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  • 1.
    Aitomäki, Y.
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Hagström, Bengt
    RISE - Research Institutes of Sweden, Swerea, Swerea IVF.
    Långström, R.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Fernberg, P.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Novel reactive bicomponent fibres: Material in composite manufacturing2012In: Journal of Nanostructured Polymers and Nanocomposites, ISSN 17904439, Vol. 8, no 1, p. 11-majArticle in journal (Refereed)
    Abstract [en]

    The hypotheses that reactive uncured, thermoset bicomponent fibres can be prepared and mixed with reinforcing fibres and ultimately used in preparation of a composite was tested and is described. It is thought that such fibres have the two potential advantages: (1) to enable manufacturing with particle doped resins e.g. nanocomposites which add functionality to composites and (2) increased efficiency of structural composite manufacturing by increasing the level of automation. The structure of the thermoset fibres comprises of a sheath of thermoplastic and a core of uncured thermoset resin. Once manufactured, the fibres were wound with a reinforced fibre onto a plate, consolidated and cured. The resulting composite was examined and compared to other composites made with the same manufacturing method from commercially available materials. The results show that a laminate can be produced using these reactive bicomponent fibres. The resin system successfully impregnates the reinforcing carbon fibres and that the thermoplastic separates from the epoxy resin system during consolidation. In comparison to reference material, the bicomponent laminate shows promising characteristics. However, the processes developed are currently on a lab-scale and considerable improvement of various bicomponent fibre properties, such as the strength, are required before the technology can be used on a larger scale.

  • 2.
    Aitomäki, Yvonne
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Hagström, Bengt
    RISE - Research Institutes of Sweden, Swerea, Swerea IVF.
    Långström, Runar
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Fernberg, Patrik
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Novel reactive bicomponent fibres: Material in composite manufacturing2012In: Journal of Nanostructured Polymers and Nanocomposites, ISSN 17904439, Vol. 8, no 1, p. s.5-11Article in journal (Refereed)
    Abstract [en]

    The hypotheses that reactive uncured, thermoset bicomponent fibres can be prepared and mixed with reinforcing fibres and ultimately used in preparation of a composite was tested and is described. It is thought that such fibres have the two potential advantages: (1) to enable manufacturing with particle doped resins e.g. nanocomposites which add functionality to composites and (2) increased efficiency of structural composite manufacturing by increasing the level of automation. The structure of the thermoset fibres comprises of a sheath of thermoplastic and a core of uncured thermoset resin. Once manufactured, the fibres were wound with a reinforced fibre onto a plate, consolidated and cured. The resulting composite was examined and compared to other composites made with the same manufacturing method from commercially available materials. The results show that a laminate can be produced using these reactive bicomponent fibres. The resin system successfully impregnates the reinforcing carbon fibres and that the thermoplastic separates from the epoxy resin system during consolidation. In comparison to reference material, the bicomponent laminate shows promising characteristics. However, the processes developed are currently on a lab-scale and considerable improvement of various bicomponent fibre properties, such as the strength, are required before the technology can be used on a larger scale.

  • 3.
    Allen, D.H.
    et al.
    Texas AandM University.
    Holmberg, Anders
    RISE, Swerea, Swerea SICOMP.
    Ericson, M.
    Volvo Car Components Corporation.
    Lans, L.
    Volvo Car Corporation.
    Svensson, N.
    Xdin AB.
    Holmberg, S.
    Volvo Car Components Corporation.
    Modeling the viscoelastic response of GMT structural components2001In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 61, no 4, p. 503-515Article in journal (Refereed)
    Abstract [en]

    A glass-mat-reinforced thermoplastic (GMT) composite material has been fabricated from randomly oriented continuous glass fibers embedded in a polypropylene matrix. The mechanical constitution of this composite has been characterized by using a linear viscoelastic micromechanically based material model. This material model has subsequently been implemented to several finite-element computer codes for analysis of structural components fabricated from polypropylene GMT. In this paper several example problems have been studied in order to determine the applicability of this modeling approach to predicting time-dependent deformations due to creep in GMT components. These example problems have been solved by utilizing two commercially available codes: ABAQUS, and ANSYS. Furthermore, results obtained with the codes have been compared to both analytic and experimental results, with varying degrees of success. The paper details these results for each of the example problems considered herein. © 2001 Elsevier Science Ltd. All rights reserved.

  • 4.
    Al-Ramahi, Nawres
    et al.
    Luleå University of Technology, Sweden ; Middle Technical University, Iraq.
    Joffe, Roberts
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP. Luleå University of Technology, Sweden .
    Varna, Janis
    Luleå University of Technology, Sweden .
    Investigation of end and edge effects on results of numerical simulation of single lap adhesive joint with non-linear materials2018In: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 87, p. 191-204Article in journal (Refereed)
    Abstract [en]

    This paper presents systematic numerical study of stresses in the adhesive of a single-lap joint with the objective to improve understanding of the main material and geometrical parameters determining performance of adhesive joints. For this purpose a 3D model as well as 2D model, optimized with respect to the computational efficiency by use of novel displacement coupling conditions able to correctly represent monoclinic materials (off-axis layers of composite laminates), are employed. The model accounts for non-linearity of materials (adherend and adhesive) as well as geometrical non-linearity. The parameters of geometry of the joint are normalized with respect to the dimensions of adhesive (e.g. thickness) thus making analysis of results more general and applicable to wide range of different joints. Optimal geometry of the single-lap joint allowing to separate edge effect from end effects is selected based on results of the parametric analysis by using peel and shear stress distributions in the adhesive layer as a criterion. Three different types of single lap joint with similar and dissimilar (hybrid) materials are considered in this study: a) metal-metal; b) composite-composite; c) composite-metal. In case of composite laminates, four lay-ups are evaluated: uni-directional ([08]T and [908]T) and quasi-isotropic laminates ([0/45/90/-45]S and [90/45/0/-45]S). The influence of the abovementioned parameters on peel and shear stress distributions in the adhesive layer is examined carefully and mechanical parameters governing the stress concentrations in the joint have been identified, this dependence can be described by simple but accurate fitting function. The effect of the used material model (linear vs non-linear) on results is also demonstrated.

