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  • 1.
    Andersons, J.
    et al.
    University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Estimation of the tensile strength of an oriented flax fiber-reinforced polymer composite2011In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 42, no 9, 1229-1235 p.Article in journal (Refereed)
    Abstract [en]

    Unidirectional orientation of natural fibers in a polymer composite ensures the highest efficiency of reinforcement. Flax fiber reinforcement is discontinuous due to limited fiber length and heterogeneous due to the presence of elementary fibers and their bundles. In order to assess the upper limit of tensile strength of such slightly misoriented, nominally UD natural fiber composite, a statistical strength model of continuous UD fiber reinforced composites is applied. It is found that the experimental strength of UD flax composites, produced from rovings or manually aligned fibers, approaches the theoretical limit only at relatively low fiber volume fraction ca. 0.2, being markedly below it at higher fiber content.

  • 2.
    Andersons, J.
    et al.
    University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hojo, M.
    Ochiai, S.
    Kyoto University.
    Fibre fragment distribution in a single-fibre composite tension test2001In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 32, no 4, 323-332 p.Article in journal (Refereed)
    Abstract [en]

    Single fibre fragmentation tests are performed for brittle fibres with Weibull strength distribution and different surface treatments. The fragmentation process is modelled and closed-form expressions for break spacing distribution are obtained. The model accounts for the effect of finite fibre length on the initial fragmentation as well as for break interaction on the advanced fragmentation stage. It is assumed that the exclusion zone due to fibre-matrix interface failure and stress recovery in the fibre is linearly dependent on the applied load. This assumption is validated experimentally. The derived theoretical average fragment length dependence on applied load is used to determine the fibre strength distribution parameters and the effective interfacial shear stress for carbon/epoxy single fibre composites with different fibre surface treatment and for glass/vinylester single fibre composite. Fragment length distribution is predicted for several load levels. Predictions are in good agreement with experimental data

  • 3.
    Andersons, J.
    et al.
    University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hojo, M.
    Mesoscopic Materials Research Center, Kyoto University.
    Ochiai, S.
    Mesoscopic Materials Research Center, Kyoto University.
    Glass fibre strength distribution determined by common experimental methods2002In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 62, no 1, 131-145 p.Article in journal (Refereed)
    Abstract [en]

    The tensile strength of brittle fibres is routinely described by the Weibull distribution. The parameters of the distribution can be obtained from tests on single fibres and fibre bundles or from model composite tests. However, there is growing evidence that the distribution parameters obtained by different experimental techniques differ systematically. In order to investigate the possible causes of such discrepancies, single-fibre tension, fibre bundle, and single-fibre fragmentation tests are employed in this study to obtain strength distribution of commercial E-glass fibres. The results reveal parameter dependence on the approach used to extract the distribution parameters from experimental data. Particularly, in the case of single-fibre tension tests, the shape parameter obtained from average fibre strength vs. length data is larger than that obtained at a fixed gauge length. It is assumed that the apparent fibre strength scatter is caused by both the inherent flaw structure along a fibre and by the fibre-to-fibre strength variability within a batch, due to slightly differing processing and handling history of the fibres. Fibre fragmentation test results are used to derive the Weibull distribution parameters applicable to the fibre batch. The strength distribution obtained is compared with strength data for the single fibres, and reasonably good agreement is observed.

  • 4.
    Andersons, J.
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Sandmark, R.
    Materials division, SINTEF SI.
    Constrained fragmentation of composites under uniaxial loading1995In: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 31, no 1, 26-33 p.Article in journal (Refereed)
  • 5.
    Andersons, J.
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sparnins, Edgars
    Institute of Polymer Mechanics, University of Latvia.
    Weichert, D.
    Institute of General Mechanics, RWTH-Aachen University.
    Modeling the effect of reinforcement discontinuity on the tensile strength of UD flax fiber composites2011In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 46, no 15, 5104-5110 p.Article in journal (Refereed)
    Abstract [en]

    To exploit the potential of natural fibers as reinforcement of polymer matrix composites, aligned bast fiber composite materials are being produced and studied. Bast fiber reinforcement is discontinuous due to the limited length of natural fibers, which needs to be reflected in predictive models of mechanical properties of composites. The strength in tension in the fiber direction of an aligned flax fiber-reinforced composite is modeled assuming that a cluster of adjacent fiber discontinuities is the origin of fracture. A probabilistic model of tensile strength, developed for UD composites containing a microdefect, is applied. It follows from the theoretical analysis that the experimental tensile strength as a function the fiber volume fraction can be described with acceptable accuracy assuming the presence of a cluster of ca. 4 × 4 elementary fiber discontinuities

