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  • 101.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Compressive strength of unidirectional polymer composites obtained from test of multidirectional laminates2001Inngår i: 2001 Mechanics and Materials Summer Conference: June 27-29, 2001 Sheraton San Diego Hotel and Marina ; technical program and book of abstracts ; MMC2001, 2001Konferansepaper (Fagfellevurdert)
  • 102.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Damage evolution modeling in multidiractional laminates and the resulting nonlinear response1999Inngår i: ICCM-12 Europe: 12th International Conference on Composite Materials ; Palais des Congrès, Paris [July 5th - 9th] 1999 / [ed] Thierry Massard, Tours: ICCM , 1999Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Stiffness reduction in [S,90n]s symmetric laminates, containing orthotropic sub-laminates (S) is analyzed as a function of crack density in 900 layer. Closed form expressions relating stiffness changes to the transverse crack density are used to compute stiffness changes due to accumulated damage. Weibull strength distribution of 900 layer is assumed and Shear Lag and Hashin’s models are used for calculation of stress distribution in 900 layer with cracks. Weibull parameters are obtained from experimental data for [02, 904]s laminate and then used for other lay-ups. Strength approach and Monte-Carlo simulation is used to estimate damage evolution in 900 layer and crack density as a function of applied strain is obtained. It is used to predict stiffness changes in [S,90n]s laminates as a function of applied strain. Predictions are compared with experimental data for [±θ, 904]s θ= 0,15,30,40 GF/EP laminates. Comparison shows fairly good agreement between prediction and experimental.

  • 103.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Effect of bundle waviness on compressive strength and notch sensitivity of non-crimp fabric composites2002Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Non-Crimp Fabrics (NCF) and vinylester resins seem to give lower compression strength data than similar prepreg-based composites. However, the lower data turned out to be not only material issue, but a problem associated with testing methodology, namely design of test fixtures and specimen configuration. Specimen geometry optimization study led to research concerning notch sensitivity of NCF. Investigations were performed testing specimens with circular center holes and symmetric sharp edge notches. In all cases reduction of compressive strength, corresponding to the net cross-section, due to introduced notches was not observed. Although NCF composites showed rather low compressive strength if compared with similar prepreg materials, they also exhibit almost complete notch insensitivity. This can be explained by irregular and uneven internal structure of NCF composite. Due to complex internal geometry NCF composite fails close to an internal defect, prior to the failure in vicinity of the notch, where stress concentration takes place.

  • 104.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Failure analysis of fiber bundles with waviness in composites under compression2004Inngår i: MACM 2004 conference proceedings: Proceedings of the Tenth International Conference on Marine Applications of Composite Materials, Composites education association , 2004Konferansepaper (Fagfellevurdert)
  • 105.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Fiber/matrix interface fracture toughness identification in single fiber fragmentation test1997Inngår i: Material identification using mixed numerical experimental methods: proceedings of the EUROMECH Colloquium held in Kerkrade, The Netherlands, 7-9 April 1997 / [ed] Hugo Sol, Encyclopedia of Global Archaeology/Springer Verlag, 1997Konferansepaper (Fagfellevurdert)
  • 106.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Inelastic response of laminated due to damage accumulation2000Inngår i: Composites from fundamentals to exploitation: [the premier composites conference in Europe ; proceedings] / ECCM9, 4 - 7 June 2000, Brighton Conference Centre, UK, London: Institute of Materials , 2000Konferansepaper (Fagfellevurdert)
  • 107.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Manufacturing and characterization of polypropylene reinforced with carbon nano-tubes2004Inngår i: From nano-scale interactions to engineering structures: ECCM 11, 11th European Conference on Composite Materials ; May 31 - June 3, 2004, Rhodes, Greece / [ed] Costas Galiotis, 2004Konferansepaper (Annet vitenskapelig)
  • 108.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Mechanics of non-crimp fabric reinforced composites in ship structures2002Inngår i: MACM 2002 conference proceedings: proceedings of the Ninth International Conference on Marine Applications of Composite Materials ; March 19 - 21, 2002, Radisson Oceanfront Resort, Melbourne, Florida, USA, Composites education association , 2002Konferansepaper (Fagfellevurdert)
  • 109.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Berglund, Lars
    Luleå tekniska universitet.
    Acoustic emission from composite laminates with simple damage characteristics1995Inngår i: Fifth International Symposium on Acoustic Emission from Composite Materials, July 10-14, 1995, Sundsvall's KonferensCenter, Hotel Sundsvall, Sundsvall Sweden, Columbus, Ohio: American Society for Nondestructive Testing , 1995, s. 179-186Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Interpretation of acoustic emission (AE) signals in terms of damage mechanisms in composite materials and structures is often difficult. This is because of the multitude of damage mechanisms. In the present study, glass fiber/epoxy (GF/EP) (0m/90n)s cross-ply laminates were studied in unixial tensile loading. Since the damage mechanisms in such laminates are primarily matrix cracking, acoustic emission interpretation was facilitated. Real-time optical microscopy and AE studies were conducted in order to identify details of the damage development. It was found that a multitude of secondary cracking events occurred at higher strains. These events may explain why stress analysis models based on straight and regularly spaced transverse cracks are not successful. In addition, it was clearly demonstrated that in order to interpret damage development with some confidence from AE-data, direct observations of damage events must also be performed.