  • 5.
    Andersons, J.
    et al.
    University of Latvia.
    Sparniņš, E.
    University of Latvia.
    Nyström, Birgitha
    RISE, Swerea, Swerea SICOMP.
    Joffe, Roberts
    RISE, Swerea, Swerea SICOMP.
    Scale effect of the tensile strength of flax-fabric-reinforced polymer composites2011In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 30, no 23, p. 1969-1974Article in journal (Refereed)
    Abstract [en]

    The development of UD natural fiber composites, considered for application as structural materials, necessitates evaluation of the scale effect of their strength. Alignment of the fibers in flax bast fiber composites can be achieved by employing textile reinforcement, such as yarns and fabrics. Cutting specimens for mechanical tests out of such textile-reinforced composite plates results in a complex non-uniform reinforcement structure at their edges, which may affect the strength of specimens. Scale effect of the tensile strength in the fiber direction of flax-fabric-reinforced composites is studied in the current work. A model accounting for both volume and edge effect of the specimens on their tensile strength is proposed. © The Author(s) 2011.

  • 6.
    Andersson, B.
    et al.
    Aeronautical Research Institute of Sweden.
    Sjögren, Anders
    RISE, Swerea, Swerea SICOMP.
    Berglund, L.
    Luleå University of Technology.
    Micro- and meso-level residual stresses in glass-fiber/vinyl-ester composites2000In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 60, no 10, p. 2011-2028Article in journal (Refereed)
    Abstract [en]

    Residual stresses in glass-fiber composites were studied on the micro and meso scales by computational and experimental methods. Transmitted polarized light images of thin sections were compared with 3D finite-element solutions of a sample containing 1410 fibers. Calculated point-wise stresses were derived from a linear thermoelastic model with negligibly small numerical errors. Regions with calculated maximum compressive stresses showed good agreement with experimentally observed optical bands. A material with poor interfacial adhesion showed weaker optical effects indicating fiber/matrix debonding. On the basis of these results it seems likely that irreversible matrix deformation and debonding can take place in the curing phase. (C) 2000 Elsevier Science Ltd. All rights reserved.Residual stresses in glass-fiber composites were studied on the micro and meso scales by computational and experimental methods. Transmitted polarized light images of thin sections were compared with 3D finite-element solutions of a sample containing 1410 fibers. Calculated point-wise stresses were derived from a linear thermoelastic model with negligibly small numerical errors. Regions with calculated maximum compressive stresses showed good agreement with experimentally observed optical bands. A material with poor interfacial adhesion showed weaker optical effects indicating fiber/matrix debonding. On the basis of these results it seems likely that irreversible matrix deformation and debonding can take place in the curing phase.

  • 7.
    André, Alann
    RISE, Swerea, Swerea SICOMP.
    Utilization of National Instrument equipment for strain and load measurement recording2013Report (Refereed)
  • 8.
    André, Alann
    et al.
    RISE, Swerea, Swerea SICOMP.
    Haghani, R.
    Chalmers University of Technology.
    Biel, A.
    University of Skövde.
    Application of fracture mechanics to predict the failure load of adhesive joints used to bond CFRP laminates to steel members2012In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 27, no 1, p. 331-340Article in journal (Refereed)
    Abstract [en]

    The use of bolted or welded elements to upgrade metallic structures has been a common practice for many years. Moreover, the use of adhesively bonded carbon fiber reinforced polymer (CFRP) laminates, as an alternative method, has attracted a great deal of attention in recent years. One important aspect of the design of adhesive joints used to bond CFRP laminates to steel substrates is the determination of the properties of the CFRP/adhesive/steel interfaces, which have not yet been established in codes or standards. The purpose of this paper is experimentally to determine the fracture properties of the adhesive material and to evaluate the accuracy of numerical methods using this information, in order to predict the strength of adhesive joints in steel members bonded with CFRP laminates. The results from four series of experimental tests are compared with numerical results and discussed in terms of load-bearing capacity and failure modes. © 2011 Elsevier Ltd. All rights reserved.

  • 9.
    André, Alann
    et al.
    RISE, Swerea, Swerea SICOMP.
    Johnsson, H.
    Luleå Univ. of Technology.
    Flax fiber-reinforced glued-laminated timber in tension perpendicular to the grain: Experimental study and probabilistic analysis2010In: Journal of materials in civil engineering, ISSN 0899-1561, E-ISSN 1943-5533, Vol. 22, no 9, p. 827-835Article in journal (Refereed)
    Abstract [en]

    The weak mechanical properties of wood in tension perpendicular to the grain are often the origin of catastrophic brittle failure. In order to enhance the tension strength perpendicular to the grain and achieve a more ductile failure, flax fiber and glass fiber-reinforced polymer (FRP) composites were used to strengthen glue-laminated (glulam) timber specimens. Three series of specimen of glulam timber (flax fiber reinforced, glass fiber reinforced, and unreinforced), with a grand total of 28 specimens, were tested in tension perpendicular to the grain. For an approximate amount of FRP reinforcement of 1.2% in volume (thickness of ∼0.7 mm), an increase of the tensile strength of up to 74% was shown, with a stiffness increase of up to 41%. For all reinforced specimens, semiductile failures were observed. A parametric study was carried out using both the Monte Carlo (MC) method and the first-order second moment (FOSM) method. It is shown that the mean values obtained during experiments are in agreement with those from the MC simulation. However, the standard deviations from the MC simulation are larger. From the FOSM analysis, it is demonstrated that the variation in glulam stiffness perpendicular to the grain is not the first parameter driving the variation for the reinforced system. The variation in mechanical properties of the flax fibers appeared to be the driving parameter for the strength of the system. © 2010 ASCE.

  • 10.
    André, Alann
    et al.
    RISE, Swerea, Swerea SICOMP.
    Kliger, R.
    Chalmers University of Technology.
    Asp, Leif
    RISE, Swerea, Swerea SICOMP.
    Compression failure mechanism in small scale timber specimens2014In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 50, p. 130-139Article in journal (Refereed)
    Abstract [en]

    Understanding the failure mechanism of wood loaded in compression parallel to the grain has been shown to be an important parameter in the design of timber beams strengthened with fibre-reinforced plastics (FRP). In this paper, a constitutive relationship for wood under uniaxial compression load parallel to the grain was determined experimentally. Several parameters, such as silviculture, moisture content and radial position in the log in relation to the pith from where the specimen was sawn, were considered. Small clear-wood specimens were used. The strain localisation in the failure region (kinkband) was monitored using the digital image correlation method. The results show that silviculture and moisture content are two very important parameters which influence the compression failure mechanism. Furthermore, there is a significant difference in behaviour between specimens from the juvenile region of the log and specimens from mature wood. Based on experimental results, two numerical models were built, considering either a global or a local constitutive relationship. It was demonstrated that both numerical models yield accurate results and that, depending on the experimental equipment available, a constitutive relationship could be extracted and used as input in these numerical models. © 2013 Elsevier Ltd. All rights reserved.