  • 6.
    Andersons, J.
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Leterrier, Y.
    École Polytechnique Fédérale de Lausanne.
    Joffe, Roberts
    Statistical model of coating fragmentation under equibiaxial load1998In: Materials and Manufacturing Processes, ISSN 1042-6914, E-ISSN 1532-2475, Vol. 13, no 4, 597-602 p.Article in journal (Refereed)
    Abstract [en]

    A statistical model of coating cracking under equibiaxial tension is proposed based on a Weibull strength distribution for the coating. Crack length and spacing distributions are derived assuming that cracks initiate in random locations and propagate straight till stopping upon encountering a geometiical obstacle (another crack). The theoretical distributions are verified by comparing with simulated cracking patterns obtained by the Monte-Carlo method. An analysis of crack patterns of SiO2 coatings on a PET film under biaxial tension is performed. Qualitative agreement with the theoretical crack spacing distribution is observed.

  • 7.
    Andersons, J.
    et al.
    University of Latvia.
    Sparnins, Edgars
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Prediction of crack onset strain in composite laminates at mixed mode cracking2009In: 5th International EEIGM/AMASE/FORGEMAT Conference on Advanced Materials Research, Bristol: IOP Publishing Ltd , 2009, Vol. 5Conference paper (Refereed)
    Abstract [en]

    Failure process of continuous fiber reinforced composite laminates in tension usually starts with appearance of intralaminar cracks. In composite laminates with complex lay-ups and/or under combined loading, intralaminar cracks may develop in plies with different reinforcement directions. A necessary part of mixed mode cracking models is the criterion of failure. For propagation-controlled fracture it is usually formulated in terms of energy release rates and their critical values of the particular composite material. Intralaminar fracture toughness of unidirectionally reinforced glass/epoxy composite was experimentally determined at several mode I and mode II ratios. It is found that the crack propagation criterion, linear in terms of the energy release rates, reasonably well approximates the test results. The determined mixed mode cracking criterion was applied to predict intralaminar crack onset in cross-ply glass/epoxy composite under tensile loading. The predicted crack onset strain values agree with test results at small off-axes angles of the cracking ply (on-axis and 15° off-axis loading), but underestimate crack onset at larger reinforcement angles with respect to the loading direction. The discrepancy is likely to be caused by the deviation of linearity in laminate response before cracking onset in these laminates, related to non-linear shear characteristics of unidirectional plies. The applicability of strength-based fracture criterion for initiation-controlled cracking is discussed.

  • 8.
    Andersons, J.
    et al.
    University of Latvia, Riga.
    Sparnins, Edgars
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Stiffness and strength of flax fiber/polymer matrix composites2006In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 27, no 2, 221-229 p.Article in journal (Refereed)
    Abstract [en]

    Flax fiber composites with thermoset and thermoplastic polymer matrices have been manufactured and tested for stiffness and strength under uniaxial tension. Flax/polypropylene and flax/maleic anhydride grafted polypropylene composites are produced from compound obtained by coextrusion of granulated polypropylene and flax fibers, while flax fiber mat/vinylester and modified acrylic resin composites are manufactured by resin transfer molding. The applicability of rule-of-mixtures and orientational averaging based models, developed for short fiber composites, to flax reinforced polymers is considered.

  • 9.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Initiation and propagation controlled intralaminar cracking in cross-ply laminates: Chapter 102009In: Encyclopedia of Polymer Composites: Properties, Performance and Applications, New York: Nova Science Publishers, Inc., 2009Chapter in book (Other academic)
  • 10.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mechanical damage characteristics of elementary hemp fibers and scale effect of fiber strength2012In: High Performance Structure and Materials VI: papers presented at the 6th International Conference on High Performance Structures and Materials held at the Wessex Institute of Technology in the New Forest, UK] / [ed] W.P. De Wilde; C.A. Brebbia; S. Hernandez, Southampton: WIT Press, 2012, 157-167 p.Conference paper (Refereed)
    Abstract [en]

