different joints (the parameters are: materialcombinations, material models, geometry of adhesive layer, constraints and BCs) withcomprehensive analysis and recommendations for optimal numerical model that can beused in joint design.

  • 18.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Modniks, Janis
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Madsen, Bo
    Technical University of Denmark, Risø Campus, Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark.
    Nättinen, Kalle
    Bemis Flexible Packaging Europe, Bemis Valkeakoski Oy.
    Apparent interfacial shear strength of short-flax-fiber/starch acetate composites2016In: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 64, p. 78-85Article in journal (Refereed)
    Abstract [en]

    The paper deals with an indirect industry-friendly method for identification of the interfacial shear strength (IFSS) in a fully bio-based composite. The IFSS of flax fiber/starch acetate is evaluated by a modified Bowyer and Bader method based on an analysis of the stress-strain curve of a short-fiber-reinforced composite in tension. A shear lag model is developed for the tensile stress-strain response of short-fiber-reinforced composites allowing for an elasticperfectly plastic stress transfer. Composites with different fiber volume fractions and a variable content of plasticizer have been analyzed. The apparent IFSS of flax /starch acetate is within the range of 5.5 to 20.5 MPa, depending on composition of the material. The IFSS is found to be greater for composites with a higher fiber loading and to decrease with increasing content of plasticizer. The IFSS is equal or greater than the yield strength of the neat polymer, suggesting good adhesion, as expected for the chemically compatible constituents.

  • 19.
    Joffe, Roberts
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hajlane, Abdelghani
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kaddami, Hamid
    Cadi Ayyad University, Faculty of Sciences and Techniques.
    Effect of surface modification of regenerated cellulose fibers on moisture absorption and fiber/matrix adhesion2016In: ECCM 2016: Proceeding of the 17th European Conference on Composite Materials, European Conference on Composite Materials , 2016Conference paper (Refereed)
    Abstract [en]

    This paper describes the effect of surface modification of regenerated cellulose fibers by chemical treatment and deposition of cellulose nano-crystals onto fibers. The effect of this modification on themoisture absorption by fibers and interface properties with epoxy matrix has been studies. The preliminary results show positive trends in reducing moisture uptake by fibers and improving interfacial shear strength.The deposition of cellulose nano-crystals at different concentrations onto regenerated cellulose fibers creates a network covering surface of fibers and interconnecting them. This resulted in rather significant reduction of the moisture absorption compare to untreated fibers (8% vs 12% respectively)and improving interfacial shear strength of regenerated cellulose fiber/epoxy system. The increase of the interfacial shear strength measured from bundle pull-out test on fibers conditioned at 64% relative humidity has been observed. Thus, the hierarchical structure created by grafting nano-crystals onmicro-sized cellulose fibers resulted in improvement of fiber/matrix adhesion by reducing water absorption.

  • 20.
    Hajlane, Abdelghani
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kaddami, Hamid
    Cadi Ayyad University, Faculty of Sciences and Techniques.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Environmentally friendlier method to deposit cellulose nanocrystals on regenerated cellulose filaments and effect of the treatment on mechanical properties of fibers2016In: ECCM 2016: Proceeding of the 17th European Conference on Composite Materials, European Conference on Composite Materials , 2016Conference paper (Refereed)
    Abstract [en]

    This paper presents environmentally friendlier technique for deposition of cellulose nano-whiskers onto the surface of regenerated cellulose fibres using γ-methacryloxypropyltrimethoxysilane as coupling agent. The result of this treatment is hierarchical reinforcement consisting of micro-scale fibres and nano-scale cellulose crystal network. In order to evaluate influence of treatment on fibre performance, tensile tests of fibre bundles were carried out. The results show that there is significant impact on stiffness of fibres only by first modification by silane, whereas grafting of cellulose nanowhiskers onto the surface of the fibre allowed recovery of initial properties. It is assumed that thetreatment may have induced the misalignment of macromolecular chains and crystalline cellulose phase with respect to the fibre axis.