  • 11.
    André, Alann
    et al.
    RISE, Swerea, Swerea SICOMP.
    Kliger, R.
    Chalmers University of Technology.
    Haghani, R.
    Chalmers University of Technology.
    Timber reinforced FRP: Compression failure mechanism2012In: Proceedings of the 6th International Conference on FRP Composites in Civil Engineering, CICE 2012Conference paper (Refereed)
    Abstract [en]

    When it comes to strengthening, structural timber engineering has seen polymer composite materials becoming key materials over the last decades. A great number of studies have already shown that the majority of the results were promising. Several strengthening systems applied to structural timber or glued-laminated timber beams revealed that the ultimate failure mode remains in tension regardless of the reinforced system. However, the collapse can be controlled and postponed by optimising the strengthening system. It has been shown that strengthening timber on the tension and compression side simultaneously increases the stiffness and moment capacity more than if the reinforcement was only positioned on the tension side. This is mainly due to the ductility of wood in compression which is fully utilised when strengthening is located on both sides. The main objective behind this study is to develop an experimental method to determine the compressive behaviour of small clear timber specimens reinforced with CFRP.

  • 12.
    André, Alann
    et al.
    RISE, Swerea, Swerea SICOMP.
    Kliger, R.
    Chalmers University of Technology.
    Olsson, Robin
    RISE, Swerea, Swerea SICOMP.
    Compression failure mechanism in small-scale wood specimens reinforced with CFRP: An experimental study2013In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 41, p. 790-800Article in journal (Refereed)
    Abstract [en]

    The optimal use of Carbon Fibre Reinforced Polymer (CFRP) when strengthening timber beams loaded in bending involves considering placing the reinforcement on both the tension and the compression side, in order to utilise the ductile compression failure of the wood to the full. In this respect, a knowledge and understanding of the compression failure mechanism of the timber/CFRP system becomes a point of paramount importance. However, no testing method specific to the compression loading of small wood specimens reinforced with CFRP is currently available. This investigation focuses on the experimental developments of the geometry and test set-up necessary in order to determine the compression failure mechanism of small wood block specimens reinforced with CFRP loaded in compression parallel to the grain. The method is based on an existing testing method for unreinforced wood specimens. The Digital Image Correlation (DIC) method is used to monitor deformation during experiments. The experimental results of reinforced specimens are compared with those of paired unreinforced specimens tested in a previous study. The experimental method presented in this study shows that specific geometry and test considerations must be implemented when compared with the existing method for unreinforced specimens. © 2012 Elsevier Ltd. All rights reserved.

  • 13.
    André, Alann
    et al.
    RISE, Swerea, Swerea SICOMP.
    Nilsson, Sören
    RISE, Swerea, Swerea SICOMP.
    Asp, Leif
    RISE, Swerea, Swerea SICOMP.
    Finite element delamination study of a notched composite plate under flexural loads2009In: ICCM International Conferences on Composite MaterialsConference paper (Refereed)
    Abstract [en]

    The delamination process in notched composite plates under flexural loading has been investigated using finite element analysis. Cohesive elements implemented in the commercial finite element package ABAQUS have been used in the region around the drilled-hole, and positioned between layers where delamination was observed during experiments presented in an accompanying paper. The delamination initiation and subsequent propagation was studied between the layers at the tension side separately and simultaneously. For all FE models, the load displacement curve was in good agreement with the one from experiments. However, the amount of damage reported from the fractography study was more extensive than that predicted by the models. Finally, it was shown that the models with only one cohesive layer show significantly different results to that of the model with four cohesive layers in terms of size of the degradation area.

  • 14.
    Apruzzese, P.
    et al.
    Imperial College London.
    Falzon, B.G.
    Monash University.
    Olsson, R.
    RISE, Swerea, Swerea SICOMP.
    Modelling the postbuckling behaviour of impacted composite aerostructures2009In: ICCM International Conferences on Composite MaterialsConference paper (Refereed)
    Abstract [en]

    Two approaches to modelling the effects of embedded defects and impact damage in composite aerostructures are presented. These differ in the manner n which the damage is represented; one as an equivalent delamination and the other as a soft inclusion with non-linear homogenized material properties. These techniques are applied to study the effects of defects and impact damage on the performance of composite panels.

  • 15.
    Asp, Leif
    RISE, Swerea, Swerea SICOMP.
    Local models for NCF composite materials mechanical performance prediction2007In: ICCM International Conferences on Composite MaterialsConference paper (Refereed)
    Abstract [en]

    This paper presents models for NCF reinforced composite materials performance prediction developed within the European research project FALCOM. The research project was conducted during the years 2002 and 2005 and was led by QinetiQ, UK. In total nine European countries were represented in FALCOM. The models consider material heterogeneity on three scales. On the micro-scale homogenization of the fibre bundle is performed. On the meso-scale formulations of Representative Volume Elements with different degrees of sophistication are defined. Finally on the macro-scale models span from straightforward employment of laminate theory to full through-thickness 3D-representation of the meso-scale features. The paper illustrates the diversity of local performance models for NCF composite analysis presenting a selection of models developed in the FALCOM project.

  • 16.
    Asp, Leif
    RISE, Swerea, Swerea SICOMP.
    Multifunctional composite materials for energy storage in structural load paths2013In: Plastics, rubber and composites, ISSN 1465-8011, E-ISSN 1743-2898, Vol. 42, no 4, p. 144-149Conference paper (Refereed)
    Abstract [en]

    This paper presents an overview of the research performed to date by a Swedish interdisciplinary team of scientists striving to develop multifunctional composite materials for storage of electric energy in mechanical load paths. To realise structural batteries from polymer composites, research pursued on carbon fibres for use as negative electrode in the battery as well as on polymer electrolytes for use as polymer matrix in the composite is reported. The work on carbon fibres comprises characterisation of the electrochemical capacity of commercial carbon fibre grades and how this is affected by mechanical load. Co-polymers are studied for their multifunctional performance with respect to lithium ion conductivity and stiffness. Also, rational processing of these polymer electrolytes and the effect of processing on their properties are addressed. © 2013 Institute of Materials, Minerals and Mining.