    Ecological and economical considerations foster replacement of man-made fibers by natural renewable fibers in various industrial applications. Bast fibers of such plants as, e.g., flax, hemp, jute etc., are particularly attractive as a reinforcement of polymer-matrix composites due to their high specific stiffness and strength in the axial direction. The elementary bast fibers exhibit pronounced scatter of strength. It necessitates probabilistic description of their strength via a distribution function that reflects damage morphology and severity in fibers. Fiber fracture is shown to originate from mechanical defects of the bast cell wall, the most prominent of them being kink bands. While the number of kink bands in a fiber is easily determined by optical microscopy, direct experimental measurement of their strength is complicated. Therefore, alternative approaches are sought, enabling extraction of strength characteristics of the kink bands from fiber tests via appropriate probabilistic models. Analytical distribution function of bast fiber strength has been derived, allowing for the effect of mechanical damage in the form of kink bands. The fiber characteristics measured have been used to evaluate the kink band density and strength distributions. The theoretical distribution is verified against experimental tensile strength data of elementary hemp fibers at several gauge lengths and found to provide acceptable accuracy in predicting the scale effect of strength.

  • 11. Andersons, Janis
    et al.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sparnins, Edgars
    Institute of Polymer Mechanics, University of Latvia.
    Evaluation of interfacial shear strength by tensile tests of impregnated flax fiber yarns2012In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 46, no 3, 351-357 p.Article in journal (Refereed)
    Abstract [en]

    Adhesion of flax fibers and polymer matrix as well as mutual bonding of elementary fibers in a technical fiber are among the principal factors governing the mechanical response of flax fiber reinforced polymer-matrix composites. A method for evaluation of adhesion is proposed based on tension tests of impregnated fiber yarns, with subsequent characterization by optical microscopy of length distribution of fibers pulled out of the yarn fracture surfaces. An elementary probabilistic model is derived relating aspect ratio distribution of the pulled out fibers to the fiber tensile strength distribution and the effective interfacial shear strength. The method was applied to flax fiber/vinylester resin yarns and an estimate of interfacial shear strength at 17 MPa was obtained.

  • 12.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sparnins, Edgars
    Statistical model of the transverse ply cracking in cross-ply laminates by strength and fracture toughness based failure criteria2008In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 75, no 9, 2651-2665 p.Article in journal (Refereed)
    Abstract [en]

    Cross-ply laminate subjected to tensile loading provides a relatively well understood and widely used model system for studying progressive cracking of the transverse ply. This test allows to identify material strength and/or toughness characteristics as well as to establish relation between damage level and the composite stiffness reduction. The transverse ply cracking is an inherently stochastic process due to the random variability of local material properties of the plies. The variability affects both crack initiation (governed by the local strength) and propagation (governed by the local fracture toughness). The primary aim of the present study is elucidation of the relative importance of these phenomena in the fragmentation process at different transverse and longitudinal ply thickness ratios. The effect of the random crack distribution on the mechanical properties reduction of the laminate is also considered. Transverse ply cracking in glass fiber/epoxy cross-ply laminates of the lay-ups [02/902]s, [0/902]s, and [0/904]s is studied. Several specimens of each lay-up were subjected to uniaxial quasistatic tension to obtain crack density as a function of applied strain. Crack spacing distributions at the edge of the specimen also were determined at a predefined applied strain. Statistical model of the cracking process is derived, calibrated using crack density vs. strain data, and verified against the measured crack spacing distributions.

  • 13.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sparnins, Edgars
    Rubenis, Oskars
    Institute of Polymer Mechanics, University of Latvia.
    Progressive cracking mastercurves of the transverse ply in a laminate2009In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 30, no 8, 1175-1182 p.Article in journal (Refereed)
    Abstract [en]

    In this study, progressive cracking of a transverse layer in a cross-ply composite laminate subjected to tensile loading is considered. Using the results of a probabilistic cracking model, approximate relations for crack density as a function of stress are derived for initiation-controlled and propagation-controlled cracking. It is shown that the crack density evolution in the transverse ply can be represented by a mastercurve in suitably normalized coordinates. The mastercurve approach is applied to progressive cracking in glass/epoxy laminates

  • 14.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Modniks, Janis
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    An Improved Method For Identification Of The Interfacial Shear Strength By Tensile Tests Of Short-Fiber Composites2015In: Proceedings of 7th International Conference on Composites Testing and Model Identification / [ed] C. González; C. López; J. LLorca, Madrid, Spain: IMDEA, Madrid (SPAIN) , 2015Conference paper (Refereed)
  • 15.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Modniks, Janis
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Madsen, Bo
    Technical University of Denmark, Risø Campus, Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark.
    Nättinen, Kalle
    Bemis Flexible Packaging Europe, Bemis Valkeakoski Oy.
    Apparent interfacial shear strength of short-flax-fiber/starch acetate composites2016In: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 64, 78-85 p.Article in journal (Refereed)
    Abstract [en]