  • 21.
    Varna, Janis
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pupure, Liva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Incremental forms of Schapery’s model: convergence and inversion to simulate strain controlled ramps2016In: Mechanics of time-dependant materials, ISSN 1385-2000, E-ISSN 1573-2738, Vol. 20, no 4, p. 535-552Article in journal (Refereed)
    Abstract [en]

    Schapery’s nonlinear viscoelastic model is written in incremental form, and three different approximations of nonlinearity functions in the time increment are systematically analysed with respect to the convergence rate. It is shown that secant slope is the best approximation of the time shift factor, leading to significantly higher convergence rate. This incremental form of the viscoelastic model, Zapas’ model for viscoplasticity, supplemented with terms accounting for damage effect is used to predict inelastic behaviour of material in stress controlled tests. Then the incremental formulation is inverted to simulate stress development in ramps where strain is the input parameter. A comparison with tests shows good ability of the model in inverted form to predict stress–strain response as long as the applied strain is increasing. However, in strain controlled ramps with unloading, the inverted model shows unrealistic hysteresis loops. This is believed to be a proof of the theoretically known incompatibility of the stress and strain controlled formulations for nonlinear materials. It also shows limitations of material models identified in stress controlled tests for use in strain controlled tests.

  • 22.
    Pupure, Liva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Natural fiber composite: Challenges simulating inelastic response in strain-controlled tensile tests2016In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 50, no 5, p. 575-587Article in journal (Refereed)
    Abstract [en]

    Problems occurring, when nonlinear time-dependent material model with parameters identified in creep tests is applied to simulate high-strain response in strain-controlled tests, are described and analyzed. Reasons for discrepancies with experimental loading curves are revealed. Presented numerical/experimental examples deal with three bio-based composites showing highly nonlinear behavior due to damage, nonlinear viscoelasticity and viscoplasticity. Schapery's approach for viscoelasticity and Zapas' model for viscoplasticity are used. The model is generalized to include microdamage effect. It is shown that the main problem in simulations at high stresses is the reliability of data from creep test for model identification in this region because creep rupture limits the available data region and extrapolation to higher stresses is rather uncertain. Alternative solution is to employ relaxation tests at high strains to obtain the missing information. However, it would work only in absence of viscoplastic strains: viscoelastic relaxation functions cannot be determined by maintaining constant total strain if viscoplastic-strain is developing. Based on sensitivity analysis of composite response to variations of the elastic modulus, damage, viscoelastic and viscoplastic parameters, suggestions are made for improving (further “tuning”) the model in high stress region by using tensile stress–strain curves in quasi-static loading.

  • 23.
    Tsampas, Spyros
    et al.
    Swerea SICOMP AB.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    The effect of high temperature on the mechanical performance of novel high Tg polymide-based carbon fibre-reinforced laminates2016In: ECCM 2016: Proceeding of the 17th European Conference on Composite Materials, European Conference on Composite Materials , 2016Conference paper (Refereed)
    Abstract [en]

    In this study, the outcomes from the mechanical testing of the carbon fibre-reinforced polyimide composite system T650/NEXIMID® MHT-R at ambient and elevated temperatures are presented. These results are compared to assess the effect of mechanical loading at 320°C on the performance of the system in tension, compression and Short-Beam Shear. The experimental campaign indicated that the mechanical loading at 320°C had a trivial effect on the tensile properties (fibre-dominated) whilst a more pronounced effect was noted on the compression and Short-Beam Shear (matrix and fibre/matrix interface-dominated properties).