  • 17.
    Asp, Leif
    RISE, Swerea, Swerea SICOMP.
    Structural battery materials2012In: ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite MaterialsConference paper (Refereed)
    Abstract [en]

    Since four years Swerea SICOMP has been leading a team of Swedish researchers developing structural battery materials from polymer composites. The research performed in the Swedish project KOMBATT (Lightweight structural energy storage materials) is funded by the Swedish foundation for strategic research (SSF). The research addresses two technical challenges in particular. Firstly, solid polymer electrolytes that efficiently transfer loads in the composite and simultaneously transports lithium ions, while being electrically insulating, must be developed. Secondly, the ability of the reinforcement, i.e. The carbon fibres, to intercalate lithium ions as part of the chemical redox reactions, while maintaining its mechanical properties must be assured. This paper is the first in a series of papers at this conference from the KOMBATT project team and presents background and overview of the project.

  • 18.
    Asp, Leif
    et al.
    RISE, Swerea, Swerea SICOMP.
    Juntikka, Rickard
    RISE, Swerea, Swerea SICOMP.
    High velocity impact on NCF reinforced composites2009In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 69, no 9, p. 1478-1482Article in journal (Refereed)
    Abstract [en]

    In the current paper, a series of high velocity impact tests using φ{symbol}50 and φ{symbol}25 mm ice spheres and 0.32 g granite stones on non-crimp fabric (NCF) composite plates are reported. The impact tests were performed using an air gun and velocities between 100 m/s and 199 m/s. The impact events were monitored using a high-speed camera, with a 20 million frames per second capacity, as well as by a displacement transducer for out-of-plane displacement measurements of the impacted plates. NCF composite plates of two different thicknesses were impacted. The composites were manufactured from carbon fibre and epoxy resin by vacuum infusion. Engineering type models were employed to predict impact response and impact damage formation. Comparison between predicted and resulting damage for the impact test validates the application of a semi-empirical model for predicting impact velocity thresholds for damage formation. Analytical models relying on the assumption of solid impact bodies cannot be employed for these types of impact. © 2008 Elsevier Ltd. All rights reserved.

  • 19.
    Asp, Leif
    et al.
    RISE, Swerea, Swerea SICOMP.
    Juntikka, Rickard
    RISE, Swerea, Swerea SICOMP.
    High velocity impact on NCF reinforced composites2008In: Special Issue on the 12th European Conference on Composite Materials, ECCM 2006, Vol. 69, no 9, p. 1478-1482Conference paper (Refereed)
    Abstract [en]

    In the current paper, a series of high velocity impact tests using /50 and /25 mm ice spheres and 0.32 g granite stones on non-crimp fabric (NCF) composite plates are reported. The impact tests were performed using an air gun and velocities between 100 m/s and 199 m/s. The impact events were monitored using a high-speed camera, with a 20 million frames per second capacity, as well as by a displacement transducer for out-of-plane displacement measurements of the impacted plates. NCF composite plates of two different thicknesses were impacted. The composites were manufactured from carbon fibre and epoxy resin by vacuum infusion. Engineering type models were employed to predict impact response and impact damage formation. Comparison between predicted and resulting damage for the impact test validates the application of a semi-empirical model for predicting impact velocity thresholds for damage formation. Analytical models relying on the assumption of solid impact bodies cannot be employed for these types of impact. © 2008 Elsevier Ltd.

  • 20.
    Asp, Leif
    et al.
    RISE, Swerea, Swerea SICOMP.
    Marklund, Erik
    RISE, Swerea, Swerea SICOMP.
    Varna, J.
    Luleå University of Technology.
    Olsson, R.
    RISE, Swerea, Swerea SICOMP.
    Multiscale modelling of non-crimp fabric composites2012In: ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE), Vol. 3, no PARTS A, B, AND C, p. 581-590Conference paper (Refereed)
    Abstract [en]

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

  • 21.
    Asp, Leif
    et al.
    RISE, Swerea, Swerea SICOMP.
    Nilsson, S.
    Aeronautical Research Institute of Sweden, FFA.
    Singh, S.
    DERA Farnborough.
    An experimental investigation of the influence of delamination growth on the residual strength of impacted laminates2001In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 32, no 9, p. 1229-1235Article in journal (Refereed)
    Abstract [en]

    This study concerns an experimental investigation to establish data for validation of residual strength models for impacted composite panels. The work focuses on compression tests of panels with embedded artificial delaminations at various depths. Accompanying tests on undamaged and impact-damaged panels are reported and the relevance of the tests on artificially delaminated panels is assessed. In the experiments both the artificially delaminated and the impacted plates failed by delamination growth. Consequently, the same mechanism governed failure in the two cases. Hence, the artificially delaminated plate test is reliable for validation of methods developed for analysis of the residual strength of impact-damaged panels. However, for impacted plates, the load at global plate buckling was consistently 10% lower than that of the artificially delaminated plates and 20% lower than that of the undamaged plates. Hence, conservative prediction of the global buckling load of an impacted composite panel require s methods that consider influence of stiffness reduction of the damaged zone. © 2001 Elsevier Science Ltd. All rights reserved.

  • 22.
    Asp, Leif
    et al.
    RISE, Swerea, Swerea SICOMP.
    Sjögren, A.
    Aero. Research Institute of Sweden.
    Greenhalgh, E.S.
    DERA.
    Delamination Growth and Thresholds in a Carbon/Epoxy Composite under Fatigue Loading2001In: Journal of composites technology & research, ISSN 0884-6804, E-ISSN 1945-7537, Vol. 23, no 2, p. 55-68Article in journal (Refereed)
    Abstract [en]

    This paper presents a study on delamination growth in Mode I, Mode II and mixed mode under fatigue loading in an HTA/6376C composite. The computed slopes of the modified Paris plots were high. Therefore, threshold values of the strain energy release rate for delamination growth were determined. Low fatigue threshold values revealed a significant effect of fatigue loading. The largest effect was found for the ENF test (Mode II) for which the fatigue threshold value was only 10% of the critical strain energy release rate in static tests. Threshold values for MMB (mixed mode) and DCB (Mode I) tests were 15% and 23% of the static values, respectively. Fractographic evaluation revealed identical initial failure mechanisms in fatigue and static loading conditions for the ENF specimen. The ENF specimen failed by formation and coalescence of microcracks. The low fatigue threshold for the ENF specimen was explained by microscopical observations on the specimen edge. It was also shown that the fracture surfaces generated in static and fatigue DCB and MMB tests were similar.

