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  • 1. Andre, A.
    et al.
    Norrby, Monica
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Nilsson, S.
    Nyman, Teresia
    KTH.
    An experimental and numerical study of the effect of some manufacturing defects2013In: ICCM International Conferences on Composite Materials, International Committee on Composite Materials , 2013, p. 4105-4112Conference paper (Refereed)
    Abstract [en]

    During the manufacturing process of composite structural parts, layer of fabrics or unidirectional prepreg may have to be cut in order to fulfil production requirements. From a general mechanical point of view, cutting fibres in a composite part has a large negative impact on the mechanical properties. However, such interventions are necessary in particular cases, for example due to draping of complex geometries. A rather extensive test program was launched to investigate the effects of defects that typically could arise during manufacturing. The overall purpose of the test program was to determine knock-down factors on strength for typical manufacturing defects that occasionally arise and sometimes are hard to avoid in production: cuts/gaps and fibre angle deviations. Four types of specimens were tested, reference, intersection of cuts in adjacent layers combined with a bolt hole, cut in a zero degree ply combined with a bolt hole and specimens with misaligned fibres. The specimens with misaligned fibres were tested with three different fibre angles. In addition to the experimental procedure, FE-analyses utilising cohesive elements were conducted, and after mechanical tests, Non Destructive Investigation (NDI) and fractographic investigations were performed. An excellent correlation between analyses and experiments were obtained. 

  • 2. André, Alain
    et al.
    Norrby, Monica
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Nilsson, Sören
    Nyman, Tonny
    An Experimental And Numerical Study Of The Effect Of Some Manufacturing Defects2013In: Proceedings of the 19th International conference on composite materials, ICCM-19, 2013Conference paper (Refereed)
    Abstract [en]

    Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.

  • 3. Björnsson, A.
    et al.
    Jonsson, M.
    Lindbäck, J. E.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Johansen, K.
    Robot-forming of prepreg stacks - Development of equipment and methods2016In: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials, European Conference on Composite Materials, ECCM , 2016Conference paper (Refereed)
    Abstract [en]

    Within the aerospace industry the manufacturing of composite components with complex shapes, such as spars, ribs and beams are often manufactured using manual layup and forming of prepreg material. Automated processes for prepreg layup and efficient forming techniques like vacuum forming are sometimes difficult to employ to these type of products due to technical limitations. This paper describes the development of tools and the forming sequence needed to automate sequential forming of a complex shape using an industrial robot. Plane prepreg stacks are formed to the final shape using a dual-arm industrial robot equipped with rolling tools. Tests show that the developed tools and the employed sequence can be used to form stacks to the desired shape with acceptable quality. 

  • 4.
    Grankall, Tommy
    et al.
    Saab AB, SE-58188 Linkoping, Sweden.;KTH Royal Inst Technol, Dept Aeronaut & Vehicle Engn, Teknikringen 8, SE-10044 Stockholm, Sweden..
    Hallander, Per
    Saab AB, SE-58188 Linkoping, Sweden.;KTH Royal Inst Technol, Dept Aeronaut & Vehicle Engn, Teknikringen 8, SE-10044 Stockholm, Sweden..
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Geometric compensation of convex forming tools for successful final processing in concave cure tools - An experimental study2019In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 116, p. 187-196Article in journal (Refereed)
    Abstract [en]

    To enable shimless composite part assembly it is desired to manufacture composite spars in concave, female tools. However, due to restricted access this process is often associated with a high degree of manual operations or expensive highly specialized production equipment. This study investigates a sequential manufacturing operation where the material is automatically laid up flat and hot formed onto a convex forming tool. Thereafter it is placed in the concave tool for curing. The study investigates four different ways to geometrically compensate the forming tool to simplify seating and enhance part quality. All compensations require material movement in-between forming and curing; this movement was tracked using Micro-CT. Micrographing and optical shape measurements show that a correct compensation provides high quality parts without adding labour intensive manufacturing steps.

  • 5.
    Grankäll, Tommy
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. KTH, Superseded Departments (pre-2005), Aeronautical and Vehicle Engineering.
    Hallander, Per
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Geometric compensation of convex forming tools for successful final processing in concave cure tools – An experimental study2019In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 116, p. 187-196Article in journal (Refereed)
  • 6.
    Hagnell K., Mathilda
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Langbeck, B.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Cost efficiency, integration and assembly of a generic composite aeronautical wing box2016In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 152, p. 1014-1023Article in journal (Refereed)
    Abstract [en]

    This paper presents a cost-efficiency study of part integration with respect to reduced assembly effort within aeronautical composite structures. The study is performed through the use, and continuous improvement upon, a previously developed cost model. Focus are on the assembly and basic inspection a wing box, part of a section of a full wing, where involved parts are all considered to be manufactured from carbon fibre reinforced plastic (CFRP). Treated cases range from traditional, mechanical joining, to high integration either through co-curing or co-bonding of composite structures. The outcome of presented cost study shows that increased integration decreases the overall production cost of said considered wing box. In general it is shown that co-curing or co-bonding reduces a number of cost-expensive assembly steps in comparison to mechanical joining.

  • 7. Hallander, P.
    et al.
    Sjölander, Jens
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Petersson, M.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Interface manipulation towards wrinkle-free forming of stacked UD prepreg layers2016In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 90, p. 340-348Article in journal (Refereed)
    Abstract [en]

    The aim of this paper is to experimentally study how forming behaviour can be changed by local manipulation of prepreg interfacial characteristics. Different methods for surface modification are examined, however all were aimed at enabling significantly increased interply friction. The paper shows that by using increased friction in between layers, these neighbouring pairs will act together during forming, thereby either improving or exacerbating the forming outcome. For the geometry utilized, wrinkle free forming was obtained when the cross-plied layers were paired to deform mainly through intraply shear during forming. The method is supported by the appended numerical analysis and interaction between forming mechanisms and radius thinning is instigated as part of the experimental outcome.