  • 24.
    Hajlane, Abdelghani
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Miettinen, A.
    University of Jyvaskyla, Department of Physics.
    Madsen, Bo
    Technical University of Denmark, Department of Wind Energy, Risø Campus.
    Beauson, J.
    Techical University of Denmark, Department of Wind Energy, Riso Campus.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Use of micro-tomography for validation of method to identify interfacial shear strength from tensile tests of short regenerated cellulose fibre composites2016In: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 139, article id 012021Article in journal (Refereed)
    Abstract [en]

    The interfacial shear strength of short regenerated cellulose fibre/polylactide composites was characterized by means of an industry-friendly adhesion test method. The interfacial shear strength was back-calculated from the experimental tensile stress-strain curves of composites by using a micro-mechanical model. The parameters characterizing the microstructure of the composites, e.g. fibre length and orientation distributions, used as input in the model were obtained by micro-tomography. The investigation was carried out on composites with untreated and surface treated fibres with various fibre weight contents (5wt%, 10wt%, and 15wt% for untreated fibres, and 15wt% for treated fibres). The properties of fibres were measured by an automated single fibre tensile test method. Based on these results, the efficiency of the fibre treatment to improve fibre/matrix adhesion is evaluated, and the applicability of the method to measure the interfacial shear strength is discussed. The results are compared with data from previous work, and with other results from the literature

  • 25.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Modniks, Janis
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    An Improved Method For Identification Of The Interfacial Shear Strength By Tensile Tests Of Short-Fiber Composites2015In: Proceedings of 7th International Conference on Composites Testing and Model Identification / [ed] C. González; C. López; J. LLorca, Madrid, Spain: IMDEA, Madrid (SPAIN) , 2015Conference paper (Refereed)
  • 26.
    Pupure, Liva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Applications and limitations of non-linear viscoelastic model for simulation of behaviour of polymer composites2015Conference paper (Refereed)
    Abstract [en]

    There are two alternative formulation of non-linear viscoelastic model to describe strain and stress controlled tests. Both models for non-linear viscoelastic materials are not compatible, and cannot be directly inverted if so required in certain cases. In order to do it numerical procedures has to be employed. Methodology for simulating nonlinear stress-strain response in iso-strain situations of fiber composites based on properties on constituents is presented.

  • 27.
    Pupure, Liva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Identification Of Parameters For Direct And Inverted Model To Predict Performance Of Materials Exhibiting Non-Linear Viscoelastic Behavior2015In: Proceedings of 7th International Conference on Composites Testing and Model Identification / [ed] C. González; C. López; J. LLorca, Madrid, Spain: IMDEA, Madrid (SPAIN) , 2015Conference paper (Refereed)
  • 28.
    Miettinen, Arttu
    et al.
    University of Jyväskylä.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pupure, Liva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Madsen, Bo
    Technical University of Denmark, Risø Campus, Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark.
    Identification of true microstructure of composites based on various flax fibre assemblies by means of three-dimensional tomography2015Conference paper (Refereed)
    Abstract [en]

    Lately it has been demonstrated that natural fibres may be an environmentally superior alternative for, e.g., glass fibres. In order to estimate properties of composite materials made of natural fibres, models designed for synthetic fibres are often used. The models usually do not account for irregularities in the material, e.g., suboptimal fibre orientation due to the twisting angle of fibres in yarns. Use of models without taking those features into account might lead to unreliable results. Methods to quantify the microstructural properties of natural fibre composites with X-ray microtomography and three-dimensional image analysis are demonstrated in this work. The methods are applied to flax fibre composites made from three different kinds of pre-forms. Microstructural parameters estimated with the methods are used in micromechanical models for the stiffness of the composite. Comparison between rule-of-mixtures and classical laminate theory is made, highlighting the requirement for accurate parameter estimation and use of a model that accounts for significant structural features of the material.

  • 29.
    Fernberg, S. Patrik
    et al.
    Luleå tekniska universitet, Swerea SICOMP AB, Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Tsampas, Spyros
    Swerea SICOMP AB.
    Mannberg, Peter
    Swerea SICOMP AB.
    Influence of post-cure on carbon fibre polyimide composites with glass transition temperatures above 400ºC2015Conference paper (Refereed)
    Abstract [en]