  • 23.
    Bachinger, Angelika
    et al.
    RISE, Swerea, Swerea SICOMP.
    Marklund, Erik
    RISE, Swerea, Swerea SICOMP.
    Rössler, J.
    Hellström, Peter
    RISE, Swerea, Swerea SICOMP.
    Asp, Leif
    RISE, Swerea, Swerea SICOMP.
    Stiffness-modifiable composite for pedestrian protection2014In: 16th European Conference on Composite Materials, ECCM 2014Conference paper (Refereed)
    Abstract [en]

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

  • 24.
    Bjornsson, Andreas
    et al.
    Linköping University, Sweden.
    Jonsson, Marie
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Johansen, Kerstin
    Linköping University, Sweden.
    Automated material handling in composite manufacturing using pick-and-place systems - a review2018In: Robotics and Computer-Integrated Manufacturing, ISSN 0736-5845, E-ISSN 1879-2537, Vol. 51, p. 222-229Article in journal (Refereed)
    Abstract [en]

    With increasing use of fiber reinforced polymer composites follows a natural pursuit for more rational and effective manufacturing. Robotic pick-and-place systems can be used to automate handling of a multitude of materials used in the manufacturing of composite parts. There are systems developed for automated layup of prepreg, dry fibers and thermoplastic blanks as well as to handle auxiliary materials used in manufacturing. The aim of this paper is to highlight the challenges associated with automated handling of these materials and to analyze the main design principles that have been employed for pick-and-place systems in terms of handling strategy, reconfigurability, gripping technology and distribution of gripping points etc. The review shows that it is hard to find generic solutions for automated material handling due to the great variety in material properties. Few cases of industrial applications in full-scale manufacturing could be identified. 

  • 25.
    Björnsson, Andreas
    et al.
    Linköping University, Sweden.
    Jonsson, Marie
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Eklund, Daniel
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Lindbäck, Jan Erik
    Saab AB, Sweden.
    Björkman, Mats
    Linköping University, Sweden.
    Getting to grips with automated prepreg handling2017In: Production Engineering, ISSN 0944-6524, E-ISSN 1863-7353, Vol. 11, no 4-5, p. 445-453Article in journal (Refereed)
    Abstract [en]

    Automated manufacturing of composite parts based on prepreg material is receiving increased interest with the rising use of composite materials for high-performance applications. The two main automation alternatives for prepreg layup, automated tape layup and fiber placement, are not cost-effective for all types of products, and manual labor is common for the manufacturing of complex parts in low manufacturing volumes. Alternatives to the two dominant automation solutions have been pursued, but so far these have had a limited impact in industrial applications. This paper presents four different solutions for automated layup of prepreg plies to flat laminates that can be formed in a subsequent forming process, which decrease the system complexity. The solutions target products where the layup of flat laminates today is done manually due to technical limitations or cost considerations. The layup solutions must manage challenges caused by material properties such as low material rigidity and tack, and be able to handle a high number of ply shapes. All four solutions are designed for prepreg that is covered with a stiff backing paper. The aim of the paper is to analyze and compare the four solutions. It can be concluded that the most versatile solution is a dual-arm robot equipped with simple end effectors. The dual-arm solution presents a possibility to control the pick-up and lay-down motions that make peeling motions possible, which is advantageous when picking material that has tacked to the pickup surface.

  • 26.
    Blanco, N.
    et al.
    EPS-University of Girona.
    Gamstedt, E.K.
    Royal Institute of Technology (KTH).
    Asp, Leif
    RISE, Swerea, Swerea SICOMP.
    Costa, J.
    EPS-University of Girona.
    Mixed-mode delamination growth in carbon-fibre composite laminates under cyclic loading2004In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 41, no 15, p. 4219-4235Article in journal (Refereed)
    Abstract [en]

    Delamination growth under fatigue loads in real composite components generally develops in a non-constant propagation mode. The aim of the investigation described in this article was to develop a model capable of predicting the fatigue delamination growth in a general case, under varying mode mix conditions. The crack growth development in essentially unidirectional laminates of carbon-fibre reinforced epoxy was analysed in terms of the Paris law for different constant propagation modes: mode I (double-cantilever beam test), mode II (end-notched flexure test) and different mixed-modes I/II (mixed-mode bending test). The dependence of the Paris law parameters on mode mix is compared with the existing models in the literature. It is shown that these models do not reproduce the non-monotonic dependence on mode mix which has been observed in experimental data. Therefore, an improved phenomenological model is introduced and compared with the experimental data obtained by other researchers. To check the ability of the model to predict variable mixed-mode fatigue delamination, the mixed-mode end-loaded split test was employed and the experimental results were compared to the predictions of the model. The underlying mechanisms responsible for the dependency of the crack propagation rates on the degree of mode mix are also discussed on the basis of fractographic analysis. © 2004 Elsevier Ltd. All rights reserved.

  • 27.
    Bru, Thomas
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Asp, Leif
    Chalmers University of Technology, Sweden.
    Olsson, Robin
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Vyas, Gaurav
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Biaxial transverse compression testing for a fibre reinforced polymer material2018Conference paper (Refereed)
    Abstract [en]

    Unidirectional laminates have been tested under uniaxial transverse compression and under biaxialtransverse compression. Failure occurred by shear in an inclined failure plane parallel to the fibres.The transverse shear response of the material on the failure plane was evaluated from the tests. In thebiaxial tests, the failure load was considerably higher than in the uniaxial tests. For a given transverseshear strain the transverse shear stress was also higher in the case of biaxial compression. It is alsoshown that using waisted specimens instead of prismatic specimens does not seem to bring noticeablebenefits for through-thickness uniaxial compression tests. The experimental results presented here areimportant input to the development and the validation of damage models of fibre reinforced polymermaterials accounting for the matrix nonlinear response in shear and compression.