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

  • 16.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Sparnins, Edgars
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    The onset of mixed mode intralaminar cracking in a cross-ply composite laminate2008In: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 44, no 6, 549-556 p.Article in journal (Refereed)
    Abstract [en]

    The intralaminar fracture toughness of a unidirectionally reinforced glass/epoxy composite is determined experimentally at several mode I and mode II loading ratios. The crack propagation criterion, expressed as a quadratic form in terms of single-mode stress intensity factors (alternatively, linear in terms of energy release rates), approximates the test results reasonably well. The mixed-mode cracking criterion obtained is used to predict the intralaminar crack on set in a cross-ply glass/epoxy composite under off-axis tensile loading.

  • 17.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Sparnins, Edgars
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Uniformity of filament strength within a flax fiber batch2009In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 44, no 2, 685-687 p.Article in journal (Refereed)
  • 18.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Sparnins, Edgars
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wallström, Lennart
    Strength distribution of elementary flax fibres2005In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 65, no 3-4, 693-702 p.Article in journal (Refereed)
    Abstract [en]

    Flax fibres, along with a number of other natural fibres, are being considered as an environmentally friendly alternative of synthetic fibres in fibre-reinforced polymer composites. A common feature of natural fibres is a much higher variability of mechanical properties. This necessitates study of the flax fibre strength distribution and efficient experimental methods for its determination. Elementary flax fibres of different gauge lengths are tested by single fibre tension in order to obtain the stress-strain response and strength and failure strain distributions. The applicability of single fibre fragmentation test for flax fibre failure strain and strength characterization is considered. It is shown that fibre fragmentation test can be used to determine the fibre length effect on mean fibre strength and limit strain.

  • 19.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Sparnins, Edgars
    Nyström, Birgitha
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Scale effect of the tensile strength of flax-fabric-reinforced polymer composites2011In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 30, no 23, 1969-1974 p.Article in journal (Refereed)
    Abstract [en]

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

  • 20.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Sparnins, Edgars
    Porike, Evija
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Strength distribution of elementary flax fibres due to mechanical defects2008In: 11th International Inorganic-Bonded Fiber Composites Conference (IIBCC): Madrid, Nov. 4 - 7, 2008. Proceedings / [ed] Blanco Suárez; Maria Ángeles, Madrid: Universidad Complutense de Madrid , 2008Conference paper (Refereed)
  • 21.
    Andersons, Janis
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Sparnins, Edgars
    Rubenis, Ojars
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Estimation of laminate stiffness reduction due to cracking of a transverse ply by employing crack initiation- and propagation-based master curves2008In: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 44, no 5, 441-450 p.Article in journal (Refereed)
    Abstract [en]

    The applicability range of toughness-and strength-based criteria for progressive cracking of a transverse layer in a cross-ply composite laminate subjected to tensile loading is considered. Using a deterministic cracking model, approximate relations for the crack density as a function of stress are derived for initiation-and propagation-controlled types of cracking. The master-curve approach is applied to progressive cracking in glass/epoxy laminates. The accuracy of estimation of laminate stiffness reduction by using crack density master curves is evaluated.

  • 22.
    Ansari, Farhan
    et al.
    Department of Fiber and Polymer Technology, KTH Royal Institute of Technology.
    Granda, Luis A.
    Laboratory of Paper Engineering and Polymer Materials (LEPAMAP) Group, Department of Chemical Engineering, University of Girona.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Berglund, Lars A.
    Department of Fiber and Polymer Technology, KTH Royal Institute of Technology.
    Vilaseca, Fabiola
    Department of Fiber and Polymer Technology, KTH Royal Institute of Technology.
    Experimental evaluation of anisotropy in injection molded polypropylene/wood fiber biocomposites2017In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 96, 147-154 p.Article in journal (Refereed)
    Abstract [en]