  • 8. Hallander, P.
    et al.
    Sjölander, Jens
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Effects on forming when using aligned multi wall carbon nanotubes in multi-stacked prepreg2015In: ICCM International Conferences on Composite Materials, International Committee on Composite Materials , 2015Conference paper (Refereed)
    Abstract [en]

    Automated tape lay-up (ATL) combined with Hot Drape Forming (HDF) offer cost competitive manufacturing for large composite components. However, not carefully performed HDF of composite laminates could end up with out-of-plane fibre wrinkling. Previous studies with this technique has shown that the stacking sequence have a significant influence on wrinkle development during 3D-forming. One possible explanation to this might be the relatively high interply friction for the combination of [0] and [45] layers. Prepregs containing thermoplastic toughener particles show a higher level of interply friction compared to prepregs which do not contains such particles. It is therefore likely that interfacial particles in general will increase the interply friction. Such particles could be thermoplastic toughener or aligned multiwall carbon nanotubes (MWCNT). The aim of this study is to show how locally arranged MWCNTs in prepreg interlayers affect the global forming behaviour. An initial study of intraply shear and interply friction is performed with purpose to investigate how pregpreg with MWCNT interlayers on general influence the forming. Further an experimental forming study is performed with aligned MWCNT in the [-45] / [0] interlayers of a quasi-isotropic prepreg stacking sequence. A numerical study is also performed simulating the forming of the experimental spar geometry. The results show that the intraply shear resistance of the MWCNT containing material is 100% higher than for the reference. Further the interply friction is 3 to 4 times higher for the MWCNT containing material compared to the reference. The experimental spar study shows increased out-of-plane wrinkling in the joggled spar flange when using MWCNT in the [-45]/[0] interlayers. The numerical study strengthen the experimental results by showing increased compression across the fibre direction in the [0] layer when adding contact surfaces in the [-45]/[0] interlayers. 

  • 9. Hallander, P.
    et al.
    Sjölander, Jens
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Forming induced wrinkling of composite laminates with mixed ply material properties; an experimental study2015In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 78, p. 234-245Article in journal (Refereed)
    Abstract [en]

    One disadvantage of multi-layer forming of unidirectional (UD) prepreg tape is the risk of out-of-plane wrinkling. This study aims to show how mixed ply material properties affect global wrinkling behaviour. An experimental study was performed using pre-stacked UD prepreg on a forming tool with varying cross sections. Parameters studied include local interply friction, effects of co-stacking and fibre stresses in critical fibre directions. Experimental evaluation was performed on out-of-plane defect height, type and location. The study shows that fibre stresses in some fibre directions were crucial for the shearing required to avoid wrinkling. The same fibre stresses may cause wrinkling if the lamina is stacked in a non-beneficial order. Changing the friction locally, or reducing the number of difficult combinations of fibre angles, improves the forming outcome slightly. However, in order to make a significant improvement, co-stacking or different fibre stacking is required.

  • 10.
    Hallander, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Sjölander, Jens
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Petersson, Mikael
    Saab AB.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Interface manipulation towards wrinkle-free forming of stacked UD prepreg layersIn: Article in journal (Other academic)
    Abstract [en]

    The aim of this paper is to experimentally study how forming behaviour can be changed by local manipulation of prepreg interfacial characteristics. Different methods for surface modification are examined, however all were aimed at enabling significantly increased interply friction. The paper shows that by using increased friction in between layers, these neighbouring pairs will act together during forming, thereby either improving or exacerbating the forming outcome. For the geometry utilized, wrinkle free forming was obtained when the cross-plied layers were paired to deform mainly through intraply shear during forming. The method is supported by the appended numerical analysis and interaction between forming mechanisms and radius thinning is instigated as part of the experimental outcome.

  • 11.
    Hallander, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Sjölander, Jens
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Forming of composite spars including interlayers of aligned, multiwall, carbon nanotubes: an experimental study2016In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569Article in journal (Refereed)
    Abstract [en]

    Carbon nanotubes offer the potential for improved or changed matrix properties, thereby enabling the creation of novel, multifunctional composite materials. By using highly-aligned, multiwall, carbon nanotubes (MWCNT) with thermoset resins, good dispersion and distribution of nanotubes is obtained. To date, research has mainly focused on improving the growth process of the aligned MWCNTs, however little has been done on the processing of composites that include MWCNTs as interlayers in the stack.  The aim of this work is to study how the aligned MWCNTs are affected within composite part forming. The study shows that MWCNTs are influenced by the shearing that occurs during forming, but still maintain their integrity. To some extent, the shear pattern observed in the MWCNTs after deformation provides an indication of deformation modes. However, the presence of MWCNTs also significantly influences the forming characteristics of the prepreg stack.

  • 12.
    Hallander, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Automated forming of pre-stacked UD prepregs2011In: 22nd annual International SICOMP conference, 2011Conference paper (Refereed)
  • 13. Hallander, Per
    et al.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Mattei, Christoph
    Peterson, Mikael
    Nyman, Tonny
    An experimental study of mechanisms behind wrinkle development during forming of composite laminates2013In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 50, p. 54-64Article in journal (Refereed)
    Abstract [en]

    A general problem when forming quasi-isotropic, multilayer unidirectional (UD) prepreg over a double curved geometry is out-of-plane wrinkling. The presented study aims to show the existence of compression in the laminate in a recess area that is globally under tension during forming. Further it aims to investigate the influence of compression on the out-of-plane wrinkle development.