    The current communication present results from work on polymeric composites with extreme temperature performance. We are studying carbon fibre composites based on a new phenyl ethynyl terminated polyimide formulation NEXIMID® MHT-R (Nexam Chemicals AB, Sweden) based on hexafluoroisopropylidene bisphthalic dianhydride (6-FDA), 4-(Phenylethynyl)Phthalic Anhydride (4-PEPA) and ethynyl bis-phthalic anhydride (EBPA). This study in particular investigates how post-cure conditions such as time, temperature and atmosphere influence Tg of the composites. In addition to this we also trace and analyse the consequences of post-cure on weight loss and occurrence of micro-cracks. We are considering three different post-curing temperatures: 400°C, 420°C and 440°C in the study. Two different atmospheres, air and inert by nitrogen, were also investigated. In summary the results reveal that remarkably high Tg, up to around 460°C, is achieved with only very limited weight loss. It was also observed that some, but limited amounts of, micro-cracks are developed within the laminates due to the inevitable high thermal stresses generated upon cooling from cure temperature.

  • 30.
    Olofsson, Kurt
    et al.
    Swerea SICOMP AB.
    Hedlund, Emil
    Swerea SICOMP AB.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ahlqvist, Fredrik
    Swerea SICOMP AB.
    Local Point Cutting of Fibre Materials for Eased Automation2015Conference paper (Other academic)
  • 31.
    Tsampas, Spyros
    et al.
    Swerea SICOMP AB.
    Fernberg, S. Patrik
    Luleå tekniska universitet, Swerea SICOMP AB, Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mechanical performance of novel high Tg polyimide matrix carbon fibre-reinforced laminates2015Conference paper (Refereed)
    Abstract [en]

    In this study, an assessment of the mechanical performance of a newly developed carbon fibre-reinforced polyimide composite system T650/NEXIMID® MHT-R is presented. This system was subjected to a series of mechanical tests at ambient temperature in order to determine the tensile, compressive, flexural and interlaminar shear properties. Moreover, an additional testing campaign was conducted, using a T650/NEXIMID® MHT-R laminate in which the sizing had been thermally removed prior to manufacturing, in order to investigate the effect of fiber treatment on the mechanical performance. The experimental results indicated that the T650/NEXIMID® MHT-R composites along with exceptionally high Tg (~370-420ºC) exhibited very good elastic properties in comparison with other polyimide and epoxy-based systems and, although slightly lower than the best results from literature, promising strength values. Finally, the thermal removal of the sizing did not affect the tensile, compression and flexural properties, however the interlaminar shear strength was significantly deteriorated.

  • 32.
    Pupure, Liva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Modeling of Natural Fiber Composites2015In: Natural Fiber Composites, CRC Press, Taylor & Francis Group, , 2015, p. 221-253Chapter in book (Refereed)
  • 33.
    Joffe, Roberts
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Andersons, Janis
    Institute of Polymer Mechanics, University of Latvia.
    Modeling the tensile strength of hemp fibers and short hemp fiber reinforced composites2015In: Natural Filler and Fibre Composites: Development and Characterisation, Southampton: WIT Press, 2015, p. 13-26Chapter in book (Refereed)
  • 34.
    Doroudgarian, Newsha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pupure, Liva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Moisture uptake and resulting mechanical response of biobased composites: II. Composites2015In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 36, no 8, p. 1510-1519Article in journal (Refereed)
    Abstract [en]

    The durability of entirely bio-based composites with respect to the exposure to elevated humidity was evaluated. Different combinations of bio-based resins (Tribest, EpoBioX, Envirez) and cellulosic fibers (flax and regenerated cellulose fiber rovings and fabrics) were used to manufacture unidirectional and cross-ply composite laminates. Water absorption experiments were performed at various humidity levels (41%, 70%, and 98%) to measure apparent diffusion coefficient and moisture content at saturation. Effect of chemical treatment (alkali and silane) of fibers as protection against moisture was also studied. However, fiber treatment did not show any significant improvement and in some cases the performance of the composites with treated fibers was lower than those with untreated reinforcement. The comparison of results for neat resins and composites showed that moisture uptake in the studied composites is primarily due to cellulosic reinforcement. Tensile properties of composites as received (RH = 24%) and conditioned (RH = 41%, 70%, and 98%) were measured in order to estimate the influence of humidity on behavior of these materials. Results were compared with data for glass fiber reinforced composite, as a reference material. Previous results from study of unreinforced polymers showed that resins were resistant to moisture uptake. Knowing that moisture sorption is primarily dominated by natural fibers, the results showed that some of the composites with bio-based resins performed very well and have comparable properties with composites of synthetic epoxy, even at elevated humidity.

