Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7148

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  • Article
    Homogenization of 3d Laminated Micro-Structures Including Bending Effects
    (Pergamon-elsevier Science Ltd, 2024) Oezdemir, Izzet
    In this paper, a homogenization method which captures intrinsic size effect associated with fiber diameter is revisited and adapted for three-dimensional laminated micro -structures. Based on a unit-cell composed of matrix and reinforcement layers, enhanced deformation gradients varying through the thickness, are introduced with the aid of an additional kinematic variable reflecting the difference between the homogenized and constituent level deformation gradients. In the current work, as opposed to the original formulation, higher order terms are preserved for both phases and therefore bending stiffness of the matrix phase can be taken into account as well. The formulation is implemented within the commercial finite element solver Abaqus through user element (UEL) subroutine considering a finite strain hyperelastic response for the reinforcement layers and a von Mises type hyper-elastoplastic one for the matrix phase. Explicitly discretized unit-cells with varying reinforcement phase fraction, layer inclination angle and layer thicknesses are used as references to assess the predictive capabilities of the homogenized model and the significance of bending stiffness of the phases. Similarly, explicitly discretized model of a beam type structure with a crossed lamellar micro -structure is used to evaluate the performance of the homogenized model under more general, non-periodic boundary conditions. The findings of both cases support the effectiveness of the homogenized model.
  • Article
    Citation - WoS: 12
    Citation - Scopus: 16
    Misorientation and Grain Boundary Orientation Dependent Grain Boundary Response in Polycrystalline Plasticity
    (Springer, 2021) Yalçınkaya, Tuncay; Özdemir, İzzet; Tandoğan, İzzet Tarık
    This paper studies the evolution of intergranular localization and stress concentration in three dimensional micron sized specimens through the Gurtin grain boundary model (J Mech Phys Solids 56:640-662, 2008) incorporated into a three dimensional higher-order strain gradient crystal plasticity framework (Yalcinkaya et al. in Int J Solids Struct 49:2625-2636, 2012). The study addresses continuum scale dislocation-grain boundary interactions where the effect of crystal orientation mismatch and grain boundary orientation are taken into account through the grain boundary model in polycrystalline metallic specimens. Due to the higher-order nature of the model, a mixed finite element formulation is used to discretize the problem in which both displacements and plastic slips are considered as primary variables. For the treatment of grain boundaries within the solution algorithm, an interface element is formulated and implemented together with the bulk plasticity model. The capabilities of the framework is demonstrated through 3D polycrystalline examples considering grain boundary conditions, grain boundary strength, the orientation distribution and the specimen size. A detailed grain boundary condition and stress concentration analysis is presented. The advantages and the disadvantages of the model is discussed in detail through numerical examples.
  • Article
    Citation - WoS: 32
    Citation - Scopus: 37
    Void Growth Based Inter-Granular Ductile Fracture in Strain Gradient Polycrystalline Plasticity
    (Elsevier, 2021) Yalçınkaya, Tuncay; Tandoğan, İzzet Tarık; Özdemir, İzzet
    The precipitation hardened, high strength aerospace alloys (e.g. Al 7000 alloy series) suffer from loss of fracture toughness due to the heat treatment leading to intergranular ductile fracture. Depending on the quenching and aging processes, large precipitates at the grain boundaries with wide precipitate free zones might develop. Therefore the grain boundaries constitute a potential location for micro void formation and evolution under the effect of external loads. This is a common problem of such materials where there is considerable ductile intergranular fracture, which is normally attributed to the embrittlement effects of the environment in other type of alloys. In this context, for the modeling of such a degradation process, the current paper develops a physics based intergranular cracking model of polycrystalline materials where a strain gradient crystal plasticity model is combined with cohesive zone elements whose traction separation relation is based on the evolution of micro-voids at the grain boundaries. The framework successfully predicts the intergranular crack formation and propagation, taking into account different microstructural features, such as porosity, pore shape, grain orientation distribution, and grain boundary conditions.