  • 110.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Berglund, Lars
    Luleå tekniska universitet.
    Analysis of single fiber fragmentation data1995Inngår i: Deformation and fracture of composites : 3rd International conference: Papers and programme, London: Institute of metals , 1995, s. 126-131Konferansepaper (Fagfellevurdert)
  • 111. Joffe, Roberts
    et al.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Berglund, Lars
    Luleå tekniska universitet.
    Interfacial debonding in model composites1996Konferansepaper (Annet vitenskapelig)
  • 112.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Berglund, Lars
    Luleå tekniska universitet.
    Interfacial fracture toughness characterization in single fibre fragmentation test1995Inngår i: Ninth International Conference Mechanics of Composite Materials: book of abstracts ; Riga, Latvia, October 17-20, 1995, 1995Konferansepaper (Fagfellevurdert)
  • 113.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Wallström, Lennart
    Flax fibers for structural composites: characterization and properties2003Inngår i: Book of abstracts: International Workshop on Natural Fiber Composites, 2003Konferansepaper (Annet vitenskapelig)
  • 114.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Wallström, Lennart
    Berglund, Lars
    Luleå tekniska universitet.
    Natural fiber composites based on flax - matrix effects2001Inngår i: Modelling for saving resources: International scientific colloquium MSR 2001. Riga, May 17 - 18, 2001 : proceedings / University of Latvia, 2001Konferansepaper (Fagfellevurdert)
  • 115.
    Katerelos, Dionisis
    et al.
    LTU, TFM, Polymerteknik.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Labou, Diamantoula
    FORTH/ICE-HT, Patras.
    Wallström, Lennart
    Effect of stretching on the mechanical performance of polypropylenedoped with multi-wall carbon nanotubes2008Konferansepaper (Annet vitenskapelig)
  • 116.
    Katerelos, Dionysios
    et al.
    LTU.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Labou, D.
    FORTH/ICE-HT, Patras.
    Wallström, Lennart
    Alteration of the mechanical behaviour of polypropylene owing to successive introduction of multiwall carbon nanotubes and stretching2009Inngår i: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 45, nr 4, s. 423-434Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Stretching effects on the morphology of polypropylene/carbon nanotube composites is the focus of this work. The material under investigation was composed of isotactic polypropy lene (iPP) and multiwall car bon nanotubes (MWCNTs) in amount of 0.5 wt.%. The iPP and CNTs were mixed under sonication in a solvent, and the homogenized mixture was melted and pressed. The rectangular plates produced from the material were stretched by a constant load at a fixed temperature in order to obtain extended specimens. The scanning electron microscopy, a thermal gravimetric analysis, and the differential scanning calorimetry were employed to study variations in the structural morphology of the material. A dynamic mechanical analysis showed that the strain-induced crystallization of polypropylene and the possible Stone-Wales transformation of the carbon nanotubes due to stretching improved the mechanical performance of the nanocomposites considered.

