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Article Citation - WoS: 5Citation - Scopus: 5A Large-Deformation Gradient Damage Model for Single Crystals Based on Microdamage Theory(Mdpi, 2020) Aslan, Ozgur; Bayraktar, EminThis work aims at the unification of the thermodynamically consistent representation of the micromorphic theory and the microdamage approach for the purpose of modeling crack growth and damage regularization in crystalline solids. In contrast to the thermodynamical representation of the microdamage theory, micromorphic contribution to flow resistance is defined in a dual fashion as energetic and dissipative in character, in order to bring certain clarity and consistency to the modeling aspects. The approach is further extended for large deformations and numerically implemented in a commercial finite element software. Specific numerical model problems are presented in order to demonstrate the ability of the approach to regularize anisotropic damage fields for large deformations and eliminate mesh dependency.Article Citation - WoS: 10Citation - Scopus: 11Toughening Mechanism Analysis of Recycled Rubber-Based Composites Reinforced With Glass Bubbles, Glass Fibers and Alumina Fibers(Mdpi, 2021) Kabakci, Gamze Cakir; Aslan, Ozgur; Bayraktar, EminRecycling of materials attracts considerable attention around the world due to environmental and economic concerns. Recycled rubber is one of the most commonly used recyclable materials in a number of industries, including automotive and aeronautic because of their low weight and cost efficiency. In this research, devulcanized recycled rubber-based composites are designed with glass bubble microsphere, short glass fiber, aluminum chip and fine gamma alumina fiber (gamma-Al2O3) reinforcements. After the determination of the reinforcements with matrix, bending strength and fracture characteristics of the composite are investigated by three-point bending (3PB) tests. Halpin-Tsai homogenization model is adapted to the rubber-based composites to estimate the moduli of the composites. Furthermore, the relevant toughening mechanisms for the most suitable reinforcements are analyzed and stress intensity factor, K-Ic and critical energy release rate, G(Ic) in mode I are determined by 3PB test with single edge notch specimens. In addition, 3PB tests are simulated by finite element analysis and the results are compared with the experimental results. Microstructural and fracture surfaces analysis are carried out by means of scanning electron microscopy (SEM). Mechanical test results show that the reinforcement with glass bubbles, aluminum oxide ceramic fibers and aluminum chips generally increase the fracture toughness of the composites.Article Citation - WoS: 2Citation - Scopus: 2Assessment of Tensile Properties of Cast High Mg Containing Al-Mg Aluminum Alloy With Correlation of Computed Tomography Scans and Optical Crack Surface Analysis(Springer int Publ Ag, 2023) Gul, K. Armagan; Dispinar, Derya; Kayali, E. Sabri; Aslan, OzgurIn the casting of aluminum alloys, melt cleanliness has been crucial to achieve desirable final properties. Alloying elements, casting method and degassing procedures have been applied to obtain an internal structure free from defects. Most common defects have been double oxide metal films called bifilms. These defects have been detrimental to mechanical properties. Efforts in industry and academia have focused on removing those defects. Reduced pressure test (RPT) and optical evaluation of cross section of specimens have been the most preferred method of bifilm index evaluation method to assess melt quality. As this method is 2D cross-section analysis, there has not been a direct method to correlate mechanical properties with 3D volume analysis of both RPT and tensile specimens. Computed tomography scanning/imaging has been a promising and emerging method for 3D internal structure evaluation to evaluate internal defects. Subsequent mechanical properties fluctuation in correlation with defect quantity and size may be built in this methodology. In the present study, casting of aluminum alloys with high magnesium content and different alloying elements has been done. Effect of melt quality and defect quantities on internal structures have been investigated via RPT tests and computed tomography scans (CTS). Correlation of CTS and tensile tests has been shown. Tensile test specimen surfaces have been investigated via optical imaging, and bifilm effects have been shown. Alloy quality correlations with tensile tests have been established.Article Citation - Scopus: 1Analytical Solutions of Model Problems for Large-Deformation Micromorphic Approach To Gradient Plasticity(Mdpi, 2021) Aslan, Ozgur; Bayraktar, EminThe objective of this work is to present analytical solutions for several 2D model problems to demonstrate the unique plastic fields