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  • 1.
    Almgren, K. M.
    et al.
    RISE, STFI-Packforsk.
    Kerholm, M.
    RISE, STFI-Packforsk.
    Gamstedt, E. K.
    RISE, STFI-Packforsk.
    Salmen, Lennart
    RISE, STFI-Packforsk.
    Lindström, Mikael
    RISE, STFI-Packforsk.
    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.

  • 2.
    Andersons, J.
    et al.
    University of Latvia.
    Sparniņš, E.
    University of Latvia.
    Nyström, Birgitha
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Joffe, Roberts
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Scale effect of the tensile strength of flax-fabric-reinforced polymer composites2011In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 30, no 23, p. 1969-1974Article in journal (Refereed)
    Abstract [en]

    The development of UD natural fiber composites, considered for application as structural materials, necessitates evaluation of the scale effect of their strength. Alignment of the fibers in flax bast fiber composites can be achieved by employing textile reinforcement, such as yarns and fabrics. Cutting specimens for mechanical tests out of such textile-reinforced composite plates results in a complex non-uniform reinforcement structure at their edges, which may affect the strength of specimens. Scale effect of the tensile strength in the fiber direction of flax-fabric-reinforced composites is studied in the current work. A model accounting for both volume and edge effect of the specimens on their tensile strength is proposed. © The Author(s) 2011.

  • 3.
    Fernberg, Patrik
    et al.
    RISE, Swerea, Swerea SICOMP.
    Sandlund, Erik
    RISE, Swerea, Swerea SICOMP.
    Lundström, T.S.
    Luleå University of Technology.
    Mechanisms controlling particle distribution in infusion molded composites2006In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 25, no 1, p. 59-70Article in journal (Refereed)
    Abstract [en]

    This article presents results from an experimental investigation in which two grades of aluminatrihydroxide (ATH) particles are added to liquid resin and used in infusion molding experiments. Based on the results, potential key mechanisms controlling resin flow and hence also the final particle distribution are proposed. A pore doublet model is proposed to explain the seemingly random spatial distribution of particle-dense regions within the final material. These dense regions are found within flow channels, at locations where local shear strain rates are low. This suggests that they are formed as a consequence of a Bingham type of viscosity behavior observed for the suspension and/or due to filtering of particles during fiber bundle impregnation. © 2006 SAGE Publications.

  • 4.
    Giannadakis, K.
    et al.
    Lulea University of Technology, Sweden.
    Mannberg, Peter
    RISE, Swerea, SICOMP. Lulea University of Technology, Sweden.
    Joffe, Roberts
    RISE, Swerea, SICOMP. Lulea University of Technology, Sweden.
    Varna, J.
    Lulea University of Technology, Sweden.
    The sources of inelastic behavior of Glass Fibre/Vinylester non-crimp fabric [±45]s laminates2011In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 30, no 12, p. 1015-1028Article in journal (Refereed)
    Abstract [en]

    The non-linear and time-dependent stress-strain response of NCF [±45]s laminates in tension is studied. Testing methodology is suggested to separate and quantify the effect of damage development, non-linear viscoelastic effects, and viscoplasticity on the inelastic response. This is achieved by decomposition of viscoelastic and viscoplastic response, both of them being affected by microdamage accumulated during the service life. Material model based on Schapery's work on viscoelasticity and Zapas viscoplastic function with added damage terms is presented and used. Simulation is performed and validated with constant stress rate tensile tests, identifying the non-linear viscoelasticity and viscoplasticity as the major sources of the non-linear response.

  • 5.
    Kluge, N. J.
    et al.
    Luleå University of Technology, Sweden.
    Lundström, T. S.
    Luleå University of Technology, Sweden.
    Westerberg, L. G.
    Luleå University of Technology, Sweden.
    Olofsson, Kurt
    RISE, Swerea, SICOMP.
    Compression moulding of sheet moulding compound: Modelling with computational fluid dynamics and validation2015In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 34, no 6, p. 479-492Article in journal (Refereed)
    Abstract [en]

    Compression moulding experiments of sheet moulding compound, visual observations of a vacuum test with prepregs and numerical models with two main approaches for computational fluid dynamics simulations of the mould filling phase are presen ed. One assumes that there are layers near the mould surfaces with much less viscosity and the other only use one viscosity model. The numerical experiments showed that the pressure could be accurately predicted with both approaches. The property ne essary to predict correct pressure with altered mould closing velocities was that the bulk material had to obey shear-thinni g effects. Preheating effects before compression were neglected, but altering the heating time until the prepreg was assumed to start flow had a significant effect. The experiments confirmed that the pressure is predominantly affected by the mould c osing velocity. Regardless of the considered process settings, a first pressure top always appeared approximately at the logarithmic strain 0.25. A second top was associated with a slowdown of the press. The location of this was affected by the velocity and the vacuum, the latter indicating that vacuum assistance prevents a build-up of back pressure. Furthermore, heated prepreg above a critical temperature is observed to swell immediately as vacuum assistance is applied.

  • 6.
    Nyström, Birgitha
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Joffe, Roberts
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Långström, Runar
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Microstructure and strength of injection molded natural fiber composites2007In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 26, no 6, p. 579-599Article in journal (Refereed)
    Abstract [en]

    Injection molded short natural fiber composites (NFC) are studied in this article. Micromechanical models are employed to investigate effects of fiber length distribution, fiber orientation, and fiber/matrix adhesion on mechanical performance of NFCs. A parametric study showed that length/diameter ratio strongly affects the composite strength, whereas fiber strength has very little influence on strength of the composites when fiber/matrix adhesion is poor. In order to verify conclusions based on theoretical predictions, modeling results are compared with experimental results of wood powder-, flax-, pulp-, and glass fiber composites. Recommendations on improvement of strength of NFC through change of the internal structure of the materials are formulated based on results of this investigation. © 2007 SAGE Publications.