  • 117. Katerelos, Dionysos
    et al.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Labou, D.
    FORTH/ICE-HT, Patras.
    Wallström, Lennart
    FORTH/ICE-HT, Patras.
    Erratum: Alteration of the mechanical behaviour of polypropylene owing to successive introduction of multiwall carbon nanotubes and stretching2009Inngår i: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 45, nr 5, s. 543-Artikkel i tidsskrift (Annet vitenskapelig)
  • 118.
    Kislev, T
    et al.
    Hebrew University of Jerusalem.
    Marom, G
    Hebrew University of Jerusalem.
    Berglund, Lars
    Luleå tekniska universitet.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Nairn, JA
    University of Utah.
    Wagner, HD
    Weizmann Institute of Science, Rehovot.
    On the nature of opaque cylindrical regions formed at fibre break sites in a fragmentation test2002Inngår i: Advanced Composites Letters, ISSN 0963-6935, Vol. 11, nr 1, s. 7-13Artikkel i tidsskrift (Fagfellevurdert)
  • 119.
    Madsen, Bo
    et al.
    Risø, DTU.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Peltola, Heidi
    VTT.
    Nättinen, Kalle
    VTT.
    Short cellulosic fiber/starch acetate composites: micromechanical modeling of Young’s modulus2011Inngår i: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 45, nr 20, s. 2119-2131Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study is presented to predict the Young’s modulus of injection-molded short cellulosic fiber/plasticized starch acetate composites with variable fiber and plasticizer content. A modified rule of mixtures model is applied where the effect of porosity is included, and where the fiber weight fraction is used as the basic independent variable. The values of the input model parameters are derived from experimental studies of the configuration of the composites (volumetric composition, dimensions, and orientation of fibers), as well as the properties of the constituent fiber and matrix phases (density and Young’s modulus). The measured Young’s modulus of the composites varies in the range 1.1–8.3 GPa, and this is well predicted by the model calculations. A property diagram is presented to be used for the tailor-making of composites with Young’s modulus in the range 0.2–10 GPa.

  • 120.
    Madsen, Bo
    et al.
    Risø, DTU.
    Lilholt, Hans
    Risø, DTU.
    Thygesen, Anders
    Risø, DTU.
    Arnold, Elaine
    NetComposites.
    Weager, Brendon
    NetComposites.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Aligned flax fibre/polyactate composites: a materials model system to show the potential of biocomposites in engineering applications2008Inngår i: 13th European Conference on Composite Materials: 2-5 June 2008, Stockholm, Sweden, 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The potential of biocomposites in engineering applications is demonstrated by using aligned flax fibre/polylactate composites as a materials model system. The failure stress of flax fibres is measured by tensile testing of single fibres and fibre bundles. For both fibre configurations, it is found that failure stress is decreased by increasing the tested fibre volume. Based on two types of flax fibre preforms: carded sliver and uniaxial non-crimp fabric, aligned flax fibre/polylactate composites were fabricated with variable fibre content. The volumetric composition and tensile properties of the composite were measured. For composites with a fibre content of 37 % by volume, stiffness is about 20 GPa and failure stress is about 180 MPa. The tensile properties of the composites are analysed with a modified rule of mixtures model, which includes the effect of porosity. The experimental results are well predicted by the model. The back-calculated effective stiffness and failure stress of the flax fibres are in the ranges 56-60 GPa and 515-730 MPa, respectively. Finally, model predictions are used to present overall guidelines for the comparisons between tensile performance of flax fibre composites and traditional fibre composites (exemplified by glass fibre composites). The stiffness per volume, per weight and per cost is compared for these two types of composites.

  • 121.
    Madsen, Bo
    et al.
    Risø, DTU.
    Lilholt, Hans
    Risø, DTU.
    Thygesen, Anders
    Risø, DTU.
    Arnold, Elaine
    NetComposites.
    Weager, Brendon
    NetComposites.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Aligned flax fibre/polylactate composites: a materials model system to show the potential of biocomposites in engineering applications2008Inngår i: Journal of Nanostructured Polymers and Nanocomposites, ISSN 1790-4439, Vol. 4, nr 4, s. 141-148Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The potential of biocomposites in engineering applications is demonstrated by using aligned flax fibre/polylactate composites as a materials model system. The failure stress of flax fibres is measured by tensile testing of single fibres and fibre bundles. For both fibre configurations, it is found that failure stress is decreased by increasing the tested fibre volume. Based on two types of flax fibre preforms: carded sliver and unidirectional non-crimp fabric, aligned flax fibre/polylactate composites were fabricated with variable fibre content. The volumetric composition and tensile properties of the composite were measured. For composites with a fibre content of 37 % by volume, stiffness is about 20 GPa and failure stress is about 180 MPa. The tensile properties of the composites are analysed with a modified rule of mixtures model, which includes the effect of porosity. The experimental results are well predicted by the model. The back-calculated effective stiffness and failure stress of the flax fibres are in the ranges 56-60 GPa and 515-730 MPa, respectively. Finally, the model is used for parametric analysis and overall guidelines for the comparisons between tensile performance of flax fibre composites and traditional fibre composites (exemplified by glass fibre composites) are presented. The stiffness per volume, per weight and per cost is compared for these two types of composites.