  • 28.
    Bru, Thomas
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP. Chalmers University of Technology, Sweden.
    Hellström, Peter
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Gutkin, Renaud
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Ramantani, Dimitra
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Peterson, Göran
    Volvo Group Trucks Technology, Sweden.
    Characterisation of the mechanical and fracture properties of a uni-weave carbon fibre/epoxy non-crimp fabric composite2016In: Data in Brief, E-ISSN 2352-3409, Vol. 6, p. 680-695Article in journal (Refereed)
    Abstract [en]

    A complete database of the mechanical properties of an epoxy polymer reinforced with uni-weave carbon fibre non-crimp fabric (NCF) is established. In-plane and through-the-thickness tests were performed on unidirectional laminates under normal loading and shear loading. The response under cyclic shear loading was also measured. The material has been characterised in terms of stiffness, strength, and failure features for the different loading cases. The critical energy release rates associated with different failure modes in the material were measured from interlaminar and translaminar fracture toughness tests. The stress–strain data of the tensile, compressive, and shear test specimens are included. The load–deflection data for all fracture toughness tests are also included. The database can be used in the development and validation of analytical and numerical models of fibre reinforced plastics (FRPs), in particular FRPs with NCF reinforcements.

  • 29.
    Bru, Thomas
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP. Chalmers University of Technology, Sweden.
    Olsson, Robin
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Gutkin, Renaud
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Vyas, Gaurav M.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Use of the Iosipescu test for the identification of shear damage evolution laws of an orthotropic composite2017In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 174, p. 319-328Article in journal (Refereed)
    Abstract [en]

    The experimental evaluation of the shear response of fibre-reinforced plies is a requirement for accurate material models predicting progressive damage. In the first part of the paper, the quality of the Iosipescu shear test is investigated with full-field strain measurements and finite element analyses. In the second part, the in-plane and through-thickness shear response of an orthotropic carbon/epoxy uni-weave non-crimp fabric composite are compared, and the stress–strain curves used as input for two continuum damage mechanics models. Both models were able to predict accurately the nonlinear shear behaviour of the material. The model parameters and the damage evolution laws could easily be extracted from cyclic Iosipescu tests.

  • 30.
    Bru, Thomas
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP. Chalmers University of Technology, Sweden.
    Waldenström, Paul
    KTH Royal Institute of Technology, Sweden.
    Gutkin, Renaud
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Olsson, Robin
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Vyas, Gaurav M.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Development of a test method for evaluating the crushing behaviour of unidirectional laminates2017In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 51, no 29, p. 4041-4051Article in journal (Refereed)
    Abstract [en]

    More fundamental test methods are needed to assist the development of physically based and truly predictive simulation tools for composite materials under crash conditions. In this paper, a unidirectional flat specimen that can be used to validate the predicted behaviour from a simulation to the physical behaviour in the experiment is developed. A systematic experimental investigation is conducted to evaluate the influence of the trigger geometry on the crushing response by selecting two trigger types and different trigger angles. For longitudinal crushing, the traditional bevel trigger leads to out-of-plane failure by splaying with a limited amount of in-plane fracture, while the proposed trigger achieves a high amount of compressive fragmentation failure. For transverse crushing, the symmetry of the proposed new trigger improves the specimen stability during the crushing process. It is also observed that the weft threads of the unidirectional fabric reinforcement used for the tests have a strong influence on the longitudinal crushing response. The boundary conditions of the test and the information on the specimen failure gleaned from video recordings and microscopic inspections are discussed in order to facilitate a future correlation with modelling results. © 2017, © The Author(s) 2017.

  • 31.
    Canturri, C.
    et al.
    Imperial College London.
    Greenhalgh, E.S.
    Imperial College London.
    Pinho, S.T.
    Imperial College London.
    Nilsson, Sören
    RISE, Swerea, Swerea SICOMP.
    Delamination growth mechanism from embedded defects in compression2011In: ICCM International Conferences on Composite MaterialsConference paper (Refereed)
  • 32.
    Carlson, Tony
    et al.
    RISE, Swerea, Swerea SICOMP.
    Asp, L.E.
    RISE, Swerea, Swerea SICOMP.
    Plasma treatment- a route for improved adhesion between pet and epoxy in multifunctional composite capacitors?2012In: ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite MaterialsConference paper (Refereed)
    Abstract [en]

    This paper presents an approach towards realising novel multifunctional polymer composites. A series of structural capacitor materials made from carbon fibre reinforced polymers have been developed, manufactured and tested. The capacitors were made using three thicknesses of DuPont Mylar A thermoplastic PET as dielectric separator employing carbon fibre/epoxy pre-pregs as structural electrodes. Plasma treatment was used as a route for improved epoxy/PET adhesion employing a number of treatment times, 5, 10, 15, 20 and 25s. The manufactured materials have been mechanically and electrically tested to evaluate their multifunctional efficiency. Plasma treatment have been shown to give some improvements to the interlaminate shear strength but not to any significant degree.

  • 33.
    Carlson, Tony
    et al.
    RISE, Swerea, Swerea SICOMP.
    Asp, Leif
    RISE, Swerea, Swerea SICOMP.
    Carbon fibre composites capacitors for short term electric energy storage in structural applications2011In: ICCM International Conferences on Composite MaterialsConference paper (Refereed)
  • 34.
    Carlson, Tony
    et al.
    RISE, Swerea, Swerea SICOMP.
    Asp, Leif
    RISE, Swerea, Swerea SICOMP.
    Structural carbon fibre composite/PET capacitors-Effects of dielectric separator thickness2013In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 49, p. 16-21Article in journal (Refereed)
    Abstract [en]

    This paper presents an approach towards realising novel multifunctional polymer composites with combined structural and electric energy storing ability. A series of structural capacitors were made using three thicknesses of DuPont Mylar A thermoplastic PET as a dielectric separator employing carbon fibre/epoxy pre-pregs as structural electrodes. Plasma treatment was used as a route for improved epoxy/PET adhesion. The manufactured materials were mechanically and electrically tested to evaluate their multifunctional efficiency. The multifunctional materials developed show good potential for replacing steel, aluminium and other materials with lower specific mechanical properties but do not match the high specific mechanical and electrical performance of monofunctional composites and capacitors. © 2013 Elsevier Ltd. All rights reserved.

