Civil Engineering / İnşaat Mühendisliği

Permanent URI for this collectionhttps://hdl.handle.net/11147/13

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  • Conference Object
    Citation - WoS: 2
    Citation - Scopus: 3
    Micromechanical Modeling of Inter-Granular Localization, Damage and Fracture
    (Elsevier, 2018) Yalçınkaya, Tuncay; Özdemir, İzzet; Fırat, Ali Osman; Tandoğan, İzzet Tarık
    The recent developments in the production of miniaturized devices increases the demand on micro-components where the thickness ranges from tens to hundreds of microns. Various challenges, such as size effect and stress concentrations at the grain boundaries, arise due to the deformation heterogeneity observed at grain scale. Various metallic alloys, e.g. aluminum, exhibit substantial localization and stress concentration at the grain boundaries. In this regard, inter-granular damage evolution, crack initiation and propagation becomes an important failure mechanism at this length scale. Crystal plasticity approach captures intrinsically the heterogeneity developing due to grain orientation mismatch. However, the commonly used local versions do not possess a specific GB model and leads to jumps at the boundaries. Therefore, a more physical treatment of grain boundaries is needed. For this purpose, in this work, the Gurtin GB model (Gurtin (2008)) is incorporated into a strain gradient crystal plasticity framework (Yalcinkaya et al. (2011), Yalcinkaya et al. (2012), Yalcinkaya (2017)), where the intensity of the localization and stress concentration could be modelled considering the effect of grain boundary orientation, the mismatch and the strength of the GB. A zero thickness 12-node interface element for the integration of the grain boundary contribution and a 10-node coupled finite element for the bulk response are developed and implemented in Abaqus software as user element subroutines. 3D grain microstructure is created through Voronoi tessellation and the interface elements are automatically inserted between grains. After obtaining the localization, the mechanical behavior of the GB is modelled through incorporation of a potential based cohesive zone model (see Park et al. (2009), Cerrone et al. (2014)). The numerical examples present the performance of the developed tool for the intrinsic localization, crack initiation and propagation in micron-sized specimens. (C) 2018 The Authors. Published by Elsevier B.V.
  • Conference Object
    Citation - WoS: 1
    Citation - Scopus: 2
    Three Dimensional Grain Boundary Modeling in Polycrystalline Plasticity
    (American Institute of Physics, 2018) Yalçınkaya, Tuncay; Özdemir, İzzet; Fırat, Ali Osman
    At grain scale, polycrystalline materials develop heterogeneous plastic deformation fields, localizations and stress concentrations due to variation of grain orientations, geometries and defects. Development of inter-granular stresses due to misorientation are crucial for a range of grain boundary (GB) related failure mechanisms, such as stress corrosion cracking (SCC) and fatigue cracking. Local crystal plasticity finite element modelling of polycrystalline metals at micron scale results in stress jumps at the grain boundaries. Moreover, the concepts such as the transmission of dislocations between grains and strength of the grain boundaries are not included in the modelling. The higher order strain gradient crystal plasticity modelling approaches offer the possibility of defining grain boundary conditions. However, these conditions are mostly not dependent on misorientation of grains and can define only extreme cases. For a proper definition of grain boundary behavior in plasticity, a model for grain boundary behavior should be incorporated into the plasticity framework. In this context, a particular grain boundary model ([l]) is incorporated into a strain gradient crystal plasticity framework ([2]). In a 3-D setting, both bulk and grain boundary models are implemented as user-defined elements in Abaqus. The strain gradient crystal plasticity model works in the bulk elements and considers displacements and plastic slips as degree of freedoms. Interface elements model the plastic slip behavior, yet they do not possess any kind of mechanical cohesive behavior. The physical aspects of grain boundaries and the performance of the model are addressed through numerical examples.
  • Conference Object
    Citation - WoS: 1
    Citation - Scopus: 1
    Intrinsic and Statistical Size Effects in Microforming
    (American Institute of Physics, 2017) Yalçınkaya, Tuncay; Demirci, Aytekin; Simonovski, Igor; Özdemir, İzzet
    This paper analyzes the intrinsic (grain size dependent) and the statistical (grain number and orientation distribution dependent) size effects of micron level polycrystalline metallic specimens under plastic deformation through a strain gradient crystal plasticity framework. The macroscopic and local behavior of specimens from very limited number of grains to high number of grains are studied and the results are discussed in detail taking into account different boundary conditions.
  • Conference Object
    Citation - WoS: 1
    Citation - Scopus: 1
    Strain Gradient Polycrystal Plasticity for Micro-Forming
    (American Institute of Physics, 2016) Yalçınkaya, Tuncay; Simonovski, Igor; Özdemir, İzzet
    The developments in the micro-device industry has produced a substantial demand for the miniaturized metallic components with ultra-thin sheet materials that have thickness dimensions on the order of 50-500 μm which are produced through micro-forming processes. It is essential to have predictive tools to simulate the constitutive behavior of the materials at this length scale taking into account the physical and statistical size effect. Recent studies have shown that on the scale of several micrometers and below, crystalline materials behave differently from their bulk equivalent due to micro-structural effects (e.g. grain size, lattice defects and impurities), gradient effects (e.g. lattice curvature due to a non-uniform deformation field) and surface constraints (e.g. hard coatings or free interfaces). These effects could lead to stronger or weaker material response depending on the size and unique micro-structural features of the material. In this paper a plastic slip based strain gradient crystal plasticity model is used to address the effect of microstructural features (e.g. grain size, orientation and the number of grains) on the macroscopic constitutive response and the local behavior of polycrystalline materials.