  • 7.
    Oksman, Kristiina
    RISE, Swerea, Swerea SICOMP.
    High quality flax fibre composites manufactured by the resin transfer moulding process2001In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 20, no 7, p. 621-627Article in journal (Refereed)
    Abstract [en]

    In this work the use of high quality natural fibres as reinforcements was studied using the resin transfer moulding (RTM) processing technique. The fibres were unidirectional high quality ArcticFlax and the matrix was an epoxy resin. The mechanical properties of the composites were compared to conventional RTM manufactured glass fibre composites, traditionally retted UD-flax fibre composites and to the pure epoxy. The results from mechanical testing showed that the (50/50) high quality ArcticFlax/epoxy composite has a stiffness of about 40 GPa compared to the stiffness in pure epoxy of 3.2 GPa. The same composite has a tensile strength of 280 MPa compared to 80 MPa of the epoxy. RTM showed to be a suitable processing technique for natural fibre composites when high quality laminates are preferred.

  • 8.
    Rouhi, Mohammad
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Juntikka, Magdalena
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Landberg, Johan
    RISE - Research Institutes of Sweden, Materials and Production, IVF.
    Wysocki, Maciej
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials.
    Assessing models for the prediction of mechanical properties for the recycled short fibre composites2019In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 38, no 10, p. 454-466Article in journal (Refereed)
    Abstract [en]

    Processing of polymer fibre composites has a remarkable influence on their mechanical performance. These mechanical properties are even more influenced when using recycled reinforcement. Therefore, we place particular attention on the evaluation of micromechanical models to estimate the mechanical properties and compare them against the experimental results of the manufactured composites from recycled carbon fibre material. For the manufacturing process, an epoxy matrix and carbon fibre production cut-offs as reinforcing material are incorporated using a vacuum infusion process. In addition, continuous textile reinforcement in combination with the epoxy matrix is used as reference material to evaluate the degradation of mechanical performance of the recycled composite. The experimental results show higher degradation of the composite strength compared to the stiffness properties. Observations from the modelling also show the same trend as the deviation between the theoretical and experimental results is lower for stiffness comparisons than the strength calculations. Yet still, good mechanical performance for specific applications can be expected from these materials.

  • 9.
    Svanberg, Magnus
    et al.
    RISE, Swerea, Swerea SICOMP.
    Altkvist, C.
    Saab AB.
    Nyman, T.
    Saab AB.
    Prediction of shape distortions for a curved composite C-spar2005In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 24, no 3, p. 323-339Article in journal (Refereed)
    Abstract [en]

    This paper presents predictions and validations of shape distortions of a curved C-spar, using a simulation tool developed in the general purpose FE-program ABAQUS. The simulation tool is based on a simplified mechanical constitutive model that accounts for the mechanisms identified in a previous experimental study concerning the influence from the cure schedule on shape distortions. The main objective of the present paper is to validate the simplified constitutive model and a simplified simulation approach. The feasibility for simulation of shape distortions of a component with relatively complex shape has also been investigated. © 2005 Sage Publications.

  • 10.
    Vahlund, Fredrik
    RISE, Swerea, Swerea SICOMP.
    Using a finite volume approach to simulate the mould filling in compression moulding2003In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 22, no 6, p. 499-515Article in journal (Refereed)
    Abstract [en]

    A mould filling simulation of an automotive hood geometry was performed using a general purpose finite volume computational fluid dynamics (CFD) code. The simulation was performed as a homogenous multi-phase model using mass sinks to remove excess air from the computational domain and performed in three-dimensions. The kinematic boundary condition was modelled using a hydrodynamic friction at the mould boundaries corresponding to that in the Barone and Caulk approximation. The fibre orientation distribution was simulated throughout the closure phase using the Folgar Tucker equation for the reorientation of the fibres and orientation tensors to describe the local orientation for each element. The paper presents the methodology for, and the possibilities of, using a general purpose CFD code for these kinds of simulations. Both mould filling simulations in general can be performed and special cases where the standard simplifications of the governing equations are not valid can be investigated.

  • 11.
    Zrida, H.
    et al.
    Lulea University of Technology.
    Marklund, Erik
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Ayadi, Z.
    Ecole Européenne D'Ingénieurs en Génie des Matériaux.
    Varna, J.
    Lulea University of Technology.
    Effective stiffness of curved 0°-layers for stiffness determination of cross-ply non-crimp fabric composites2014In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 33, no 14, p. 1339-1352Article in journal (Refereed)
    Abstract [en]

    The effect of the 0°-tow waviness on axial stiffness of cross-ply non-crimp fabric composites is analysed using multiscale approach. The curved 0°- and 90°-layers are represented by flat layers with effective stiffness properties and classical laminate theory is used to calculate the macroscopic stiffness. The effective 0°-layer stiffness is calculated analysing isolated curved 0°-layers subjected not only to end loading, but also to surface loads. The surface loads are identified in a detailed finite element analysis and approximated by a sinus shaped function with amplitude depending on the waves parameters. The sinus shaped surface loads are then applied to an isolated curved 0°-layer finite element model together with end loading to calculate the effective stiffness of the layer. Finally, the effective 0°-layer stiffness was successfully used to calculate the macroscopic stiffness of the composite proving validity of the approach being used and showing that, without losing accuracy, elastic properties in the 90°-layers with bundle structure can be replaced by the transverse stiffness of the homogenised 90°-layer material. © 2014 The Author(s).

1 - 11 of 11
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