  • 35.
    Miettinen, Arttu
    et al.
    University of Jyväskylä.
    Ojala, Antti
    VTT Technical Research Centre of Finland, Espoo.
    Wikström, Lisa
    VTT Technical Research Centre of Finland, Espoo.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Madsen, Bo
    Technical University of Denmark, Risø Campus, Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark.
    Nättinen, Kalle
    VTT Technical Research Centre of Finland, Espoo.
    Kataja, Markku
    Department of Physics, University of Jyväskylä.
    Non-destructive automatic determination of aspect ratio and cross-sectional properties of fibres2015In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 77, p. 188-194Article in journal (Refereed)
    Abstract [en]

    We propose a novel method for computerized estimation of the length/diameter distribution of fibres in short-fibre reinforced composite. Having its basis in X-ray micro-computed tomography, the method is non-destructive and does not require user intervention. In addition to the aspect ratio, the method is also capable of estimating other geometrical properties of fibre cross-sections. Based on results on specially fabricated model material, the accuracy and precision of the method seems to be reasonable. An application to the manufacturing process of wood fibre reinforced thermoplastic composite is also shown, indicating a significant decrease in the aspect ratio of fibres during the processing steps.

  • 36.
    Pupure, Liva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    On viscoplasticity characterization of natural fibres with high variability2015In: Advanced Composites Letters, ISSN 0963-6935, Vol. 24, no 6, p. 125-129Article in journal (Refereed)
    Abstract [en]

    Zapas model has shown good results in characterizing viscoplasticity in polymers and composites. Typically all viscoplastic parameters for this model are obtained in creep and strain recovery tests at different stress levels and at different test length. Obtaining parameters for highly variable bio-based materials is more challenging: trends are hidden in the scatter and data fitting is complicated. This paper suggests "single specimen methodology" for complete viscoplastic characterization and identification

  • 37.
    Joffe, Roberts
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Madsen, Bo
    Technical University of Denmark, Risø Campus.
    Nättinen, Kalle
    VTT Technical Research Centre of Finland, Espoo.
    Miettinen, Arttu
    University of Jyväskylä.
    Strength of cellulosic fiber/starch acetate composites with variable fiber and plasticizer content2015In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 49, no 8, p. 1007-1017Article in journal (Refereed)
    Abstract [en]

    In this experimental study, the performance of injection-molded short flaxand hemp fibers in plasticized starch acetate were analyzed in terms ofstrength. Parameters involved in the analysis are a variable fiber andplasticizer content. The measured strength of the composites varies in therange of 12–51 MPa for flax fibers and 11-42 MPa for hemp fibers, which issignificantly higher than the properties of the unreinforced starch acetatematrix. The micro-structural parameters used in modeling of compositestrength were obtained from optical observations and indirectmeasurements. Some of these parameters were qualitatively verified by Xraymicrotomography.

  • 38.
    Moreno, Silvia Suñer
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Tipper, Joanne
    Institute of Medical and Biological Engineering, University of Leeds.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ultra High Molecular Weight Polyethylene/Graphene Oxide Nanocomposites: Thermal, Mechanical and Wettability Characterisation2015In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 78, p. 185-191Article in journal (Refereed)
    Abstract [en]

    Numerous carbon nanostructures have been investigated in the last years due to their excellent mechanical properties. In this work, the effect of the addition of graphene oxide (GO) nanoparticles to UHMWPE and the optimal %wt GO addition were investigated. UHMWPE/GO nanocomposites with different GO wt% contents were prepared and their mechanical, thermal, structural and wettability properties were investigated and compared with virgin UHMWPE. The results showed that the thermal stability, oxidative resistance, mechanical properties and wettability properties of UHMWPE were enhanced due to the addition of GO. UHMWPE/GO materials prepared with up to 0.5 wt% GO exhibited improved characteristics compared to virgin UHMWPE and nanocomposites prepared with higher GO contents.

