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  • 1.
    Adekunle, Kayode
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Cho, Sung-Woo
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Patzelt, Christian
    Blomfeldt, Thomas
    Skrifvars, Mikael
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Impact and flexural properties of flax fabrics and Lyocell fiber-reinforced bio-based thermoset2011Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 30, nr 8, s. 685-697Artikkel i tidsskrift (Fagfellevurdert)
    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 280 MPa, 32 GPa, 250 MPa, 25 GPa, and 75 kJ/m2, 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. Fieldemission scanning electron microscopy was used to study the micro-structural properties of the composites.

  • 2. Adekunle, Kayode
    et al.
    Cho, Sung-Woo
    Patzelt, Christian
    Blomfeldt, Thomas
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Skrifvars, Mikael
    Impact and flexural properties of flax fabrics and Lyocell fiber-reinforced bio-based thermoset2011Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 30, nr 8, s. 685-697Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 3.
    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 spectroscopy2008Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 27, nr 16-17, s. 1709-1721Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 4. 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 Spectroscopy2008Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 27, nr 16-17, s. 1709-1721Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 5.
    Andersons, J.
    et al.
    University of Latvia.
    Sparniņš, E.
    University of Latvia.
    Nyström, Birgitha
    RISE - Research Institutes of Sweden, Material och produktion, SICOMP.
    Joffe, Roberts
    RISE - Research Institutes of Sweden, Material och produktion, SICOMP.
    Scale effect of the tensile strength of flax-fabric-reinforced polymer composites2011Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 30, nr 23, s. 1969-1974Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 6.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Sparnins, Edgars
    Nyström, Birgitha
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Scale effect of the tensile strength of flax-fabric-reinforced polymer composites2011Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 30, nr 23, s. 1969-1974Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 7.
    Berglund, Lars A.
    et al.
    Luleå tekniska universitet.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Yuan, Jie
    Linköpings universitet.
    Transverse Cracking and Local Delamination in [04/90n]s and [90n/04]s Carbon Fiber/Toughened Epoxy Laminates1992Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 11, nr 6, s. 643-660Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    [04/90n]s and [90n/04 ]s laminates were used to study 90°-layer failure mechanisms in HTA/6376 carbon fiber/toughened epoxy. The different stacking sequences were chosen to vary the stress states, since experimental results show differences in failure strains as well as in the local delamination behavior at the crack tip. Differences in the onset of transverse cracking and local delamination behavior between [04/90m]s and [90 n/04]s laminates was discussed using a model based on linear elastic fracture mechanics (LEFM). Although quantitative LEFM-predictions do not agree with data for the carbon fiber/toughened epoxy investigated, the general predictions for differences in and causes of local delamination behavior were confirmed by experimental data. The fact that the main features were correctly predicted, encourages the development of some modified LEFM-approach to describe toughened matrix composites.

  • 8.
    Fernberg, Patrik
    et al.
    RISE, Swerea, Swerea SICOMP AB.
    Sandlund, Erik
    RISE, Swerea, Swerea SICOMP AB.
    Lundström, T.S.
    Luleå University of Technology.
    Mechanisms controlling particle distribution in infusion molded composites2006Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 25, nr 1, s. 59-70Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 9.
    Fernberg, S.P.
    et al.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Sandlund, E.J.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Mechanisms controlling particle distribution in infusion molded composites2006Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 25, nr 1, s. 59-70Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 10.
    Frishfelds, Vilnis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Jakovics, Andris
    Faculty of Physics and Mathematics, University of Latvia.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Automatic recognition and analysis of scanned non-crimp fabrics for calculation of their fluid flow permeability2007Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 26, nr 3, s. 285-296Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Automatic recognition of scanned images of distorted bi-axial fiber bundle arrangements is considered in order to obtain the overall permeability of the formed fiber network. Scanned images are pre-processed with color normalization followed by usage of a threshold to find the pixels belonging to the bundles, the threads keeping the bundles together, and the distinct gaps formed between the bundles. Since the scanned images virtually have a perfect grayscale, the intensity can be treated as a corresponding signal of the image. Next the regular character of the fiber network is investigated using Fourier analysis on the fiber bundles as well as on the threads. The direction, position, and spatial separation of the fiber bundle and the threads are obtained in this way. In order to recognize the bottom fiber bundle layer a fine structure technique is used. Small clusters falsely identified as belonging to the bottom bundle layer are removed by application of a threshold to the perimeter of the cluster. The gaps in the top bundle layer are identified more clearly in this way. Next, a local Fourier analysis is applied to obtain the local distortion of the bundle and the thread structure yielding the characteristic distribution of the gaps between the bundles. Finally the distribution of the width of the threads is obtained by simply identifying the minimal distance between the sides of the threads.

