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  • 1. Braz, T. B. C.
    et al.
    Cimini, C.A., Jr.
    Wennhage, Per
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Nyman, T.
    Thick ply versus thin ply composite laminate stiffened panel buckling and post-buckling behavior2017Ingår i: ICCM International Conferences on Composite Materials, International Committee on Composite Materials , 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    For their weight reduction, thin web panels are often used in airspace industry. In this study, a basic fuselage section is represented by a stiffened panel composed by skin, frame, stiffeners and attachments, as conceived by Arakaki and Faria [1]. In this panel design, the structure withholds large loads after the buckling of the web. This study presents a comparison between thick and thin ply composite laminates behavior under shear buckling loads. The two concepts were modeled using the commercial finite element software Abaqus®. Buckling and post-buckling nonlinear behavior for both thick ply and thin ply laminates was analyzed and results were compared. 

  • 2.
    Burman, Magnus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Rosén, Anders
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Spectrum Slam Fatigue Loading of Sandwich Materials for Marine Structures2010Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Sandwich materials are more frequently used in high speed craft and ferries. The motivation is reduced weight and associated operational cost. The hull structure in these vessels is subjected to repeated (fatigue) slamming loads (high strain rate loading). Scantling societies treat sandwich materials differently in their design rules. In common reduction or safety factors on the static strength of sandwich materials are used calculating the design stress. In most rules there is no explicit consideration of fatigue performance nor of the altered material properties related to high strain rate loading. In this work actual response measurements on a high speed vessel are used to formulate a tentative slam fatigue loading spectrum for sandwich core materials. This spectrum is then used in the testing of one type of core material common in hulls panels, Divinycell H200. The slam spectrum fatigue results are then compared to fatigue test results based on constant amplitude loading based on a method of equivalent stress. Earlier studies indicate that slamming fatigue do not affect the life compared to constant amplitude loading. However there are also studies that indicate that both a static overload (post the yield point) prior to fatigue loading, and block sequence fatigue loadings with initial high amplitudes followed by low amplitude have a detrimental effect of the fatigue life. In the current study both various amplitudes and high strain rates are included in the fatigue loading sequence. The spectrum fatigue results match the fatigue life from the constant amplitude loading. However, the number of samples is limited and the different effects of fatigue at high strain rates and fatigue block sequence are not fully clarified. It is possible that those effects may counteract each other in the current work. Further studies on sandwich foam core material properties and improvement of methods for material characterization is concluded to be of interest and will follow.

  • 3.
    Dionisi, Filippo
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner. Politecnico di Milano, Italy.
    Harnden, Ross
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    A model to analyse deformations and stresses in structural batteries due to electrode expansions2017Ingår i: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 179, s. 580-589Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In order to aid design of future structural battery components an analytical model is developed for modelling volume expansions in laminated structural batteries. Volume expansions are caused by lithium ion intercalation in carbon fibre electrodes. An extended version of Classical Lamination Plate Theory (CLPT) is used to allow analysis of unbalanced and unsymmetric lay-ups. The fibre intercalation expansions are treated analogously to a thermal problem, based on experimental data, with intercalation coefficients relating the fibre capacity linearly to its expansions. The model is validated using FEM and allows the study of the magnitude of interlaminar stresses and hence the risk of delamination damage due to the electrochemically induced expansions. It also enables global laminate deformations to be studied. This allows information about favourable lay-ups and fibre orientations that minimise deformations and the risk of delamination to be obtained. Favourable configurations for application to a solid state mechanical actuator are also given.

  • 4.
    Ekh, Johan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Schön, Joakim
    Swedish Defence Research Agency, FOI, Sweden.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Simple and efficient prediction of bearing failure in single shear, composite lap joints2013Ingår i: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 105, s. 35-44Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A straightforward procedure to predict bearing strength in bolted composite structures has been developed. The method is based on a finite element analysis, using structural elements, followed by a post-processing procedure. Bolt-hole clearance, friction between member plates, fastener clamp-up and fastener deformation is accounted for. Forces calculated in the FE-analysis are converted into a local stress field which is used in an existing criterion to predict fiber microbuckling in the most critically loaded lamina. Predictions were compared with experiments which validated the method. The small computational cost required by the procedure suggests that the method is applicable on large scale structures and suitable to use in conjunction with iterative schemes such as optimization and statistical investigations.

  • 5.
    Ekh, Johan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Schön, Joakim
    Prediction of Bearing Failure in Composite Single-lap JointsManuskript (preprint) (Övrigt vetenskapligt)
  • 6.
    Eric, Jacques
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Kjell, Maria
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Behm, Mårten
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Impact of the mechanical loading on the electrochemical capacity of carbon fibres for use in energy storage composite materials2011Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Reducing system mass for improvements in system performance has become a priority for future applications such as mobile phones or electric vehicles which require load bearing components and electrical energy storage devices. Structure and energy storage are usually subsystems with the highest mass contributions but energy storage components are structurally parasitic. A novel solution is a multifunctional lightweight design combining these two functions in a single material entity able to simultaneously bear mechanical loads as a carbon fiber composite component and store electrochemical energy as a lithium-ion battery.

  • 7.
    Fagerberg, Linus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Effects of anisotropy and multiaxial loading on the wrinkling of sandwich panels2005Ingår i: Journal of Sandwich Structures and Materials, ISSN 1099-6362, E-ISSN 1530-7972, Vol. 7, nr 3, s. 177-194Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The works that have been already published on sandwich face wrinkling consider isotropic or almost isotropic sandwich configurations. Hence, only the critical wrinkling load needs to be evaluated in the principal compressive stress direction. This is insufficient for a sandwich panel with a higher degree of anisotropy. This paper presents a method for estimating the wrinkling behavior of highly anisotropic sandwich panels under biaxial loading. The method is based on the assumption that wrinkling occurs at the angle where the ratio of applied load to sustainable wrinkling loads reaches a global maximum. In addition to the description of the analytical theories, the paper presents comparisons with finite element calculations and testing of real sandwich configurations. The results indicate that the derived model works excellently both for uni- and biaxial loadings, though a small factor of safety is required as with all other standard wrinkling theories.