generated by the implementation of micromorphic approach for gradient plasticity. The approach is presented for finite deformations and several macroscopic and nonstandard microscopic boundary conditions are applied to a gliding plate to illustrate the capability to predict the size effects and inhomogeneous plastic fields promoted by the gradient terms. The constitutive behavior of the material undergoing plastic deformation is analyzed for softening, hardening and perfect plastic response and corresponding solutions are provided. The analytical solutions are also shown to match with the numerical results obtained by implementing a user element subroutine (UEL) to the commercial finite element software Abaqus/Standard.Conference Object Citation - WoS: 15Citation - Scopus: 17Numerical Modeling of Hydrogen Diffusion in Metals Accounting for Large Deformations(Pergamon-elsevier Science Ltd, 2015) Aslan, OzgurWhile the deleterious effects of hydrogen on metals and alloys are well known, the precise role of hydrogen in the underlying microscopic mechanisms is still not well understood and as of yet, the modeling attempts on hydrogen embrittlement and hydrogen induced cracking have not led to a proper method for life-time prediction. This work aims at the development of a robust numerical strategy in order to solve the non-linear coupled problem presented in the work of Anand [1]. The numerical implementation is performed for finite element method and the analysis are done to address the issue of hydrogen transport and hydrogen-embrittlement-related failures in metals. Specifically, problems related to the mechanism of hydrogen enhanced localized plasticity (HELP) is studied and macroscale shear localization phenomenon resulting from hydrogen induced material softening is considered at the phenomenological level. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Article A Coupled Modelling and Simulation Approach to Electromagnetic Sheet Metal Forming(Taylor & Francis Ltd, 2025) Aslan, Ozgur; Kabakci, Gamze Cakir; Sait, Ferit; Camalan, Caner; Baranoglu, Besim; Bayraktar, Emin; Cakir Kabakci, GamzeThis study presents a coupled numerical and experimental investigation of electromagnetic forming (EMF) for aluminium sheets. A custom simulation framework is developed in ABAQUS/Standard using user-defined material (UMAT) and load (DLOAD) subroutines. The magnetic pressure exerted on the workpiece is computed through a finite difference-based solution of Maxwell's equations and applied to the mechanical solver. The mechanical response of the material is modelled using a strain-rate-sensitive plasticity law calibrated for aluminium 7075-O. Experimental forming trials are performed using a custom-built EMF setup, and the results are compared with numerical predictions to validate the model. The comparison shows strong agreement in deformation profiles, confirming the predictive capability of the proposed simulation strategy. This work offers a reliable computational tool for optimising EMF processes and provides insights into material behaviour under high strain rate electromagnetic loading.Article Citation - WoS: 3Citation - Scopus: 3Classification of Different Recycled Rubber-Epoxy Composite Based on Their Hardness Using Laser-Induced Breakdown Spectroscopy (libs) With Comparison Machine Learning Algorithms(Mdpi, 2023) Yilmaz, Vadi Su; Yılmaz, Vadi Su; Eseller, Kemal Efe; Aslan, Ozgur; Aslan, Özgür; Bayraktar, Emin; Eseller, Kemal Efe; Yılmaz, Vadi Su; Aslan, Özgür; Eseller, Kemal Efe; Electrical-Electronics Engineering; Department of Electrical & Electronics Engineering; Mechanical Engineering; Electrical-Electronics Engineering; Mechanical Engineering; Department of Electrical & Electronics EngineeringThis paper aims toward the successful detection of harmful materials in a substance by integrating machine learning (ML) into laser-induced breakdown spectroscopy (LIBS). LIBS is used to distinguish five different synthetic polymers where eight different heavy material contents are also detected by LIBS. Each material intensity-wavelength graph is obtained and the dataset is constructed for classification by a machine learning (ML) algorithm. Seven popular machine learning algorithms are applied to the dataset which include eight different substances with their wavelength-intensity value. Machine learning algorithms are used to train the dataset, results are discussed and which classification algorithm is appropriate for this dataset is determined.Article Citation - WoS: 1Citation - Scopus: 1Effect of Ti-V and Nb Addition on the Properties of Almg7cu1.2 Alloy(Springer Int Publ Ag, 2025) Gul, Armagan; Dispinar, Derya; Aslan, OzgurIn the development of aluminum casting alloys, considerable attention is given to the impact of various alloying elements, with numerous studies exploring how these elements influence the material's