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  • 101.
    Holmberg, Anders
    et al.
    RISE, Swerea, Swerea SICOMP.
    Engberg, David
    RISE, Swerea, Swerea SICOMP.
    Egenskaper hos textila armeringar vid drapering och formning: en översikt2008Report (Refereed)
  • 102.
    Holmberg, Anders
    et al.
    RISE, Swerea, Swerea SICOMP.
    Lindmark, Sive
    RISE, Swerea, Swerea SICOMP.
    Serrander, Tore
    RISE, Swerea, Swerea SICOMP.
    Mekanisk Provning av Vakuuminjicerade Rovicore Laminat1999Report (Refereed)
  • 103.
    Holmberg, Anders
    et al.
    RISE, Swerea, Swerea SICOMP.
    Mattsson, David
    RISE, Swerea, Swerea SICOMP.
    Lundmark, Peter
    RISE, Swerea, Swerea SICOMP.
    Svanberg, Magnus
    RISE, Swerea, Swerea SICOMP.
    On diffusion in heterogeneous materials and diffusion simulations in ANSYS2008Report (Refereed)
  • 104.
    Holmberg, Anders
    et al.
    RISE, Swerea, Swerea SICOMP.
    Svanberg, Magnus
    RISE, Swerea, Swerea SICOMP.
    Rekommendationer för användning av brottvillkor och designfaktorer baserat på erfarenheter från WWFE2006Report (Refereed)
  • 105.
    Jacques, Eric
    et al.
    KTH Royal Institute of Technology, Sweden.
    Lindbergh, Göran
    KTH Royal Institute of Technology, Sweden.
    Zenkert, Dan
    KTH Royal Institute of Technology, Sweden.
    Leijonmarck, Simon
    RISE - Research Institutes of Sweden (2017-2019), Materials and Production, SICOMP.
    Hellqvist Kjell, Maria
    KTH Royal Institute of Technology, Sweden.
    Piezo-Electrochemical Energy Harvesting with Lithium-Intercalating Carbon Fibers2015In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 7, no 25, p. 13898-13904Article in journal (Refereed)
    Abstract [en]

    (Figure Presented) 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 μW/g for current densities in the order of 1 mA/g, but this has a potential of being increased significantly.

  • 106.
    Jao Jules, Ericka
    RISE, Swerea, Swerea SICOMP.
    Critical strain invariants and normalised durability database of carbonepoxy systems2006Report (Refereed)
  • 107.
    Jao Jules, Ericka
    RISE, Swerea, Swerea SICOMP.
    Manufacturing induced defects2008Report (Refereed)
  • 108.
    Jasiuniene, Elena
    et al.
    Kaunas University of Technology, Lithuania.
    Mazieka, Liudas
    Kaunas University of Technology, Lithuania.
    Samaitis, Vykintas
    Kaunas University of Technology, Lithuania.
    Cicenas, Vaidotas
    Kaunas University of Technology, Lithuania.
    Mattsson, David
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Ultrasonic non-destructive testing of complex titanium/carbon fibre composite joints2019In: Ultrasonics, ISSN 0041-624X, E-ISSN 1874-9968, Vol. 95, p. 13-21Article in journal (Refereed)
    Abstract [en]

    Ultrasonic inspection is widely used for non-destructive evaluation of composite adhesive joints. However, there are serious challenges in applying ultrasonic testing on metal to composite hybrid joints, because they are multi-layered, made out of dissimilar materials and relatively thin. The ultrasonic signals reflected by different layers are overlapped, scattered and attenuated. The aim of this research was to develop an ultrasonic inspection technique suitable for defect detection in hybrid metal to composite joints where the metal part has pin arrays, which entangle with the composite part. The immersion pulse echo technique was used to collect data. In order to overcome the problems related to the rough surface and non-parallel layers a novel signal post-processing algorithm for reconstruction of the joint area was developed and validated experimentally. It is shown that using the proposed technique the positions of different defects can be determined.

