Civil Engineering / İnşaat Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/13
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Article Citation - WoS: 1Citation - Scopus: 1A Magnetically Driven Elastic Rod Type Bi-Directional Swimmer at Stokes Flow(Springer, 2022) Özdemir, İzzetIn this paper, a flexible rod type micro-swimmer is proposed which achieves swimming direction reversal on the fly by forming a chiral helix-like geometry through external magnetic excitation. Furthermore an accompanying low Reynolds number flow-structure interaction analysis framework is developed which effectively combines a geometrically non-linear shear deformable beam model with regularized Stokeslet method in a monolithic implicit solution algorithm. This framework is used to investigate the basic characteristics of the proposed micro-swimmer in terms of dimensionless groups reflecting the interplay between different forces involved.Article Citation - WoS: 12Citation - Scopus: 16Misorientation and Grain Boundary Orientation Dependent Grain Boundary Response in Polycrystalline Plasticity(Springer, 2021) Yalçınkaya, Tuncay; Özdemir, İzzet; Tandoğan, İzzet TarıkThis 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: 3Citation - Scopus: 3Magnetically Driven Foldable Shell Type Swimmers at Stokes Flow(Springer, 2019) Özdemir, İzzetThis paper focuses on the interaction of low Reynolds number (Re) flows and thin shell type deformable structures in the context of flexible body locomotion and addresses the coupled field problem through a numerical solution framework. The thin structure is discretized by enhanced three-node finite elements and coupled with boundary element based treatment of Stokes flow in a monolithic manner. The locomotion is triggered and driven by an external magnetic field that generates displacement dependent body couples over the magnetically sensitive parts of the flexible structure. A particular novelty of the paper is the use of internal hinges through which very large rotations and structural deformations can be combined in an efficient way. Using this concept; new, on the fly locomotion direction reversal mechanisms can be generated as demonstrated by the foldable bi-directional swimmer.Book Part Citation - Scopus: 4Strain gradient crystal plasticity: Intergranularmicrostructure formation(Springer, 2019) Özdemir, İzzet; Yalçınkaya, TuncayThis chapter addresses the formation and evolution of inhomogeneous plastic deformation field between grains in polycrystalline metals by focusing on continuum scale modeling of dislocation-grain boundary interactions within a strain gradient crystal plasticity (SGCP) framework. Thermodynamically consistent extension of a particular strain gradient plasticity model, addressed previously (see also, e.g., Yalcinkaya et al, J Mech Phys Solids 59:1-17, 2011), is presented which incorporates the effect of grain boundaries on plastic slip evolution explicitly. Among various choices, a potential-type non-dissipative grain boundary description in terms of grain boundary Burgers tensor (see, e.g., Gurtin, J Mech Phys Solids 56:640-662, 2008) is preferred since this is the essential descriptor to capture both the misorientation and grain boundary orientation effects. 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. The capabilities of the framework is demonstrated through 3D bicrystal and polycrystal examples, and potential extensions and currently pursued multi-scale modeling efforts are briefly discussed in the closure. © Springer Nature Switzerland AG 2019. All rights reserved.