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  • 1. Ansari, F.
    et al.
    Sjöstedt, A.
    Larsson, Per Tomas
    RISE, Innventia.
    Berglund, L. A.
    Wågberg, L.
    Hierarchical wood cellulose fiber/epoxy biocomposites: Materials design of fiber porosity and nanostructure2015In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 74, p. 60-68Article in journal (Refereed)
    Abstract [en]

    Delignified chemical wood pulp fibers can be designed to have a controlled structure of cellulose fibril aggregates to serve as porous templates in biocomposites with unique properties. The potential of these fibers as reinforcement for an epoxy matrix (EP) was investigated in this work. Networks of porous wood fibers were impregnated with monomeric epoxy and cured. Microscopy images from ultramicrotomed cross sections and tensile fractured surfaces were used to study the distribution of matrix inside and around the fibers - at two different length scales. Mechanical characterization at different relative humidity showed much improved mechanical properties of biocomposites based on epoxy-impregnated fibers and they were rather insensitive to surrounding humidity. Furthermore, the mechanical properties of cellulose-fiber biocomposites were compared with those of cellulose-nanofibril (CNF) composites; strong similarities were found between the two materials. The reasons for this, some limitations and the role of specific surface area of the fiber are discussed.

  • 2.
    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.

  • 3.
    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.

  • 4.
    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.

  • 5.
    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.

  • 6.
    Gamstedt, E.K.
    et al.
    Royal Institute of Technology (KTH).
    Skrifvars, Mikael
    RISE, Swerea, Swerea SICOMP.
    Jacobsen, T.K.
    LM Glasfiber A/S.
    Pyrz, R.
    Aalborg University.
    Synthesis of unsaturated polyesters for improved interfacial strength in carbon fibre composites2002In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 33, no 9, p. 1239-1252Article in journal (Refereed)
    Abstract [en]

    Carbon fibres are gaining use as reinforcement in glass fibre/polyester composites for increased stiffness as a hybrid composite. The mechanics and chemistry of the carbon fibre-polyester interface should be addressed to achieve an improvement also in fatigue performance and off-axis strength. To make better use of the versatility of unsaturated polyesters in a carbon fibre composite, a set of unsaturated polyester resins have been synthesized with different ratios of maleic anhydride, o-phthalic anhydride and 1,2-propylene glycol as precursors. The effective interfacial strength was determined by micro-Raman spectroscopy of a single-fibre composite tested in tension. The interfacial shear strength with untreated carbon fibres increased with increasing degree of unsaturation of the polyester, which is controlled by the relative amount of maleic anhydride. This can be explained by a contribution of chemical bonding of the double bonds in the polymer to the functional groups of the carbon fibre surface. © 2002 Elsevier Science Ltd. All rights reserved.

  • 7.
    McElroy, Mark
    et al.
    NASA Langley Research Center, USA.
    Jackson, Wade
    NASA Langley Research Center, USA.
    Olsson, Robin
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Hellström, Peter
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Tsampas, Spyros
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Pankow, Mark
    North Carolina State University, USA.
    Interaction of delaminations and matrix cracks in a CFRP plate, Part I: A test method for model validation2017In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 103, p. 314-326Article in journal (Refereed)
    Abstract [en]

    Isolating and observing the damage mechanisms associated with low-velocity impact in composites using traditional experiments can be challenging, due to damage process complexity and high strain rates. In this work, a new test method is presented that provides a means to study, in detail, the interaction of common impact damage mechanisms, namely delamination, matrix cracking, and delamination-migration, in a context less challenging than a real impact event. Carbon fiber reinforced polymer specimens containing a thin insert in one region were loaded in a biaxial-bending state of deformation. As a result, three-dimensional damage processes, involving delaminations at no more than three different interfaces that interact with one another via transverse matrix cracks, were observed and documented using ultrasonic testing and X-ray computed tomography. The data generated by the test is intended for use in numerical model validation. Simulations of this test are included in Part II of this paper.