  • 109.
    Jekabsons, N.
    et al.
    Luleå University of Technology.
    Fernberg, Patrik
    RISE, Swerea, Swerea SICOMP.
    Prediction of progressive fracture of SMC by application of bridging laws2003In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 63, no 15, p. 2133-2142Article in journal (Refereed)
    Abstract [en]

    Experimentally obtained load vs. displacement curves from compact tension tests (CT) of two different SMC materials are analyzed in this paper. Three different CT specimen geometries are considered. Progressive fracture is attained in all tests. This gives rise to a long post-peak tail part in the load vs. displacement curve. By implementing bridging laws and volumetric stiffness degradation of bulk SMC in an FEM model we are able to reproduce the two larger geometries considered (50 mm × 50 mm and 100 mm × 100 mm) with high accuracy. Discrepancy between model predictions and experiments for the smallest geometry considered (20 × 20 mm) was observed. This was due to premature compressive failure on the side opposite to the CT specimen precrack. The successful use of bridging laws strongly suggests that they are intrinsic properties governing fracture behavior of SMC materials. The fact that our bridging laws were determined based on independent tests on different specimen geometry is adding strong arguments to preceding conclusion. © 2003 Elsevier Ltd. All rights reserved.

  • 110.
    Joffe, Roberts
    RISE, Swerea, Swerea SICOMP.
    Stress relaxation in bolted composite joints2008Report (Refereed)
  • 111.
    Juntikka, Rickard
    RISE, Swerea, Swerea SICOMP.
    Modelling composite progressive damage in Ansys, available material models and alternative theories for a usermat model2006Report (Refereed)
  • 112.
    Juntikka, Rickard
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Olsson, Robin
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Experimental and modelling study of hail impact on composite plates2009Conference paper (Refereed)
    Abstract [en]

    Foreign object impact is a serious threat to aircraft, hail or bird impact may seriously degrade the performance of aircraft structures. This work focuses on hail impact experiments and modelling for characterising the impact event and damage initiation in composite material.

  • 113.
    Katerelos, D.G.
    et al.
    Institute of Chemical Engineering and High Temperature Processes, Greece.
    Lundmark, Peter
    RISE, Swerea, Swerea SICOMP.
    Varna, J.
    Lulea University of Technology.
    Galiotis, C.
    Institute of Chemical Engineering and High Temperature Processes, Greece.
    Raman spectroscopy investigation of stiffness change and residual strains due to matrix cracking2006In: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 42, no 6, p. 535-546Article in journal (Refereed)
    Abstract [en]

    The matrix cracking models developed for cross-ply composite laminates have been poorly extended in the past to more complex geometries used in practice, and they are still under development. In this paper, a new detailed analysis of the effect of matrix cracking on the behaviour of cross-ply and [0/45] s laminates under uniaxial tension is attempted. The model used in this work is applicable both to cross-ply laminates and unbalanced systems. It gives exact closed-form expressions for all thermomechanical properties of a general symmetric laminate with cracks in arbitrary layers. The theoretical approach is backed by experimental data obtained by microscopic strain-state variation measurements within a specimen, with using the technique of laser Raman spectroscopy. Glass-fibre-reinforced epoxy systems were investigated. Embedded aramid fibres-sensors within the 0° ply and near the 0°/θ ° interface were necessary due to the poor Raman signal of glass. Using experimental Raman data, the residual strain and the stiffness reduction are determined as functions of increase in crack density. The stiffness reduction is predicted with a high accuracy, whereas the measured residual strains are larger than predicted. The good results for the reduction in the elastic modulus show that the basic assumption of the model is accurate. The difference is explained by the viscoelastic-viscoplastic behaviour of the off-axis layer in shear, which in creases the "apparent" residual strain. © Springer Science+Business Media, Inc. 2006.

  • 114.
    Khosroshahi, S. F.
    et al.
    University of Padova, Italy.
    Tsampas, Spyros
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Galvanetto, U.
    University of Padova, Italy.
    Feasibility study on the use of a hierarchical lattice architecture for helmet liners2018In: Materials Today Communications, ISSN 2352-4928, Vol. 14, p. 312-323Article in journal (Refereed)
    Abstract [en]

    Helmets are the most important piece of protective equipment for motorcyclists. The liner of the helmet is the main part of the helmet which dissipates the impact energy and mitigates the load transmitted to the head. Therefore, optimizing the material that absorbs most of the impact energy would improve the helmet's protection capacity. It is known that the energy absorption of the helmet liner can be optimized by means of using liners with varying properties through the thickness, however currently the majority of used liners exhibit constant properties through the thickness. Advances in the field of topology optimization and additive manufacturing provide the ability of building complex geometries and tailoring mechanical properties. Along those lines, in the present work the feasibility of using a hierarchical lattice liner for helmets was studied. Finite element method was employed to study whether a hierarchical lattice liner could reduce the risk of head injuries in comparison to currently used liner materials. The results show that using a hierarchical lattice liner has the potential of significantly reducing the risk of head injury compared to a helmet with traditional EPS liner and could potentially be considered as the new generation of energy absorbing liners for helmets.

