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  • 1.
    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.

  • 2.
    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.

  • 3.
    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.

  • 4.
    Hedlund, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Doktorand, Uppsala Universitet.
    Kamf, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Gamstedt, Kristoffer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Fast Optimization Methodology for Press-fitted Composite Hollow Cylinder Flywheel Energy StorageIn: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085Article in journal (Refereed)
    Abstract [en]

    An optimization strategy for a hollow flywheel energy storage is presented. Several press-fitted shells of anisotropic materials (such as carbon composites) are studied by an analytical model based on a plane stress assumption. The optimization target is stored energy. The optimizer constraints (which were evaluated at full and zero charge level, respectively) were based on strain-based models for fatigue life of composites, and stress-based fatigue life models for high-strength aluminum. A compiled library was built within the scope of this work, and used to run a robust global grid-search optimizing method. The analytical model was compared against a finite element method solution, and the (single-core) library was seen to be at least 5 orders of magnitude faster. 

  • 5.
    Hernandez-Perez, Adrian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Hagglund, R.
    Carlsson, L. A.
    Aviles, F.
    Analysis of twist stiffness of single and double-wall corrugated boards2014In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 110, p. 7-15Article in journal (Refereed)
    Abstract [en]

    The twist stiffness of single and double-wall corrugated board is analyzed using first order shear deformation (FOSD) theory. Results are compared to finite element analysis (FEA) and dynamic test data for a large range of torsion loaded rectangular board specimens. The FOSD approach and FEA employ a homogenized core. In addition, a structural finite element model was developed where the web core is represented by shell elements. According to FOSD analysis, the twist stiffness is linearly dependent on the transverse shear moduli of the web core along both principal directions of the core. Good agreement between the torsional stiffness predictions by analytical and numerical approaches and test results is found for the range of single and double-wall boards examined. The FOSD solution is significantly less computationally demanding than FEA, and appears viable for prediction of the twist stiffness of corrugated board.

  • 6.
    Isaksson, Per
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Carlsson, L. A.
    Florida Atlantic Univ, Dept Mech Engn, Boca Raton, FL 33431 USA..
    Analysis of the out-of-plane compression and shear response of paper-based web-core sandwiches subject to large deformation2017In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 159, p. 96-109Article in journal (Refereed)
    Abstract [en]

    The mechanical response of three different structural core sandwich panels in out-of-plane compression and shear has been analyzed. Specific core shapes examined are arc-tangent, wavy trapezoidal and hemispherical. Unit cells consisting of representative elements of the core attached to face sheets were selected for analysis. Both face sheets and core were assumed made from paper. Finite element analysis employing large deformation and rotations and orthotropic elastic-plastic behavior was used. The results show that the arc-tangent and trapezoidal cores are prone to collapse by extensive bending and buckling, whereas the hemispherical core behaved more stably in compression and shear. Core sheets with a hemispherical shape were prepared from copy paper sheets in a specially designed forming machine. Sandwich test specimens were prepared from this core and tested in out-of-plane compression, and the load-displacement response was compared to predictions from finite element simulations. The experimental and finite element results were consistent.

1 - 6 of 6
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