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  • 1. Adekunle, Kayode
    et al.
    Cho, Sung-Woo
    Patzelt, Christian
    Blomfeldt, Thomas
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Skrifvars, Mikael
    Impact and flexural properties of flax fabrics and Lyocell fiber-reinforced bio-based thermoset2011In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 30, no 8, p. 685-697Article in journal (Refereed)
    Abstract [en]

    A bio-based thermoset resin was reinforced with flax fabrics and Lyocell fiber. The effect of different weave architectures was studied with four flax fabrics with different architectures: plain, twill (two different types), and dobby. The effect of the outer ply thickness was studied and characterized with flexural and impact testing. Composites manufactured with plain weave reinforcement had the best mechanical properties. The tensile strength, tensile modulus, flexural strength, flexural modulus, and impact strength were 280MPa, 32GPa, 250MPa, 25GPa, and 75 kJ/m (2), respectively. Reinforcements with twill-weave architecture did not impart appreciable flexural strength or flexural modulus even when the outer thickness was increased. Plain- and dobby (basket woven style)-weave architectures gave better reinforcing effects and the flexural properties increased with an increase in outer thickness. Water absorption properties of the composites were studied and it was observed that the hybridization with Lyocell fiber reduced the water uptake. Field-emission scanning electron microscopy was used to study the micro-structural properties of the composites.

  • 2. Almgren, Karin M.
    et al.
    Åkerholm, Margaretha
    Gamstedt, Kristofer
    Salmén, Lennart
    Lindström, Mikael
    Effects of Moisture on Dynamic Mechanical Properties of Wood Fiber Composites Studied by Dynamic FT-IR Spectroscopy2008In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 27, no 16-17, p. 1709-1721Article in journal (Refereed)
    Abstract [en]

    Wood fiber reinforced polylactide is a biodegradable composite where both fibers and matrix are from renewable resources. In the development of such new materials, information on mechanical behavior on the macroscopic and the molecular level is useful. In this study, dynamic Fourier transform infrared (FT-IR) spectroscopy is used to measure losses at the molecular level during cyclic tensile loading for bonds that are characteristic of the cellulosic fibers and the polylactid matrix. This molecular behavior is compared with measured macroscopic hysteresis losses for different moisture levels. The results show that moisture ingress will transfer the load from the fibers to the matrix, and that a more efficient fiber-matrix interface would diminish mechanical losses. Although the dynamic FT-IR spectroscopy method is still qualitative, this investigation shows that it can provide information on the stress transfer of the constituents in wood fiber reinforced plastics.

  • 3.
    Jerpdal, Lars
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Scania CV AB, Sweden.
    Stahlberg, Daniel
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Influence of fibre stretching on the microstructure of self-reinforced poly(ethylene terephthalate) composite2016In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 35, no 21, p. 1634-1641Article in journal (Refereed)
    Abstract [en]

    Self-reinforced poly(ethylene terephthalate) laminates were prepared from woven fabric by compression moulding. The fabric was stretched to different degrees during heating before hot consolidation to simulate a manufacturing process where the material is stretched through forming. High tenacity poly(ethylene terephthalate) fibres with different degrees of stretching were prepared for a comparison to laminates. Tensile tests were made to characterize mechanical properties, while dynamical mechanical analysis, differential scanning calorimetry, FTIR spectroscopy and X-ray diffraction analysis were employed to study microstructural changes caused by the stretching. Tensile tests show that 13% stretching of the fabric increases the laminate tensile stiffness by 34%. However, same degree of stretching for pure fibres increases the fibre tensile stiffness by 111%. Crystallinity and molecular conformations are not influenced by stretching while shrinkage upon heating increases with degree of stretching. Shrinkage is known to be related to disorientation of non-crystalline regions whereof the conclusion from this study is that the increased tensile properties are due to orientation of the non-crystalline regions of the fibre.

  • 4.
    Jerpdal, Lars
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Scania CV, Södertälje, Sweden .
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Influence of fibre shrinkage and stretching on the mechanical properties of self-reinforced poly(ethylene terephthalate) composite2014In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 33, no 17, p. 1644-1655Article in journal (Refereed)
    Abstract [en]

    Self-reinforced poly(ethylene terephthalate) composite laminates were manufactured from fabric using a hot press. Fabric was either allowed to shrink or exposed to stretching during different phases of the manufacturing process. Composite macrostructure, crimp, was investigated and results showed that shrinkage affects fibre crimp more than stretching does. Mechanical tests showed that shrinkage do not significantly affect mechanical properties while stretching fabric by 10% during heating results in 50% increase in tensile stiffness. The lack of correlation between crimp and mechanical properties indicates that mechanical properties for self-reinforced poly(ethylene terephthalate) composites are dominated by their microstructure, molecular orientation, which may be affected by the manufacturing process.