  • 8.
    Molker, Henrik
    et al.
    Volvo Car Corporation, Sweden; Chalmers University of Technology, Sweden.
    Gutkin, Renaud
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Asp, Leif E.
    Chalmers University of Technology, Sweden.
    Implementation of failure criteria for transverse failure of orthotropic Non-Crimp Fabric composite materials2017In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 92, p. 158-166Article in journal (Refereed)
    Abstract [en]

    In this paper a set of failure criteria for Non-Crimp Fabric (NCF) reinforced composites is implemented in a Finite Element (FE) software. The criteria, implemented at the ply level, predict transverse failure of NCF reinforced composites, in particular accounting for their inherent orthotropic properties. Numerical simulations are compared with tests on specimens with a generic design feature found in automotive structures. The current implementation enables correct prediction of failure mode and location.

  • 9.
    Nilsson, Greger
    et al.
    RISE, Swerea, Swerea SICOMP.
    Fernberg, S.P.
    Luleå University of Technology.
    Berglund, L.A.
    Luleå University of Technology.
    Strain field inhomogeneities and stiffness changes in GMT containing voids2002In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 33, no 1, p. 75-85Article in journal (Refereed)
    Abstract [en]

    During compression moulding of glass mat thermoplastics (GMT), voids may form. However, it is not clear whether voids are as critical to mechanical performance in GMT as in thermoset composites. The present investigation also considers the general problem of damage mechanisms in GMT. Conventional tensile tests, acoustic emission, a stiffness degradation test and a speckle technique for strain field measurements are used as well as optical microscopy of polished cross-sections. The void content (up to 5%) does not significantly influence the strength or stiffness degradation process. The reason is the large inhomogeneity of the strain fields in GMT. Failure occurs in locally soft regions and void effects are of secondary importance. Details of the failure process are discussed, emphasising the large local strains in matrix-rich regions. © 2001 Published by Elsevier Science Ltd.

  • 10.
    Nordlund, M.
    et al.
    Luleå University of Technology.
    Fernberg, Patrik
    RISE, Swerea, Swerea SICOMP.
    Lundström, T.S.
    Luleå University of Technology.
    Particle deposition mechanisms during processing of advanced composite materials2007In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 38, no 10, p. 2182-2193Article in journal (Refereed)
    Abstract [en]

    Liquid composite moulding of advanced composite materials often comprises infiltration of a particle-filled resin into a multi-scale porous fabric. These injections/infusions are subject to severe particle depositions inside the reinforcement, leading to undesired inhomogeneous mechanical and functional properties. Hence, the mechanisms for particle depositions are investigated by detailed meso-scale experiments, analysed by microscopic imaging and micro-particle image velocimetry, and macroscopic infusions of a biaxial non-crimp fabric. It is shown that two main particle deposition mechanisms are filtration during fibre bundle impregnation and filtration induced by stationary flow through fibre bundles. It is also clarified where in the reinforcement the particles will deposit. Finally, a number of suggestions on how to process advanced composite materials with a more homogeneous particle distribution are launched. © 2007 Elsevier Ltd. All rights reserved.

  • 11.
    Oldenbo, M.
    et al.
    Volvo Car Corporation.
    Fernberg, Patrik
    RISE, Swerea, Swerea SICOMP.
    Berglund, L.A.
    Royal Institute of Technology.
    Mechanical behaviour of SMC composites with toughening and low density additives2003In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 34, no 9, p. 875-885Article in journal (Refereed)
    Abstract [en]

    A new type of SMC material (Flex-SMC) developed for automotive exterior body panels has been investigated. Flex-SMC contains hollow glass micro-spheres and thermoplastic toughening additives. A conventional SMC (Std-SMC) was used as a reference material. Materials were tested in monotonic tension and compression. Stiffness degradation with strain as well as fracture toughness was determined. In situ SEM was used to study failure mechanisms. Flex-SMC has a density almost 20% lower than Std-SMC and has higher impact resistance. The damage threshold strain of the Flex-SMCs is higher than for Std-SMC. Flex-SMCs have more than twice the fracture toughness of Std-SMC. The major reason identified is that Flex-SMCs shows extensive fibre pullout. © 2003 Elsevier Ltd. All rights reserved.