  • 115.
    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.

  • 116.
    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.

  • 117.
    Larsson, R.
    et al.
    Chalmers University of Technology.
    Rouhi, Mohammad
    Chalmers University of Technology.
    Wysocki, Maciej
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Free surface flow and preform deformation in composites manufacturing based on porous media theory2012In: European journal of mechanics. A, Solids, ISSN 0997-7538, E-ISSN 1873-7285, Vol. 31, no 1, p. 12-janArticle in journal (Refereed)
    Abstract [en]

    In the present contribution an infusion simulation tool is developed, applicable to a quite wide range of composites manufacturing technologies. The paper focusses on isothermal, infusion like manufacturing processes involving highly deformable preforms and a free surface resin flow. There are two major issues addressed at the modelling of the infusion processes: The first one is the highly deformable preform and its shape due to the interaction between external pressure loading and the intrinsic fluid pressure. The second issue concerns the migrating free surface due to resin infiltration into the fibrous preform. To resolve these both issues simultaneously, a compressible two-phase porous media formulation is put forward involving an additional liquid mass balance relationship as compared to the standard compressible porous media formulation. As a result a governing equation for saturation degree evolution is established, which is used to monitor the free surface problem directly in terms of the compressible continuum formulation traversing into incompressibility with increasing partial saturation degree. A staggered finite element based solution procedure is advocated for the total solution advancement, involving, on the one hand, the saturation dependent porous media formulation, and, on the other hand, the computation of the saturation degree. The proposed formulation has been implemented and numerical results are provided, showing the convergence of the staggered approach, and the assessment of the proposed approach against a 1D analytical model. In addition, the infusion of a "hat" beam is considered. © 2011 Elsevier Masson SAS. All rights reserved.

  • 118.
    Larsson, Ragnar
    et al.
    Chalmers University of Technology, Sweden.
    Gutkin, Renaud
    Volvo Car Corporation, Sweden.
    Rouhi, Mohammad
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Damage growth and strain localization in compressive loaded fiber reinforced composites2018In: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 127, p. 77-90Article in journal (Refereed)
    Abstract [en]

    To increase the use of polymeric structural composites, a major issue is to properly account for intra-laminar failure mechanisms, such as fiber kinking which is typically induced in compression. We propose a new set of continuum damage models that are able to predict fiber kinking response under compression. A structure tensor based formulation is established at the unidirectional ply level, where the elastic material response is governed by transverse isotropy. To consider geometrical effects in conjunction with fiber kinking instability, a continuum damage formulation at finite strain is developed. The fracture area progression includes a convective and a local damage production involving a finite progression speed. In this framework, two damage evolution models are considered; one non–local model including the gradient damage effect and a local one, without the gradient enhancement. The models are implemented in a FE–code and validated for a compression loaded specimen. The models are computationally robust and can predict the localized nature of fiber kinking. A thorough sensitivity study is presented to show how the different formulations influence the predicted responses.

  • 119.
    Larsson, Ragnar
    et al.
    Chalmers University of Technology, Sweden.
    Rouhi, Mohammad
    Chalmers University of Technology, Sweden.
    Gutkin, Renaud
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Modelling of kink-band growth based on the geometrically non-linear theory2016In: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials, 2016Conference paper (Other academic)
    Abstract [en]

    We propose a new and computationally ecient continuum damage based model, able to predict fibre /matrix shear failure under longitudinal compression for a UD ply. A structure tensor based continuum damage formulation is placed in context with the UD ply, where the elastic material response is governed by transverse isotropy. To represent the proper energy dissipation, an elastic damage model is formulated in the invariants of fibre/matrix shear and fibre compression, including failure initiation and progressive damage modeling. We are guided by the anisotropic elastic model to define four strain invariants, representing key features of the UD-ply microstructure. The damage model is applied to a Non-Crimp Fabric (NCF) composite and compared to a state of the art model based on kinking theory [6]. Instead of invoking the geometric instability into the material model, a key feature is to consider the geometrical fibre kinking instability on the macro-level based on a finite strain formulation