properties. However, the selection of alloying elements alone does not ensure optimal final quality. The casting process and melt treatment methods also play a critical role in achieving a defect-free structure, particularly when paired with defect characterization and final property assessment. Therefore, it is essential to investigate the interplay between alloying element choice, melt treatment, and defect evaluation in tandem. In this study, copper and magnesium main alloying elements have been chosen along with master alloys of Ti-V-Nb as grain refiners for the aluminum cast alloy. Phase formations have been investigated by simulated phase diagrams. Casting experiments have been done using a tilt pouring method into sand molds, and small bubble degassing equipment has been used to ensure the alloying and melt quality satisfying required mechanical strength. Composition and alloying have been validated by spectral analysis and XRF measurements. Microstructural analyses have been performed by both digital microscopy and scanning electron microscopy. EDS mappings have been carried out for alloying elements distributions. Internal defect distribution and defect structure have been evaluated by computed tomography (CT) scans. Both as-cast and heat-treated specimens have undergone tensile and hardness tests to characterize the mechanical behaviors. CT scans and mechanical behaviors have beencorrelated, and defect metrics have been investigated and classified according to defect surface, defect volumes and projected areas on XY-XZ-YZ planes. Contour maps of defect metrics and tensile properties have been analyzed to generate input to finite element simulations for latter stages studies, and correlation of strength-defect regressions has yielded parametric results to understand structural defects-mechanical performance relations. GTN and Beremin localization models capable of depicting material behavior in the presence of defects have been used to link the experimental and virtual validation assessments. In view of test results, a maximum of 0.125 wt% Nb content in AlMgCu-TiV alloy has been proposed having a tensile strength reaching 300 MPa-7.5% elongation at 0.75% Nb content with grain refinement effect owing to Al-Nb, Al-Ti, Al-V aluminide particles and good dispersion of Nb, Ti, V elements on the microstructure as assessed by EDS mapping. CT scan reconstruction images and metrics have successfully connected tensile strength and elongation with defect volume and defect surface area for the proposed alloy. In this context, the volume and surface area of defects have been evaluated as critical metrics in evaluating the mechanical properties of Al7MgCu1.2 cast alloys. Defect localization and failure point detection during plastic deformation zone have been demonstrated by Beremin model which can lead to future studies leveraging these metrics to validate material strength using damage models such as Gurson, GTN or Beremin for crack initiation and propagation methodologies.Conference Object Static and Fatigue Behaviour of Recycled Thinsheet "ti-Al Based Composites Produced by Hot Forging Diffusion Process(Springer international Publishing Ag, 2024) Zambelis, Georges; Gatamorta, Fabio; Aslan, Ozgur; Miskioglu, Ibrahim; Bayraktar, EminWithin the framework of the common research project, the mechanical properties and fatigue behaviour of recycled thin sheet Ti-Al-based composites reinforced with atomized scrap aluminium (AA7075) and Nb elements have been evaluated. All the thin sheet sandwich structures were produced by the hot forging process, which is a semi-solid-forming process similar to partial melting hot forging. The effect of the chemical bonds during the production of these multifunctional sandwich composite structures was analysed using 3-point bending tests under static and dynamic (fatigue) loading conditions. Additional tensile tests have been carried out to evaluate the mating effect. Interface and microstructure of these composites have also been evaluated using scanning electron microscopy.Conference Object Development of Ni-Al Composites Reinforced With Recycled Aa7075+aa1050 and Ceramics Produced by the Sintering Plus Forging Process(Springer international Publishing Ag, 2024) Gatamorta, Fabio; Klinkova, Olga; Aslan, Ozgur; Miskioglu, Ibrahim; Bayraktar, EminIn this study, the microstructural formation and static/cyclic compression behavior of "Ni-Al+AA7075 +AA1050"-based composites reinforced with ceramics (TiC-TiB2) have been evaluated. It is aimed at creating a new design to be an alternative to traditional alloys/composites used in the aeronautical industry. These composites are generally produced using a combined method that we call "sinter + forging processes". The static and dynamic properties and also the microstructure (including the distribution of reinforcement elements) are evaluated in detail.