  • 11.
    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 laminates2011Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 30, nr 12, s. 1015-1028Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 12.
    Giannadakis, Konstantinos
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mannberg, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    The sources of inelastic behavior of glass fibre/vinylester non-crimp fabric [±45]s laminates2011Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 30, nr 12, s. 1015-1028Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 13.
    Hassan, Mohammad L.
    et al.
    National Research Centre.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hassan, Enas A.
    National Research Centre.
    Fadel, Shiamaa M
    National Research Centre.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Improving cellulose/polypropylene nanocomposites properties with chemical modified bagasse nanofibers and maleated polypropylene2014Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 33, nr 1, s. 26-36Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The properties of cellulose/polypropylene (PP) nanocomposites with n-octadecyl-modified bagasse nanofibers (MBNF) were compared to those with maleated polypropylene (MAPP) coupling agent. The nanocomposites were prepared by twin-screw extrusion with bagasse nanofiber (BNF) content varying from 2.5 to 10 wt%. The compression molded nanocomposites sheets were characterized regarding their tensile strength properties, dynamic mechanical thermal properties, crystallinity, water absorption, transparency and loss of strength due to composting in soil. As a compatibilizer to improve the tensile strength properties and transparency of PP/cellulose nanofibers nanocomposites, MAPP was more effective than n-octadecyl-modified cellulose nanofibers. The crystallinity of the nanocomposites was lower than that of neat PP except for those prepared using high loading of MBNF. Dynamic mechanical thermal analysis (DMTA) of the prepared materials showed that adding the different nanofibers (treated or untreated) resulted in better mechanical thermal properties above glass transition temperature (Tg) of PP. Water absorption capability in all nanocomposites was weakened while that in PP/MBNF was the lowest. No significant differences were found between the nanocomposites with different kinds of nanofibers regarding the loss of their tensile strength after compositing in soil up to six months.

  • 14.
    Holmstedt, Elise
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Åkerstedt, Hans O.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan T.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Modelling transport and deposition of non-spherical micro- and nano-particles in composites manufacturing2018Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 37, nr 8, s. 507-519Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In liquid moulding processes, a fabric is impregnated with a fluid that may contain particles aimed at giving the final product additional and possible smart properties. It is therefore interesting to be able to reveal how the distribution and orientation of such particles are affected by the processing condition. During the manufacturing of the fabric, relatively large channels are formed between bundles of fibres where the impregnating fluid may flow. There are also micro-channels within the bundle that are impregnated by the fluid in the larger channels mainly by capillary action. With focus on fibre bundles along the main flow direction, three main stages of the flow are the flow is leading within the bundles, the flow is moving at equal rate within the bundles and between them and the flow is leading in the channels between the bundles. The latter one of these is in focus in this study, and the capillary action from the larger channels to the micro-channels is modelled as a constant radial velocity. Brownian, gravitational and hydrodynamic forces acting on the particles are studied. The introduction of a radial velocity component drastically increases the deposition rate, and it is clear that while particle shape has a great influence on deposition rates in a flow moving strictly in the direction of the channel, when a radial flow component is introduced the differences seem to disappear.

  • 15.
    Jabbari, Mostafa
    et al.
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Åkesson, Dan
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Skrifvars, Mikael
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Taherzadeh, Mohammad J
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Novel lightweight and highly thermally insulative silica aerogel-doped poly (vinyl chloride)-coated fabric composite2015Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 34, nr 19, s. 1581-1592Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Novel lightweight and highly thermal insulative aerogel-doped poly(vinyl chloride)-coated fabric composites wereprepared on woven fabrics made of polyester fibres using knife coating method, and their performances were comparedwith neat composite. The composites were prepared by incorporating a commercial aerogel to a ‘green’ poly(vinylchloride) (PVC) plastisol. The effect of aerogel-content, thermal insulating property, thermal degradation, surface characteristics,tensile and physical properties of the composites were investigated. Results revealed that aerogel couldreduce thermal conductivity, density and hydrophilicity of the composites dramatically without significant decrease inother properties. Experimental results showed that thermal insulation properties were enhanced by 26% (from 205 to152 mW/m-K), density decreased by 17% (from 1.132 to 0.941 g/cm3) and hydrophobicity increased by 16.4% (from76.02 to 88.671.48) with respect to the unmodified coated fabric. Analyses proved that composite with 3% aerogel isthe lightest by weight, while 4% showed the highest thermal insulation. The results showed that 4% is the criticalpercentage, and preparation of composites with aerogel content higher than 4% has limitations with the given formulationdue to high viscosity of plastisol. The prepared composite has potential applications in many fields such asdevelopment of textile bioreactors for ethanol/biogas production from waste materials, temporary houses and tents,facade coverings, container linings and tarpaulins. The prepared composite can be considered ‘green’ due to usage of anon-phthalate environment-friendly plasticiser.