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

  • 23.
    Berglund, Lars
    et al.
    Kungliga tekniska högskolan, KTH.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Effects of voids on failure mechanisms in RTM laminates1994Conference paper (Other academic)
  • 24.
    Doroudgarian, Newsha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Anglada, Marc
    Universitat Politècnica de Catalunya.
    Mestra, Alvaro
    Universitat Politècnica de Catalunya.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Bio-based composites with different moisture contents under static and dynamic loading2013In: 6th international conference on composites testing and model identification: held 22-24 April 2013 in Aalborg, Denmark / [ed] O.T. Thomsen; Bent F. Sørensen; Christian Berggreen, 2013Conference paper (Refereed)
  • 25.
    Doroudgarian, Newsha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pupure, Liva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mechanical behavior of bio-based composites and their constituents at different humidity levels2013Conference paper (Refereed)
    Abstract [en]

    During the few past years the development of natural fiber composites for structural applications has gained the momentum. Mainly the efforts in development of these materials were focused on the composites with synthetic matrices. But most recently several bio-based resins (Tribest, EpoBioX etc.) have been introduced, allowing production of whole bio-based composites. The latest results demonstrated that these composites are comparable with glass fiber reinforced polymers in terms of stiffness. However due to variability of fiber properties and limited filament length it is complicated to arrange and control fiber alignment in composites as well as ensure stable, predictable composite properties. Therefore, another type of reinforcement with natural origin has caught attention of researchers – Regenerated Cellulose Fibers (RCF). These fibers are continuous with constant, reproducible cross-section and properties but with one significant disadvantage - they exhibit highly non-linear behavior. Thus, this reinforcement should be treated as material with time-dependent properties. Schepary developed model for time-dependent materials. This model has been successfully applied to short fiber (natural and synthetic) and long synthetic fiber composites. However, in order to apply this model, large number of time-consuming tests on studied composites must be performed. Therefore, our objective is to improve this model in such a way that only input of properties of constituents is required to predict behavior of material with any composition. Visco-elasticity and viscoplasticity has been analyzed by performing creep tests at different time steps and stress levels, and extent of damage is evaluated by performing stiffness degradation tests of fibers, matrix and composite.

  • 26.
    Doroudgarian, Newsha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pupure, Liva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Moisture uptake and resulting mechanical response of biobased composites:: II. Composites2015In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 36, no 8, 1510-1519 p.Article in journal (Refereed)
    Abstract [en]

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

  • 27.
    Doroudgarian, Newsha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pupure, Liva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sensivity to moisture and its effect on mechanical behavior of bio-based resins reinforced with cellulosic fibers2013In: 21st anniversary of the bio-environmental polymer society, 2013Conference paper (Refereed)
  • 28.
    Edgren, Fredrik
    et al.
    SICOMP AB, Swedish Institute of Composites.
    Asp, Leif
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Failure of NCF composites subjected to combined compression and shear loading2006In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 66, no 15, 2865-2877 p.Article in journal (Refereed)
    Abstract [en]

    Earlier studies have shown that formation of kink bands is the mechanism that is likely to govern failure of compression loaded non-crimp fabric (NCF) composite laminates. Because of this, a failure criterion for prediction of failure caused by kinking under multiaxial (axial compression and shear) loading has been adapted to a NCF composite system. The criterion has been validated for compression tests of quasi-isotropic laminates tested in uniaxial compression. By performing compression tests of the laminate at different off-axis angles, it was possible to vary the ratio of compressive axial stress/shear stress in the specimens. The test results proved that the criterion works well for predictions of kinking governed failure for the present material system. Detailed fractographic studies confirmed that formation of kink bands was the mechanism responsible for specimen failure. Kink bands were also found to develop at loads significantly lower than load at specimen failure.

  • 29.
    Engstrom, Jonas
    et al.
    Swerea SICOMP AB.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fernberg, Patrik
    Swerea SICOMP AB.
    Characterization of carbon nanotube doped carbon fiber prepreg laminate2012In: Proceedings of the 15th European Conference on Composite Materials / [ed] Marino Quaresimin; Laszlo Kollar; Leif Asp, Venice, 2012Conference paper (Refereed)
    Abstract [en]

    The current paper reports results from a preliminary study on PREGCYL™ NC R2HM-01 which is a carbon nanotube doped prepreg produced by Nanocyl. The work consisted of sample manufacturing in autoclave, microcopy analysis with XHR-SEM and mechanical testing. The mechanical testing consisted of tensile tests of unidirectional (in longitudinal direction) and cross-ply laminates. Test of unidirectional laminates showed that stiffness of the PREGCYL material is slightly higher than that of MTM55 composites (111GPa vs 102GPa). The results from tests of cross-ply laminates indicated that damage (transverse cracks) initiation is delayed in PREGCYL composites compare to the MTM55 material. Damage accumulation also seems to be slower in nano-doped composites.

