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  • 1.
    Espadas Escalante, Juan José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics. Uppsala University.
    On numerical analyses of woven composite laminates: Homogenization, damage and fracture2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This dissertation analyzes various mechanical properties of textile reinforced composite laminates.

    The dissertation is based on a total of six published works, which are essentially numerical, although experimental elements are available. The numerical methods used are based on high-resolution finite element models in combination with sophisticated phase-field theories for brittle fracture. A key result is that important mechanical properties in engineering applications, such as fracture or damage resistance, can be substantially affected by the arrangement of the constituent materials at the meso level.

    List of papers
    1. A phase-field model for strength and fracture analyses of fiber-reinforced composites
    Open this publication in new window or tab >>A phase-field model for strength and fracture analyses of fiber-reinforced composites
    2019 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 174, p. 58-67Article in journal (Refereed) Published
    Abstract [en]

    A phase-field model for brittle fracture is proposed and evaluated for strength and fracture analyses of composites. In addition to the elastic properties, this approach makes use of only the fracture toughness and the strength of the material. The capability of the method is shown in analyses of composites at two scales. In laminates, strengths of notched laminates are estimated, including hole size effects. In a lamina, cracks developed in both transverse tension and compression are analyzed and compared to other numerical methods in the literature. The effects of a spectral and a hydrostatic-deviatoric decomposition of the strain energy density, two variants often used in phase-field formulations, are studied. It is shown that the choice of the decomposition affects the fracture development. Results are compared to experiments and simulations in the literature showing the capabilities of the phase-field approach.

    Place, publisher, year, edition, pages
    Elsevier, 2019
    Keywords
    Computational mechanics, Strength, Fracture, Finite element analysis (FEA)
    National Category
    Composite Science and Engineering
    Identifiers
    urn:nbn:se:uu:diva-368254 (URN)10.1016/j.compscitech.2018.10.031 (DOI)000469407500008 ()
    Available from: 2018-12-03 Created: 2018-12-03 Last updated: 2019-07-05Bibliographically approved
    2. A study on the influence of boundary conditions in computational homogenization of periodic structures with application to woven composites
    Open this publication in new window or tab >>A study on the influence of boundary conditions in computational homogenization of periodic structures with application to woven composites
    2017 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 160, p. 529-537Article in journal (Refereed) Published
    Abstract [en]

    The influence of boundary conditions (BCs) in the estimation of elastic properties of periodic structures is investigated using computational homogenization with special focus on planar structures. Uniform displacement, uniform traction, periodic, in-plane periodic and a proposed mix of periodic and traction BCs are used. First, the effect of the BCs is demonstrated in structures with one-, two- and three-dimensional periodicity. Mixed BCs are shown to most accurately represent the behavior of layered structures with a small number of repeating unit cells. Then, BCs are imposed on a twill woven composite architecture. Special attention is devoted to investigate the sensitivity of the estimated properties with respect to the BCs and to show differences when considering a single lamina or a laminate. High sensitivity of the in-plane extensional modulus and Poisson's ratio with respect to the type of BCs is found. Moreover, it is shown that the mix of BCs and in-plane periodic BCs are capable to represent an experimental strain field.

    Keywords
    Computational homogenization, Mixed boundary conditions, Heterogeneous structures, Elastic properties, Woven composites, Finite element method
    National Category
    Composite Science and Engineering
    Identifiers
    urn:nbn:se:uu:diva-359307 (URN)10.1016/j.compstruct.2016.10.082 (DOI)000390470300044 ()
    Available from: 2018-08-31 Created: 2018-08-31 Last updated: 2019-07-05Bibliographically approved
    3. The effect of free-edges and layer shifting on intralaminar and interlaminar stresses in woven composites
    Open this publication in new window or tab >>The effect of free-edges and layer shifting on intralaminar and interlaminar stresses in woven composites
    2018 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 185, p. 212-220Article in journal (Refereed) Published
    Abstract [en]

    The free-edge effects and relative layer shifting in the interlaminar and intralaminar stresses of plain woven composite laminates under uniaxial extension is investigated numerically using a finite element approach. A computational framework of the free-edge problem for periodic structures with finite width is applied to woven laminates. First, two-layered laminates with three different shifting configurations are studied considering repeating unit cells simulating finite and infinite width. For each configuration, two different widths are considered by trimming the model at different locations in order to investigate different free-edge effects. Then, two four-layered laminates with no shifting and a maximum shifting configuration are analyzed to illustrate the effect of neighboring layers in the stresses. For each shifting configuration, different delamination mechanisms are expected. When considering more layers, it is found that the stacking configuration affects the state of stress and the free-edge effects depending on the shifting. In general, a different behavior than that of unidirectional tape laminates is found, since the interlaminar and intralaminar stresses can be higher than those generated at the free-edges. Particularly, for the maximum shifting configuration results are in agreement with experimental results in the literature where no debonding between yarns was observed at the free-edges.