  • 12. Prakobna, K
    et al.
    Berthold, Fredrik
    RISE, Innventia.
    Medina, L
    Berglund, L.A
    Mechanical performance and architecture of biocomposite honeycombs and foams from core-shell holocellulose nanofibers2016In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 88, p. 116-122Article in journal (Refereed)
    Abstract [en]

    CNFs (cellulose nanofibers) based on holocellulose have a pure cellulose fibril core, with a hemicellulose coating. The diameter is only around 6-8 nm and the hemicellulose surface coating has anionic charge. These CNFs are used to prepare honeycomb and foam structures by freeze-drying from dilute hydrocolloidal suspensions. The materials are compared with materials based on "conventional" cellulose CNFs from sulfite pulp with respect to mechanical properties in compression. Characterization methods include FE-SEM of cellular structure, and the analysis includes comparisons with similar materials from other types of CNFs and data in the literature. The honeycomb structures show superior out-of-plane properties compared with the more isotropic foam structures, as expected. Honeycombs based on holocellulose CNFs showed better properties than sulfite pulp CNF honeycombs, since the cellular structure contained less defects. This is related to better stability of holocellulose CNFs in colloidal suspension.

  • 13.
    Rouhi, Mohammad S.
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Wysocki, Maciej
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Larsson, Ragnar
    Experimental assessment of dual-scale resin flow-deformation in composites processing2015In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 76, p. 215-223Article in journal (Refereed)
    Abstract [en]

    In this paper we are concerned with the assessment of sub-models within a two-phase continuum mechanical FE framework for process modeling of composites manufacturing. In particular, the framework considers the inclusion of two deformation dependent models describing resin flow related to: (1) meso-scale wetting and compaction of individual plies and (2) overall preform deformation and macroscopic Darcian flow. Using micro-mechanical modeling, we model the physics of these sub-processes in relation to the recently developed Out-Of-Autoclave (OOA) prepergs. The models are placed in context with a compression–relaxation experiment, employed to study the preform deformations considered separated from other sub-processes. Finally, calibrations and model validations are carried out against the relaxation experiment to relate the FE framework to the mechanical response of the preform. Therefore, using the above experiment, parameter values out of the literature and those estimated from micrographs gave a fair agreement between the simulation and experiments.

  • 14.
    Rouhi, Mohammad S.
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Wysocki, Maciej
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Larsson, Ragnar
    Modeling of coupled dual-scale flow–deformation processes in composites manufacturing2013In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 46, p. 108-116Article in journal (Refereed)
    Abstract [en]

    The present contribution is a part of the work towards a framework for holistic modeling of composites manufacturing. Here we focus our attention onto the particular problem of coupled dual-scale deformation–flow process such as the one arising in RTM, Vacuum Assisted Resin Infusion (VARI) and Vacuum Bag Only (VBO) prepregs. The formulation considers coupling effects between macro-scale preform processes and meso-scale ply processes as well as coupling effects between the solid and fluid phases. The framework comprises a nonlinear compressible fiber network saturated with incompressible fluid phase. Internal variables are introduced in terms of solid compressibility to describe the irreversible mesoscopic infiltration and reversible preform compaction processes. As a main result a coupled displacement–pressure, geometrically nonlinear, finite element simulation tool is developed. The paper is concluded with a numerical example, where a relaxation–compression test of a planar fluid filled VBO preform at globally un-drained and partly drained conditions is considered.

  • 15.
    Rouhi, Mohammad
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Wysocki, Maciej
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Larsson, R.
    Chalmers University of Technology.
    Modeling of coupled dual-scale flow-deformation processes in composites manufacturing2013In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 46, no 1, p. 108-116Article in journal (Refereed)
    Abstract [en]

    The present contribution is a part of the work towards a framework for holistic modeling of composites manufacturing. Here we focus our attention onto the particular problem of coupled dual-scale deformation-flow process such as the one arising in RTM, Vacuum Assisted Resin Infusion (VARI) and Vacuum Bag Only (VBO) prepregs. The formulation considers coupling effects between macro-scale preform processes and meso-scale ply processes as well as coupling effects between the solid and fluid phases. The framework comprises a nonlinear compressible fiber network saturated with incompressible fluid phase. Internal variables are introduced in terms of solid compressibility to describe the irreversible mesoscopic infiltration and reversible preform compaction processes. As a main result a coupled displacement-pressure, geometrically nonlinear, finite element simulation tool is developed. The paper is concluded with a numerical example, where a relaxation-compression test of a planar fluid filled VBO preform at globally un-drained and partly drained conditions is considered. © 2012 Elsevier B.V. All rights reserved.