  • 8.
    Fagerberg, Linus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Imperfection-induced wrinkling material failure in sandwich panels2005Ingår i: Journal of Sandwich Structures and Materials, ISSN 1099-6362, E-ISSN 1530-7972, Vol. 7, nr 3, s. 195-219Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, sandwich wrinkling or local face sheet instability is treated in the context of material failure. Traditionally, test results rarely complied well with the predicted failure load and a knock down factor often had to be used. The reason for this is often referred as the effect of initial geometric imperfections. In this paper, imperfections are included in the natural waveform given by the linear stability analysis, i.e., a short wavelength sinusoidal buckling shape. These initial imperfections lead to increased displacements during loading giving rise to both, an in-plane compressive strain and a varying bending strain. These strains can then be related to material failure criteria, one for the face sheet compressive strain and one for the core normal strain. An analytical model is derived and compared with experimental results and several issues are revealed. The panel strength measured using a realistic initial imperfection amplitude agrees very well with the derived model, giving a prediction somewhat below the values obtained from the traditional approach. This verifies that the actual wrinkling failure is below the theoretical instability load. The model is able to distinguish between different failure modes, face sheet compression failure or core-adhesive joint tensile failure, giving good correlation with the experimental findings. Thus, it appears that using initial imperfections as a basis for wrinkling analysis provides a better foundation for the failure analysis than the ordinary stability analysis, and it also allows to determine which failure mode is predominant. Finally, it is shown that the choice of the core material can be made based on the theory presented to obtain a more efficient sandwich panel.

  • 9.
    Fagerberg, Linus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Reasonable Knock-Down Factors for Sandwich Face Wrinkling2008Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Design rules and formulas used to predict wrinkling failure of sandwich structures ofteninclude a knockdown factor to compensate for "imperfections" in the sandwich structure. The knockdown is usually based on experience and empirically derived from compression testing. It can be substantially large and clearly affect the design. For example the most widely used Hoff's formula suggests a reduction of 45%, from 0.91 to 0.5, due to the effect of imperfections. The wrinkling formulae are also often simplified, thus neglecting the effect of the stacking sequence of the face sheet laminate. These types of rough “rule of thumb” design constraints must be re-evaluated and questioned.Today’s modern design methods and highly optimised structures seek a weigh treduction of the few last percent. This demands a higher level of accuracy in the designprocess and yesterday’s methods must be improved to meet the demand. In this paper an alternative method to derive a reasonable knockdown factor is presented and it is shown that this factor can also be predicted based on constituent material properties and assumed amplitude of initial imperfections. The design method previously published by the authors in [1] is extended to fully anisotropic materials anda first ply failure criterion. The results have thus far been confirmed by tests and good agreement has been achieved.

  • 10.
    Hagberg, Johan
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemiteknik, Tillämpad elektrokemi.
    Maples, Henry A.
    Polymer and Composite Engineering (PaCE) Group, Institute of Materials Chemistry and Research, Faculty of Chemistry, University of Vienna, Währinger Straße 42, A-1090 Vienna, Austria .
    Alvim, Kayne S. P.
    Polymer and Composite Engineering (PaCE) Group, Institute of Materials Chemistry and Research, Faculty of Chemistry, University of Vienna, Währinger Straße 42, A-1090 Vienna, Austria .
    Xu, Johanna
    Polymeric Composite Materials, Department of Engineering Sciences and Mathematics, Luleå University of Technology, SE-97187 Luleå, Sweden .
    Johannisson, Wilhelm
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Bismarck, Alexander
    Polymer and Composite Engineering (PaCE) Group, Institute of Materials Chemistry and Research, Faculty of Chemistry, University of Vienna, Währinger Straße 42, A-1090 Vienna, Austria ; Polymer and Composite Engineering (PaCE) Group, Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK .
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Lindbergh, Göran
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemiteknik, Tillämpad elektrokemi.
    Lithium iron phosphate coated carbon fiber electrodes for structural lithium ion batteries2018Ingår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 162, s. 235-243Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A structural lithium ion battery is a material that can carry load and simultaneously be used to store electrical energy. We describe a path to manufacture structural positive electrodes via electrophoretic deposition (EPD) of LiFePO4 (LFP), carbon black and polyvinylidene fluoride (PVDF) onto carbon fibers. The carbon fibers act as load-bearers as well as current collectors. The quality of the coating was studied using scanning electron microscopy and energy dispersive X-ray spectroscopy. The active electrode material (LFP particles), conductive additive (carbon black) and binder (PVDF) were found to be well dispersed on the surface of the carbon fibers. Electrochemical characterization revealed a specific capacity of around 60–110 mAh g−1 with good rate performance and high coulombic efficiency. The cell was stable during cycling, with a capacity retention of around 0.5 after 1000 cycles, which indicates that the coating remained well adhered to the fibers. To investigate the adhesion of the coating, the carbon fibers were made into composite laminae in epoxy resin, and then tested using 3-point bending and double cantilever beam (DCB) tests. The former showed a small difference between coated and uncoated carbon fibers, suggesting good adhesion. The latter showed a critical strain energy release rate of ∼200–600 J m−2 for coated carbon fibers and ∼500 J m−2 for uncoated fibers, which also indicates good adhesion. This study shows that EPD can be used to produce viable structural positive electrodes.