  • 30.
    Fernberg, Patrik
    et al.
    Swerea SICOMP AB.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Damage detection in carbon fibre cross-ply laminates by aid of carbon nanotube doped resin2008In: 13th European Conference on Composite Materials: 2-5 June 2008, Stockholm, Sweden, 2008Conference paper (Refereed)
    Abstract [en]

    The possibility to use resistance variations of carbon nanotube (CNT) doped carbon fibre reinforced plastics (CFRP) to characterise the level of microstructural damage in the form of transverse cracking is experimentally investigated in the current work. The resistance of CNT-doped and unmodified CFRP was measured after they had been subjected to stepwise increased tensile loading. Both increase and decrease resistance was observed which made it difficult to make any firm statement that the changes we observed were due to damage. The conductivity along carbon fibres is dominating electrical conductivity of the studied cross-ply laminate. Any disturbance of conductive CNT based nanocomposite matrix by transverse cracks in 90-layer therefore caused too small changes of resistance to be measured with current experimental setup.

  • 31.
    Fernberg, Patrik
    et al.
    Swerea SICOMP AB.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Edgren, Fredrik
    Volvo Aero Corporation.
    Carbon nanotube treated carbon fibre preforms for improved properties of aeronautical grade composites2012In: Proceedings of the 15th European Conference on Composite Materials / [ed] Marino Quaresimin; Laszlo Kollar; Leif Asp, Padova: University of Padova , 2012Conference paper (Refereed)
    Abstract [en]

    The current paper reports work on development of enhanced carbon fibre composites manufactured by resin transfer moulding (RTM). In particular, the possibility to obtain a toughened composite through deposition of carbon nanotubes (CNT) on the fibres is investigated. The hypothesis is that deposition of CNT on the fibre surface has two major advantages: a) filtering problems during manufacturing are eliminated and b) CNT can contribute to a local toughening in the vicinity of fibres, where stress concentrations often are high. Unidirectional and multi-axial composites, with and without CNT-modification, were manufactured using conventional RTM-technique and HexFlow®RTM6 epoxy resin. The composites were characterized by means of mechanical testing (interlaminar shear strength, ILSS) and microscopy. Significant improvements by 13 to37 % in ILSS values were achieved with the addition of CNT. Stiffness degradation tests were also performed. The results from these tests were not completely conclusive. Some treatments promoted stiffness degradation whereas others had no apparent effect.

  • 32.
    Fernberg, Patrik
    et al.
    Swerea SICOMP AB.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Nilsson, Greger
    Swerea SICOMP AB.
    Strain and damage sensing during loading of carbon nanotube doped composites2009In: ICCM 17, Edinburgh: 17th International Conference on Composite Materials ; 27 Jul 2009 - 31 Jul 2009, Edinburgh International Convention Centre, Edinburgh, UK, London: IOM Communications , 2009Conference paper (Refereed)
    Abstract [en]

    This work explores the possibility to use resistance changes in a carbon nanotube (CNT) doped composites to monitor deformations and damage. Most other studies in the field are done on simplified uniaxial loading whereas current work also evaluates the possibilities to monitor strain in more complex loading case, such as bending.

  • 33.
    Fernberg, Patrik
    et al.
    SICOMP AB, Swedish Institute of Composites.
    Nilsson, Greger
    SICOMP AB, Swedish Institute of Composites.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Piezoresistive performance of long fibre composites with carbon nanotube doped matrix2007In: Proceedings of COMP07: 6th International Symposium on Advanced Composites, 16-18 May, 2007, Corfu, Greece, 2007Conference paper (Refereed)
    Abstract [en]

    The electrical and mechanical properties of carbon nanotube doped epoxy resin and composites based on this matrix were studied. The investigation was carried out on neat nanocomposites and on structural composites i.e. when the nanocomposite is used as matrix in composite materials reinforced with long continuous fibers. Tensile tests showed that carbon nanotube (CNT) doped epoxy exhibited a clear piezoresistive behavior. It was however also shown that geometrical changes of the specimen also contribute significantly to resistance changes during tensile loading. Particular effort was made to establish the relations between transverse cracking in glass fibre cross-ply laminates with nanotube doped matrix and resistance changes. It was shown that resistance changes during tensile loading of composites containing CNT doped matrix gives highly relevant information about the damage state of the material. In an unloaded state the resistance change is proportional to the relative change of stiffness. This work demonstrates that there are three different mechanisms which contribute to resistance changes of a composite specimen subjected to tensile strain. These three mechanisms are: a) geometrical changes of the specimen b) piezoresistive material response and c) accumulation of micro-damage