  • 120. Larsson, Ragnar
    et al.
    Rouhi, Mohammad
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Wysocki, Maciej
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Infusion modelling using two-phase porous media theory2010Conference paper (Other academic)
  • 121. Larsson, Ragnar
    et al.
    Rouhi, Mohammad
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Wysocki, Maciej
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Modeling resin flow and preform deformation in composite manufacturing based on partially saturated porous media theory2010Conference paper (Other academic)
  • 122. Larsson, Ragnar
    et al.
    Rouhi, Mohammad
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Wysocki, Maciej
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Resin Flow and Preform Deformation in Composites Manufacturing Based on a Partially Saturated Porous Medium2011Conference paper (Other academic)
  • 123.
    Leijonmarck, simon
    et al.
    KTH Royal Institute of Technology.
    Carlson, Tony
    RISE, Swerea, Swerea SICOMP.
    Lindbergh, G.
    KTH Royal Institute of Technology.
    Asp, Leif
    RISE, Swerea, Swerea SICOMP.
    Maples, H.
    Imperial College London.
    Bismarck, A.
    Imperial College London.
    Solid polymer electrolyte-coated carbon fibres for structural and novel micro batteries2013In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 89, p. 149-157Article in journal (Refereed)
    Abstract [en]

    We report a method to deposit a thin solid polymer electrolyte (SPE) coating around individual carbon fibres for the realization of novel battery designs. In this study an electrocoating method is used to coat methacrylate-based solid polymer electrolytes onto carbon fibres. By this approach a dense uniform, apparently pinhole-free, poly(methoxy polyethylene glycol (350) monomethacrylate) coating with an average coating thickness of 470. nm was deposited around carbon fibres. Li-triflate, used as supporting electrolyte remained in the coating after the electrocoating operation. The Li-ion content in the solid polymer coating was found to be sufficiently high for battery applications. A battery device was built employing the SPE coated carbon fibres as negative electrode demonstrating reversible specific capacity of 260. mA. h/g at low currents (C/10), suggesting that these coated carbon fibres can be employed in future structural composite batteries. © 2013 Elsevier Ltd.

  • 124.
    Leijonmarck, Simon
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Mathew, A.
    Luleå University of Technology, Sweden.
    Oksman, K.
    Luleå University of Technology, Sweden.
    Lindbergh, G.
    KTH Royal Institute of Technology, Sweden.
    Asp, Leif
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Direct electropolymerization of polymer electrolytes onto carbon fibers - A route to structural batteries?2014Conference paper (Refereed)
    Abstract [en]

    In an effort to further reduce weight of carbon fibre reinforced composites, the concept of structural batteries has arisen. A structural battery is a multifunctional material managing both energy storage and enabling of structural integrity. More specific, the carbon fibres in the composites are used as negative electrode in a Li-ion battery. A crucial part of such a battery is the preparation of a thin, ionically conductive and stiff polymer matrix. One route to realize this is the use of electropolymerization, which can cover each individual fibre with polymer. In this study, the surface morphology of coated carbon fibres is investigated with electron microscopy and atomic force microscopy. Additionally, the curing degree as a function of process temperature during polymerization is tested.

  • 125.
    Lindgren, M.
    et al.
    Luleå University.
    Skrifvars, Mikael
    RISE, Swerea, Swerea SICOMP.
    Sandlund, Erik
    RISE, Swerea, Swerea SICOMP.
    Pettersson, Joakim
    RISE, Swerea, Swerea SICOMP.
    Styrene emissions from the spray-up and vacuum injection processes - A quantitative comparison2002In: AIHAJ - Journal of Occupational and Environmental Hygiene, ISSN 1529-8663, E-ISSN 2163-3711, Vol. 63, no 2, p. 184-189Article in journal (Refereed)
    Abstract [en]

    Styrene emissions were studied during manufacturing of two identical glass-fiber reinforced plastic boats by two different manufacturing methods. The manufacturing methods were spray-up, which is an open method, and vacuum injection, which is a closed method. Changing the manufacturing process from an open method to a closed method decreased the styrene evaporation dramatically in this particular case. By using vacuum injection, the styrene emission during the laminate application was reduced by 98% compared with the styrene emission during laminate application by spray-up. Gel coat application by spraying will remain a major source for styrene emissions. The greatest environmental benefit is achieved with closed manufacturing methods when products without gel coat are made. The whole manufacturing process can then be performed in a closed system virtually free from emissions.

