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  • 1.
    Asp, Leif
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Marklund, Erik
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Varna, J.
    Luleå University of Technology.
    Olsson, Robin
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Multiscale modelling of non-crimp fabric composites2012Conference paper (Refereed)
    Abstract [en]

    Damage initiation and evolution in NCF composites leading to final failure includes a multitude of mechanisms and phenomena on several length scales. From an engineering point-of-view a computational scheme where all mechanisms would be explicitly addressed is too complex and time consuming. Hence, methods for macroscopic performance prediction of NCF composites, with limited input regarding micro- And mesoscale details, are requested. In this paper, multi-scale modelling approaches for in-plane transverse strength of NCF composites are outlined and discussed. In addition a simplistic method to predict transverse tensile and compressive strength for textile composites featuring low or no fibre waviness is presented. Copyright © 2012 by ASME.

  • 2.
    Bachinger, Angelika
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Marklund, Erik
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP. Luleå University of Technology, Sweden.
    Rössler, J.
    Hellström, Peter
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Asp, Leif
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP. Chalmers University of Technology, Sweden.
    Stiffness-modifiable composite for pedestrian protection2014Conference paper (Refereed)
    Abstract [en]

    A novel functional material allowing stiffness-reduction upon external stimulation was developed. Implementation of such technology in the design of a car front has high potential to result in increased protection of vulnerable road users (VRUs). The composite material is obtained by coating carbon fibres with a thermoplastic polymer in a continuous process, followed by infusion with an epoxy resin. The process is scalable for industrial use. The coating process was optimized regarding coating efficiency, energy consumption, risks involved for operating personnel and environment, and tailored to gain the optimal coating thickness obtained from numerical calculations. A drastic decrease in transversal stiffness could be detected for the composite material by dynamic mechanical thermal analysis (DMTA), when the temperature was increased above the glass transition temperature of the thermoplastic interphase. The ability of the material to achieve such temperature and associated reduction in stiffness by the application of current was verified using a special 3-point bending setup developed for this task.

  • 3.
    Carlstedt, David
    et al.
    Chalmers University of Technology, Sweden.
    Marklund, Erik
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP. Luleå University of Technology, Sweden.
    Asp, Leif
    Chalmers University of Technology, Sweden.
    Effects of state of charge on elastic properties of 3D structural battery composites2019In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 169, p. 26-33Article in journal (Refereed)
    Abstract [en]

    The effects of state of charge (SOC) on the elastic properties of 3D structural battery composites are studied. An analytical model based on micromechanical models is developed to estimate the effective elastic properties of 3D structural battery composite laminae at different SOC. A parametric study is performed to evaluate how different design parameters such as volume fraction of active materials, stiffness of constituents, type of positive electrode material, etc. affect the moduli of the composite lamina for extremes in SOC. Critical parameters and configurations resulting in large variations in elastic properties due to change in SOC are identified. As the extreme cases are of primary interest in structural design, the effective elastic properties are only estimated for the electrochemical states corresponding to discharged (SOC = 0) and fully charged (SOC = 1) battery. The change in SOC is simulated by varying the volume and elastic properties of the constituents based on data from literature. Parametric finite element (FE) models for square and hexagonal fibre packing arrangements are also analysed in the commercial FE software COMSOL and used to validate the analytical model. The present study shows that the transverse elastic properties E2 and G23 and the in-plane shear modulus G12 are strongly affected by the SOC while the longitudinal stiffness E1 is not. Fibre volume fraction and the properties of the coating (such as stiffness and Poisson's ratio) are identified as critical parameters that have significant impact on the effect of SOC on the effective elastic properties of the composite lamina. For configurations with fibre volume fraction Vf ≥ 0.4 and Young's modulus of the coating of 1 GPa or higher, the transverse properties E2 and G23 change more than 30% between extremes in SOC. Furthermore, for configurations with high volume fractions of electrode materials and coating properties approaching those of rubber the predicted change in transverse stiffness E2 is as high as +43%. This shows that it is crucial to take effects of SOC on the elastic properties into account when designing 3D structural battery composite components. © 2018 Elsevier Ltd

  • 4.
    Kopp, Alexander
    et al.
    German Aerospace Center DLR, Germany.
    Stappert, Sven
    German Aerospace Center DLR, Germany.
    Mattsson, David
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Olofsson, Kurt
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Marklund, Erik
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP. Luleå University of Technology, Sweden.
    Kurth, Guido
    Bayern Chemie GmbH, Germany.
    Mooij, Erwin
    Delft University of Technology, The Netherlands.
    Roorda, Evelyne
    Delft University of Technology, The Netherlands.
    The Aurora space launcher concept2018In: CEAS Space Journal, ISSN 1868-2502, E-ISSN 1868-2510, Vol. 10, no 2, p. 167-187Article in journal (Refereed)
    Abstract [en]