    An experimental study is performed with pre-stacked UD prepreg on a forming tool with varying cross section. Investigated parameters include lay-up sequence, prepreg ply thickness, inter-ply friction and prepreg ply impregnation. Experimental evaluation is performed on the out-of-plane defect height, type, location and number. Further, measurements are performed on the outer-ply deformation in the z-direction and inside the formed component using Micro CT. The study show that compression is to some degree always developed during forming of a recess area but that the lay-up sequence has a dominant effect on the wrinkling development.

  • 14.
    Hallnader, Per
    et al.
    SAAB AB, Sweden.
    Nyman, Tonny
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Influence of the forming process on the shape distortion of a composite c-shaped aerospace spar2012In: ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite Materials, European Conference on Composite Materials, ECCM , 2012Conference paper (Refereed)
    Abstract [en]

    Shape distortions are generally considered influenced by several factors including thermal contraction, curing kinetics, fibre content, lay-up (balanced / unbalanced) and anomalies developed during manufacturing. In this work influences from forming on the shape distortion of a C-shaped composite spar with a recess area on one side is investigated. The forming influences considered are fibre angle deviation, inbuilt residual fibre compression (RF compression) and inbuilt residual fibre tension (RF tension). Abnormalities due to various stacking sequences and choice of lay-up process are especially focused upon.

  • 15.
    Hallnader, Per
    et al.
    Saab AB, Sweden.
    Ydrefors, Lisa
    Exova.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Forming of prepreg composite parts with aligned multi wall carbon nanotubes2013In: 19th International Conference on Composite Matrials, 2013Conference paper (Refereed)
  • 16.
    Horberg, Erik
    et al.
    Saab AB, Broderna Ugglas Gata, SE-58188 Linkoping, Sweden.;KTH Royal Inst Technol, Dept Aeronaut & Vehicle Engn, Teknikringen 8, SE-10044 Stockholm, Sweden..
    Nyman, Tonny
    Saab AB, Broderna Ugglas Gata, SE-58188 Linkoping, Sweden.;KTH Royal Inst Technol, Dept Aeronaut & Vehicle Engn, Teknikringen 8, SE-10044 Stockholm, Sweden..
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Thickness effect on spring-in of prepreg composite L-profiles - An experimental study2019In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 209, p. 499-507Article in journal (Refereed)
    Abstract [en]

    This paper presents the results and analysis of an experimental study of laminate thickness effects on the spring-in and shape distortion of thermoset composite L profiles. The primary objective is to achieve a broader understanding of how shape distortion is affected by laminate bending stiffness and part thickness of L-shaped laminates whose thickness varies between 1 and 12 mm. The larger thicknesses in particular have not received much attention in previous research. This work further aims at distinguishing the pure (geometrical) thickness effect from that of the coupled laminate bending stiffness by comparing laminates with different lay-ups. The work is performed on test specimens subjected to both a standard cure cycle and post-cure heat treatment at elevated temperatures. In parallel, finite element (FE) analysis is performed to evaluate if variation in the bending stiffness or the laminate thickness affects the predicted spring-in angle. The results clearly show spring-in dependence on laminate thickness and bending stiffness, whereas this dependence is not well predicted by the FE approaches. It is concluded that both effects exist and that shape distortions are more strongly related to bending stiffness than to laminate thickness.

  • 17.
    Jerpdal, Lars
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Scania CV AB, Sweden.
    Stahlberg, Daniel
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Influence of fibre stretching on the microstructure of self-reinforced poly(ethylene terephthalate) composite2016In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 35, no 21, p. 1634-1641Article in journal (Refereed)
    Abstract [en]

    Self-reinforced poly(ethylene terephthalate) laminates were prepared from woven fabric by compression moulding. The fabric was stretched to different degrees during heating before hot consolidation to simulate a manufacturing process where the material is stretched through forming. High tenacity poly(ethylene terephthalate) fibres with different degrees of stretching were prepared for a comparison to laminates. Tensile tests were made to characterize mechanical properties, while dynamical mechanical analysis, differential scanning calorimetry, FTIR spectroscopy and X-ray diffraction analysis were employed to study microstructural changes caused by the stretching. Tensile tests show that 13% stretching of the fabric increases the laminate tensile stiffness by 34%. However, same degree of stretching for pure fibres increases the fibre tensile stiffness by 111%. Crystallinity and molecular conformations are not influenced by stretching while shrinkage upon heating increases with degree of stretching. Shrinkage is known to be related to disorientation of non-crystalline regions whereof the conclusion from this study is that the increased tensile properties are due to orientation of the non-crystalline regions of the fibre.

  • 18.
    Jerpdal, Lars
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Scania CV, Södertälje, Sweden .
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Influence of fibre shrinkage and stretching on the mechanical properties of self-reinforced poly(ethylene terephthalate) composite2014In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 33, no 17, p. 1644-1655Article in journal (Refereed)
    Abstract [en]

    Self-reinforced poly(ethylene terephthalate) composite laminates were manufactured from fabric using a hot press. Fabric was either allowed to shrink or exposed to stretching during different phases of the manufacturing process. Composite macrostructure, crimp, was investigated and results showed that shrinkage affects fibre crimp more than stretching does. Mechanical tests showed that shrinkage do not significantly affect mechanical properties while stretching fabric by 10% during heating results in 50% increase in tensile stiffness. The lack of correlation between crimp and mechanical properties indicates that mechanical properties for self-reinforced poly(ethylene terephthalate) composites are dominated by their microstructure, molecular orientation, which may be affected by the manufacturing process.