  • 39.
    Miettinen, Arttu
    et al.
    University of Jyväskylä.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pupure, Liva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Madsen, Bo
    Technical University of Denmark, Risø Campus, Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark.
    X-Ray Microtomography Of Natural Fibre Composites2015In: Proceedings of 7th International Conference on Composites Testing and Model Identification / [ed] C. González; C. López; J. LLorca, Madrid, Spain: IMDEA, Madrid (SPAIN) , 2015Conference paper (Refereed)
  • 40.
    Joffe, Roberts
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Andersons, Janis
    Institute of Polymer Mechanics, University of Latvia.
    Mechanical Characterization and Properties of Cellulose Fibers2014In: Handbook of Green Materials: Processing Technologies, Properties and Applications, Singapore: World Scientific Publishing Co Pte Ltd , 2014, p. 7-23Chapter in book (Refereed)
    Abstract [en]

    The objective of this chapter is to present experimental methods that are suitable for characterization of cellulose fibers. An overview of different techniques to obtain and analyze fiber strength distribution is presented. The differences of internal structure and mechanical behavior between natural and synthetic fibers, applicability and validity of experimental methods, as well as test conditions are discussed. Some of the techniques developed for synthetic fibers can be directly applied to the characterization of natural fibers, while others should be modified in order to adapt for the specific limitations of reinforcement with natural origin.

  • 41.
    Pupure, Liva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Division of Materials Science, Composite Centre Sweden, Luleå University of Technology.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Division of Materials Science, Composite Centre Sweden, Luleå University of Technology.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Division of Materials Science, Composite Centre Sweden, Luleå University of Technology.
    Modelling of mechanical behaviour of polymeric composites with nonlinear constituents2014In: 16th European Conference on Composite Materials, ECCM 2014: Seville, Spain, 22 - 26 June 2014, European Conference on Composite Materials, ECCM , 2014Conference paper (Refereed)
    Abstract [en]

    There is need to model behaviour of time-dependent non-linear material in stress or/and strain controlled experiments. This study explores possibility to apply model in both forms developed by Schapery for viscoelastic materials. Viscoelasticity has been analysed using experimental data from creep and relaxation tests. Incremental simulation procedure, which inverts model, where strains are expressed through stresses, is used to simulate relaxation curves for bio-based polymer. Comparison of viscoelastic parameters obtained from simulated and experimental relaxation curves has been performed.

  • 42.
    Pupure, Liva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Doroudgarian, Newsha
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Moisture uptake and resulting mechanical response of biobased composites: I. Constituents2014In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 35, no 6, p. 1150-1159Article in journal (Refereed)
    Abstract [en]

    The mechanical properties of the biobased fiber and resins have been characterized and moisture influence on the behavior of these materials has been studied. Commercially available biobased thermoset resins (Tribest, EpoBioX, Palapreg, Envirez SA, and Envirez SB) and regenerated cellulose fibers (Cordenka) have been conditioned at different levels of relative humidity (as received, dried, 41, 70, and 90%) to obtain materials with different moisture content. The following properties of polymers were measured: tensile, flexural (3P-bending), impact strength (unnotched Charpy), and fracture toughness (compact tension). The results of characterization of biobased thermosets were compared against data for epoxy Araldite LY556, which is used as reference resin. RCF bundles (with and without twist, extracted from fabric) as well as single fibers separated from these bundles were tested in tension. In general biobased resins performed well, moreover EpoBioX showed better properties than synthetic epoxy. POLYM. COMPOS

  • 43.
    Mannberg, Peter
    et al.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Nyström, Birgitha
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Service life assessment and moisture influence on bio-based composites2014In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 49, no 15, p. 5265-5270Article in journal (Refereed)
    Abstract [en]