    This paper gives an overview about the Aurora reusable space launcher concept study that was initiated in late-2015/early-2016. Within the Aurora study, several spaceplane-like vehicle configurations with different geometries, propulsion systems and mission profiles will be designed, investigated and evaluated with respect to their technical and economic feasibility. The first part of this paper will discuss the study logic and the current status of the Aurora studies and introduces the first vehicle configurations and their system design status. As the identification of highly efficient structural designs is of particular interest for Aurora, the structural design and analysis approach will be discussed in higher level of detail. A special design feature of the Aurora vehicle configurations is the utilization of the novel thin-ply composite material technology for structural mass reductions. Therefore, the second part of this paper will briefly discuss this technology and investigate the application and potential mass savings on vehicle level within simplified structural analysis studies. The results indicate that significant mass savings could be possible. Finally, an outlook on the next steps is provided.

  • 5.
    Larijani, Nasim
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Marklund, Erik
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Wysocki, Maciej
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Metal onto polymer composite casting: Degradation behaviour and mechanical performance2009Conference paper (Refereed)
    Abstract [en]

    A general three dimensional finite element model for modelling thermal degradation of polymer composites due to thermal loading is presented. In particular, the model is intended for modelling the thermal degradation of polymer composites due to "metal onto composites casting" with lightweight alloys. The model is implemented as a user defined subroutine into the general purpose FEpackage ABAQUS©. The applicability of the code was demonstrated by analysing the casting process of an aluminium alloy onto composite rods, resulting in a shrinkage fit. To succeed in manufacturing of this type of joint, a delicate balance between thermal loadings, metal shrinkage, composite degradation and the overall cooling must be met. The proposed subroutine together with finite element models provides the spatial distribution of these field variables, allowing for subsequent optimization of the assembly. In order to asses the quality of the composite/metal joints pull-out tests of cylindrical composite rods were performed and compared to numerical simulation predictions.

  • 6.
    Lundmark, Peter
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Marklund, Erik
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Olofsson, Kurt
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Utvärdering av projektledarkurs Tankar och reflektioner ett halvt år senare2009Report (Refereed)
  • 7.
    Marklund, Erik
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Smältfogning av termoplastbaserade kompositer och lättmetall2012Report (Refereed)
  • 8.
    Marklund, Erik
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Asp, Leif
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Olsson, Robin
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Transverse strength of unidirectional non-crimp fabric composites: Multiscale modelling2014In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 65, p. 47-56Article in journal (Refereed)
    Abstract [en]

    A multiscale approach is used to predict transverse tensile and transverse compressive strength of unidirectional non-crimp fabric (NCF) composites. Numerical analysis on fibre/matrix scale is performed to obtain the transverse strength of the fibre bundle to be further used in an analytical mesoscale model to predict the strength of the unidirectional NCF composite. Design of unidirectional layer composites with the same fibres, interface, matrix and volume fractions as in the bundle is suggested as an alternative method for bundle strength determination. Good agreement of both methods for bundle transverse strength determination is demonstrated. The simple analytical model used on mesoscale gives accurate predictions of the tensile transverse strength whereas the compressive strength is underestimated. The necessity of including bundle waviness in models when bidirectional NCF composites are analysed is demonstrated by FEM stress analysis and by experimental data showing differences in transverse cracking pattern due to bundle waviness. © 2014 Elsevier Ltd. All rights reserved.

  • 9.
    Marklund, Erik
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Eitzenberger, J.
    Luleå University of Technology.
    Varna, J.
    Luleå University of Technology.
    Nonlinear viscoelastic viscoplastic material model including stiffness degradation for hemp/lignin composites2008In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 68, no 9, p. 2156-2162Article in journal (Refereed)
    Abstract [en]

    In repeating tensile tests with increasing maximum strain for every loading cycle the hemp/lignin composites clearly showed a nonlinear behavior and hysteresis loops in loading and unloading. The explanation for this behavior is the inherent viscoelastic nature for this type of material, but also noticeable stiffness degradation with increasing strain level. Creep tests performed at different stress levels revealed a nonlinear viscoelastic response and after recovery viscoplastic strain was detected for high stress levels. It is demonstrated that Schapery's model is suitable to model nonlinear viscoelasticity whereas viscoplastic strain may be described by a nonlinear functional presented by Zapas and Crissman. In a creep test this functional leads to a power law with respect to time and stress. In order to include stiffness reduction due to damage Schapery's model has been modified by incorporating a maximum strain-state dependent function reflecting the elastic modulus reduction with increasing strain measured in tensile tests. A generalized incremental model of the constitutive equation for viscoelastic case has been used to validate the developed material model in a linear stress controlled loading and unloading ramp. The model successfully describes the main features for the investigated material and shows good agreement with test data within the considered stress range. © 2008 Elsevier Ltd. All rights reserved.