  • 19.
    Jerpdal, Lars
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Volkswagen AG, Group Research, Wolfsburg, Germany.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Ståhlberg, D.
    Herzig, A.
    Process induced shape distortions of self-reinforced poly(ethylene terephthalate) composites2018In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 193, p. 29-34Article in journal (Refereed)
    Abstract [en]

    This paper investigates shape distortion and tensile properties of hot consolidated Self-reinforced poly(ethylene terephthalate) (SrPET) by evaluating the influence from stretching before consolidation and annealing after consolidation. Spring-in angle and warpage is measured from V-shaped samples that are hot consolidated from a woven fabric that is stretched to different degrees during forming. Following the same process conditions, tensile stiffness is measured from plane laminates. This study confirms that stretching the SrPET-material during forming enhances the tensile modulus but introduces shape distortions with negative spring-in and increases warpage. However also non-stretched SrPET components experience spring-back in the same level as glass- or carbon reinforced PET composite, which is unexpected. The tensile modulus is reduced and spring-in angle further influenced when the SrPET-samples are exposed to higher temperature after consolidation. This study shows how easily the characteristics of a component made from SrPET-material are influenced by stresses developed during material forming and further by release of these stresses when exposed to higher temperatures as in post processes or even in the use phase of the component.

  • 20.
    Karlsson Hagnell, Mathilda
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Kumaraswamy, Siddharth
    Volvo Car Corporation.
    Nyman, Tonny
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Saab AB.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    From aviation to automotive - a study on material selection and its implication on cost and weight efficient structural composite and sandwich designsManuscript (preprint) (Other academic)
    Abstract [en]

    The structural design of composite materials is often challenging as its driven by a trade-off between lightweight structural performance and production costs. Addressing this design trade-off, this paper presents a methodology and case study that compares the weight- and production cost-potential of different composite materials and structural designs solutions through the use of a proposed application-bound design cost. Representative design solutions; monolithic, u-beam-, sandwich-insert- and sandwich-stiffened, are each optimized with respect to bending and torsional stiffness of increased severity to chart an extrapolated application map with respect to cost and stiffness. Optimized sandwich designs are shown to have lowest design cost where full stiffness is achieved. Alternative fibre materials researched; glass fibre, recycled carbon fibre, lignin-based fibres and hemp fibres, all reduce costs but at compromised stiffness. Ultimately, the case study demonstrates the impact of early design and material selection and justifies introducing novel fibre systems to reduce design cost.

  • 21.
    Karlsson Hagnell, Mathilda
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    A composite cost model for the aeronautical industry: Methodology and case study2015In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 79, p. 254-261Article in journal (Refereed)
    Abstract [en]

    This paper presents a novel composite production cost estimation model. The strength of the model is its modular construction, allowing for easy implementation of different production methods and case studies. The cost model is exemplified by evaluating the costs of a generic aeronautical wing, consisting of skin, stiffeners and rib feet. Several common aeronautical manufacturing methods are studied. For studied structure, hand layup is the most cost-effective method for annual volumes of less than 150 structures per year. For higher production volumes automatic tape layup (All) followed by hot drape forming (HDF) is the most cost-effective choice.

  • 22.
    Karlsson Hagnell, Mathilda
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Cost and weight efficient assembly of aeronautical composite structures2015In: ICCM International Conferences on Composite Materials, International Committee on Composite Materials , 2015Conference paper (Refereed)
    Abstract [en]

    Composite materials and integrated structures are weight-efficient, but not necessarily cost-efficient. In order to compare weight benefits with production cost penalties, the influence of each must be studied simultaneously. Production costs are challenging to estimate as they depend on production method choice as well as involved process variables such as annual production volume. In order to enable simultaneous analysis of cost and weight it is therefore necessary to develop tools that assist in production cost estimation. This paper presents the continuation of previous work, where the manufacturing costs of a composite structure is studied using a novel cost estimation tool, here extended to include that of assembly costs. Focus of this paper is assembly of aeronautical structures. The model is finally applied and discussed through estimating the assembly costs of two cases; that of a co-cured structure and that of a mechanically joined structure. The case study shows that the co-cured wing box is more cost-efficient than that of the mechanically joined wing box. Regarding weight, the mechanically joined structure increases the structural weight by about 1 kg, which corresponds to a weight increase of 1 %. Important cost drivers for the mechanically joined wing box are fastening, drilling and shimming costs, each representing about 20 % of the total cost as the annual production volume increases to 1000 produced structures per year. Important cost drivers for the co-cured wing box is the cost of part positioning and autoclave curing, representing about 40 % of the total cost each as the annual production volume increases to 1000 produced structures per year. 

  • 23.
    Karlsson Hagnell, Mathilda
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    The economic and mechanical potential of closed loop material usage and recycling of fibre-reinforced composite materialsManuscript (preprint) (Other academic)
    Abstract [en]

    This paper presents a novel recyclate value model derived from the retained mechanical performance of retrieved fibres in fibre-reinforced composites. The proposed recyclate value model was used to perform an economic analysis for establishing the future closed-loop material usage of fibre-reinforced composite materials. State-of-the-art recycling of carbon and glass-reinforced thermosets was adopted and resulted in a proposed recycling hierarchy in order to achieve a more sustainable environment and raw material cost reduction. The recyclate value model showed that approximately 50% material cost reductions can be achieved at comparable mechanical performance by using recycled fibre instead of virgin fibre in appropriate applications. From the aspect of lightweight design this cost reduction provides the designer with new material choices, appropriate for lower cost and diverse stiffness designs. The proposed closed-loop hierarchy documents the importance of further improvement of fibrous material recycling, including sorting according to mechanical performance, in order to identify application areas previously not utilised and to maximise material sustainability and value throughout the material's lifetime.