    A race towards a more sustainable society is going on worldwide and decreasing dependence on fossil resources in energy and transport sectors is main goals. One path to decreased oil usage is development of lightweight materials from renewable resources like bio-based composites. However these new bio-based materials have not only to compete in mechanical performance, they also have to restrain environmental loads like moisture and temperature over time. In this study two bio-based composites have been compared to an oil-based composite in terms of long-term properties and water absorption behaviour. The long-term behaviour is determined by dynamic mechanical thermal analysis, DMTA, and time temperature superposition, TTSP. The water uptake is determined by submersion of specimens into water and tracking their weight change over time. The moisture influence is characterised in form of water uptake and change in the master curves created by TTSP procedure. The results show that there is a significant difference in long-term performance between the bio-based and oil-based composites. It is realized that the bio-based composites can be a good alternative for some applications especially when taking their eco-friendly nature into account.

  • 44.
    Mannberg, Peter
    et al.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Nyström, Birgitha
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Service life assessment and moisture influence on bio-based thermosetting resins2014In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 49, no 10, p. 3687-3693Article in journal (Refereed)
    Abstract [en]

    In this study, three different types of bio-based resins are compared to a conventional oil-based epoxy in terms of moisture uptake, long-term properties and its influence of moisture and glass transition temperature, Tg. Moisture uptake is determined by means of gravimetric method, time temperature superposition (TTSP), and Tg data obtained in dynamic mechanical thermal analysis (DMTA). Moisture uptake show Fickian diffuison behavour for all resins, saturation level and diffusion coefficient however differ. The long-term properties is characterised by creep compliance master curves created by means of TTSP. The examined bio-based resins are compatible to the reference epoxy in term of stability up to 3–10 years. Comparison between master curves for virgin, wet, and dried material show that moisture present in the specimen increases creep rate, and that some of this increase remains after drying of samples. Tg measurements show that moisture inside the specimen decreases Tg; this is anticipated because of the plasticizing effect of water. The overall conclusions are that the bio-based resins of polyester, and epoxy type are comparable in performance with oil-based epoxy, LY556 and they can be used to develop high-performance composites

  • 45.
    Moreno, Silvia Suñer
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Tipper, Joanne
    Institute of Medical and Biological Engineering, University of Leeds.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    UHMWPE/GO nanocomposites for orthopaedic applications: thermal, mechanical and tribological characterization2014Conference paper (Refereed)
    Abstract [en]

    Metal-on-Polyethylene (MoP) is the bearing combination most commonly used in total joint replacements. However, the degradative oxidation behaviour of ultra high molecular weight polyethylene (UHMWPE) leads to high amounts of wear debris, which contributes to the development of aseptic loosening and eventually to the failure of the implant. In order to address this issue, investigations have focused on the development of novel materials with improved characteristics. Recently, Graphene oxide (GO) has generated great interest as reinforcement for polymer matrices due to its excellent mechanical properties. The aim of this study was to investigate the possibilities of UHMWPE/GO nanocomposites for their use in joint implants.UHMWPE/GO nanocomposites with different wt% GO content, up to 2 wt%, were manufactured under optimised conditions using a ball milling technique. Thermal, mechanical and structural characterizations of the UHMWPE/GO nanocomposites and conventional UHMWPE were carried out by means of Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), uniaxial tensile tests and High Resolution Scanning Electron Microscopy (HR-SEM). Contact angle measurements were carried out to investigate the wettability of the materials. In addition, the tribological performance of the novel nanocomposites will be assessed with a six-station multidirectional pin on plate wear simulator under hip kinematics.The results showed that GO has the ability to improve the performance of conventional UHMWPE. The incorporation of GO enhanced the thermal stability and oxidative resistance of conventional UHMWPE. Under optimised conditions, the mechanical properties and wettability of the nanocomposites were also improved. These findings suggest that UHMWPE/GO nanocomposites might be an interesting alternative to conventional UHMWPE for their use in orthopaedic aplications and more research concerning the biocompatibility and tribological performance of this material is currently under investigation.