  • 122.
    Mannberg, Peter
    et al.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Nyström, Birgitha
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Service life assessment and moisture influence on bio-based thermosetting resins2014Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 49, nr 10, s. 3687-3693Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 123.
    Mannberg, Peter
    et al.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Nyström, Birgitha
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Wallström, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Service life assessment and moisture influence on bio-based composites2014Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 49, nr 15, s. 5265-5270Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 124.
    Mannberg, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Rozite, Liva
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Nyström, Birgitha
    Swerea SICOMP AB.
    Service life assessment and moisture influence on composites from renewable feedstock2012Inngår i: Proceedings of Mechanics of Composite Materials XVII International Conference, 2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Composite materials are an important and growing material group in a large number of industries such as aeronautics, marine, automotive, energy production and infrastructure. The most common composite materials is manufactured from fibres such as glass fibres and carbon fibres together with oil based resins i.e. polyester, vinyl ester and epoxy. An increasing use calls for alternative environmental friendly, biobased, constituents. The new biobased materials have not only to compete in mechanical properties but it also has to restrain environmental loads like moisture and temperature over time. In the present work are predictions of the long term properties of biobased resins made. The work also presents the influence of moisture, comparison with creep test data and comparison with oil based resin. The long term property prediction is made by using dynamic mechanical thermal analysis, DMTA, measurements and time temperature superposition, TTSP, [1,2]. The procedure is to make DMTA measurements in 3p-bening mode of the storage modulus at different frequencies at increasing temperature. The method used in this case was to measure the modulus at 0.1, 0.3, 1, 3 and 10 Hz at temperatures 25 – 175°C with 5°C intervals. The frequencies where then transformed to time by Eq. (1) below t=2/πω (1)where ω is the frequency. 25°C were chosen as reference temperature where as all other curves where shifted horizontally creating a continuous master curve. The modulus time master curve was then inverted creating creep compliance time master curve, this curve is compared to creep test. The moisture behaviour is characterised in form of water uptake, change in glass transition temperature, Tg, and change in dynamic response. The water uptake is determined by submersion into water and tracking the weight change over time. The glass transition temperature is determined in DMTA by conducting a temperature sweep at constant frequency. The change in Tg is used as a knock down factor and a vertical shift of the master curve. An attempt to determine the dynamic response of wet samples has also been made with the insight that higher temperatures will dry the sample during testing leading to a non homogenous moisture distribution within the sample. The results from the study show on differences between TTSP and creep data, it also shows the differences between different biobased resins and a comparison to oil based epoxy. REFERENCES1. Christensen R.M., “Theory of viscoelasticity, an introduction” 2nd edition, Academic Press, 1982.2. Ward I.M. and Hadley D.W., “An Introduction to the mechanical properties of solid polymers” 1st edition, John Wiley & Sons, 1993.

  • 125. Mattsson, David
    et al.
    Joffe, Roberts
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Damage in NCF composites under tension: effect of layer stacking sequence2008Inngår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 75, nr 9, s. 2666-2682Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Non-crimp fabric (NCF) cross-ply composites response to tensile loading is investigated showing large effect of the fabric layer stacking sequence: much larger elastic modulus reduction was observed in [0/90/0/90]S than in [90/0/90/0]S case. Since transverse cracks in 90°-bundles may give modulus decrease about 5%, the observed 40% stiffness reduction is attributed to failure and delamination of bundles oriented in the direction of the applied load. Analysis of micrographs shows extensive delaminations and 0°-bundle breaks. FE calculations showed that failure of 0°-bundles at the surface is energetically more favorable. However, the fracture resistance of surface bundles is higher due to smaller bundle waviness and the density of bundle cracks on the surface was not larger than inside. Two possible reasons for the higher stiffness reduction in the [0/90/0/90]S NCF composite were suggested: (a) If two imperfect 0°-bundle layers are separated by a 90°-bundle layer their resistance to failure is lower than when they are situated next to each other; (b) the effect of each surface 0°-bundle break on the composite stiffness is larger (due to less constraint from the surrounding material the opening of surface bundle breaks is much larger).

  • 126. Mattsson, David
    et al.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Methodology for characterization of internal structure parameters governing performance in NCF composites2007Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 38, nr 1, s. 44-57Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mechanical performance of non-crimp fabric composites is very dependent on their internal meso- and micro-structure which is defined by the manufacturing process of the fabric and composite processing conditions. This paper identifies the most important parameters which control mechanical properties of these materials. The identification is based on experimental observations and available theoretical findings. Characteristics of the internal structure of non-crimp fabric composites are analyzed in context of their significance for in-plane elastic and failure properties. Methodology for determination of most typical geometrical parameters of composites using optical observations of cross-sections of manufactured laminates is described. The methodology is applied to characterize cross-ply and quasi-isotropic composite laminates. These results are analyzed and a comparison between the laminates is performed.