  • 126.
    Liu, H.
    et al.
    Åbo Akademi University.
    Näsman, J.H.
    Åbo Akademi University.
    Skrifvars, Mikael
    RISE, Swerea, Swerea SICOMP.
    Radical alternating copolymerization: A strategy for hyperbranched materials2000In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 38, no 17, p. 3074-3085Article in journal (Refereed)
    Abstract [en]

    Novel hyperbranched polymers were synthesized in a high yield without gelation through the free-radical alternating copolymerization of an AB/B′ (allyloxy maleic acid/maleic anhydride) system, in which group B and monomer B′ both could only alternately polymerize with group A. The arm number of the produced highly branched polymers was equal to the product of the linear chain length and the probability of pendent B groups being growing centers. The molecular weight of these novel hyperbranched polymers increased with increasing initiator concentration and prolonged polymerization times. The AB/B′ system, used as described, provides a new general methodology for highly branched and functional polymers.

  • 127.
    Liu, H.
    et al.
    Åbo Akademi University.
    Wilén, C.-E.
    Åbo Akademi University.
    Skrifvars, Mikael
    RISE, Swerea, Swerea SICOMP.
    Reaction of epoxy resin and hyperbranched polyacids2000In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 38, no 24, p. 4457-4465Article in journal (Refereed)
    Abstract [en]

    The condensation reaction between two different epoxy resins and a hyperbranched polyester (MAHP) [poly(allyloxy maleic acid-co-maleic anhydride)] was studied. We compared two kinds of diglycidyl ether bisphenol A type of epoxy resins with different molecular weights, that is, epoxy resin GY240 (M = 365 g/mol) and GT6064 (M = 1540 g/mol) in this reaction. The results showed a marked difference in their reaction pattern in terms of ability to form crosslinked polymer networks with MAHP. For the former low-molecular-weight epoxy resin, no crosslinking could be observed in good solvents such as THF or dioxane within the set of reaction conditions used in this study. Instead, polymers with epoxide functional degrees between 0.34 and 0.5 were formed. By contrast, the latter high-molecular-weight epoxy resin, GT6064, rapidly produced highly crosslinked materials with MAHP under the same reaction conditions. The spherical-shape model of hyperbranched polymer was applied to explain this difference in reaction behavior. Hence, we have postulated that low-molecular-weight epoxy resins such as GY240 are unable to crosslink the comparatively much bigger spherically shaped MAHP molecules. However, using high-molecular-weight epoxy resins greatly enhances the probability of crosslinking in this system. Computer simulations verified the spherical shape and condensed bond density of MAHP in good solvents, and submicron particle analysis showed that the average MAHP particle size was 9 nm in THF. Furthermore, the epoxy-functionalized polyesters were characterized by 1H NMR and FTIR, and the molecular weights and molecular-weight distributions were determined by size-exclusion chromatography.

  • 128.
    Loukil, Mohamed
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP. Linköping University, Sweden.
    Varna, Janis
    Luleå University of Technology, Sweden.
    Crack face sliding displacement (CSD) as an input in exact GLOB-LOC expressions for in-plane elastic constants of symmetric damaged laminates2019In: International journal of damage mechanics, ISSN 1056-7895, E-ISSN 1530-7921Article in journal (Refereed)
    Abstract [en]

    The crack opening and crack sliding displacements of both faces of an intralaminar crack are the main parameters defining the significance of each crack in laminate stiffness degradation, according to the previously published GLOB-LOC approach for symmetric laminates with an arbitrary number of cracks in all plies. In the exact stiffness expressions of this approach, the crack density is always multiplied by crack opening displacement and crack sliding displacement. The dependence of crack opening displacement on geometrical and elastic parameters of adjacent plies was studied previously and described by simple fitting functions. The crack sliding displacement has been analyzed for low-crack densities only and the proposed finite element method-based fitting expressions are oversimplified not including the out-of-plane ply stiffness effects. Based on finite element method analysis, more accurate expressions for so-called non-interactive cracks are suggested in the presented article. For the first time the shear stress perturbations are analyzed and interaction functions are presented with the feature that they always lead to slightly conservative predictions. The presented simple fitting functions, when used in the GLOB-LOC model, give predictions that are in a good agreement with finite element method results and with experimental data for laminates with damaged off-axis plies in cases when crack face sliding is of importance. The significance of including crack sliding displacement in stiffness predictions is demonstrated. 