  • 16.
    Svanberg, Magnus
    et al.
    RISE, Swerea, Swerea SICOMP.
    Holmberg, Anders
    RISE, Swerea, Swerea SICOMP.
    An experimental investigation on mechanisms for manufacturing induced shape distortions in homogeneous and balanced laminates2001In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 32, no 6, p. 827-838Article in journal (Refereed)
    Abstract [en]

    Manufacturing induced shape distortions is a common problem for composite manufacturers. For single curved geometries the phenomenon is known as spring-in. Today a lot of effort is spent to develop modelling tools for prediction of spring-in and shape distortions in general. However, good experimental data is rare in the literature and there are no established constitutive models capable of account for the effect from different cure schedules. In this paper, experimental data for spring-in of glass-fibre epoxy composites are presented. The experiments were performed with angle brackets manufactured by RTM, in a steel mould with accurate temperature control. Different in-mould temperature have been used to point out and separate different mechanisms responsible for spring-in. © 2001 Elsevier Science Ltd.

  • 17.
    Svanberg, Magnus
    et al.
    RISE, Swerea, Swerea SICOMP.
    Holmberg, Anders
    RISE, Swerea, Swerea SICOMP.
    Prediction of shape distortions Part I. FE-implementation of a path dependent constitutive model2004In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 35, no 6, p. 711-721Article in journal (Refereed)
    Abstract [en]

    There is a great interest, especially from the aircraft industry, to increase the ability to understand and predict development of shape distortions and residual stresses during manufacture of polymer composite components. An increased ability to predict shape distortions will result in more cost efficient development, improved performance and optimised manufacturing of composites. To be able to predict residual stresses and shape distortions a model is needed that accounts for all important mechanisms involved. In a previous work by the authors, it was demonstrated that such - models must account for thermal expansion (different in glassy and rubbery state), chemical shrinkage due to the crosslinking reaction and finally frozen-in deformations. The present paper presents a simple mechanical constitutive model that accounts for the mechanisms mentioned above. The model is a limiting case of linear visco-elasticity that permits us to replace the rate dependence by a path dependence on the state variables: strain, degree of cure and temperature. This means significant savings in computational time, memory requirements and costs for material characterisation as compared to conventional visco-elastic models. This is the first of two papers, the second paper deals with experimental validation and analysis of mechanical boundary conditions during prediction of shape distortion. © 2004 Elsevier Ltd. All rights reserved.

  • 18.
    Svanberg, Magnus
    et al.
    RISE, Swerea, Swerea SICOMP.
    Holmberg, Anders
    RISE, Swerea, Swerea SICOMP.
    Prediction of shape distortions. Part II. Experimental validation and analysis of boundary conditions2004In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 35, no 6, p. 723-734Article in journal (Refereed)
    Abstract [en]

    During cure of thermoset composite structures residual stresses and/or shape distortions are always present. Residual stresses can cause apparent strength reduction or failure, even prior demoulding, respectively, shape distortions can deform a component so that the component becomes useless. For this reason a lot of effort has been spent to develop simulation tools to be able to foresee problems related to residual stresses and/or shape distortions and make the first part right. In a companion paper a process model for shape distortion predictions was developed and implemented into ABAQUS. In the present paper the model is validated for a material and cure schedule typical for RTM and autoclave processes. Comparisons between predicted and experimental shape distortion shows that the model and simulation approach used capture both effects from different cure schedules as well as the mechanical interaction between composite and tooling during in-mould cure. The results show that changing the mechanical boundary conditions significantly affects the shape distortion prediction. Therefore accurate modelling of the composite-tooling interaction is an important part of a shape distortion analysis. © 2004 Elsevier Ltd. All rights reserved.