  • 16.
    Jerpdal, Lars
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. Scania CV AB, Sweden.
    Stahlberg, Daniel
    Åkermo, Malin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Influence of fibre stretching on the microstructure of self-reinforced poly(ethylene terephthalate) composite2016Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 35, nr 21, s. 1634-1641Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 17.
    Jerpdal, Lars
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. Scania CV, Södertälje, Sweden .
    Åkermo, Malin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Influence of fibre shrinkage and stretching on the mechanical properties of self-reinforced poly(ethylene terephthalate) composite2014Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 33, nr 17, s. 1644-1655Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 18.
    Järneteg, Anette
    et al.
    Linköpings universitet.
    Berglund, Lars
    Luleå tekniska universitet.
    A simple procedure for the evaluation of fiber size effects on the properties of filament wound glass fiber composites1992Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 11, nr 1, s. 98-102Artikkel i tidsskrift (Fagfellevurdert)
  • 19. Kluge, Jimmy
    et al.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Ljung, Anna-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Westerberg, Lars-Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Nyman, Tony
    Saab Aeronautics, SE-582 54 Linköping, SWEDEN.
    An Experimental Study of Temperature Distribution in an Autoclave2016Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 35, nr 7, s. 566-578Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, the temperature distribution on an industrial mold tool is monitored during autoclave runs with three settings. In one of the settings, the temperature and pressure follow a scheme used in real moldings, while in the other two cases, the temperature is increased as fast as possible with and without an applied pressure. The temperature difference over the tool is relatively large and varies between 29℃ and 76℃ validating a detailed investigation of the temperature at different points. Two results of this are that positions on the up-stream side of the tool are heated faster than positions down-stream and the heating over the tool is symmetric while that within is asymmetric. Roughly estimated heat transfer coefficients reveal that the temperature ramping has no significant effect on the local heat transfer coefficients while the applied pressure more than doubled them. In addition flow field measurements with particle image velocimetry are performed, revealing a very slow flow near the roof of the autoclave and a velocity peak near the floor of it, indicating that the flow profile within the autoclave and variation in heat transfer coefficients should be considered in autoclave simulations.

  • 20. Kluge, Jimmy
    et al.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Westerberg, Lars-Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Nyman, Tony
    Saab Aeronautics, SE-582 54 Linköping, SWEDEN.
    Modelling Heat Transfer Inside an Autoclave: Effect of Radiation2016Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 35, nr 14, s. 1126-1142Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, computational fluid dynamics simulations are performed to predict the temperature distribution on a part during an autoclave run. Data from an experimental study are used as input to the simulations and also for comparison with the numerical results. A conjugate heat transfer approach was used for the simulations, where best agreement with experiments was obtained from the simulation that included thermal radiation and utilized an experimentally obtained velocity profile as inlet velocity. A yet more detailed inlet velocity profile and more advanced turbulent model could result in an even better agreement.

  • 21. Kluge, Jimmy
    et al.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Westerberg, Lars-Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Olofsson, Kurt
    Swerea SICOMP AB.
    Compression moulding of sheet moulding compound: Modelling with computational fluid dynamics and validation2015Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 34, nr 6, s. 479-492Artikkel i tidsskrift (Fagfellevurdert)
    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 presented. 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 necessary to predict correct pressure with altered mould closing velocities was that the bulk material had to obey shear-thinning 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 closing 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.