  • 46.
    Pupure, Liva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pupurs, Andrejs
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    An analysis of the nonlinear behavior of lignin-based flax composites2013In: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 49, no 2, p. 139-154Article in journal (Refereed)
    Abstract [en]

    A lignin composite reinforced with 30% flax fibers at two levels of relative humidity, 34 and 66%, was used in this study. The nonlinearity of the composite was analyzed by studying the degradation of its modulus and the development of viscoelastic and viscoplastic strains. The reduction in the modulus of lignin-based composites in tension starts before the maximum in the stress-strain curve is reached and can be as large as 50%. With increasing relative humidity, these effects are slightly magnified. The time-dependent phenomena in tension were examined in short-term creep and strain recovery tests, demonstrating a rather high viscoplastic strain in lignin composites. Both viscoelastic and viscoplastic strains are larger at a higher relative humidity

  • 47.
    Joffe, Roberts
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Andersons, Janis
    Institute of Polymer Mechanics, University of Latvia.
    Nordström, Ylva
    Innventia AB, SE-114 86 Stockholm, Sweden.
    Sjöholm, Elisabeth
    Innventia AB, SE-114 86 Stockholm, Sweden.
    Analysis of the Tensile Strength of Softwood Lignin Based Carbon Fibers by Use of the Weibull Statistics2013Conference paper (Refereed)
    Abstract [en]

    This paper presents analysis of mechanical properties of carbon fibers produced from softwood kraft lignin. The average tensile strength of these fibers is approximately 300 MPa. The analysis is based on the Weibull statistical distribution, the experimental results and predictions based on Weibull statistics show a fairly good fit.

  • 48.
    Doroudgarian, Newsha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Anglada, Marc
    Universitat Politècnica de Catalunya.
    Mestra, Alvaro
    Universitat Politècnica de Catalunya.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Bio-based composites with different moisture contents under static and dynamic loading2013In: 6th international conference on composites testing and model identification: held 22-24 April 2013 in Aalborg, Denmark / [ed] O.T. Thomsen; Bent F. Sørensen; Christian Berggreen, 2013Conference paper (Refereed)
  • 49.
    Rozite, Liva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Nyström, Birgitha
    Swerea SICOMP AB.
    Characterization and analysis of time dependent behavior of bio-based composites made out of highly non-linear constituents2013In: Challenges in Mechanics of Time-Dependent Materials and Processes in Conventional and Multifunctional Materials: Proceedings of the 2012 Annual Conference on Experimental and Applied Mechanics / [ed] B. Antoun; H.J. Qi; R. Hall; G.P. Tandon; H. Lu; C. Lu, New York: Encyclopedia of Global Archaeology/Springer Verlag, 2013, Vol. 2, p. 109-115Conference paper (Refereed)
    Abstract [en]

    The objective of this investigation is to predict mechanical behavior of bio-based composites and their constituents by generalizing existing models to capture their time-dependent behavior. In order to identify and quantify parameters needed for the modeling, extensive damage tolerance tests as well as creep experiments are carried out.

  • 50.
    Hajlane, Abdelghani
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaddami, H.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Design and characterization of cellulose fibers with hierarchical structure for polymer reinforcement2013Conference paper (Refereed)
    Abstract [en]

    This paper describes an approach to manufacture hierarchical composites from environmentally friendly materials by grafting cellulose whiskers onto regenerated cellulose fibers (Cordenka 700). Fourier Transform Infrared spectroscopy, Scanning Electron Microscopy and X-ray diffraction analysis were performed to verify the degree of modification. The mechanical properties of the unmodified and modified fibers were analyzed using fiber bundle tensile static and loading-unloading tests. To show the effect of cellulose whiskers grafting on the Cordenka fibers, epoxy based composites were manufactured and tensile tests done on transverse uni-directional specimens. The mechanical properties were significantly increased by fiber modification and addition of the nano-phase into composite reinforced with micro-sized fibers.

1234 1 - 50 of 198
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