  • 24.
    Karlsson Hagnell, Mathilda
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    The economic and mechanical potential of closed loop material usage and recycling of fibre-reinforced composite materials2019In: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 223, p. 957-968Article in journal (Refereed)
    Abstract [en]

    This paper presents a novel recyclate value model derived from the retained mechanical performance of retrieved fibres in fibre-reinforced composites. The proposed recyclate value model was used to perform an economic analysis for establishing the future closed-loop material usage of fibre-reinforced composite materials. State-of-the-art recycling of carbon and glass-reinforced thermosets was adopted and resulted in a proposed recycling hierarchy in order to achieve a more sustainable environment and raw material cost reduction. The recyclate value model showed that approximately 50% material cost reductions can be achieved at comparable mechanical performance by using recycled fibre instead of virgin fibre in appropriate applications. From the aspect of lightweight design this cost reduction provides the designer with new material choices, appropriate for lower cost and diverse stiffness designs. The proposed closed-loop hierarchy documents the importance of further improvement of fibrous material recycling, including sorting according to mechanical performance, in order to identify application areas previously not utilised and to maximise material sustainability and value throughout the material's lifetime.

  • 25.
    Kaufmann, Markus
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Cost/weight optimization of composite prepreg structures for best draping strategy2010In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 41, no 4, p. 464-472Article in journal (Refereed)
    Abstract [en]

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

  • 26.
    Kaufmann, Markus
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Material Selection for a Curved C-Spar Based on Cost Optimization2011In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 48, no 3, p. 797-804Article in journal (Refereed)
    Abstract [en]

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

  • 27.
    Larberg, Ylva R.
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    In-plane properties of cross-plied unidirectional prepreg2007In: 16th International Conference on Composite Materials, ICCM-16, 2007Conference paper (Refereed)
    Abstract [en]

    Sheet forming of thermoset composites is a promising method to achieve reduction in manufacturing time and therefore cost. The behaviour of weaves has been thoroughly investigated and the PJN assumption is widely used. Cross-plied UD prepreg may initially show similar behaviour to weaves; however, the complete deformation is more complex, including slippage. Thus, the forming of cross-plies can offer a possibility of increased drapability compared to woven fabrics, but imposes difficulties in predicting forming limits and final fibre angles. The work presented herein aims to characterise the in-plane properties of cross-plied UD prepreg with the bias extension test method. Understanding the deformation modes and its limits could reduce the number of iterations from idea to component in production. The forming of a preplied stack depends on many parameters. The study shows that a higher crosshead rate consequently results in a higher load response. In addition, the type of deformation mode changes due to both speed and temperature.

  • 28.
    Larberg, Ylva
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    In-plane deformation of multi-layered unidirectional thermoset prepreg - Modelling and experimental verification2014In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 56, p. 203-212Article in journal (Refereed)
    Abstract [en]

    Sheet forming of unidirectional prepregs is gaining increased interest as a cost efficient alternative manufacturing method. Its potential lies within the use of automatically and efficiently stacked flat prepregs, which in a second step can be formed. A successful forming requires understanding of the properties of the uncured material. Here, the in-plane deformation behaviour of two different unidirectional thermoset prepregs is investigated. Experimental measurements are performed, showing the importance of stacking sequence and its effect on the forming behaviour of stacked prepreg. Finite element models are developed, using material models calibrated from bias extension tests and interlaminar friction tests. The method developed can be used to predict the reaction force and fibre reorientation during in-plane forming of thermoset prepreg, for one of the considered material systems. Further, it enables prediction of the effect of stacking sequence, which is promising for future full-scale forming simulations.

  • 29.
    Larberg, Ylva
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    On the interply friction of different generations of carbon/epoxy prepreg systems2011In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 42, no 9, p. 1067-1074Article in journal (Refereed)
    Abstract [en]

    Using pre-stacked material that is formed as a first step in the manufacturing process offers reduced process cycle time for production of complex structural components. The forming is achieved by forcing layers to deform by e.g. intraply deformation and interply slippage, where the latter is the scope of this study. The prepreg-prepreg friction is experimentally determined for four unidirectional carbon/epoxy prepreg systems. The materials differ considering volume fraction of fibres, fibre stiffness and phase of thermoplastic toughener (solved or particles). The study shows large individual differences between the tested materials, where the material systems with particle tougheners seem to obey a boundary lubrication friction, while the other materials show hydrodynamically dominated friction. A large difference between the high and low friction materials, almost a factor of 10, correlates to trends seen in the herein performed surface roughness measurements. Vacuum as well as autoclave consolidated materials are tested.

  • 30.
    Larberg, Ylva
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    On the interply friction of different generations of unidirectional prepreg materials2008In: Proceedings of 13th European Conference on Composite Materials (ECCM 13), 2008Conference paper (Refereed)
    Abstract [en]

    With the aim of reducing cost of prepreg composite components, manufacturing methods are developed and refined. An automatic tape laying machine can shorten the process cycle by stacking prepreg flat and thereafter allow for forming into desired shapes. Forming of stacked prepreg requires knowledge about the uncured properties of prepreg, such as viscosity of the matrix, intra- and interply deformation properties. This study focuses on the interply friction, i.e. the friction at the prepreg-prepreg interface, and how this affects the forming. The conclusions presented here show that the difference between prepreg material systems is significant. Further, it is concluded that the prepreg-prepreg friction is governed by a combination of Coulomb and hydrodynamic friction, where different mechanical phenomena dominate depending on the test conditions.