  • 127. McCartney, N.
    et al.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Inelastic response of symmetric laminates due to inclined cracks1998Inngår i: Book of abstracts: Tenth International Conference Mechanics of Composite Materials : April 20 - 23, 1998, Riga, Latvia / [ed] Vitaut P. Tamuzs, Inst of polymer mechanics , 1998Konferansepaper (Fagfellevurdert)
  • 128.
    Miettinen, Arttu
    et al.
    University of Jyväskylä.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Madsen, Bo
    Risø, DTU.
    Nättinen, Kalle
    VTT Technical Research Centre of Finland, Espoo.
    Kataja, Markku
    University of Jyväskylä.
    Quantitative analysis of length-diameter distribution and cross-sectional properties of fibers from three-dimensional tomographic images2013Inngår i: Processing of fibre composites – challenges for maximum materials performance: Proceedings of 34th Risø International Symposium on Materials Science / [ed] Bo Madsen; Hans Lilholt; Y Kusano; S Fäster; B Ralph, Roskilde, Denmark: Risø National Laboratory for Sustainable Energy, Danmarks Tekniske Universitet , 2013, s. 303-311Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A number of rule-of-mixture micromechanical models have been successfully used to predict mechanical properties of short fiber composites. However, in order to obtain accurate predictions, detailed description of the internal structure of the material is required. This information is often obtained from optical microscopy of polished cross-sections of composite. This approach gives accurate yet local results, but a rather large number of optical images have to be processed to achieve a representative description of the morphology of the material. In this work a fully automatic algorithm for estimating the length-diameter distribution of solid or hollow fibers, utilizing three-dimensional X-ray tomographic images, is presented. The method is based on a granulometric approach for fiber length distribution measurement, combined with a novel algorithm that relates cross-sectional fiber properties to fiber length. The work opens up a possibility to assess multivariate distributions of fiber length and diameter, cross-sectional area or other microstructural fiber properties. As an example, the description of microstructure of different composites with natural fibers is presented, along with verification of the results.

  • 129.
    Miettinen, Arttu
    et al.
    University of Jyväskylä.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pupure, Liva
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Madsen, Bo
    Technical University of Denmark, Risø Campus, Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark.
    Identification of true microstructure of composites based on various flax fibre assemblies by means of three-dimensional tomography2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 130.
    Miettinen, Arttu
    et al.
    University of Jyväskylä.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pupure, Liva
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Madsen, Bo
    Technical University of Denmark, Risø Campus, Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark.
    X-Ray Microtomography Of Natural Fibre Composites2015Inngår i: Proceedings of 7th International Conference on Composites Testing and Model Identification / [ed] C. González; C. López; J. LLorca, Madrid, Spain: IMDEA, Madrid (SPAIN) , 2015Konferansepaper (Fagfellevurdert)
  • 131.
    Miettinen, Arttu
    et al.
    University of Jyväskylä.
    Ojala, Antti
    VTT Technical Research Centre of Finland, Espoo.
    Wikström, Lisa
    VTT Technical Research Centre of Finland, Espoo.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Madsen, Bo
    Technical University of Denmark, Risø Campus, Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark.
    Nättinen, Kalle
    VTT Technical Research Centre of Finland, Espoo.
    Kataja, Markku
    Department of Physics, University of Jyväskylä.
    Non-destructive automatic determination of aspect ratio and cross-sectional properties of fibres2015Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 77, s. 188-194Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 132.
    Modniks, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Andersons, Janis
    Institute of Polymer Mechanics, University of Latvia.
    Model of the mechanical response of short flax fiber reinforced polymer matrix composites2011Inngår i: 11th International Conference on the Mechanical Behavior of Materials (ICM11) / [ed] Mario Guagliano; Laura Vergani, Elsevier, 2011, s. 2016-2021Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Natural-fiber-reinforced short-fiber composites are finding more applications lately, therefore there is a need for estimation of the mechanical properties of such composites based on the properties of the constituents. The fibersthemselves also possess complicated internal structure, resulting in anisotropy of their properties. Taking into account the internal structure of bast fiber, we evaluate the elastic properties of a composite unit cell, consisting of a fiber ofaverage length and matrix according to the fiber volume fraction in the composite. The unit cell properties are used to estimate the stiffness of a misaligned short-fiber composite by means of orientation averaging. The results obtained are compared with the experimental stress-strain diagrams of short flax fiber/polypropylene matrix composite. Usually the mechanical response of short-fiber/polymer matrix composite is non-linear due to the inelastic matrixbehavior. Accounting for the non-linear deformation of the matrix in the unit cell by modeling it as an elastic-plastic material, we also estimate its non-linear response under uniaxial loading.