    Keywords
    Woven composites, Finite element method, Intralaminar stresses, Interlaminar stresses, Free-edge effects, Multiscale modeling
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:uu:diva-341485 (URN)10.1016/j.compstruct.2017.11.014 (DOI)000418961000018 ()
    Available from: 2018-02-28 Created: 2018-02-28 Last updated: 2019-07-05Bibliographically approved
    4. A study of induced delamination and failure in woven composite laminates subject to short-beam shear testing
    Open this publication in new window or tab >>A study of induced delamination and failure in woven composite laminates subject to short-beam shear testing
    2019 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 205, p. 359-369Article in journal (Refereed) Published
    Abstract [en]

    Failure in woven composite laminates subject to global shear load is studied. Laminates are manufactured, tested and analyzed using X-ray computed tomography, scanning electron microscopy and finite element models. It is found that the stress distribution along the thickness direction is dependent on the layer shifting that alters different yarn interactions, which in turn, affects delamination and failure onset A suggested failure mechanism is in agreement with experimental observations.

    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:uu:diva-368250 (URN)10.1016/j.engfracmech.2018.10.015 (DOI)000453766000026 ()
    Available from: 2018-12-03 Created: 2018-12-03 Last updated: 2019-07-05Bibliographically approved
    5. Analysis of the Influence of Layer Shifting on the Elastic Response and Damage Nucleation and Growth in Woven Composite Laminates
    Open this publication in new window or tab >>Analysis of the Influence of Layer Shifting on the Elastic Response and Damage Nucleation and Growth in Woven Composite Laminates
    2018 (English)In: NASA Technical MemorandumsArticle in journal (Refereed) Published
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-368253 (URN)
    Available from: 2018-12-03 Created: 2018-12-03 Last updated: 2019-07-05
    6. Mesoscale analysis of the transverse cracking kinetics in woven composite laminates using a phase-field fracture theory
    Open this publication in new window or tab >>Mesoscale analysis of the transverse cracking kinetics in woven composite laminates using a phase-field fracture theory
    2019 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 216, article id 106523Article in journal (Refereed) Published
    Abstract [en]

    A phase-field approach to fracture is used to simulate transverse cracking kinetics in composite laminates. First, a typical unidirectional tape laminate is modeled and the transverse cracking evolution with the consequent reduction in the in-plane modulus of elasticity is estimated. Then, a four-layered plain weave composite is modeled using different layer shifting configurations. Predictions in the transverse cracking evolution become improved as the shifting configuration of the laminate model become closer to experimental observations. Simulations predict that some cracks do not form perpendicularly to the loading direction, as it has been observed experimentally in similar locations. Only the fracture toughness and the in situ transverse strength of the ply are required without prior knowledge of the position of the cracks or an ad hoc criterion for crack evolution. All the simulations are compared qualitatively and quantitatively to experiments published elsewhere.

    Keywords
    Composites, Fibre reinforced materials, Fracture mechanics, Damage mechanics, Crack growth
    National Category
    Applied Mechanics
    Research subject
    Engineering science with specialization in Applied Mechanics
    Identifiers
    urn:nbn:se:uu:diva-388533 (URN)10.1016/j.engfracmech.2019.106523 (DOI)000477573000028 ()
    Available from: 2019-07-01 Created: 2019-07-01 Last updated: 2019-09-20Bibliographically approved
  • 2.
    Espadas-Escalante, Juan José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Bednarcyk, Brett A.
    NASA, Glenn Res Ctr, Cleveland, OH 44135 USA.
    Pineda, Evan J.
    NASA, Glenn Res Ctr, Cleveland, OH 44135 USA.
    Isaksson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Modeling the influence of layer shifting on the properties and nonlinear response of woven composites subject to continuum damage2019In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 220, p. 539-549Article in journal (Refereed)
    Abstract [en]

    The influence of relative layer shifting on the elastic and damage response of plain weave composite laminates is analyzed using a continuum damage mechanics approach in combination with the finite element method. First, the homogenized properties of the woven composite as a function of the number of layers and of layer shifting are presented. Next, the damage development in various shifting configurations is studied using different damage constitutive models for the matrix and the fiber bundles. It is shown that the impact of layer shifting on both the elastic response and the nonlinear damage response is significant. Most notably, the model captures changes in the damage mechanisms within the woven composite that occur due to layer shifting, resulting in stiffer, more brittle behavior, which has been shown experimentally in the literature. Model results in the linear and nonlinear regimes are shown to be consistent with both an independent analytical model and reported experiments.