  • 31.
    Larberg, Ylva
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Norrby, Monica
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    On the in-plane deformability of cross-plied unidirectional prepreg2011In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 46, no 8, p. 929-939Article in journal (Refereed)
    Abstract [en]

    The work presented herein aims to characterise the in-plane properties of cross-plied unidirectional prepreg using the bias extension method. The study is focusing on carbon fibre/epoxy material systems and testing is performed at elevated temperatures to enhance formability. Using digital image correlation (DIC), the specimen deformation and fibre rotation is captured during tests. The study shows that the cross-plied unidirectional material deforms at different characteristic length scales as deformation continues: first seemingly continuous and later in form of bands. Further, the different type of prepreg materials investigated behaves differently; for one type the pin-jointed net theory fit well, enabling simple estimation of resulting fibre angle, while for another not. Different loading speed, temperatures and layup methods are investigated in order to pin-point its influence on the deformability.

  • 32.
    Larberg, Ylva
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Sjölander, Jens
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Hallander, Per
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Forming simulation of multi-layered unidirectional thermoset prepregsArticle in journal (Other academic)
  • 33.
    Mellin, Pelle
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Swerea KIMAB.
    Jönsson, Christina
    Swerea IVF.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Fernberg, Patrik
    Swerea SICOMP.
    Nordenberg, Eva
    Siemens Industrial Turbomachinery AB.
    Brodin, Håkan
    Siemens Industrial Turbomachinery AB.
    Strondl, Annika
    Swerea KIMAB.
    Nano-sized by-products from metal 3D printing, composite manufacturing and fabric production2016In: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 139, p. 1224-1233Article in journal (Refereed)
    Abstract [en]

    Recently, the health and environmental perspective of nano-materials has gained attention. Most previous work focused on Engineered Nanoparticles (ENP). This paper examines some recently introduced production routes in terms of generated nano-sized by-products. A discussion on the hazards of emitting such particles and fibers is included. Fine by-products were found in recycled metal powder after 3D printing by Selective Laser Melting (SLM). The process somehow generated small round metal particles (~1e2 mm) that are possibly carcinogenic and respirable, but not small enough to enter by skin-absorption. With preventive measures like closed handling and masks, any health related effects can be prevented. The composite manufacturing in particular generated ceramic and carbonaceous particles that are very small and respirable but do not appear to be intrinsically toxic. The smallest features in agglomerates were about 30 nm. Small particles and fibers that were not attached in agglomerates were found in a wide range of sizes, from 1 μm and upwards. Preventive measures like closed handling and masks are strongly recommended. In contrast, the more traditional production route of fabric production is investigated. Here, brushing residue and recycled wool from fabric production contained few nano-sized by-products.

  • 34.
    Mårtensson, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Volvo Car Group, Sweden.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Cost and weight efficient partitioning of composite automotive structures2015In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569Article in journal (Refereed)
    Abstract [en]

    To make carbon fiber composites not only weight but also cost effective in high volume production the different cost drivers need to be addressed and new design philosophies considered. This study analyzes integral and differential design approaches when partitioning large complex composite structures. The influence of different partition philosophies are investigated based on a framework of composites manufacturing cost modelling and structural optimization and the effects are exemplified by a case study. The results show that depending on how the partitioning is made the structural performance and the manufacturing cost is affected. More particularly, if the partitioning is made with the most beneficial philosophy differential designs can improve both these important parameters.

  • 35.
    Mårtensson, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Volvo Car Corporation, Sweden.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Effects of manufacturing constraints on the cost and weight efficiency of integral and differential automotive composite structures2015In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 134, p. 572-578Article in journal (Refereed)
    Abstract [en]

    The introduction of carbon fibre composites into the high volume automotive sector challenges the design process, since these components not only need to be light but also producible in a cost-efficient manner. One way forward is to introduce manufacturing constraints into the design process, but such constraints affect the freedom of design and opportunities to tailor material properties. This work examines the trade-offs between cost-effective design for manufacturing and the weight optimization of composite structures. This will be achieved by introducing restrictions to the number of plies allowed in structural optimization in order to simplify pre-operations and reduce overall manufacturing investments. Both integral and differential design solutions are considered. It was observed that differential solutions were always more cost and weight efficient than the integral solution, however too severe manufacturing constraints result in an expensive final part due to the additional weight.

  • 36.
    Mårtensson, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. Volvo Car Corporation, Sweden .
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    INTEGRAL OR DIFFERENTIAL DESIGN FOR A COST EFFECTIVE COMPOSITE AUTOMOTIVE BODY STRUCTURE2014In: 16th European Conference on Composite Materials, ECCM 2014, European Conference on Composite Materials , 2014Conference paper (Refereed)
    Abstract [en]

    The business case needs to be improved in order to make carbon fibre composites useful for the automotive industry. It is often claimed that one of composite greatest advantages over metals is the ability to be manufactured in large complex integral geometries. By reducing the number of tools and avoiding or minimising the assembly processes, an integral solution is commonly seen as more cost effective. In high volume manufacturing these claimed advantages might be questioned. This paper presents an investigation of how complexity and size of a structure affect the manufacturing design choice between integral and differential design. The study is based on a conceptual cost model with a part cost and assembly module for carbon fibre composite manufacturing. The result shows that an integral design solution is not necessary the most cost effective option. Instead, dependent of the size and complexity of the part a divided structure may both minimise total material cost and tool cost.