  • 10.
    Marklund, Erik
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Hallström, Frida
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Slutrapport Castcomp2009Report (Refereed)
  • 11.
    Marklund, Erik
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Hellström, Peter
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Wingborg, Jon
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Evaluation of CFRP-Hybrix integrated joints2013Report (Refereed)
  • 12.
    Marklund, Erik
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Varna, J.
    Luleå University of Technology.
    Micromechanical modelling of wood fibre composites2009Conference paper (Refereed)
    Abstract [en]

    A concentric cylinder model for an A/-phase composite with orthotropic properties of constituents was previously presented by the authors. With only minor modifications the model allows for including also free hygroexpansion terms in the elastic stress-strain relationship in order to deal with orthotropic phase swelling. Thus the effect of wood fibre ultrastructure and cell wall hygroelastic properties on wood fibre composite hygroexpansion may be analysed. Multiscale modelling was performed to calculate the hygroexpansion coefficients of both the fibre cell wall and the aligned wood fibre composite. Furthermore, the fibre's helical structure leads to an extension-twist coupling and thus a free fibre will deform axially and also rotate upon loading in longitudinal fibre direction. Within the composite, however, the fibre rotation will be restricted. Therefore, the decision was to compare the composite performance in the two extreme cases (i) free rotation (ii) no rotation of the fibre in the composite.

  • 13.
    Marklund, Erik
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Varna, J.
    Lulea University of Technology.
    Modeling the effect of helical fiber structure on wood fiber composite elastic properties2009In: Applied Composite Materials, ISSN 0929-189X, E-ISSN 1573-4897, Vol. 16, no 4, p. 245-262Article in journal (Refereed)
    Abstract [en]

    The effect of the helical wood fiber structure on in-plane composite properties has been analyzed. The used analytical concentric cylinder model is valid for an arbitrary number of phases with monoclinic material properties in a global coordinate system. The wood fiber was modeled as a three concentric cylinder assembly with lumen in the middle followed by the S3, S2 and S1 layers. Due to its helical structure the fiber tends to rotate upon loading in axial direction. In most studies on the mechanical behavior of wood fiber composites this extension-twist coupling is overlooked since it is assumed that the fiber will be restricted from rotation within the composite. Therefore, two extreme cases, first modeling fiber then modeling composite were examined: (i) free rotation and (ii) no rotation of the cylinder assembly. It was found that longitudinal fiber modulus depending on the microfibril angle in S2 layer is very sensitive with respect to restrictions for fiber rotation. In-plane Poisson's ratio was also shown to be greatly influenced. The results were compared to a model representing the fiber by its cell wall and using classical laminate theory to model the fiber. It was found that longitudinal fiber modulus correlates quite well with results obtained with the concentric cylinder model, whereas Poisson's ratio gave unsatisfactory matching. Finally using typical thermoset resin properties the longitudinal modulus and Poisson's ratio of an aligned softwood fiber composite with varying fiber content were calculated for various microfibril angles in the S2 layer. © 2009 Springer Science+Business Media B.V.

  • 14.
    Marklund, Erik
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Varna, J.
    Lulea University of Technology.
    Modeling the hygroexpansion of aligned wood fiber composites2009In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 69, p. 1108-1114Article in journal (Refereed)
    Abstract [en]

    The effect of wood fiber ultrastructure and cell wall hygroelastic properties on wood fiber composite hygroexpansion has been analyzed. An analytical concentric cylinder model extended to include also free hygroexpansion of orthotropic phase materials has been used on several length scales. Using properties of the three main wood polymers, cellulose, hemicellulose and lignin the longitudinal and transverse hygroexpansion coefficients for the microfibril unit cell were obtained and the volume fraction change of the wood polymers in the microfibril unit cell depending on relative humidity was calculated. The fiber cell wall was modeled regarding each individual S1, S2 and S3 layer and the cell wall longitudinal hygroexpansion coefficient was determined depending on microfibril angle in the S2 layer. A homogenization procedure replacing the S1, S2 and S3 layers with one single layer was found not to influence the results significantly for low microfibril angles. Finally the hygroexpansion coefficients of an aligned softwood fiber composite were calculated. © 2009 Elsevier Ltd. All rights reserved.