  • 22.
    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 validation2015Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 34, nr 6, s. 479-492Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 23. Lundström, Staffan
    et al.
    Gebart, Rikard
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Lundemo, C.Y.
    Void formation in RTM1993Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 12, nr 12, s. 1339-1349Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The problem of void formation in composites processing is very important since the physical and mechanical properties as well as the finish of the product are strongly influenced by the presence of voids. Examples of properties that are adversely affected by voids are the strength and the weather resistance of the composite. The knowl edge about void formation in the RTM process is still very limited compared to what is known about autoclave production of composites, and it is not clear whether the voids are created by diffusion growth, mechanical entrapment or some other mechanism.

  • 24.
    Lundström, Staffan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Holmgren, Allan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Dissolution of voids during compression moulding of SMC2010Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 29, nr 12, s. 1826-1837Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During compression molding of sheet molding compounds air bubbles are formed that can deteriorate several properties of the final composite. The story of such bubbles is directly set by the local pressure distribution during pressing. A number of experiments have therefore been performed in order to derive the relation between the pressure and dissolution rate of some gases into relevant resins. The experimental results follow Henry's law up to a pressure of 0.7 MPa and the rate of dissolution is highest for CO2 in pure polyester. When applying the results to the process in focus it is found that even large bubbles can be dissolved into the liquid resin during manufacturing. Hence, there is a potential to produce parts with very low void content.

  • 25.
    Lundström, T. Staffan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Transversal flow-induced deformation of fibres during composites manufacturing and the effect on permeability2013Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 32, nr 15, s. 1129-1135Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Low Reynolds number flow of a viscous fluid through bundles in non-crimp stitched fabrics is considered for different arrangements of the fibres within the bundles. Using a previous derived model, two-dimensional Navier–Stokes solutions are sampled for the flow between a few fibres with a subsequent minimisation of the dissipation rate in the total system of fibres. Based on the detailed geometry of the fabrics flow induced elastic deformations of the fibre bundles are then derived and the overall permeability is computed for different pressure gradients. The permeability of random arrays of a large number of as well mono-dispersed as poly-dispersed fibres increases as the flow-induced deformation increases and despite the relative shift of the fibres is small the overall change in permeability is essential. For a system with gaps between bundles the change in permeability depends on the orientation of the flow field with respect to the geometry studied while for a regular packing the alteration in permeability is negligible.

  • 26. Mariatti, M.
    et al.
    Nasir, M.
    Ismail, H.
    Bäcklund, Jan
    KTH, Tidigare Institutioner, Flygteknik.
    Effect of hole drilling techniques on tensile properties of continuous fiber impregnated thermoplastic (COFIT) plain weave composites2004Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 23, nr 11, s. 1173-1186Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 27. Nyman, T.
    et al.
    Bredberg, A.
    Schon, J.
    Schön, J., Aero. Res. Institute of Sweden, P.O. Box 11021, 5-161 11 Bromma, Sweden.
    Equivalent damage and residual strength for impact damaged composite structures2000Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 19, nr 6, s. 428-448Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Determining structural durability and damage tolerance of aircraft-composite structures is an important task, not only in the design process but also when the aircraft is in operational use. There are many sources and types of damage, e.g., fatigue cracking, environmental degradation, or damage introduced by foreign objects. When occurring, all types of damage need immediate attention for determination of the effect on aircraft performance or functionality. There is a need in other words for simplified predictive methods for rapid assessment of occurring damage, where impact damage is the most important damage mode. In this paper two residual strength models are presented, the so-called soft inclusion and delamination buckling theory, and compared to experimental results on impact damaged composite structures. Those experiments span a variety of impact events, from 8 J to 55 J and different layups. The investigation has been supported by FE-technique for determination of the stress distribution in the buckled state and for characterization of the damaged region. It can be concluded that for low-energy impact, through conservative assumptions on stiffness reduction, that the soft inclusion is unconservative for residual strength prediction. In contrast the delamination buckling theory shows good agreement for various impact energy levels, thicknesses and layups. The importance of repeated loading for composite structures with artificial delaminations is also demonstrated. If repeated loaded, the local buckling strain is strongly reduced as compared to a non-repeated loaded structure. It can also be shown that artificial delaminations, though deep-lying, can grow in a stable manner if pre-buckled.