  • 5. Mariatti, M.
    et al.
    Nasir, M.
    Ismail, H.
    Bäcklund, Jan
    KTH, Superseded Departments, Aeronautical Engineering.
    Effect of hole drilling techniques on tensile properties of continuous fiber impregnated thermoplastic (COFIT) plain weave composites2004In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 23, no 11, p. 1173-1186Article in journal (Refereed)
    Abstract [en]

    The effect of hole drilling technique on tensile properties of COFIT plain weave composite using circular hole was investigated. As expected, the tensile properties of COFIT woven system decrease with increasing hole sizes. The laminate, which was drilled by orbital technique, seems to impart higher tensile properties and better damage resistance compared to those of conventional drilling technique. In order to predict the laminate strength with the presence of open hole, the Point Stress Criterion was used. Results indicate that good agreement was obtained between experimental and estimation tensile strengths.

  • 6. Oldenbo, M.
    et al.
    Mattsson, D.
    Varna, J.
    Berglund, Lars A.
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Global stiffness of a SMC panel considering process induced fiber orientation2004In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 23, no 1, p. 37-49Article in journal (Refereed)
    Abstract [en]

    A material model, that translates into a stiffness matrix, the second order fiber orientation tensor, described by Advani and Tucker, and the stiffness matrix of a composite with aligned ellipsoidal inclusions, has been implemented in a FE programme and validated. The stiffness of a SMC panel with known state of fiber orientation is calculated using FEM. The influence of process induced fiber orientation is analysed. The fiber orientation for a realistic charge pattern for the panel has been obtained through mould filling simulation in a separate project. It is found that the fiber orientation has a rather small impact on the global stiffness. Only 0.8% lower stiffness compared to isotropic material model is obtained taking into account the fiber orientation distribution. The main reason for the low impact of the process induced fiber orientation is that the charge is symmetrically placed in the mould leading to a symmetric fiber orientation distribution.

  • 7.
    Stig, Fredrik
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Tahir, Mohammad Waseem
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    An experimental study of the influence from fibre architecture on the permeability of 3D-woven textiles2015In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 34, no 17, p. 1444-1453Article in journal (Refereed)
    Abstract [en]

    In this work experimental measurements of the permeability of fully interlaced 3D-woven carbon fibre preforms are performed using the unsaturated parallel flow method. The effect on the permeability from three different parameters is studied by altering the architecture of woven preforms and varying mould sizes in a duct flow set-up. Influences from the geometrically different surface layers of the woven preforms, from fibre volume fraction and from warp yarn crimp are studied. The measurements show negligible influence on the permeability from crimp and the fraction of weave surface layers while the fibre volume fraction has a prominent influence. However, the effect is not consistent in terms of fibre volume fraction variation alone but depends on how it is varied.

  • 8.
    Xu, Johanna
    et al.
    Lulea Univ Technol, Dept Engn Sci & Math, S-97189 Lulea, Sweden..
    Lindbergh, Göran
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.
    Varna, Janis
    Lulea Univ Technol, Dept Engn Sci & Math, S-97189 Lulea, Sweden..
    Multiphysics modeling of mechanical and electrochemical phenomena in structural composites for energy storage: Single carbon fiber micro-battery2018In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 37, no 10, p. 701-715Article in journal (Refereed)
    Abstract [en]

    This paper presents a framework for multiphysics modeling of a novel type of multifunctional composite material, structured on microscale, with ability to function as battery cell in addition to carry mechanical load. The micro-battery consists of a single carbon fiber surrounded by very thin solid electrolyte coating and embedded in a matrix which is a porous material containing active particles able to intercalate lithium. During battery operation (discharging and charging) the structural battery constituents undergo volume changes, caused by lithium-ion movement. The presented mathematical model is solved numerically using COMSOL software and results are used to analyze the physical phenomena occurring in the structural battery material. Parametric analysis is performed to reveal the significance of geometrical parameters like fiber volume fraction in the battery and the porosity content in the matrix on the multifunctional performance of the composite unit including its swelling/shrinking during charging/discharging.

  • 9.
    Zimmermann, Kristian
    et al.
    EADS Innovation Works, Munich, Germany.
    Van den Broucke, B.
    Assessment of process-induced deformations and stresses in ultra thick laminates using isoparametric 3D elements2012In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 31, no 3, p. 163-178Article in journal (Refereed)
    Abstract [en]

    Shape distortions are a common problem experienced during the manufacturing of fiber reinforced plastics and are commonly investigated for thinner components. The following study presents the analysis of shape distortions and residual stresses in Ultra-thick laminates using a coupled thermomechanical approach. Existing studies frequently use high resolution meshes with multiple elements over ply thickness. This approach is not feasibly for thicker structures due to the computational effort. A new curing cycle, adapted to the requirements of Ultra-thick laminates, is deployed. Residual stresses need to be quantified and accounted for in the structural analysis. Several test components are manufactured in non-crimped fabric, to generate comparable data on heat distribution within the laminate and to measure the spring-in angle. For the FE analysis 3D stacked composite brick elements are used. These combine several plies within each element and present an efficient way to analyse thicker composite structures. Substantial residual stresses are calculated in the curved section of the laminate. A discrepancy in the calculated and measured spring-in angle is most likely explained by the usage of a single-sided steel tooling and several debulking steps.

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