  • 19.
    Trey, Stacy
    et al.
    SP- Sveriges Tekniska Forskningsinstitut, Trätek.
    Gamstedt, E. Kristofer
    Mäder, Edith
    Jönsson, Sonny
    Johansson, Mats
    Glass fiber reinforced high glass transition temperature thiol–ene networks2011In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 42, no 11, p. 1800-1808Article in journal (Refereed)
  • 20.
    Wilhelmsson, D
    et al.
    Chalmers University of Technology, Sweden.
    Gutkin, Renaud
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Edgren, F
    GKN Aerospace Sweden AB, Sweden.
    Asp, L E
    Chalmers University of Technology, Sweden.
    An experimental study of fibre waviness and its effects on compressive properties of unidirectional NCF composites2018In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 107, p. 665-674Article in journal (Refereed)
    Abstract [en]

    In this paper a comprehensive experimental study on effects of different fibre waviness characteristics on the compressive properties of unidirectional non-crimp fabrics (NCF) composites is presented. The fibre waviness ranges from periodic to random with medium to large misalignment angles. As expected, fibre waviness is found to strongly impair the compressive mechanical properties of the composite. It is demonstrated that the maximum fibre misalignment alone can be used to accurately predict strength with analytical kinking criteria. Furthermore, there is a direct correlation between waviness and a knock-down factor on stiffness with approximately 5%/degree mean fibre misalignment angle. Analysis of the extension of the misaligned regions (defects) provides additional evidence that defect extension in the transverse direction is more critical than in the longitudinal direction, supporting earlier theoretical predictions in the open literature.

  • 21.
    Wysocki, Maciej
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Toll, S.
    KTH Royal Institute of Technology.
    Larsson, R.
    Chalmers University of Technology.
    Asp, Leif
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP.
    Anisotropic and tension-compression asymmetric model for composites consolidation2010In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 41, no 2, p. 284-294Article in journal (Refereed)
    Abstract [en]

    A constitutive model for anisotropic and tension-compression asymmetric response of a fibrous preform is developed and solved using a FE software. Applicability of the method to complex geometries is demonstrated by analysis the consolidation of an axisymmetric filament wound pressure vessel made from commingled yarns. Three different winding patterns are considered. In conclusions, the consolidation of the whole vessel, except at the opening, is prevented by the loading mode, where the pressure is applied on the interior. To succeed in manufacturing of this type of pressure vessel, use of an oversized preform that allows extension in the fibre direction is suggested. © 2009 Elsevier Ltd. All rights reserved.

  • 22.
    Zhuang, Linqi
    et al.
    Texas A&M University, USA; Luleå University of Technology, Sweden.
    Pupurs, Andrejs
    RISE - Research Institutes of Sweden, Swerea, Swerea SICOMP. Luleå University of Technology, Sweden.
    Varna, Janis
    Luleå University of Technology, Sweden.
    Talreja, Ramesh
    Texas A&M University, USA ; Luleå University of Technology, Sweden.
    Ayadi, Zoubir
    University of Lorraine, France.
    Effects of inter-fiber spacing on fiber-matrix debond crack growth in unidirectional composites under transverse loading2018In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 109, p. 463-471Article in journal (Refereed)
    Abstract [en]

    The energy release rate (ERR) of a fiber–matrix debond crack in a unidirectional composite subjected to transverse tension is studied numerically. The focus of the study is the effect of the proximity of the neighboring fibers on the ERR. For this, a hexagonal pattern of fibers in the composite cross-section is considered. Assuming one fiber to be debonded at certain initial debond arc-length, the effect of the closeness of the surrounding six fibers on the ERR of the crack is studied with the inter-fiber distance as a parameter. Using an embedded cell consisting of discrete fibers in a matrix surrounded by the homogenized composite, a finite element model and the virtual crack closure technique are used to calculate the ERR. Results show that the presence of the local fiber cluster accelerates the crack growth up to a certain initial crack angle, beyond which the opposite effect occurs. It is also found that the residual stress due to thermal cooldown reduces the ERR. However, the thermal cooldown is found to enhance the debond growth in plies within a cross-ply laminate.

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