  • 28.
    Nyström, B.
    et al.
    Luleå University of Technology.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Långström, R.
    SICOMP AB, Swedish Institute of Composites.
    Microstructure and strength of injection molded natural fiber composites2007Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 26, nr 6, s. 579-599Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 29.
    Nyström, Birgitha
    et al.
    RISE - Research Institutes of Sweden, Material och produktion, SICOMP.
    Joffe, Roberts
    RISE - Research Institutes of Sweden, Material och produktion, SICOMP.
    Långström, Runar
    RISE - Research Institutes of Sweden, Material och produktion, SICOMP.
    Microstructure and strength of injection molded natural fiber composites2007Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 26, nr 6, s. 579-599Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 30. Oksman, Kristiina
    High quality flax fibre composites manufactured by the resin transfer moulding process2001Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 20, nr 7, s. 621-627Artikkel i tidsskrift (Fagfellevurdert)
    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 s tiffness in pure epoxy of 3.2 GPa. The same composite has a tensile s trength 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

  • 31.
    Oksman, Kristiina
    RISE, Swerea, Swerea SICOMP AB.
    High quality flax fibre composites manufactured by the resin transfer moulding process2001Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 20, nr 7, s. 621-627Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 32. Oldenbo, M.
    et al.
    Mattsson, D.
    Varna, J.
    Berglund, Lars A.
    KTH, Tidigare Institutioner                               , Fiber- och polymerteknologi.
    Global stiffness of a SMC panel considering process induced fiber orientation2004Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 23, nr 1, s. 37-49Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 33.
    Oldenbo, Magnus
    et al.
    Volvo Car Corporation.
    Mattsson, David
    Volvo Car Corporation, Exterior Engineering, Dept 93610 PV3C.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Berglund, Lars A.
    Luleå tekniska universitet.
    Global stiffness of a SMC panel considering process induced fiber orientation2004Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 23, nr 1, s. 37-49Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 34.
    Olofsson, Kurt S.
    Luleå tekniska universitet.
    Stress Development in Wet Filament Wound Pipes1997Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 16, nr 4, s. 372-390Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A computer based process model for wet filament winding has been developed. A software supplied by Stanford University has been modified for the numerical simulation. The model has been verified with manufacturing of glass fiber pipes including the industrially common case of pipes with mixed angle lay-up. Resin pressure in the composite during winding was measured and found to be relatively low supporting the assumption that it can be neglected for this process. Calculated final fiber fraction distribution agrees well with measured values on cured pipes. The model shows that fiber fraction is changed significantly during the winding stage due to compression forces. Mechanical and total strain measurements generally show good agreement with calculations. Analysis of ring gaps indicate that residual stresses are dominated by other effects than matrix shrinkage for the investigated parameter combination.

  • 35. Rajan, Rathish
    et al.
    Riihivuori, Johanna
    Rainosalo, Egidija
    Skrifvars, Mikael
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Järvelä, Pentti
    Effect of viscose fabric modification on the mechanical and water absorption properties of composites prepared through vacuum infusion2014Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 33, nr 15, s. 1416-1429Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Viscose fabric-reinforced unsaturated polyester composites were successfully prepared through vacuum infusion process. Unidirectional viscose fabric was modified by two different organosilane coupling agents and by acetylation treatment. The main objective was to study the influence of fabric treatment on the mechanical and water absorption properties of the composites. Flexural, tensile and impact properties of composites were studied. The results from mechanical testing of composites pointed out that 3-aminopropyltriethoxy silane treatment increased the flexural and impact strengths of the composites with respect to untreated fabric composite. The impact strength of 3-aminopropyltriethoxy silane-treated fabric composites almost doubled compared to the value of untreated fabric composite. Among all the composites under study, those with fabrics treated by 2 vol% 3-aminopropyltriethoxy silane in ethanol/water (95:5) solution exhibited significant improvement in water uptake resistance. An unsaturated polyester gelcoat and topcoat were applied as the outer surface on the composites with untreated fabric. This was done in order to investigate the visual surface appearance and evaluate the gelcoat and topcoat effect on water absorption after accelerated water immersion test. The regenerated cellulose fibre as reinforcement shows high potential to be used as an alternative for natural bast fibres, especially, when toughness of material matters. Chemical treatment of regenerated cellulose fibres could result in improvement in properties of polymer composites, considering that the appropriate treatment method is selected for the corresponding fibre–matrix system.