  • 11.
    Harnden, Ross
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Peuvot, Kevin
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemiteknik, Tillämpad elektrokemi.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Lindbergh, Göran
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemiteknik, Tillämpad elektrokemi.
    Multifunctional Performance of Sodiated Carbon Fibers2018Ingår i: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 165, nr 13, s. B616-B622Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An investigation is conducted into the potential for sodiated PAN-based carbon fibers (CFs) to be used in multifunctional actuation, sensing, and energy harvesting. Axial CF expansion/contraction is measured during sodiation/desodiation using operando strain measurements. The reversible expansion/contraction is found to be 0.1% - which is lower than that of lithiated CFs. The axial sodiation expansion occurs in two well-defined stages, corresponding to the sloping and plateau regions of the galvanostatic cycling curve. The results indicate that the sloping region most likely corresponds to sodium insertion between graphitic sheets, while the plateau region corresponds to sodium insertion in micropores. A voltage-strain coupling is found for the CFs, with a maximum coupling factor of 0.15 +/- 0.01 V/unit strain, which could be used for strain sensing in multifunctional structures. This voltage-strain coupling is too small to be exploited for harvesting mechanical energy. The measured axial expansion is further used to estimate the capacity loss due to solid electrolyte interphase (SEI) formation, as well as capacity loss due to sodium trapped in the CF microstructure. The outcomes of this research suggest that sodiated CFs show some potential for use as actuators and sensors in future multifunctional structures, but that lithiated CFs show more promise.

  • 12.
    Hayman, Brian
    et al.
    Univ. Oslo.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    The Influence of Defects and Damage on the Strength of FRPSandwich Panels for Naval Ships2004Ingår i: 9th Int. Symp. on Practical Design of Ships and Other Floating Structures (PRADS 2004) / [ed] Keil, H. and Lehmann, E, Seehafen Verlag GmbH, Germany , 2004, s. 719-726Konferensbidrag (Refereegranskat)
    Abstract [en]

    The paper describes a methodology for determining theinfluence of both production defects and in-servicedamage on the performance of composite sandwichpanels in ship structures, and for deciding whether,when and where replacement or repair is needed. Theapproach is based on quantitative modelling of the respectivedefect and damage types.

  • 13.
    Hellqvist Kjell, Maria
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Jacques, Eric
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Behm, Mårten
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    PAN-based carbon fiber negative electrodes for structural lithium-ion batteries2011Ingår i: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 158, nr 12, s. A1455-A1460Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Several grades of commercially-available polyacrylonitrile (PAN)-based carbon fibers have been studied for structural lithium-ion batteries to understand how the sizing, different lithiation rates and number of fibers per tow affect the available reversible capacity, when used as both current collector and electrode, for use in structural batteries. The study shows that at moderate lithiation rates, 100 mA g-1, most of the carbon fibers display a reversible capacity close to or above 100 mAh g-1 after ten full cycles. For most of the fibers, removing the sizing increased the capacity to some extent. However, the main factor affecting the measured capacity was the lithiation rate. Decreasing the current by a tenth yielded an increase of capacity of around 100 for all the tested grades. From the measurements performed in this study it is evident that carbon fibers can be used as the active negative material and current collector in structural batteries. © 2011 The Electrochemical Society.

  • 14.
    Hellqvist Kjell, Maria
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Jacques, Eric
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Behm, Mårten
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    PAN-based carbon fibers for structural lithium-ion batteries2012Ingår i: ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite Materials, European Conference on Composite Materials, ECCM , 2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    Structural batteries have the potential to become an integrated part of the device, functioning as both a structural element and as energy storage by combining electrochemical properties and mechanical properties in the same material. In addition, an increase of power and energy density on a system level could be achieved. The electrochemical properties of seven different commercially available PAN-based carbon fibers have been investigated as negative electrodes for structural lithium-ion batteries. All of the tested fibers showed some ability to intercalate lithium ions. The performance varied significantly between the different grades of fiber. Fibers with intermediate modulus showed the most promising results.

  • 15.
    Ihrner, Niklas
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Fiberteknologi.
    Johannisson, Wilhelm
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Sieland, Fabian
    University of Paderborn, Faculty of Science, Department of Chemistry, Paderborn, Germany .
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Johansson, Mats
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Structural lithium ion battery electrolytes via reaction induced phase-separation2017Ingår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, nr 48, s. 25652-25659Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For the realization of structural batteries, electrolytes where both higher ionic conductivity and stiffness are combined need to be developed. The present study describes the formation of a structural battery electrolyte (SBE) as a two phase system using reaction induced phase separation. A liquid electrolyte phase is combined with a stiff vinyl ester based thermoset matrix to form a SBE. The effect of monomer structure variations on the formed morphology and electrochemical and mechanical performance has been investigated. An ionic conductivity of 1.5 x 10(-4) S cm(-1), with a corresponding storage modulus (E') of 750 MPa, has been obtained under ambient conditions. The SBEs have been combined with carbon fibers to form a composite lamina and evaluated as a battery half-cell. Studies on the lamina revealed that both mechanical load transfer and ion transport are allowed between the carbon fibers and the electrolyte. These results pave the way for the preparation of structural batteries using carbon fibers as electrodes.

  • 16.
    Jacques, Eric
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Hellqvist Kjell, Maria
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Behm, Mårten
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Effect of lithium-ion intercalation on the tensile properties of carbon fibres for energy storage composites2012Ingår i: ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite Materials, European Conference on Composite Materials, ECCM , 2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    Carbon fibres can be used as structural electrodes because they have a high tensile properties-to-weight ratio and a graphitic structure which enables lithium-ion intercalation. Carbon fibre specimens were used as electrodes in laboratory cells. It was found that the fibre undergoes an ultimate tensile strength drop and an axial expansion which depend on the measured capacity. The results suggest that a tensile strain develops in the carbon fibre which is pre-stressed in tension and that this pre-stress correlates with the amount of lithiumions intercalated.