  • 35.
    Carlson, Tony
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Ordéus, D.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Wysocki, Maciej
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Asp, Leif
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    CFRP structural capacitor materials for automotive applications2011Conference paper (Refereed)
    Abstract [en]

    In this paper, an approach towards realising novel multifunctional polymer composites is presented. A series of structural capacitor materials made from carbon fibre reinforced polymers have been developed, manufactured and tested. The structural capacitor materials were made from carbon fibre epoxy prepreg woven lamina separated by a polymer film dielectric separator. The structural capacitor multifunctional performance was characterised measuring capacitance, dielectric strength and tearing force. The developed structural carbon fibre reinforced polymer (CFRP) capacitor designs employing polymer film dielectrics (PA, PC and PET) offer remarkable multifunctional potential. © Institute of Materials, Minerals and Mining 2011.

  • 36.
    Carlson, Tony
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Ordéus, Daniel
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Wysocki, Maciej
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Asp, Leif
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Structural capacitor materials made from carbon fibre epoxy composites2010In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 70, no 7, p. 1135-1140Article in journal (Refereed)
    Abstract [en]

    In this paper, an approach towards realising novel multifunctional polymer composites is presented. A series of structural capacitor materials made from carbon fibre reinforced polymers have been developed, manufactured and tested. The structural capacitor materials were made from carbon fibre epoxy pre-preg woven laminae separated by a paper or polymer film dielectric separator. The structural capacitor multifunctional performance was characterised measuring capacitance, dielectric strength and interlaminar shear strength. The developed structural CFRP capacitor designs employing polymer film dielectrics (PA, PC and PET) offer remarkable multifunctional potential. © 2010 Elsevier Ltd.

  • 37.
    Carlstedt, David
    et al.
    Chalmers University of Technology, Sweden.
    Marklund, Erik
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP. Luleå University of Technology, Sweden.
    Asp, Leif
    Chalmers University of Technology, Sweden.
    Effects of state of charge on elastic properties of 3D structural battery composites2019In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 169, p. 26-33Article in journal (Refereed)
    Abstract [en]

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

  • 38.
    Costa, Sergio
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP. Chalmers University of Technology, Sweden.
    Bru, Thomas
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP. Chalmers University of Technology, Sweden.
    Olsson, Robin
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Portugal, André
    INOV Contacto Programme, Portugal.
    Improvement and validation of a physically based model for the shear and transverse crushing of orthotropic composites2018In: Journal of Composite MaterialsArticle in journal (Refereed)
    Abstract [en]

    This paper details a complete crush model for composite materials with focus on shear dominated crushing under a three-dimensional stress state. The damage evolution laws and final failure strain conditions are based on data extracted from shear experiments. The main advantages of the current model include the following: no need to measure the fracture toughness in shear and transverse compression, mesh objectivity without the need for a regular mesh and finite element characteristic length, a pressure dependency of the nonlinear shear response, accounting for load reversal and some orthotropic effects (making the model suitable for noncrimp fabric composites). The model is validated against a range of relevant experiments, namely a through-the-thickness compression specimen and a flat crush coupon with the fibres oriented at 45° and 90° to the load. Damage growth mechanisms, orientation of the fracture plane, nonlinear evolution of Poisson's ratio and energy absorption are accurately predicted.

  • 39.
    Costa, Sergio
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP. Chalmers University of Technology, Sweden.
    Gutkin, Renaud
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Olsson, Robin
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Mesh objective implementation of a fibre kinking model for damage growth with friction2017In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 168, p. 384-391Article in journal (Refereed)
    Abstract [en]

    A newly developed physically based model for the longitudinal response of laminated fibre-reinforced composites during compressive damage growth is implemented in a Finite Element (FE) software. It is a mesoscale model able to capture the physics of kink-band formation by shear instability, the influence of the matrix in supporting the fibres and the rotation of the fibres during compression, resulting in more abrupt failure for smaller misalignments. The fibre kinking response is obtained by solving simultaneously for stress equilibrium and strain compatibility in an FE framework. Strain softening creates pathological sensitivity when the mesh is refined. To make the model mesh objective, a methodology based on scaling the strain with the kink-band width is developed. The FE implementation of the current model is detailed with focus on mesh objectivity, and generalized to irregular meshes. The results show that the current model can be used to predict the whole kinking response in a 3D framework and thus account for the correct energy dissipation.

  • 40.
    Costa, Sérgio
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP. Chalmers University of Technology, Sweden.
    Portugal, A
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Olsson, Robin
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Vyas, Gaurav
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Bru, Thomas
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP. Chalmers University of Technology, Sweden.
    Validation of a novel model for the compressive response of FRP:experiments with different fibre orientations2017Conference paper (Refereed)
    Abstract [en]

    Crush tests have been performed on flat unidirectional non-crimp fabric (NCF) coupons with differentfibre orientations as part of the validation of a ply-based damage model for crash. The fibre off-axisangle with respect to the crushing direction ranged from 0º to 90°. The results of the tests indicate thatthe crush stress remains unchanged for off-axis angles between 0° and 15°. The failure mode in thesespecimens was out-of-plane kinking. For 20° and 25° off-axis angles the crush stress dropped 20% andevidence of out-of-plane kinking were harder to find. For 45° off-axis angle a network of matrixcracks develops in the specimen and for 90° off-axis angle a brittle shear failure is observed. It issuggested that the out-of-plane kinking is promoted because of the natural waviness of NCF materialsand that the high in-plane shear stress generated from 20-25° off-axis loading results in a transitionfrom out-of-plane kinking to in-plane kinking. These hypotheses need, however, to be verified by anextended failure analysis of the crush specimens.

  • 41.
    Costa, Sérgio
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Portugal, André
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Olsson, Robin
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Vyas, Gaurav
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Bru, Thomas
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Validation of a novel model for the compressive response of FRP: numerical simulation2018Conference paper (Refereed)
    Abstract [en]

    A progressive damage model for matrix compression is complemented with matrix tension in a physically based manner. The interaction of damage mechanisms undergoes a preliminary validation using single elements. The crushing response is validated with two different flat specimens with the fibres oriented transversely and at 45 degrees to the load. The model combines friction with damage to model the shear response accurately, which is necessary for reliable crush simulations. The behaviour in tension is history dependent, i.e. the model accounts for the stiffness reduction and strength to carry load in tension when previously damaged occurs in compression.The validation is performed against different tests showing the reliability of the model for different fibre orientation, specimen geometry and multiaxial loading scenarios. The crush response is well captured as well as the geometry and location of the different damage mechanisms.