  • 129.
    Loukil, Mohamed
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP. Linköping University, Sweden.
    Varna, Janis
    Luleå University of Technology, Sweden.
    Effective shear modulus of a damaged ply in laminate stiffness analysis: Determination and validation2019In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793XArticle in journal (Refereed)
    Abstract [en]

    The concept of the “effective stiffness” for plies in laminates containing intralaminar cracks is revisited presenting rather accurate fitting expressions for the effective stiffness dependence on crack density in the ply. In this article, the effective stiffness at certain crack density is back-calculated from the stiffness difference between the undamaged and damaged laminate. Earlier finite element method analysis of laminates with cracked 90-plies showed that the effective longitudinal modulus and Poisson’s ratio of the ply do not change during cracking, whereas the transverse modulus reduction can be described by a simple crack density dependent function. In this article, focus is on the remaining effective constant: in-plane shear modulus. Finite element method parametric analysis shows that the dependence on crack density is exponential and the fitting function is almost independent of geometrical and elastic parameters of the surrounding plies. The above independence justifies using the effective ply stiffness in expressions of the classical laminate theory to predict the intralaminar cracking caused stiffness reduction in laminates with off-axis plies. Results are in a very good agreement with (a) finite element method calculations; (b) experimental data, and (c) with the GLOB-LOC model, which gives a very accurate solution in cases where the crack face opening and sliding displacements are accurately described.

  • 130.
    Lundmark, Peter
    RISE, Swerea, Swerea SICOMP.
    Beräkning av U-värde för hus2006Report (Refereed)
  • 131.
    Lundmark, Peter
    RISE, Swerea, Swerea SICOMP.
    Implementing strain invariant failure theory (SIFT) in ANSYS2006Report (Refereed)
  • 132.
    Lundmark, Peter
    RISE, Swerea, Swerea SICOMP.
    Validering av autokatalytisk härdkinetikmodell implementerad i ANSYS2007Report (Refereed)
  • 133.
    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)
  • 134.
    Lundmark, Peter
    et al.
    RISE, Swerea, Swerea SICOMP.
    Mattsson, David
    RISE, Swerea, Swerea SICOMP.
    Implementation and validation of strain invariant failure theory (SIFT) in ANSYS2008Report (Refereed)
  • 135.
    Lundström, TS
    et al.
    Luleå University of Technology, Sweden.
    Aitomäki, Yvonne
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Emami, N
    Luleå University of Technology, Sweden.
    A COMPARISON OF THE APPROACHES TO THE PROCESS MODELLING OF SHEET MOULDING COMPOUND2018Conference paper (Other academic)
    Abstract [en]

    Please use this document as a template for the preparation of your extended abstract for FPCM-14. The following section will detail the lay out settings for the extended abstract in Microsoft Word. If you use other text editors such as LaTex, please follow the format guidelines of the extended abstract.

  • 136.
    Lundström, T.S.
    et al.
    Luleå University of Technology.
    Sundlöf, Henrik
    RISE, Swerea, Swerea SICOMP.
    Holmberg, Anders
    RISE, Swerea, Swerea SICOMP.
    Modeling of power-law fluid flow through fiber beds2006In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 40, no 3, p. 283-296Article in journal (Refereed)
    Abstract [en]

    An apparent permeability of an idealized unidirectional reinforcement is derived for power-law fluid flow perpendicular to the fibers. The reinforcement consists of regularly ordered, parallel fibers arranged in a quadratic or hexagonal pattern. The expression is obtained starting from first principles for low Reynolds number, incompressible and isothermal flow and is expressed in terms of the radius of the fibers, the fiber volume fraction, and the power-law index. The model is successfully verified with computational fluid dynamic simulations. © 2006 SAGE Publications.

