Browsing by Author "Ozdemir, Izzet"

Now showing 1 - 4 of 4

Citation - WoS: 9
Citation - Scopus: 11
Grain Statistics Induced Size Effect in the Expansion of Metallic Micro Rings
(Pergamon-elsevier Science Ltd, 2014) Ozdemir, Izzet
This study focuses on the expansion of metallic micro rings under internal pressure using a grain level three dimensional finite element analysis in combination with a rate dependent crystal plasticity constitutive model. The size effect due to grain statistics such as grain orientations and number of grains through the thickness is investigated to a certain depth, in terms of final geometries and the scatter involved. The findings of the study could be used as the preliminary guidelines for suitable material selection in stretching dominated microforming operations. (C) 2014 Elsevier Ltd. All rights reserved.
Citation - WoS: 31
Citation - Scopus: 34
Modeling of dislocation-grain boundary interactions in a strain gradient crystal plasticity framework
(Springer, 2014) Ozdemir, Izzet; Yalcinkaya, Tuncay
This paper focuses on the continuum scale modeling of dislocation-grain boundary interactions and enriches a particular strain gradient crystal plasticity formulation (convex counter-part of Yal double dagger inkaya et al., J Mech Phys Solids 59:1-17, 2011; Int J Solids Struct 49:2625-2636, 2012) by incorporating explicitly the effect of grain boundaries on the plastic slip evolution. Within the framework of continuum thermodynamics, a consistent extension of the model is presented and 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 proposed. A fully coupled finite element solution algorithm is built-up in which both the displacement and plastic slips are considered as primary variables. For the treatment of grain boundaries within the solution algorithm, an interface element is formulated. The proposed formulation is capable of capturing the effect of misorientation of neighboring grains and the orientation of the grain boundaries on slip evolution in a natural way, as demonstrated by bicrystal specimen examples.
Citation - WoS: 4
Citation - Scopus: 4
Predicting and Measuring Surface Enlargement in Forward Rod Extrusion
(Asme, 2016) Duran, Deniz; Ozdemir, Izzet
Surface enlargement during bulk metal forming processes is one of the key parameters controlling the tribology at the tool-workpiece interface. Not only the surface roughness evolution but also the integrity of the lubricant layer critically reposes on surface enlargement. As an attempt to address this issue, in the first part of this work, a general, deformation gradient based surface enlargement description is implemented in a commercial finite element program. In the second part, forward rod extrusion tests with different area reductions are conducted using customized steel workpieces in which cylindrical copper rods are embedded through the depth. By sectioning the extruded parts and by identifying the position of the copper rods on the lateral surface, average surface enlargement values could be measured locally at different positions along the extrudate. Comparison of experiments and numerical predictions reveal that the deformation gradient based description performs reasonably well in capturing surface enlargement profiles both qualitatively and quantitatively.
Citation - WoS: 6
Citation - Scopus: 8
Topological Derivative Based Optimization of 3d Porous Elastic Microstructures
(Elsevier Science Bv, 2014) Ozdemir, Izzet
As an alternative to the well established microstructural optimization techniques, topological derivative based optimization framework has been proposed and successfully implemented for tailoring/optimizing 2D elastic composites recently, Amstutz et al. [1]. In this paper, an optimization framework for 3D porous elastic microstructures is presented which is based on the notion of topological derivative and the computational homogenization of elastic composites. The sensitivity of the homogenized elasticity tensor to the insertion of infinitesimal hollow spheres within the elastic microstructure is used as the measure for the finite element based evolutionary optimization algorithm. The capabilities of the proposed framework, which is free of any regularization parameter, is assessed by means of example problems including some comparisons with analytical bounds. (C) 2013 Elsevier B.V. All rights reserved.