  • 34.
    Fernberg, Patrik
    et al.
    Swerea SICOMP AB.
    Nilsson, Greger
    Swerea SICOMP AB.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Piezoresistive performance of long-fiber composites with carbon nanotube doped matrix2009In: Journal of Intelligent Materials Systems and Structures, ISSN 1045-389X, E-ISSN 1530-8138, Vol. 20, no 9, 1017-1023 p.Article in journal (Refereed)
    Abstract [en]

    The electrical and mechanical properties of carbon nanotube (CNT) doped epoxy resin and composites based on this matrix were studied. The investigation was carried out on neat nanocomposites and on structural composites i.e., when the nanocomposite is used as matrix in composite materials reinforced with long continuous fibers. Tensile tests showed that CNT doped epoxy exhibited clear piezoresistive behavior. It was, however, also shown that geometrical changes of the specimen also contribute significantly to resistance changes during tensile loading. Particular effort was made to establish the relations between transverse cracking in glass fiber cross-ply laminates with nanotube doped matrix and changes of electrical resistance. It was shown that changes of electrical resistance during tensile loading of composites containing CNT doped matrix gives highly relevant information about the damage state of the material. In an unloaded state the resistance change is proportional to the relative change of stiffness. This work demonstrates that there are three different mechanisms, which contribute to changes of electrical resistance of a composite specimen subjected to tensile strain. These three mechanisms are: (a) geometrical changes of the specimen (b) piezoresistive material response, and (c) accumulation of micro-damage.

  • 35.
    Fernberg, S. Patrik
    et al.
    Luleå tekniska universitet, Swerea SICOMP AB, Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Tsampas, Spyros
    Swerea SICOMP AB.
    Mannberg, Peter
    Swerea SICOMP AB.
    Influence of post-cure on carbon fibre polyimide composites with glass transition temperatures above 400ºC2015Conference paper (Refereed)
    Abstract [en]

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

  • 36.
    Giannadakis, Konstantinos
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mannberg, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    The sources of inelastic behavior of glass fibre/vinylester non-crimp fabric [±45]s laminates2011In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 30, no 12, 1015-1028 p.Article in journal (Refereed)
    Abstract [en]

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

  • 37.
    Gong, G.
    et al.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Nyström, Birgitha
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Enhanced thermal stability and flame retarding properties of recycled polyethylene based wood composites via addition of polyethylene/nanoclay masterbatch2013In: Plastics, rubber and composites, ISSN 1465-8011, E-ISSN 1743-2898, Vol. 42, no 6, 244-255 p.Article in journal (Refereed)
    Abstract [en]

    Barrier and mechanical properties of wood powder composites based on recycled polyethylene (RPE) were modified using a commercial nanoclay masterbatch. X-ray diffraction, dynamic rheology and thermogravimetric analysis measurements showed that nanoclay from the selected masterbatch was well dispersed and formed a percolation network in both virgin and RPEs. The resulting nanocomposites promoted the thermal stability of matrix significantly. Modification efficiency of nanoclay, however, was evidently influenced by the type of matrix, where the strongest effect was achieved in a low viscosity virgin high density PE. The masterbatch was incorporated into an industrial formula designed extrusion quality RPE/wood flour composite. Processing procedures, mainly compounding cycles, and material composition, mainly clay content and type of coupling agent, were optimised. Two extrusion cycles led to higher uniformity of resulting composites than one cycle. Addition of a coupling agent, which has medium viscosity and plenty functional groups, led to enhanced tensile strength. The twice compounded composites were well stiffened and strengthened via combination of 6 wt-% clay and medium viscosity coupling agent. All composites without the addition of nanoclay burned faster after ignition and dripped much earlier and more compared to the composites containing nanoclay even with as small amount as 3 wt-% and being compounded once. The material with 6 wt-% clay showed the best sample integrity and burned slowest of all the tested composites. Furthermore, no dripping during combustion was seen for this material. This study shows that the incorporation of nanoclay using the selected masterbatch can effectively improve the flame retarding properties of RPE based wood composites

  • 38.
    Gong, Guan
    et al.
    Swerea SICOMP AB.
    Nyström, Birgitha
    Swerea SICOMP AB.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Development of polyethylene/nanoclay masterbatch for use in wood plastic composites2013In: Plastics, rubber and composites, ISSN 1465-8011, E-ISSN 1743-2898, Vol. 42, no 4, 167-175 p.Article in journal (Refereed)
    Abstract [en]