  • 17.
    Jacques, Eric
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Hellqvist Kjell, Maria
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Lithium-intercalated Carbon Fibers as Piezo-electrochemical Transducer for Energy HarvestingManuskript (preprint) (Övrigt vetenskapligt)
  • 18.
    Jacques, Eric
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Hellqvist Kjell, Maria
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Piezo-electrochemical effect in lithium-intercalated carbon fibres2013Ingår i: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 35, s. 65-67Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we have conducted experiments to investigate the coupling between electrochemical and mechanical properties of lithium (Li)-intercalating carbon fibres (CFs). The results show promising potential for new functionalities of CFs for electrochemical actuation, sensing and energy harvesting. Li-intercalation at 1 C-rate in CFs subjected to a constant tensile extension induced a free reversible longitudinal expansion strain of approximately 0.30% which can be used as mechanical actuation. Varying the tensile extension of lithiated CFs resulted in a piezoelectric response of the open-circuit potential, in the range of several mV, enabling strain sensing. If the electrical potential is kept constant during a tensile extension a piezo-electrochemical current response is found with about 50% mechanical to electrical energy conversion efficiency, enabling energy harvesting.

  • 19.
    Jacques, Eric
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Hellqvist Kjell, Maria
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    The effect of lithium-intercalation on the mechanical properties of carbon fibres2014Ingår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 68, s. 725-733Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbon fibres (CFs) can be used as lightweight structural electrodes since they have high specific tensile stiffness and ultimate tensile strength (UTS), and high lithium (Li)-intercalation capability. This paper investigates the relationship between the amount of intercalated Li and the changes induced in the tensile stiffness and UTS of polyacrylonitrile-based CF tows. After a few electrochemical cycles the stiffness was not degraded and independent of the measured capacity. A drop in the UTS of lithiated CFs was only partly recovered during delithiation and clearly larger at the highest measured capacities, but remained less than 40% at full charge. The reversibility of this drop with the C-rate and measured capacity supports that the fibres are not damaged, that some Li is irreversibly trapped in the delithiated CFs and that reversible strains develop in the fibre. However, the drop in the strength does not vary linearly with the measured capacity and the drop in the ultimate tensile strain remains lower than the CF longitudinal expansion at full charge. These results suggest that the loss of strength might relate to the degree of lithiation of defectives areas which govern the tensile failure mode of the CFs.

  • 20.
    Jacques, Eric
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Hellqvist, Kjell Maria
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Behm, Mårten
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    PERFORMANCE OF LITHIUM-INTERCALATED CARBONFIBRES FOR STRUCTURAL ELECTRODE APPLICATIONS2013Ingår i: ICCM19, 2013, s. 1-8Konferensbidrag (Övrigt vetenskapligt)
  • 21.
    Jacques, Eric
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Kjell, M. HKTH, Skolan för kemivetenskap (CHE), Kemiteknik.Zenkert, DanKTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.Lindbergh, GöranKTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.Behm, MårtenKTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    IMPACT OF MECHANICAL LOADING ON THEELECTROCHEMICAL BEHAVIOUR OF CARBON FIBERS FORUSE IN ENERGY STORAGE COMPOSITE2011Proceedings (redaktörskap) (Övrigt vetenskapligt)
  • 22.
    Jacques, Eric
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Kjell, Maria H.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Behm, Mårten
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Willgert, Markus
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Impact of electrochemical cycling on the tensile properties of carbon fibres for structural lithium-ion composite batteries2012Ingår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 72, nr 7, s. 792-798Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbon fibres are particularly well suited for use in a multifunctional lightweight design of a structural composite material able to store energy as a lithium-ion battery. The fibres will in this case act as both a high performance structural reinforcement and one of the battery electrodes. However, the electrochemical cycling consists of insertions and extractions of lithium ions in the microstructure of carbon fibres and its impact on the mechanical performance is unknown. This study investigates the changes in the tensile properties of carbon fibres after they have been subjected to a number of electrochemical cycles. Consistent carbon fibre specimens were manufactured with polyacrylonitrile-based carbon fibres. Sized T800H and desized IMS65 were selected for their mechanical properties and electrochemical capacities. At the first lithiation the ultimate tensile strength of the fibres was reduced of about 20% but after the first delithiation some strength was recovered. The losses and recoveries of strength remained unchanged with the number of cycles as long as the cell capacity remained reversible. Losses in the cell capacity after 1000 cycles were measured together with smaller losses in the tensile strength of the lithiated fibres. These results show that electrochemical cycling does not degrade the tensile properties which seem to depend on the amount of lithium ions inserted and extracted. Both fibre grades exhibited the same trends of results. The tensile stiffness was not affected by the cycling. Field emission scanning electron microscope images taken after electrochemical cycling did not show any obvious damage of the outer surface of the fibres.

  • 23.
    Jacques, Eric
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Kjell, Maria
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Behm, Mårten
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Expansion of carbon fibres induced by lithium intercalation for structural electrode applications2013Ingår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 59, s. 246-254Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbon fibres (CFs) can work as lightweight structural electrodes in CF-reinforced composites able to store energy as lithium (Li)-ion batteries. The CF has high stiffness and strength-to-weight ratios and a carbonaceous microstructure which enables Li intercalation. An innovative in situ technique for studying the longitudinal expansion of the CF and the relationship with the amount of intercalated Li is described in the present paper. The polyacrylonitrile-based CFs, T800H and unsized IMS65, were chosen for their electrochemical storage capacities. It was found that the CF expands during lithiation and contracts during delithiation. At the first electrochemical cycle, the expansion is partly irreversible which supports that the first-cycle capacity loss partly relates to Li trapped in the CF structure. For the following cycles, the capacity and the expansion are reversible. The expansion, which might relate to tensile stress, increases up to 1% as the measured capacity approaches the theoretical limit of 372 mAh/g for Li storage in graphite. Minor additional expansions due to the uneven distribution of intercalated Li in the CF structure were measured before and after lithiations. Using scanning electron microscope images the transverse expansion of fully lithiated CFs was estimated to about 10% of the cross-section area.