  • 137.
    Mannberg, Peter
    RISE, Swerea, Swerea SICOMP.
    Självuppvärmning på grund av energiförluster under viskoelastiskdeformation under högfrekvensutmattning2008Report (Refereed)
  • 138.
    Mannberg, Peter
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Holmberg, J.A.
    ABB Composites, Sweden.
    Moisture absorption and degradation of glassfibre/vinylester laminates with internal flow layers2010In: Advanced Composites Letters, ISSN 0963-6935, Vol. 19, no 2, p. 67-76Article in journal (Refereed)
    Abstract [en]

    Vacuum Infusion is a closed mould manufacturing process that can replace open mould processes. To improve resin flow it is common to add flow enhancement layers to the reinforcement stack. The basic feature for all flow enhancements is a coarse microstructure with regions of low fibre content. Degradation of mechanical properties due to environmental loading such as temperature and moisture is very important. A lot of research has been done on this area but earlier work has been done on materials without internal flow layer. The question is how well vacuum infused laminates, based on reinforcements containing internal flow layer, resist environmental ageing. Present work presents 3000 h 90°C water ageing data and differences between the material types in the rate of water uptake, Tg, mechanical properties and density was investigated. The results show that the relative weight gain is an increasing function of time. From the Tg measurements we see that Tg is increasing for the immersion aged materials. Tensile tests after 3000 h of immersion ageing show a decrease in Young's modulus, tensile strength and failure strain for the immersion aged material. Density measurements show that the average density has increased for the immersion aged materials.

  • 139.
    Mannberg, Peter
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Nyström, Birgitha
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Joffe, Roberts
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Service life assessment and moisture influence on bio-based thermosetting resins2014In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 49, no 10, p. 3687-3693Article in journal (Refereed)
    Abstract [en]

    In this study, three different types of bio-based resins are compared to a conventional oil-based epoxy in terms of moisture uptake, long-term properties and its influence of moisture and glass transition temperature, T g. Moisture uptake is determined by means of gravimetric method, time temperature superposition (TTSP), and T g data obtained in dynamic mechanical thermal analysis (DMTA). Moisture uptake show Fickian diffuison behavour for all resins, saturation level and diffusion coefficient however differ. The long-term properties is characterised by creep compliance master curves created by means of TTSP. The examined bio-based resins are compatible to the reference epoxy in term of stability up to 3-10 years. Comparison between master curves for virgin, wet, and dried material show that moisture present in the specimen increases creep rate, and that some of this increase remains after drying of samples. T g measurements show that moisture inside the specimen decreases T g; this is anticipated because of the plasticizing effect of water. The overall conclusions are that the bio-based resins of polyester, and epoxy type are comparable in performance with oil-based epoxy, LY556 and they can be used to develop high-performance composites. © 2014 Springer Science+Business Media New York.

  • 140.
    Mannberg, Peter
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Nyström, Birgitha
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Wallström, L.
    LTU.
    Joffe, Roberts
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Service life assessment and moisture influence on bio-based composites2014In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 49, no 15, p. 5265-5270Article in journal (Refereed)
    Abstract [en]

    A race towards a more sustainable society is going on worldwide, and decreasing dependence on fossil resources in energy and transport sectors are main goals. One path to decreased oil usage is development of lightweight materials from renewable resources like bio-based composites. However, these new bio-based materials not only have to compete in mechanical performance but also have to restrain environmental loads like moisture and temperature over time. In this study, two bio-based composites have been compared to an oil-based composite in terms of long-term properties and water absorption behaviour. The long-term behaviour is determined by dynamic mechanical thermal analysis, DMTA and time temperature superposition, TTSP. The water uptake is determined by submersion of specimens into water and tracking their weight change over time. The moisture influence is characterised in form of water uptake and change in the master curves created by TTSP procedure. The results show that there is a significant difference in long-term performance between the bio-based and oil-based composites. It is realised that the bio-based composites can be a good alternative for some applications especially when taking their eco-friendly nature into account. © 2014 Springer Science+Business Media New York.

  • 141.
    Marklund, Erik
    RISE - Research Institutes of Sweden, Materials and Production, SICOMP.
    Smältfogning av termoplastbaserade kompositer och lättmetall2012Report (Refereed)
  • 142.
    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.

  • 143.
    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.

  • 144.
    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)
  • 145.
    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)
  • 146.
    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.

  • 147.
    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.

  • 148.
    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.

  • 149.
    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.

  • 150.
    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.

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