  • 3.
    Espadas-Escalante, Juan José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Isaksson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    A study of induced delamination and failure in woven composite laminates subject to short-beam shear testing2019In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 205, p. 359-369Article in journal (Refereed)
    Abstract [en]

    Failure in woven composite laminates subject to global shear load is studied. Laminates are manufactured, tested and analyzed using X-ray computed tomography, scanning electron microscopy and finite element models. It is found that the stress distribution along the thickness direction is dependent on the layer shifting that alters different yarn interactions, which in turn, affects delamination and failure onset A suggested failure mechanism is in agreement with experimental observations.

  • 4.
    Espadas-Escalante, Juan José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Isaksson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Mesoscale analysis of the transverse cracking kinetics in woven composite laminates using a phase-field fracture theory2019In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 216, article id 106523Article in journal (Refereed)
    Abstract [en]

    A phase-field approach to fracture is used to simulate transverse cracking kinetics in composite laminates. First, a typical unidirectional tape laminate is modeled and the transverse cracking evolution with the consequent reduction in the in-plane modulus of elasticity is estimated. Then, a four-layered plain weave composite is modeled using different layer shifting configurations. Predictions in the transverse cracking evolution become improved as the shifting configuration of the laminate model become closer to experimental observations. Simulations predict that some cracks do not form perpendicularly to the loading direction, as it has been observed experimentally in similar locations. Only the fracture toughness and the in situ transverse strength of the ply are required without prior knowledge of the position of the cracks or an ad hoc criterion for crack evolution. All the simulations are compared qualitatively and quantitatively to experiments published elsewhere.

  • 5.
    Espadas-Escalante, Juan José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    van Dijk, Nico P.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Isaksson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    A phase-field model for strength and fracture analyses of fiber-reinforced composites2019In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 174, p. 58-67Article in journal (Refereed)
    Abstract [en]

    A phase-field model for brittle fracture is proposed and evaluated for strength and fracture analyses of composites. In addition to the elastic properties, this approach makes use of only the fracture toughness and the strength of the material. The capability of the method is shown in analyses of composites at two scales. In laminates, strengths of notched laminates are estimated, including hole size effects. In a lamina, cracks developed in both transverse tension and compression are analyzed and compared to other numerical methods in the literature. The effects of a spectral and a hydrostatic-deviatoric decomposition of the strain energy density, two variants often used in phase-field formulations, are studied. It is shown that the choice of the decomposition affects the fracture development. Results are compared to experiments and simulations in the literature showing the capabilities of the phase-field approach.

  • 6.
    Espadas-Escalante, Juan José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    van Dijk, Nico P.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Isaksson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    A study on the influence of boundary conditions in computational homogenization of periodic structures with application to woven composites2017In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 160, p. 529-537Article in journal (Refereed)
    Abstract [en]

    The influence of boundary conditions (BCs) in the estimation of elastic properties of periodic structures is investigated using computational homogenization with special focus on planar structures. Uniform displacement, uniform traction, periodic, in-plane periodic and a proposed mix of periodic and traction BCs are used. First, the effect of the BCs is demonstrated in structures with one-, two- and three-dimensional periodicity. Mixed BCs are shown to most accurately represent the behavior of layered structures with a small number of repeating unit cells. Then, BCs are imposed on a twill woven composite architecture. Special attention is devoted to investigate the sensitivity of the estimated properties with respect to the BCs and to show differences when considering a single lamina or a laminate. High sensitivity of the in-plane extensional modulus and Poisson's ratio with respect to the type of BCs is found. Moreover, it is shown that the mix of BCs and in-plane periodic BCs are capable to represent an experimental strain field.

  • 7.
    Espadas-Escalante, Juan José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    van Dijk, Nico P.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics, Byggteknik.
    Isaksson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    The effect of free-edges and layer shifting on intralaminar and interlaminar stresses in woven composites2018In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 185, p. 212-220Article in journal (Refereed)
    Abstract [en]

    The free-edge effects and relative layer shifting in the interlaminar and intralaminar stresses of plain woven composite laminates under uniaxial extension is investigated numerically using a finite element approach. A computational framework of the free-edge problem for periodic structures with finite width is applied to woven laminates. First, two-layered laminates with three different shifting configurations are studied considering repeating unit cells simulating finite and infinite width. For each configuration, two different widths are considered by trimming the model at different locations in order to investigate different free-edge effects. Then, two four-layered laminates with no shifting and a maximum shifting configuration are analyzed to illustrate the effect of neighboring layers in the stresses. For each shifting configuration, different delamination mechanisms are expected. When considering more layers, it is found that the stacking configuration affects the state of stress and the free-edge effects depending on the shifting. In general, a different behavior than that of unidirectional tape laminates is found, since the interlaminar and intralaminar stresses can be higher than those generated at the free-edges. Particularly, for the maximum shifting configuration results are in agreement with experimental results in the literature where no debonding between yarns was observed at the free-edges.

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