  • 24.
    Jacques, Eric
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Kjell, Maria
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Behm, Mårten
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Impact of mechanical loading on the electrochemical behaviour of carbon fibers for use in energy storage composite materials2011Ingår i: ICCM18 International Conferences on Composite Materials 18, 2011Konferensbidrag (Refereegranskat)
  • 25.
    Jacques, Eric
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Leijonmarck, Simon
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Hellqvist Kjell, Maria
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Piezo-Electrochemical Energy Harvesting with Lithium-Intercalating Carbon Fibers2015Ingår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 7, nr 25, s. 13898-13904Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mechanical and electrochemical properties are coupled through a piezo-electrochemical effect in Li-intercalated carbon fibers. It is demonstrated that this piezo-electrochemical effect makes it possible to harvest electrical energy from mechanical work. Continuous polyacrylonitrile-based carbon fibers that can work both as electrodes for Li-ion batteries and structural reinforcement for composites materials are used in this study. Applying a tensile force to carbon fiber bundles used as Li-intercalating electrodes results in a response of the electrode potential of a few millivolts which allows, at low current densities, lithiation at higher electrode potential than delithiation. More electrical energy is thereby released from the cell at discharge than provided at charge, harvesting energy from the mechanical work of the applied force. The measured harvested specific electrical power is in the order of 1 muW/g for current densities in the order of 1 mA/g, but this has a potential of being increased significantly.

  • 26. Jacques, Erik
    et al.
    Hellqvist Kjell, Maria
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH).
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Lindberg, Göran
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH).
    Behm, Mårten
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH).
    Performance of lithium-intercalated carbon fibres for structural electrode applications2013Ingår i: ICCM International Conferences on Composite Materials, International Committee on Composite Materials , 2013, s. 6852-6859Konferensbidrag (Refereegranskat)
  • 27.
    Johannisson, Wilhelm
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Ihrner, Niklas
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Johansson, Mats
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Carlstedt, D.
    Asp, L. E.
    Sieland, F.
    Multifunctional performance of a carbon fiber UD lamina electrode for structural batteries2018Ingår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 168, s. 81-87Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In electric transportation there is an inherent need to store electrical energy while maintaining a low vehicle weight. One way to decrease the weight of the structure is to use composite materials. However, the electrical energy storage in today's systems contributes to a large portion of the total weight of a vehicle. Structural batteries have been suggested as a possible route to reduce this weight. A structural battery is a material that carries mechanical loads and simultaneously stores electrical energy and can be realized using carbon fibers both as a primary load carrying material and as an active battery electrode. However, as yet, no proof of a system-wide improvement by using such structural batteries has been demonstrated. In this study we make a structural battery composite lamina from carbon fibers with a structural battery electrolyte matrix, and we show that this material provides system weight benefits. The results show that it is possible to make weight reductions in electric vehicles by using structural batteries. 

  • 28.
    Johannisson, Wilhelm
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Ihrner, Niklas
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Ytbehandlingsteknik.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Leijonmarck, Simon
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Analysis of Carbon Fiber Composite Electrode2015Ingår i: Proceedings of the 20th International Conference on Composite Materials Copenhagen, 19 - 24th July 2015, INTERNATIONAL COMMITTEE ON COMPOSITE MATERIALS , 2015Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    In this article a novel energy-storing composite electrode is investigated with regards to its mechanical and electrochemical properties. This composite electrode consists of carbon fibers, which provide both the mechanical reinforcement and the negative electrode in the battery cell. Also, this carbon fiber composite electrode consists of a polymer matrix that can conduct lithium ions, in order to simultaneously act as the electrolyte in the battery cell.

    Electrochemical tests were performed on the manufactured composite electrode and show extremely promising results for the battery performance. Furthermore, mechanical tests show that the composite electrode has acceptable mechanical properties for structural use.

    It is shown that the internal distances in the composite are large, and volume fraction of fibers is low. This is not only significantly limiting the mechanical properties of the composite, but also the electrochemical properties.

    Overall, the carbon fiber composite electrode is found to have suitable characteristics for further research, where many further research topics are found in order to improve and characterize the composite further. 

  • 29.
    Johannisson, Wilhelm
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zackrisson, Mats
    Jönsson, Christina
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Lindbergh, Göran
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemiteknik, Tillämpad elektrokemi.
    Modelling and design of structural batteries with life cycle assessment2019Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    A multifunctional structural battery consisting of carbon fibers, lithium-electrode coatings and a structural battery electrolyte is investigated with an analytical bottom-up model. This model has a multiphysics approach, calculating both mechanical properties and electrical energy storage. The intention of the model is twofold; first, calculating the potential mass saving with using a structural battery instead of the combination of a monofunctional carbon fiber composite and a monofunctional lithium ion battery. Second, the model is used to investigate the behavior of the mass saving due to changing variables of the structural battery. This variable sensitivity analysis is made in order to understand the behavior of the structural battery and its sensitivity to the different construction variables. The results show that the structural battery can save up to 26% of mass compared to the monofunctional parts.

    Next, the model of the structural battery is further utilized in a life cycle assessment, where the manufacturing, usage and recycling of the structural battery is investigated. The life cycle assessment examines the structural battery as the roof of an electric vehicle. This analysis is compared to the same assessment for a steel roof and standard lithium ion batteries, which shows that manufacturing the carbon fibers and structural battery with clean energy is most important for decreasing the emissions from manufacturing.

  • 30.
    Johannisson, Wilhelm
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Model of a structural battery and its potential for system level mass savings2019Ingår i: Multifunctional Materials, ISSN 2399-7532, artikel-id 035002Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Structural batteries are materials that can carry mechanical load while storing electrical energy. This is achieved by combining the properties of carbon fiber composites and lithium ion batteries. There are many design parameters for a structural battery and in order to understand their impact and importance, this paper presents a model for multifunctional performance. The mechanical behavior and electrical energy storage of the structural battery are matched to the mechanical behavior of a conventional carbon fiber composite, and the electrical energy storage of a standard lithium ion battery. The latter are both monofunctional and have known performance and mass. In order to calculate the benefit of using structural batteries, the mass of the structural battery is compared to that of the two monofunctional systems. There is often an inverse relationship between the mechanical and electrochemical properties of multifunctional materials, in order to understand these relationships a sensitivity analysis is performed on variables for the structural battery. This gives new insight into the complex multifunctional design of structural batteries.