  • 15.
    Marklund, Erik
    et al.
    Luleå University of Technology.
    Varna, J.
    Luleå University of Technology.
    Asp, Leif
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Stiffness and strength modelling of non-crimp fabric composites2011Conference paper (Refereed)
    Abstract [en]

    This work comprises methodologies for micro-meso stiffness modelling and limited analysis for strength prediction. It is intended to formulate some guidelines and recommendations when modelling NCF composites mechanical performance. For both micro- and meso stiffness modelling, analytical models are compared to FE investigations considering idealised structures. Important aspects when modelling matrix failure of NCF composite bundles are presented to highlight some of the challenges in future modelling. Possible failure criteria for modelling matrix failure within fibre bundles have been investigated; their strength, problems and weaknesses are revealed. Copyright © 2011 by Luleå University of Technology.

  • 16.
    Marklund, Erik
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Varna, J.
    Lulea University of Technology.
    Neagu, R.C.
    Ecole Polytechnique Fédérale de Lausanne (EPFL).
    Gamstedt, E.K.
    STFI-Packforsk AB.
    Stiffness of aligned wood fiber composites: Effect of microstructure and phase properties2008In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 42, no 22, p. 2377-2405Article in journal (Refereed)
    Abstract [en]

    The effect of wood fiber anisotropy and their geometrical features on wood fiber composite stiffness is analyzed. An analytical model for an N-phase composite with orthotropic properties of constituents is developed and used. This model is a straightforward generalization of Hashin's concentric cylinder assembly model and Christensen's generalized self-consistent approach. It was found that most macro-properties are governed by only one property of the cell wall which is very important in attempts to back-calculate the fiber properties. The role of lumen (whether it filled by resin or not) has a very large effect on the composite shear properties. It is shown that several of the unknown anisotropic constants characterizing wood fiber are not affecting the stiffness significantly and rough assumptions regarding their value would suffice. The errors introduced by application of the Hashin's model and neglecting the orthotropic nature of the material behavior in cylindrical axes are evaluated. The effect of geometrical deviations from circular cross-section, representing, for example, collapsed fibers, is analyzed using the finite element method (FEM) and the observed trends are discussed. © 2008 SAGE Publications.

  • 17.
    Olsson, Robin
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Marklund, Erik
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Jansson, N.
    Volvo, Sweden.
    Testing of carbon/epoxy NCF strength under mixed in-plane loading2012Conference paper (Refereed)
    Abstract [en]

    The measured stiffness and strength of a carbon/epoxy unidirectional NCF system in shear, tension and compression are compared with test results for the pure resin and for impregnated bundle material under various combinations of in-plane compressive and tensile loading. The study is a part of a project to develop mesomechanics models to predict failure of NCF materials under triaxial loading by use of data for the pure resin and for bundles impregnated by resin. A simplified analytical rule-of-mixtures model is suggested for stiffness and strength of the NCF material. Good agreement is shown for shear and tension along and transverse to the bundles. Compressive strengths are significantly underestimated, apparently due to deficiencies in the compressive test method used for the bundle material.

  • 18.
    Zrida, H.
    et al.
    Lulea University of Technology.
    Marklund, Erik
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Ayadi, Z.
    Ecole Européenne D'Ingénieurs en Génie des Matériaux.
    Varna, J.
    Lulea University of Technology.
    Effective stiffness of curved 0°-layers for stiffness determination of cross-ply non-crimp fabric composites2014In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 33, no 14, p. 1339-1352Article in journal (Refereed)
    Abstract [en]

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

  • 19.
    Zrida, H.
    et al.
    Luleå University.
    Marklund, Erik
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Ayadi, Z.
    Ecole Européenne d'Ingénieurs en Génie des Matériaux.
    Varna, J.
    Luleå University of Technology.
    Master curve approach to axial stiffness calculation for non-crimp fabric biaxial composites with out-of-plane waviness2014In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 64, p. 214-221Article in journal (Refereed)
    Abstract [en]

    The effect of 0°-tow out-of-plane waviness on the biaxial non-crimp-fabric (NCF) composite axial stiffness is investigated. Homogenizing, the bundle mesostructure of the NCF composite is replaced by layers. Then the composite is represented by a laminate with flat layers with effective stiffness properties representing the curved 0°-layer and the 90°-layer with varying thickness. It is shown that the NCF composite knock-down factor characterizing the stiffness degradation has almost the same dependence on wave parameters as the knock-down factor for the curved 0°-layer. Numerical analysis showed that 90°-layer knock-down factor versus amplitude curves for different wavelength can be reduced to one master curve which can be described by a one-parameter expression with the parameter dependent on the used material. This observation is used to obtain high accuracy for analytical predictions for knock-down factors for cases with different wavelength and amplitudes based on two FE calculations only. © 2014 Elsevier Inc. All rights reserved.

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