  • 133.
    Modniks, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Porike, E.
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Andersons, J.
    Institute of Polymer Mechanics, University of Latvia.
    Evaluation of the apparent interfacial shear strength in short-flax-fiber/PP composites2012Inngår i: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 48, nr 5, s. 571-578Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An important factor affecting the mechanical characteristics of composite materials is the adhesion of constituents which can be characterized by the interfacial shear strength (IFSS). Most of the experimental methods for the evaluation of IFSS involve model single-fiber composites. By contrast, the method proposed by Bowyer and Bader is based on an analysis of the stress-strain curve of a short-fiber-reinforced composite in tension. In the present study, the method is applied to the experimental tension curves of short-flax-fiberreinforced polypropylene to evaluate the IFSS and the fiber orientation factor of the composite. The IFSS was found to depend on the volume fraction of fibers and the treatment to improve adhesion.

  • 134.
    Moreno, Silvia Suñer
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Tipper, Joanne
    Institute of Medical and Biological Engineering, University of Leeds.
    Emami, Nazanin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    UHMWPE/GO nanocomposites for orthopaedic applications: thermal, mechanical and tribological characterization2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 135.
    Moreno, Silvia Suñer
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Tipper, Joanne
    Institute of Medical and Biological Engineering, University of Leeds.
    Emami, Nazanin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Ultra High Molecular Weight Polyethylene/Graphene Oxide Nanocomposites: Thermal, Mechanical and Wettability Characterisation2015Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 78, s. 185-191Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 136.
    Nordström, Ylva
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Sjöholm, Elisabeth
    Biorefinery Processes and Products, Innventia AB.
    Mechanical characterization and application of Weibull statistics to the strength of softwood lignin-based carbon fibers2013Inngår i: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 130, nr 5, s. 3689-3697Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mechanical characterization of the first generation of softwood kraft lignin-based carbon fibers (CF) was carried out. The single fiber tensile tests of filaments with different diameters and length were performed to evaluate stiffness and strength of carbon fibers. The average mechanical properties were measured as follows: tensile strength of approximately 300 MPa, the elastic modulus of 30 GPa and a strain at failure within interval of 0.7-1.2%. The fiber strength data was evaluated by the two-parameter Weibull statistics and parameters of this distribution were obtained. Although strength of the produced fibers is still significantly lower than that of commercially available, the experimental results and predictions based on Weibull statistics show a fairly good fit.

  • 137.
    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.

  • 138.
    Nyström, Birgitha
    et al.
    Swerea SICOMP AB.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mechanical performance and damage tolerance of bio-based polymer composites with man made cellulose fibre reinforcement2010Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    In the present study new combinations of fibres and resins from renewable resources are used as constituent materials in structural composites. Viscose fibres made from regeneratedcellulose (Cordenka) and high quality spun flax fibres are combined with two types of biobased thermosetting resins. The viscose fibres combine the main advantages of natural fibres, e.g. renewable origin and high specific properties whilst lacking many of the disadvantages of natural fibres such as limited length and variability due to location of growth and so on.The resins are Tribest which is made from vegetable oils as well as Furolite and Biorez which are made from agricultural waste. The Tribest resin has processing characteristics similar tovinylesters: being initiated with peroxide. The Furolite and Biorez resins have similarities to phenolic resins: curing with a condensation reaction where water is produced. These resinsalso have good fire retarding properties.The mechanical performance and damage tolerance of these composites have been evaluated.Comparisons are made to glass and flax fibre composites.Although composites with different fiber volume contents were manufactured and tested, the comparison of mechanical performance is somewhat favourable for Crodenka basedcomposites. Initial results for Cordenka/Tribest composites show high maximum stress.Promising values were also obtained for the Flax/Tribest composites.