    The results show that it is possible to save mass compared to monofunctional systems but that it depends strongly on the structure it is compared with. With improvements to the design of the structural battery it would be possible to achieve mass saving compared to state-of-the-art composite laminates and lithium ion batteries.

  • 31.
    Kaufmann, Markus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Czumanski, Thomas
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Manufacturing process adaptation for integrated cost/weight optimisation of aircraft structures2009Ingår i: Plastics, rubber and composites, ISSN 1465-8011, E-ISSN 1743-2898, Vol. 38, nr 2, s. 162-166(5)Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A methodology is developed that enables cost-efficient design of composite aircraft structures. In earlier work, a cost/weight optimisation framework was presented. This framework is here enhanced by a module that minimises the manufacturing cost in each iteration by adaptation of manufacturing parameters. The proposed framework is modular and applicable to a variety of parts and geometries. Commercially available software is used in all steps of theoptimisation. The framework extension is added to an existing cost/weight optimisation implementation and tested on an airliner centre wing box rear spar. Three optimisation runs are performed, and a low cost, an intermediate and a low weight design solution are found. The difference between the two extreme solutions is 4.4% in manufacturing cost and 9.7% in weight. Based on these optimisation trials, the effect of the introduced parameter adaptation module is analysed.

  • 32.
    Kaufmann, Markus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Czumanski, Thomas
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Manufacturing Process Adaptation for the Cost/Weight Optimization of Aircraft Structures2008Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Composite materials can be used in primary structures of an aircraft if a cost-efficient design is applied. In earlier work, a cost/weight optimization framework has been presented. This is now enhanced by a module that minimizes the manufacturing cost in each iteration by the adaptation of manufacturing parameters. The framework itself is modular and applicable to arbitrary parts and geometries; therefore, commercially available software modules are used. The framework extension is added to an existing cost/weight optimization implementation and tested on an airliner center wing box rear spar. Three opti-mization runs are performed, and a low-cost, an intermediate and a low-weight design solution are found. The difference between the two antagonistic solutions is 4.4% in manufacturing cost and 9.7% in weight. Based on these optimization trials, the effect of the parameter adaptation module is analyzed.

  • 33.
    Kaufmann, Markus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Mattei, Christophe
    Cost optimization of composite aircraft structures including variable laminate qualities2008Ingår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 68, nr 13, s. 2748-2754Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Composite structures can lower the weight of an airliner significantly. The increased production cost, however, requires the application of cost-effective design strategies in which cost, weight and the desired laminate quality are taken into account. This paper proposes an optimization framework for composite aircraft structures that minimizes the direct operating cost on a part level. In addition to previous models, a non-destructive testing model is implemented that calculates design allowables of a laminate based on ultrasonic scan parameters. In a case study, the effect of the laminate quality on the direct operating cost is discussed. It is investigated how the permissible flaw size and therefore the scan pitch of a composite laminate can influence the optimal solution in terms of cost and weight; thus, the manufacturing cost, the non-destructive testing cost and the weight of a component can be balanced by optimizing the laminate quality in an early design phase.

  • 34.
    Kaufmann, Markus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Wennhage, Per
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Integrated cost/weight optimization of aircraft structures2010Ingår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 41, nr 2, s. 325-334Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A methodology for a combined cost/weight optimization of aircraft components is proposed. The objective function is formed by a simplified form of direct operating cost, i.e. by a weighted sum of the manufacturing costs and the component weight. Hence, the structural engineer can perform the evaluation of a design solution based on economical values rather than pure cost or weight targets.The parameter that governs the balance between manufacturing cost and weight is called weight penalty and incorporates the effect of fuel burn, environmental impact or contractual penalties due to overweight. Unlike previous work, the analytical cost model and structural models are replaced by commercially available software packages that allow a more realistic model of the manufacturing costs; further, arbitrary constraints for the structural analysis can be implemented. By means of parametric studies it is shown that the design solution strongly depends on the magnitude of the weight penalty.

  • 35.
    Kaufmann, Markus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Wennhage, Per
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Integrated cost/weight optimization of composite skin/stringer elements2007Ingår i: Proceedings of the 16th International Conference on Composite Materials, Springer, 2007, s. 325-334Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, a methodology for a combined cost/weight optimization of composite elements is proposed. The methodology is similar to the work of Curran et al. [1], where the objective function is formed by manufacturing costs and a so-called weight penalty. This weight penalty could include the effect of fuel burn, environmental impact or con-tractual penalties due to overweight, and depends on the view of the "optimizer". In our approach, the analytical cost model is replaced by a commercial software package that allows a more realistic model of the manufacturing costs. In the spotlight is a parameter study, in which the weight penalty is varied from zero to infinity, literally varying from pure cost to pure weight opti-mization. This is done for three material configura-tions: a metal/metal, a composite/metal and a com-posite/composite skin/stringer panel. It is shown that the design solution depends on the magnitude of the weight penalty and that - depending on this magni-tude - another material configuration has to be re-garded as the optimum.

  • 36.
    Kaufmann, Markus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åkermo, Malin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Cost/weight optimization of composite prepreg structures for best draping strategy2010Ingår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 41, nr 4, s. 464-472Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The application of hand-laid carbon fiber prepreg is very expensive from a labor perspective. Therefore the manufacturing cost should be included in the design process. In this work, we propose a novel optimization framework which contains a draping simulation in combination with a detailed cost estimation package and the calculation of the structural performance based on FE. We suggest applying the methodology in two steps. First, a draping knowledge database is generated in which combinations of seed points and reference angles are evaluated in terms of fiber angle deviation, scrap, ultrasonic cuts and material shear. Second, a cost/weight optimization framework picks the best sets of plies during the subsequent optimization. The methodology is tested by means of a curved C-spar which is designed using plain weave and unidirectional prepreg. Different objectives in the generation of the draping database lead to different design solutions.