  • 37.
    Mårtensson, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. Volvo Car Corporation, Sweden .
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Integral versus differential design for high-volume manufacturing of composite structures2015In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 49, no 23, p. 2897-2908Article in journal (Refereed)
    Abstract [en]

    In order to decrease the weight of the automotive body structure and increase the energy efficiency of future cars, attention is now turning towards structural composites, mainly carbon fibre-reinforced plastics. Composites have several advantages such as their excellent weight-specific properties and the possibility to be manufactured in large integral designs for a reduced weight and potentially lower cost. However, carbon fibre composites are expensive and for a cost sensitive industry such as the automotive industry, the challenge lies in creating a favourable business case with a well-balanced trade-off between weight and cost. A method is proposed to visualise the cost and weight advantages of either pursuing an integral design or a differential design, i.e. dividing the structure into a greater number of parts that are later assembled. The method focuses on the impact on cost and weight and considers structures with different part sizes and geometrical complexities. It is shown that, depending on the manufacturing process and series volume, larger and more complex parts may become more cost effective when divided into several, later-joined sub-parts. However, for smaller and/or less complex shapes, an integral design solution is always the best choice.

  • 38.
    Mårtensson, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. Volvo Car Corporation, Sweden .
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Method for cost and weight-efficient material diversity and partitioning of a carbon fibre composite body structure2015In: Proceedings of the Institution of mechanical engineers. Part D, journal of automobile engineering, ISSN 0954-4070, E-ISSN 2041-2991Article in journal (Refereed)
    Abstract [en]

    A method for the early concept phase is proposed, which is aimed at limiting the financial and performance-related riskswhen designing a carbon fibre composite automotive body structure. The method manages the structural requirementsimposed on the complete body structure and analyses the suitability of different carbon fibre material systems and pro-cesses. It also studies whether a high level of material diversity is desirable and the way in which to identify the optimalpartition of the body structure from a material system and manufacturing process selection point of view. Furthermore,since composite materials include both laminated materials and quasi-isotropic materials, an approach is presented thatenables the comparison of these materials variants during conceptual material selection. A case study exemplifies themethod and the results show that, in spite of the cost-sensitive nature of the automotive industry, utilization of the max-imum performance of these expensive composite materials is more important than efforts to achieve a rapid manufac-turing process.

  • 39.
    Mårtensson, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    THE EFFECTS OF COST AND WEIGHT EFFICIENT STRUCTURAL DESIGN FOR MANUFACTURING OF COMPOSITE AUTOMOTIVE BODY STRUCTURES2015Conference paper (Refereed)
    Abstract [en]

    The automotive industry stands in front of a technology shift in order to adapt to future legislations on more energy efficient cars. Carbon fibre composites are by many seen as the only solution to succeed with this quest. Composite design and manufacturing methodologies need to be developed in order to reach a cost and weight effective design for high annual volumes. Potential advantages with composite materials, such as enabling manufacturing of highly integrated structures with complex geometries, i.e. integral designs, must be explored and questioned. In high series volumes, differential designs, i.e. structures divided with the intention of reducing the part complexity, seems to become more competitive.

    In this work the effect on financial and structural performance of differential and integral design solutions are addressed. Constraints on laminate and ply thickness as well as minimum ply cut area are considered and their impact on the weight optimisation evaluated. An automotive body structure section is studied and the weight and manufacturing cost is evaluated for both integral and differential design solutions. A cost model addressing both manufacturing and assembly processes are used together with finite element optimisation for the analysis. The results show that the weight efficiency for all design solutions is greatly reduced if the partitioning is made with of a clear focus. The results emphasise the importance of an efficient partitioning philosophy if the advantages of differential design are to be experienced to its fullest and to be able to create a manufacturing optimised design offering both cost and weight efficiency.

  • 40.
    Poulikidou, Sofia
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Jerpdal, Lars
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Björklund, Anna
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Akermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Environmental performance of self-reinforced composites in automotive applications - Case study on a heavy truck component2016In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 103, p. 321-329Article in journal (Refereed)
    Abstract [en]

    A screening environmental life cycle analysis (LCA) of the novel self-reinforced poly(ethylene therephthalate) (SrPET) is presented in this paper. A truck exterior panel is used as case study where a concept design made by SrPET is assessed and compared to a glass fibre reinforced composite and a thermoplastic blend that are currently used for the selected component. The results showed that the SrPET panel has 25% lower environmental impact compared to the current design, with no significant life cycle trade-offs. SrPET offers possibilities for weight reduction while maintaining good mechanical properties. As the impact during use phase is expected to decrease in the future the relative importance of manufacturing and end-of-life (EOL) will increase. Thus SrPET can be considered a competitive material for replacing existing energy intense non-recyclable composites.

  • 41.
    Rathanatavorn, Wallop
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Melander, Arne
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Welding Technology.
    Lindh-Ulmgren, Eva
    Swerea KIMAB.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Burman, Magnus
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. mburman@kth.se.
    Hybrid joining of alumnium to thermoplastics with friction stir welding2012In: Proceedings Swedish production  Symposium 2012, 2012Conference paper (Refereed)
  • 42.
    Schneider, Christof
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Kazemahvazi, Sohrab
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Compression and tensile properties of self-reinforced poly(ethylene terephthalate)-composites2013In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 32, no 2, p. 221-230Article in journal (Refereed)
    Abstract [en]

    Tensile and compression properties of self-reinforced poly(ethylene terephthalate) (SrPET) composites has been investigated. SrPET composites or all-polymer composites have improved mechanical properties compared to the bulk polymer but with maintained recyclability. In contrast to traditional carbon/glass fibre reinforced composites, SrPET composites are very ductile, resulting in high failure strains without softening or catastrophic failure. In tension, the SrPET composites behave linear elastically until the fibre-matrix interface fails, at which point the stiffness starts decreasing. As the material is further strained, strain hardening occurs and the specimen finally fails at a global strain above 10%. In compression, the composite initially fails through fibre yielding, and at higher strains through fibre bending. The stress-strain response is reminiscent of an elastic-perfectly plastic material with a high strain to failure (typically over 10%). This indicates that SrPET composites are not only candidates as semi-structural composites but also as highly efficient energy absorbing materials.