    In this work, organoclay reinforced high density polyethylene (HDPE) nanocomposites were prepared at lab scale using a batch mixer. Processing conditions, maleic anhydride modified polyethylene (MAPE) type and MAPE/clay weight ratio, were optimized. The microstructure of the resultant nanocomposites was analysed by XRD and melt rheology tests and flexural properties and thermal stability were evaluated. Three types of MAPEs with different melt flow index (MFI) and MA content all improved interaction between HDPE and clay, and promoted clay dispersion. Nanocomposites where the MAPE with MFI most similar to HDPE was used showed the best exfoliation of clay and strongest HDPE-clay interface. Mechanical properties were slightly improved while thermal stability was distinctly enhanced in these HDPE nanocomposites compared to neat HDPE and HDPE nanocomposite without MAPE. The prepared HDPE nanocomposites show potential to improve thermal stability of wood plastic composites for structural applications providing.

  • 39.
    Hajlane, Abdelghani
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaddami, H.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Design and characterization of cellulose fibers with hierarchical structure for polymer reinforcement2013Conference paper (Refereed)
    Abstract [en]

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

  • 40.
    Hajlane, Abdelghani
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kaddami, Hamid
    Laboratory of Organometallic and Macromolecular Chemistry-Composite Materials, Faculty of Sciences and Techniques, Cadi Ayyad University.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Chemical modification of regenerated cellulose fibres by cellulose nano-crystals: Towards hierarchical structure for structural composites reinforcement2017In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 100, 41-50 p.Article in journal (Refereed)
    Abstract [en]

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

  • 41.
    Hajlane, Abdelghani
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kaddami, Hamid
    Cadi Ayyad University, Faculty of Sciences and Techniques.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Environmentally friendlier method to deposit cellulose nanocrystals on regenerated cellulose filaments and effect of the treatment on mechanical properties of fibers2016In: ECCM 2016: Proceeding of the 17th European Conference on Composite Materials, European Conference on Composite Materials , 2016Conference paper (Refereed)
    Abstract [en]

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

  • 42.
    Hajlane, Abdelghani
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaddami, Hamid
    Cadi Ayyad University, Faculty of Sciences and Techniques.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Design and characterization of cellulose fibers with hierarchical structure for polymer reinforcement2013In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 20, no 6, 2765-2778 p.Article in journal (Refereed)
    Abstract [en]

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

  • 43.
    Hajlane, Abdelghani
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Miettinen, A.
    University of Jyvaskyla, Department of Physics.
    Madsen, Bo
    Technical University of Denmark, Department of Wind Energy, Risø Campus.
    Beauson, J.
    Techical University of Denmark, Department of Wind Energy, Riso Campus.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Use of micro-tomography for validation of method to identify interfacial shear strength from tensile tests of short regenerated cellulose fibre composites2016In: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 139, 012021Article in journal (Refereed)
    Abstract [en]

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

  • 44.
    Hajlane, Abdelghani
    et al.
    University Cadi Ayyad of Marrakech.
    Sahib, Anas
    University Cadi Ayyad of Marrakech.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Kaddami, Hamid
    University Cadi Ayyad of Marrakech.
    Design and characterization of cellulose fibers with highly hierarchical structure2010Conference paper (Other academic)
  • 45.
    Jekabsons, Normunds
    et al.
    Ventspils University College.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Locans, Uldis
    Ventspils University College.
    Mechanical properties of a rapidly prototyped composite: numerical modeling and parametric analysis2012In: Proceedings of Mechanics of Composite Materials XVII International Conference, Riga, 2012Conference paper (Refereed)
  • 46.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Activity: Annual International SICOMP Conference on Manufacturing and Design of Composites2010Conference paper (Other (popular science, discussion, etc.))
  • 47.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Activity: Annual International SICOMP Conference on Manufacturing and Design of Composites2010Conference paper (Other (popular science, discussion, etc.))
  • 48.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Activity: Mechanics of Composite Materials, XVI International Conference2010Conference paper (Other (popular science, discussion, etc.))
  • 49.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Activity: Mechanics of Composite Materials, XVI International Conference2010Conference paper (Other (popular science, discussion, etc.))
  • 50.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Activity: Mechanics of Composite Materials, XVI International Conference2010Conference paper (Other (popular science, discussion, etc.))
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