  • 37.
    Kaufmann, Markus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Åkermo, Malin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Material Selection for a Curved C-Spar Based on Cost Optimization2011Ingår i: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 48, nr 3, s. 797-804Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A case study for the cost optimization of aircraft structures based on the operating cost as an objective function is presented. The proposed optimization framework contains modules for estimation of the weight, manufacturing cost, nondestructive inspection cost, and structural performance; the latter is enhanced by a kinematic draping model that allows the fiber angles to be simulated more realistically. The case study includes five material systems: aircraft-grade aluminum, two types of resin-transfer molded noncrimp fabric reinforcements, and two types of M21/T800 prepreg. The results are compared in relation to each other, and it is shown that (depending on the estimated fuel burn share of the component) a different material system is favorable when optimizing for low-operating cost.

  • 38.
    Kazemahvazi, Sohrab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Ben, Russel
    Univ. Cambridge.
    Vikram, Deshpande
    Univ. Cambridge.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Impact Properties of Corrugated Composite Sandwich Cores2010Ingår i: / [ed] G. Ravichandran, 2010Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The out-of-plane impact properties of corrugated carbon fibre composite cores have been investigated experimentally. Cores with slender core members show dynamic strengthening of approximately 12 times compared to quasi-static experiments whereas cores with stocky core members show a dynamic strengthening of approximately 2 times. Carbon fibre corrugated cores have superior compressive performance in the density range of 100 kgm-3 to 300 kgm-3.

  • 39.
    Kazemahvazi, Sohrab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Kiele, Joern
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Strength of GRP-Laminates with Multiple Fragment Damages2009Ingår i: ICCM-17 17th International Conference on Composite Materials, 2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    The strength of glass fibre reinforced vinyl-ester laminates with multiple holes has been investigated experimentally. Different hole pattern configurations have been tested, primarily for unidirectional laminates. Unidirectional laminates have shown very low notch sensitivity and the laminate failure was governed by two competing failure modes; shear off failure and net section tensile failure.

  • 40.
    Kazemahvazi, Sohrab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Kiele, Jörn
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Tensile strength of UD-composite laminates with multiple holes2010Ingår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 70, nr 8, s. 1280-1287Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The residual strength of glass fibre reinforced vinyl-ester laminates with multiple holes was investigated through an experimental programme. Different types of structured hole patterns and hole densities were investigated and analysed using digital image correlation strain measuring technique. Three different failure modes could be observed when the hole patterns and the hole densities were a altered. These three failure modes were used as the foundation for a simple yet effective analytical model in order to predict the residual strength of damaged composite specimens. Finally, a number of laminates with randomly distributed holes were tested experimentally. The analytical model can predict the failure mode and failure strength of the experiments with sufficiently good fidelity.

  • 41.
    Kazemahvazi, Sohrab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Nilsson, Martin
    FOI.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Residual Strength of Full Scale GRP Laminates with Randomly Distributed Fragment Damages2013Ingår i: International Conference on Composite Materials 19, 2013Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    A typical scenario of a naval composite ship hull being exposed to air-borne hostile fire can be described as follows; shortly after detonation a scatter of fragments will travel at high speed creating patterns of penetration and perforation damages on the ship hull. Subsequent to these fragment damages a high intensity pressure wave will cause the ship hull panels to deform at an elevated strain rate. Hence, the high intensity pressure wave hits an already damaged structure motivating the study of notched laminates at high rate loading. The design procedure for handling such a complicated loading scenario could be envisaged by the following steps:

    We model the geometry of the blast situation, which could be a compartment or a panel surface. One then places the threat at some position where it explodes. By knowledge of the threat one can simulate each fragment having a particular mass, velocity and direction. Each fragment will thus hit the structure and depending on its mass, incident angle and the structure type (material, thickness, etc.) the fragment will penetrate the structure, create some damage or be completely stopped. One thus follow an arbitrary number of fragments and detect which elements they hit in the structure and if they create some damage (e.g. penetration). Such analyses are usually performed using Monte-Carlo simulations. The next step is to create an FE-mesh of the structure. But from the first step one now reduces the properties of the structure, or structural material, by the amount of damage created by the fragments. Some elements will have many holes and thus considerably lower stiffness and strength than the undamaged material. In the final step one performs the blast analysis by applying a transient shock wave with a given momentum and rise time according to the threat assumed. By adopting such a strategy it should not be necessary to model each hole or damage in the structure which would lead to enormous amounts of modelling and computational efforts.

    The aim of the present paper is to contribute to the second step in the analysis scheme by finding simple and rational methods to predict the strength reduction of composite laminates with stochastic hole patterns generated by e.g. fragments. This research is based on a methodology developed by Kazemahvazi and Zenkert [1-3] in which more details on section 2-3 can be found. For this paper the phenomenological residual strength model has been further refined and is now used to predict the strength of full scale composite panels with randomly distributed fragment damages.

  • 42.
    Kazemahvazi, Sohrab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Nilsson, Martin
    Swedish Defence Research Agency, Sweden.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Residual strength of GRP laminates with multiple randomly distributed fragment impacts2014Ingår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 60, s. 66-74Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The residual tensile strength of glass fibre reinforced composites with randomly distributed holes and fragment impact damages have been investigated. Experiments have been performed on large scale panels and small scale specimens. A finite element model has been developed to predict the strength of multi-axial panels with randomly distributed holes. Further, an effective analytical model has been developed using percolation theory. The model gives an estimation of the residual strength as function of removed surface area caused by the holes. It is found that if 8% of the area is removed, the residual strength is approximately 50% of the un-damaged strength.