  • 43.
    Sjölander, Jens
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Hallander, P.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Forming induced wrinkling of composite laminates: A numerical study on wrinkling mechanisms2016In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 81, p. 41-51Article in journal (Refereed)
    Abstract [en]

    When manufacturing composite aircraft components consisting of uni-directional prepreg laminates, Hot Drape Forming (HDF) is sometimes used. One issue with HDF is that, in contrast to hand lay-up where normally only one ply is laid up at a time, multiple plies are formed together. This limits the in-plane deformability of the stack, thus increasing the risk of out-of-plane wrinkling during forming. In this paper mechanisms responsible for creating different types of wrinkles are explained. It is shown through simulations how the wrinkles are created as a result of interaction between two layers with specific fibre directions or due to compression of the entire stack. The simulations are compared to experimental results with good agreement.

  • 44.
    Sjölander, Jens
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Automatic forming of composite aircraft beams2012In: Swedish Production Symposium, 2012Conference paper (Refereed)
  • 45.
    Stig, Fredrik
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Tahir, Mohammad Waseem
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    An experimental study of the influence from fibre architecture on the permeability of 3D-woven textiles2015In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 34, no 17, p. 1444-1453Article in journal (Refereed)
    Abstract [en]

    In this work experimental measurements of the permeability of fully interlaced 3D-woven carbon fibre preforms are performed using the unsaturated parallel flow method. The effect on the permeability from three different parameters is studied by altering the architecture of woven preforms and varying mould sizes in a duct flow set-up. Influences from the geometrically different surface layers of the woven preforms, from fibre volume fraction and from warp yarn crimp are studied. The measurements show negligible influence on the permeability from crimp and the fraction of weave surface layers while the fibre volume fraction has a prominent influence. However, the effect is not consistent in terms of fibre volume fraction variation alone but depends on how it is varied.

  • 46.
    Tahir, Mohammad Waseem
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Effect of dual scale porosity on the overall permeability of fibrous structures2014In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 103, p. 56-62Article in journal (Refereed)
    Abstract [en]

    The effect of various parameters on the overall permeability of a two dimensional dual scale fibrous structure is studied employing computational fluid dynamics. The permeability of the structure is computed using two models; one resolved and one with homogenised porosity. The homogenised porous tow model is compared with the resolved model to the level of resolution the resolved model can provide at reasonable computational cost. Good agreement is found between the two numerical models. The porous homogenised tow model is then used to study the effect of inter-tow and intra-tow porosity on the overall permeability. It is shown that the effect of intra-tow porosity on the overall permeability is insignificant, while the inter-tow porosity on the other hand has a very strong influence on the overall permeability. Good correlation is also shown with results from previous experimental and numerical studies. For relatively low tow to filament radius ratios (R-t/R-f) there can be some influence from the intra-tow porosity on the overall permeability. However, it is negligible for higher ratios (R-t/R-f > 10(2)), i.e. in the regime where most fibre reinforcements for composite materials are found.

  • 47.
    Tahir, Mohammad Waseem
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Interlaminar fracture toughness of carbon/polyamide 12 compositesManuscript (preprint) (Other academic)
  • 48.
    Tahir, Mohammad Waseem
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Interlaminar strength and 3D reinforcement of Carbon-Polyamide 12 composite material2012In: ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite Materials, European Conference on Composite Materials, ECCM , 2012Conference paper (Refereed)
    Abstract [en]

    Thermoplastic composite materials have some advantages over thermoset resin based composites, such as fast processing, recyclability, reparability etc. In the present study commingled Carbon/Polyamide 12 (PA12) is analyzed as dry yarn and after heating the matrix fibers above the melting temperature and applying ambient pressure. The results are presented as micrographs. The mode I interlaminar fracture toughness of Carbon PA12 composite materials is measured, with and without introducing through-thickness yarns, and it is found to be very high even without 3D reinforcement. The consolidation time is also found to have great effect on the measured fracture toughness.

  • 49.
    Tahir, Mohammad Waseem
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Specimen size effects on the interlaminar shear strength of thermoplastic compositesManuscript (preprint) (Other academic)
  • 50.
    Tahir, Mohammad Waseem
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Stig, Fredrik
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    A numerical study of the influence from architecture on the permeability of 3D-woven fibre reinforcement2015In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 74, p. 18-25Article in journal (Refereed)
    Abstract [en]

    Various modelling aspects of the permeability of three-dimensional (3D) woven textile preforms are studied using computational fluid dynamics (CFD). The models are built using a recently developed technique able to generate close to authentic representations of 3D textile arrangements. One objective of the study is to investigate how parameters such as the tow architecture and the level of detail in the CFD models influence the results. A second objective is to investigate how the inter and intra-tow porosity affect the permeability. They are varied in a way that somewhat resembles how they would change during compaction, although compaction as such is not modelled. It is concluded that the intra-tow porosity has little effect on the overall permeability of a 3D-woven preform. Detailed modelling of local variation of the intra-tow porosity is thus redundant, which is also demonstrated. The inter-tow porosity, on the other hand, has a prominent influence on the overall permeability. The overall permeability is inherently anisotropic but when the inter-tow porosity is increased the permeability does not increase uniformly but becomes more isotropic. Good agreement is obtained between the numerical simulations and experiments performed in a parallel study.

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