  • 36.
    Ramamoorthy, S. K.
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Di, Q.
    Adekunle, K.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Skrifvars, M.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Effect of water absorption on mechanical properties of soybean oil thermosets reinforced with natural fibers2012Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 31, nr 18, s. 1191-1200Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Natural fiber composites are known to absorb more water than glass fiber reinforced composites. In this study, hybrid natural fiber composites were prepared by combining different fiber reinforcements, and both the water absorption and the mechanical properties were studied. Compression molding technique was used to manufacture composite laminates from a bio-based resin (acrylated epoxidized soybean oil) and natural fibers: non-woven and woven jute, non-woven regenerated cellulose mat (Lyocell and viscose), and woven glass fiber. The composite laminates were cured at 160–170 C and 40 bar, with a fiber content of 40 wt%. We investigated effect of pretreatment of regenerated cellulose fiber using 4% NaOH solution. The gravimetric water absorption was tested by exposure to water for 10 days. Specimens were cut from composites with laser-cutting technique according to ISO standards, and tested for tensile, flexural, and impact strength. To determine the influence of water absorption on the mechanical properties, specimens were immersed in distilled water for 10 days before testing. As a reference, dry specimens were tested. The results showed that water absorption was reduced by producing hybrid composites with jute fibers, glass fiber, and Lyocell fiber. The tensile, flexural, and impact properties were improved by inclusion of glass fiber and Lyocell in the composite. The tensile and flexural properties of natural fiber reinforced composites were mostly affected by the influence of water, but this was improved considerably by hybridization with glass and Lyocell fibers. The viscoelastic properties of the manufactured composites and hybrid composites were studied using dynamic mechanical thermal analysis.

  • 37.
    Ramamoorthy, Sunil Kumar
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Kundu, Chanchal Kumar
    Adekunle, Kayode
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bashir, Tariq
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Skrifvars, Mikael
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Properties of green composites with regenerated cellulose fiber and soybean-based thermoset for technical applications2014Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 33, nr 2, s. 193-201Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Composites were developed by reinforcing available non-woven Lyocell and viscose in acrylated epoxidized soybean oil (AESO). Compression molding was used to make composites with 40–60 wt% fiber content. The fiber content comprises only Lyocell or viscose fiber, or mixture of these fibers in known ratio. Hybrid composites were made by a mixture of both the fibers in known ratio and it affects the properties. The effect of hybridization was evident in most tests which gives us an opportunity to tailor the properties according to requirement. Lyocell fiber reinforced composites with 60 wt% fiber content had a tensile strength and modulus of about 135 MPa and 17 GPa, respectively. Dynamic mechanical analysis showed that the Lyocell fiber reinforced composites had good viscoelastic properties. The viscose fiber reinforced composites had the high percentage elongation and also showed relatively good impact strength and flexural modulus. Good fiber-matrix adhesion reflected in mechanical properties. SEM images were made to see the fiber-matrix compatibility.

  • 38.
    Rouhi, Mohammad
    et al.
    RISE - Research Institutes of Sweden, Material och produktion, SICOMP.
    Juntikka, Magdalena
    RISE - Research Institutes of Sweden, Material och produktion, SICOMP.
    Landberg, Johan
    RISE - Research Institutes of Sweden, Material och produktion, IVF.
    Wysocki, Maciej
    RISE - Research Institutes of Sweden, Biovetenskap och material, Kemi och material.
    Assessing models for the prediction of mechanical properties for the recycled short fibre composites2019Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 38, nr 10, s. 454-466Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 39.
    Stig, Fredrik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Tahir, Mohammad Waseem
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Hallström, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åkermo, Malin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    An experimental study of the influence from fibre architecture on the permeability of 3D-woven textiles2015Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 34, nr 17, s. 1444-1453Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 40.
    Svanberg, Magnus
    et al.
    RISE, Swerea, Swerea SICOMP AB.
    Altkvist, C.
    Saab AB.
    Nyman, T.
    Saab AB.
    Prediction of shape distortions for a curved composite C-spar2005Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 24, nr 3, s. 323-339Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 41.
    Vahlund, Fredrik
    RISE, Swerea, Swerea SICOMP AB.
    Using a finite volume approach to simulate the mould filling in compression moulding2003Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 22, nr 6, s. 499-515Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 42.
    Varna, Janis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Berglund, Lars A.
    Luleå tekniska universitet.
    A Model for Prediction of the Transverse Cracking Strain in Cross-Ply Laminates1992Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 11, nr 7, s. 708-728Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A modified variational analysis based on the principle of minimum com plementary energy, is used to describe the stress state around a through-the-thickness transverse crack in [0 m/90n]s cross-ply laminates. The analysis takes into account nonlinear stress distribution in the thickness direction of the 0°-plies and contains a thermoelastic consideration. A failure criterion based on linear elastic fracture mechanics is used to pre dict the onset of transverse matrix cracking in cross-ply laminates. The predictions are compared with experimental data and with previous analyses developed in the framework of the shear lag theory or the variational approach suggested by Hashin.