  • 43.
    Kazemahvazi, Sohrab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Russell, B. P.
    University of Cambridge.
    Deshpande, V. S.
    University of Cambridge.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Blast Loading of All-Composite Prismatic Sandwich CoresManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    The compressive response of corrugated carbon bre reinforced epoxysandwich cores has been investigated using a Kolsky-bar set-up. Theloading rates tested within this study are similar to those that areexpected when a sandwich core is compressed due to a blast event.Experiments show signi cant strength enhancement as the loading rateincreases. Although material rate sensitivity accounts for some amountof the strength enhancement, it has been shown that the majority of thestrength enhancement is due to inertial stabilisation of the core members.

  • 44.
    Kazemahvazi, Sohrab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Russell, B. P.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Impact of carbon fibre/epoxy corrugated cores2012Ingår i: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 94, nr 11, s. 3300-3308Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dynamic compressive response of corrugated carbon-fibre reinforced epoxy sandwich cores has been investigated using a Kolsky-bar set-up. Compression at quasi-static rates up to v 0=200ms -1 have been tested on three different slenderness ratios of strut. High speed photography was used to capture the failure mechanisms and relate these to the measured axial compressive stress. Experiments show significant strength enhancement as the loading rate increases. Although material rate sensitivity accounts for some of this, it has been shown that the majority of the strength enhancement is due to inertial stabilisation of the core members. Inertial strength enhancement rises non-linearly with impact velocity. The largest gains are associated with a shift to buckle modes composed of 2-3 half sine waves. The loading rates tested within this study are similar to those that are expected when a sandwich core is compressed due to a blast event.

  • 45.
    Kazemahvazi, Sohrab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Tanner, Daniel
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Corrugated all-composite sandwich structures. Part 2: Failure mechanisms and experimental programme2009Ingår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 69, nr 7-8, s. 920-925Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel corrugated composite core, referred to as a hierarchical corrugation, has been developed and tested experimentally. Hierarchical corrugations exhibit a range of different failure modes depending on the geometrical properties and the material properties of the structures. In order to understand the different failure modes the analytical strength model, developed in part I of this paper, was used to make collapse mechanism maps for the different corrugation configurations. If designed correctly, the hierarchical structures can have more than 7 times higher weight specific strength compared to its monolithic counter part. The difference in strength arises mainly from the increase in buckling resistance of the sandwich core members compared to the monolithic version. The highest difference in strength is seen for core configurations with low overall density. As the density of the core increases, the monolithic core members get stockier and more resistant to buckling and thus the benefits of the hierarchical structure reduces.

  • 46.
    Kazemahvazi, Sohrab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Corrugated all-composite sandwich structures. Part 1: Modeling2009Ingår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 69, nr 7-8, s. 913-919Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An analytical model for the compressive and shear response of monolithic and hierarchical corrugated composite cores has been developed. The stiffness model considers the contribution in stiffness from the bending- and the shear deformations of the core members in addition to the stretching deformation. The strength model is based on the normal stress and shear stress distribution over each core member when subjected to a shear or compressive load condition. The strength model also accounts for initial imperfections. In part 1 of this series, the analytical model is described and the results are compared to finite element predictions. In part 2, the analytical model is compared to experimental results and the behaviour of the corrugated structures is investigated more thoroughly using failure mechanism maps.

  • 47.
    Kazemahvazi, Sohrab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Strength of multi-axial laminates with multiple randomly distributed holes2011Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Due to the increasing use of fibre reinforced plastics in the construction of naval ship hulls the ballistic and blast performance of these materials has gained particular interest during the past decade

    In the present paper we use percolation theory to develop a cost-effective phenomenological residual strength model. The model provides a closed form expression for the residual strength as function of the hole density (the amount of hole area / specimen area). The benefit of this model is that it provides a good first estimate of the residual strength using only one input variable (hole density).

  • 48.
    Kazemahvazi, Sohrab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    The Compressive and Shear Responde of Corrugated Hierarchical and Foam Filled Sandwich Structures2008Ingår i: / [ed] A. J. M. Ferreira, Porto: FEUP , 2008Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The mechanical behaviour of two types of corrugated sandwich cores are investigated experimentally and modelled analytically; (i) Corrugation with monolithic composite elements and (ii) a hierarchical sandwich structure (with sandwich core elements). An additional core design, foam filled corrugation, is investigated experimentally and compared to the aforementioned designs. Results show that the hierarchical structure has significantly higher specific strength than the monolithic and foam filled core designs.

  • 49.
    Kazemahvazi, Sohrab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Burman, Magnus
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    NOTCH AND STRAIN RATE SENSITIVITY OF NON CRIMP FABRIC COMPOSITES2007Ingår i: ICCM16, 2007Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The notch and strain rate sensitivity of noncrimp glass fibre/vinyl-ester laminates subjected to uniaxial tensile loads has been investigated experimentally. Two set of notch configurations were tested; one where circular holes were drilled and another where fragment simulating projectiles were fired through the plate creating a notch. Experiments were conducted for strain rates ranging from 10-4/s to 102/s using servo hydraulic machines. A significant increase in strength with increasing strain rate was observed for both notched and unnotched specimens. High speed photography revealed changes in failure mode, for certain laminate configurations, as the strain rate increased. The tested laminate configurations showed fairly small notch sensitivity for the whole range of strain rates.

  • 50.
    Kazemahvazi, Sohrab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Burman, Magnus
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Notch and Strain Rate Sensitivity of Non-Crimp Fabric Composites2009Ingår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 69, nr 6, s. 793-800Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The notch and strain rate sensitivity of noncrimp glass fibre/vinyl-ester laminates subjected to uniaxial tensile loads has been investigated experimentally. Two set of notch configurations were tested; one where circular holes were drilled and another where fragment simulating projectiles were fired through the plate creating a notch. Experiments were conducted for strain rates rangingfrom 10-4/s to 102/s using servo hydraulic machines. A significant increase in strength with increasing strain rate was observed for both notched and unnotched specimens. High speed photography revealed changes in failure mode, for certain laminate configurations, as the strain rate increased. The tested laminate configurations showed fairly small notch sensitivity for the whole range of strain rates.

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