  • 42.
    Craven, R.
    et al.
    Imperial College London.
    Iannucci, L.
    Imperial College London.
    Olsson, Robin
    RISE, Swerea, Swerea SICOMP.
    Buckling of a laminate with realistic multiple delaminations and fibre fracture cracks using finite element analysis2009In: ICCM International Conferences on Composite MaterialsConference paper (Refereed)
    Abstract [en]

    This paper presents a finite element study of buckling and postbuckling of sub-laminates representative of an impact damaged laminate. Multiple realistic delaminations and fibre fracture cracks are considered under compression to identify the key parameters of impact damage that affect the residual compressive strength of the laminate.

  • 43.
    Craven, R.
    et al.
    Imperial College London.
    Iannucci, L.
    Imperial College London.
    Olsson, Robin
    RISE, Swerea, Swerea SICOMP.
    Delamination buckling: A finite element study with realistic delamination shapes, multiple delaminations and fibre fracture cracks2010In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 41, no 5, p. 684-692Article in journal (Refereed)
    Abstract [en]

    This paper presents a finite element model of a carbon fibre composite laminate with multiple delaminations of realistic shape and including fibre fracture cracks loaded under compression. The modelling technique is initially applied on circular and elliptical delaminations of single ply sublaminates, which are compared with existing analytical solutions. The techniques are then applied to models with multiple delaminations of realistic shape and their behaviour in buckling and post-buckling is captured. An inverse method is used to determine the stiffness reduction caused by the damage, and shows significant stiffness reduction caused by peanut shaped delaminations. When fibre fracture cracks are added, their contribution to further stiffness reduction is minimal but they have some significant effects on the buckling shapes. © 2010 Elsevier Ltd. All rights reserved.

  • 44.
    Craven, R.
    et al.
    Imperial College London.
    Iannucci, L.
    Imperial College London.
    Olsson, Robin
    RISE, Swerea, Swerea SICOMP.
    Homogenised non-linear soft inclusion for simulation of impact damage in composite structures2011In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 93, no 2, p. 952-960Article in journal (Refereed)
    Abstract [en]

    This paper presents the development of a homogenised non-linear soft inclusion which captures the geometric and material non-linearity of impact damage zone loaded in tension and compression. The homogenised non-linear soft inclusion can present a conservative worst case damage zone or use experimental data to mimic the behaviour of a particular damage zone in a simple and computationally efficient way that can be used as a structural design tool for composite structures subjected to impact. The development of the non-linear soft inclusion, implemented in an ABAQUS/Explicit VUMAT, is presented at element and coupon level. The non-linear soft inclusion is validated against experimental coupon data and produces a conservative worst case estimate in all cases investigated. © 2010 Elsevier Ltd.

  • 45.
    Dweib, M.A.
    et al.
    Natl. Univ. I..
    Vahlund, Fredrik
    RISE, Swerea, Swerea SICOMP.
    Ó Brádaigh, C.M.
    Natl. Univ. I..
    Fibre structure and anisotropy of glass reinforced thermoplastics2000In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 31, no 3, p. 235-244Article in journal (Refereed)
    Abstract [en]

    The fibre structure and orientation distribution of two commercially available glass mat thermoplastics reinforced by continuous glass fibre was studied to investigate the anisotropic behaviour under compression moulding and mechanical loading, and to investigate the influence of the fibre structure and orientation on the anisotropic behaviour. Circular samples were deformed into ellipses when moulded, due to the anisotropic fibre orientation. The fibre content and orientation were examined in different locations of the elliptically deformed specimens. X-ray pictures were taken of the material in order to develop images of the fibres, before and after compression moulding. In another procedure, the matrix was burned off and the fibre network structures were studied in each case. A CCD camera was used to scan the fibres as digital images to measure the orientation distribution functions of the fibres. The fibre orientation measuring process was facilitated by subroutines implemented in the source code of the public domain NIH-image analysis software using simulated Fraunhofer diffraction.

  • 46.
    Edgren, Fredrik
    RISE, Swerea, Swerea SICOMP.
    Compressive failure of NCF composites2005In: 20th Technical Conference of the American Society for Composites 2005, Vol. 3, p. 1629-1644Conference paper (Refereed)
    Abstract [en]

    This study concerns compression failure of impacted Non-Crimp Fabric (NCF) composite laminates. Panels with a barely visible impact damage (BVID) have been studied under compression after impact (CAI) conditions. Monolithic laminates have been tested in CAI and the failure mechanisms are identified and discussed. The study on monolithic laminates constitutes a complement to a previous study on NCF laminate face sheets of sandwich panels in a naval application. The results from the present study confirm the findings from the study on sandwich skins; the mechanism controlling failure of CAI loaded NCF laminates is formation of kink bands. It is also found that kink bands develop at loads substantially lower than the load at panel failure. The results also indicate that the typical NCF heterogeneous structure, with fibre bundles separated with resin rich regions and fibre waviness, prevent kink bands from growing unstable immediately after initiation. Copyright © (2005) by DEStech Publications, Inc.

  • 47.
    Edgren, Fredrik
    RISE, Swerea, Swerea SICOMP.
    Hälso- och säkerhetsrisker med kolfiber-epoxi komposit2006Report (Refereed)
  • 48.
    Edgren, Fredrik
    RISE, Swerea, Swerea SICOMP.
    Progressive damage and failure models for composite materials in ABAQUS2007Report (Refereed)
  • 49.
    Edgren, Fredrik
    RISE, Swerea, Swerea SICOMP.
    Using cohesive interface elements to compare different ply drop-off strategies2007Report (Refereed)
  • 50.
    Edgren, Fredrik
    et al.
    RISE, Swerea, Swerea SICOMP.
    Asp, Leif
    RISE, Swerea, Swerea SICOMP.
    Approximate analytical constitutive model for non-crimp fabric composites2005In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 36, no 2 SPEC. ISS., p. 173-181Conference paper (Refereed)
    Abstract [en]

    In this paper, a study set on development and validation of constitutive models to account for out-of-plane fibre waviness in Non-crimp fabric (NCF) composites is presented. For this purpose, a mathematical model based on Timoshenko beam theory applied on curved beams, representing wavy tows in a NCF composite layer is employed. Stiffness knock-down factors operating at the ply level are established and introduced in laminate theory. The developed models are validated on laminates by comparison between predictions and experimental data as well as by comparison with numerical results for a cross-ply laminate. Application of the models on NCF composite laminates (cross-ply and quasi-isotropic) reveals that the models successfully predict laminate elastic properties. © 2004 Elsevier Ltd. All rights reserved.

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