  • 43.
    Varna, Janis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Persson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Claudel, Florian
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hajlane, Abdelghani
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Curvature of unsymmetric cross-ply laminates: Combined effect of thermal stresses, microcracking, viscoplastic and viscoelastic strains2017Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 36, nr 4, s. 283-293Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Curvature of unsymmetrical [0/90] specimens caused by thermal stresses changes if the specimen is subjected to large axial strains introducing intralaminar cracks in the 90-layer. It is shown that the large curvature reduction can not be explained by cracking related stress release only. The large irreversible viscoplastic strains introduced during the axial tensile loading (with 5 min holding at high strain for crack counting) give the main contribution to the curvature change. The effect of transient viscoelasticity (VE) was found to be of minor significance. Simple approach based on effective damaged layer stiffness and constant irreversible strain is used in the framework of laminate theory to extract the viscoplastic and VE strains from experimental curvature data. The obtained fitting expressions for viscoplastic- and VE-strain development are successfully used to describe curvature change in [0/902] laminate subjected to the same test procedure. It is suggested that the used curved beam tests could be efficient to characterize the viscoplastic strain development in the thin 90-layers

  • 44.
    Xu, Johanna
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Lindbergh, Göran
    School of Chemical Science and Engineering, KTH Royal Institute of Technology.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Multiphysics modeling of mechanical and electrochemical phenomena in structural composites for energy storage: Single carbon fiber micro-battery2018Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 37, nr 10, s. 701-715Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 45.
    Xu, Johanna
    et al.
    Lulea Univ Technol, Dept Engn Sci & Math, S-97189 Lulea, Sweden..
    Lindbergh, Göran
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemiteknik.
    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-battery2018Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 37, nr 10, s. 701-715Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 46.
    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 elements2012Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 31, nr 3, s. 163-178Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 47.
    Zrida, H.
    et al.
    Lulea University of Technology.
    Marklund, Erik
    RISE - Research Institutes of Sweden, Material och produktion, 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 composites2014Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 33, nr 14, s. 1339-1352Artikkel i tidsskrift (Fagfellevurdert)
    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).

  • 48.
    Zrida, Hana
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Marklund, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ayadi, Zoubir
    Institut Jean Lamour, Nancy Universite, Science et Ingénierie des Matériaux et Métallurgie (SI2M), Institut Jean Lamour, Nancy, Laboratoire de Science et Génie des Surfaces, EEIGM, Institut Jean Lamour, SI2M, EEIGM 6 Rue Bastien Lepage, F-54010 Nancy, Institut Jean Lamour, University of Lorraine, EEIGM 6 Rue Bastien Lepage, F-54010 Nancy.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Effective stiffness of curved 0°-layers for stiffness determination of cross-ply non-crimp fabric composites2014Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 33, nr 14, s. 1339-1352Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 49.
    Åkesson, Dan
    et al.
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Fazelinejad, Samaneh
    Skrifvars, Ville-Viktor
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Skrifvars, Mikael
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Mechanical recycling of polylactic acid composites reinforced with wood fibres by multiple extrusion and hydrothermal ageing2016Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 35, nr 16, s. 1248-1259Artikkel i tidsskrift (Fagfellevurdert)
  • 50.
    Åkesson, Dan
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Foltynowicz, Zenon
    Christéen, Jonas
    Skrifvars, Mikael
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Microwave pyrolysis as a method of recycling glass fibre from used blades of wind turbines2012Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 31, nr 17, s. 1136-1142Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The possibility of recycling glass fibre-reinforced composites by using microwave pyrolysis was examined. A scrap blade from a wind turbine was fragmented and microwave-pyrolysed. The glass fibre recovered after pyrolysis represented 70% of the initial mass of glass fibre-reinforced composites. The tensile strength of the glass fibre recovered was measured after pyrolysis and compared to the tensile strength of untreated glass fibre. The test showed that the fibres lost about 25% of their tenacity. Non-woven fibre mats were prepared from the recovered fibres. Laminates were then prepared from the non-woven mats obtained, together with virgin glass fibre mats. Mechanical testing of the laminates showed that it is possible to prepare composites using 25 wt% of recycled fibres, with relatively good mechanical properties.

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