  • 139.
    Nyström, Birgitha
    et al.
    Swerea SICOMP AB.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Långström, Runar
    Swerea SICOMP AB.
    Processing and properties of bio-based composites2009Konferansepaper (Annet vitenskapelig)
  • 140. Nyström, Birgitha
    et al.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Långstöm, Runar
    SICOMP AB, Swedish Institute of Composites.
    Natural fiber composites: optimization of microstructure and processing parameters2007Inngår i: Book of abstracts: European school of materials science and engineering, fourth research conference, June 7-8, 2007, Barcelona, Spain, 2007, s. 23-Konferansepaper (Annet vitenskapelig)
  • 141.
    Nyström, Birgitha
    et al.
    Swerea SICOMP AB.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Rozite, Liva
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Development of bio-based advanced composites with transport structures in mind2011Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    A world wide eco race is taking place in the transportation sectors. This race is driven by factors such as climate change awareness and oil prices. The main goal is reduction of fossil raw material dependency and minimizing the overall carbon foot-print. As well as the entering on the market of new types of hybrid engines with low fuel consumption and electric cars there is an increasing push from many car producers to incorporate renewable, recyclable lightweight materials in their vehicles. Swerea SICOMP and Luleå University of Technology have been involved in R&D on bio-based materials for transportation applications for more than 10 years. The results from ongoing research projects with focus on bio-based structural applications for transportation applications are promising. Fibres that are being studied include manmade regenerated cellulose, cellulose nano fibrils and whiskers as well as high quality flax fibre fabrics. Several new bio-based or partly bio-based resins that are entering the market are being evaluated. Results regarding processability, mechanical performance, durability and design & manufacturing show that the latest development in the field of bio-based constituents (reinforcing fibres, core materials and resins) for composites are taking large steps forward and new green options for the transportation sector will soon be available.

  • 142.
    Nättinen, K.
    et al.
    VTT Technical Research Centre of Finland, Espoo.
    Lampinen, J.
    VTT Technical Research Centre of Finland, Espoo.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Madsen, B.
    Madsen Technical University.
    BioComp: Processing and properties of starch acetate - Bast fibre composites2010Inngår i: Developments in advanced biocomposites, Espoo: VTT Building and Transport , 2010, s. 29-38Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    Composite compounds based on hemp and flax fibres in triethyl- citrateplasticised starch acetate were prepared by melt processing. Composite samples were prepared with fibre contents up to 50w%. A stiffness of 8.3 GPa and stress at a maximum load of 51 MPa were obtained with 40w% flax fibre in plasticised starch acetate with 20w% triethyl citrate. A nearly linear relation between fibre content and tensile properties was found. The impact strength of the composites was increased with the plasticiser content. The porosity content was low even at high fibre content.

  • 143.
    Nättinen, Kalle
    et al.
    VTT Technical Research Centre of Finland, Espoo.
    Hyvärinen, Sari
    VTT Technical Research Centre of Finland, Espoo.
    Joffe, Roberts
    Wallström, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Madsen, Bo
    Department of Materials Research, Riso National Laboratory for Sustainable Energy, Technical University of Denmark.
    Naturally compatible: starch acetate/cellulosic fibre composites. Part I: Processing and properties2010Inngår i: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 31, nr 3, s. 524-535Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Composite compounds based on hemp and flax fibers in triethyl citrate plasticized starch acetate were prepared by melt processing. For better properties and processability, compounds with plasticizer contents in the range 20-35 wt% were screened. Composites were prepared with fiber contents up to 50 wt%. The composite mechanical properties were measured from injection molded test specimens. A Young's modulus of 8.3 GPa and stress at maximum load of 51 MPa were obtained with 40 wt% flax fiber in a plasticized starch acetate with 20 wt% triethyl citrate. Decreasing the plasticizer and increasing the fiber content, the tensile properties were consistently improved. An almost linear relation between fiber content and the tensile properties was found. The increase of the fiber content first improved the impact strength, but at higher fiber contents resulted in a reduction of impact strength. The quality of the produced materials was found to be good; the variation in properties between duplicated compounds was acceptable low, the variation in density and fiber content along a single tensile specimen was low, and finally, the porosity content was low even at high fiber content. The latter result was verified with scanning electron microscope images of fracture surfaces of the composites.

  • 144.
    Nättinen, Kalle
    et al.
    VTT.
    Lampinen, Johanna
    VTT.
    Madsen, Bo
    Risø, DTU.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Wallström, Lennart
    Varna, Janis
    Starch acetate N-fibre composites2008Inngår i: 13th European Conference on Composite Materials: 2-5 June 2008, Stockholm, Sweden, 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Cellulosic fibre composite compounds based on hemp and flax fibres in triethyl citrate plasticised starch acetate were prepared by melt processing. Composites were prepared with fibre contents up to 50w%. A stiffness of 8.3 GPa and stress at maximum load of 51 MPa were obtained with 40w% flax fibre in a plasticised starch acetate with 20w% triethyl citrate. An almost linear relation between fibre content and the tensile properties was found. The impact strength of the composites was increased with the plasticiser content. The porosity content was low even at high fibre content.

  • 145.
    Nättinen, Kalle
    et al.
    VTT Technical Research Centre of Finland, Espoo.
    Peltola, Heidi
    VTT Technical Research Centre of Finland, Espoo.
    Madsen, Bo
    Technical University of Denmark, National Laboratory of Sustainable Energy, Materials Research Division, Riso.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Effects of process history on natural fibre properties in composites2011Inngår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 241, s. 222-CELLArtikkel i tidsskrift (Annet vitenskapelig)
  • 146.
    Olofsson, Kurt
    et al.
    Swerea SICOMP AB.
    Hedlund, Emil
    Swerea SICOMP AB.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ahlqvist, Fredrik
    Swerea SICOMP AB.
    Automated cutting of fiber materials for tailored drapeability2012Inngår i: The 5th International Swedish Production Symposium: 6th – 8th of November 2012 Linköping, Sweden, Svenska ProduktionsAkademien , 2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The aim of the current project has been to study the basic technologies needed to introduce local Point Cutting of fiber weaves (local PC) into composites manufacturing. An automated cutting machine is here used to locally increase the drapeability of standard weaves, hence easing tool loading and the automation of a production line. The two tested softwares cannot simulate draping using precut fiber weaves. Drapeability experiments can instead be used to select cutting pattern and cutting area. The used tool concept (one piece tool half, several tool parts, bag etc.) will affect the minimum size of the cutting area. Several cutting patterns have been tested including the innovative cross pattern, which works best. Micro-mechanical analysis and FE simulations show that the cured material properties can be predicted. A composite part has been successfully manufactured usinglocal PC technology.

  • 147.
    Olofsson, Kurt
    et al.
    Swerea SICOMP AB.
    Hedlund, Emil
    Swerea SICOMP AB.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ahlqvist, Fredrik
    Swerea SICOMP AB.
    Local Point Cutting of Fibre Materials for Eased Automation2015Konferansepaper (Annet vitenskapelig)
  • 148.
    Parfeev, V.M.
    et al.
    Institute of the Mechanics of Polymers.
    Kurzemnieks, A. Kh.
    Institute of the Mechanics of Polymers.
    Joffe, Roberts
    Destruction of polyethylene-oxide films during storage1995Inngår i: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 30, nr 4, s. 335-339Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In lengthy storage of PEO films the amorphous part of the material is subjected most to destruction under the effect of environmental factors; consequently, films with a higher degree of crystallinity are more suitable for storage. The resistance of individual sections of film to environmental factors is a random variable, and the nature of the encountered patterns of destruction can therefore be reproduced with the aid probabilistic models.

  • 149.
    Peltola, Heidi
    et al.
    VTT Technical Research Centre of Finland, Espoo.
    Madsen, Bo
    Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Nättinen, Kalle
    VTT Technical Research Centre of Finland, Espoo.
    Experimental study of the fiber length and orientation in injection molded natural fiber/starch acetate composites2011Inngår i: Advances in Materials Science and Engineering, ISSN 1687-8434, E-ISSN 1687-8442, Vol. 2011Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Composite compounds based on triethyl citrate plasticized starch acetate and natural fibers (hemp and flax) were prepared by melt processing. Plasticizer contents from 20 to 35 wt% and fiber contents of 10 and 40 wt% were used. The compounded composites were injection molded to tensile test specimens. The effect of process steps, melt viscosity and fiber type on the fiber length was investigated. The lengths of fully processed fibers were determined by dissolving the starch acetate matrix and measuring the length of the remaining fibers by optical microscopy and image analysis. A clear reductive effect of the pelletising and melt processing on the fiber length was noticed. Also a reduction of fiber length along the increasing fiber content and the decreasing plasticizer content was detected. This reduction was originated from the increasing shear forces during compounding, which again depended on the increased viscosity of the material. When comparing the fully processed hemp and flax fibers, hemp fibers remained longer and fibrillated more than flax fibers, leading to higher aspect ratio. Thus, the reinforcement efficiency of hemp fibers by the processing was improved, on the contrary to the reduced reinforcement efficiency of flax fibers. In addition, the analysis of fiber dispersion and orientation showed a good dispersion of fibers in the matrix, and a predominant orientation of the fibers in the melt flow direction.

  • 150.
    Pupure, Liva
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Al-Maqdasi, Zainab
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Gong, Guan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Emami, Nazanin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Effect of Nano-reinforcement on the Time-dependent Properties of Graphene Modified High Density PolyethyleneManuskript (preprint) (Annet vitenskapelig)
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