Browsing by Author "Aslan, Ozgur"

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Citation - Scopus: 1
Analytical Solutions of Model Problems for Large-Deformation Micromorphic Approach To Gradient Plasticity
(Mdpi, 2021) Aslan, Ozgur; Bayraktar, Emin
The 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.
Citation - WoS: 4
Citation - Scopus: 5
Assessing Cast Aluminum Alloys With Computed Tomography Defect Metrics: a Gurson Porous Plasticity Approach
(Mdpi, 2023) Gul, Armagan; Aslan, Ozgur; Kayali, Eyuep Sabri; Bayraktar, Emin
Aluminum alloys have inherent tendencies to produce casting defects caused by alloying or metal melt flow inside the mold. The traditional detection method for these defects includes reduced pressure tests, which assess metal quality in a destructive manner. This leaves a gap between metal quality assessments and tensile test correlations. Computed tomography (CT) scans offer crucial assistance in evaluating the internal quality of castings without damaging the structure. This provides a valuable opportunity to couple mechanical tests with numerical methods such as finite element analysis to predict the mechanical performance of the alloy. The present study aims to evaluate the internal quality of cast aluminum alloys using CT scans and to correlate the defect metrics obtained from CT scans with mechanical test results. The Gurson-type material model and finite element methodology have been used to validate the correlation studies. Therefore, we propose a more holistic approach to predicting the behavior of metals by coupling damage models with CT scans and mechanical tests. The study investigates several CT metrics such as the defect volume, total defect surface, biggest defect surface, and projected area of defects. The conclusion reveals that CT scans provide crucial assistance in evaluating the internal quality of castings, and CT defect metrics can be used to build correlations between mechanical tests and CT evaluations. The study also suggests that the concept of adjusted representative material yield parameter (ARMY) or computed representative material yield parameter (CRMY) can be used to correlate CT metrics with mechanical strength in cast materials and parts for a given aluminum alloy. Overall, the study proposes a more comprehensive methodology to assess the quality of cast aluminum alloys and couple the quality to mechanical performance.
Citation - WoS: 2
Citation - Scopus: 2
Assessment 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, Ozgur
In 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.
Citation - WoS: 1
Citation - Scopus: 1
Classification 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 Engineering
This 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.
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
This 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.
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, Emin
In 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.
Citation - WoS: 1
Citation - Scopus: 1
Effect of Ti-V and Nb Addition on the Properties of Almg7cu1.2 Alloy
(Springer Int Publ Ag, 2025) Gul, Armagan; Dispinar, Derya; Aslan, Ozgur
In 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.
Citation - WoS: 2
Citation - Scopus: 2
An Investigation of Recycled Rubber Composites Reinforced With Micro Glass Bubbles: an Experimental and Numerical Approach
(Taylor & Francis Ltd, 2024) Kabakci, Gamze Cakir; Bayraktar, Emin; Aslan, Ozgur
Recycled rubber is widely used for its lightweight and cost-effective properties but often has limited mechanical strength, restricting its applications. This study enhances the mechanical performance of devulcanised recycled rubber by reinforcing it with micro glass bubbles (GBs) featuring a density of 0.65 g/cm(3) and an elastic modulus of 3.5 GPa, offering a high strength-to-density ratio. Uniaxial compression tests were conducted on samples with GB volume fractions of 5%, 10%, and 15%. Results were validated through finite element analysis (FEA) in ABAQUS/Standard, incorporating randomised GB distributions. A 2D representative volume element (RVE) with randomly distributed GBs was modelled, applying periodic boundary conditions to simplify the composite into an equivalent homogeneous material. Numerical simulations assessed the effects of GB diameters (30, 40, and 50 mu m) and inclusion size ranges (20-50 mu m and 10-60 mu m), finding minimal impact on results. The RVE, sized at 238 mu m, accurately represented macroscale composite behaviour. Stress-strain behaviour was analysed using average stress and strain tensors. The strong agreement between experimental and numerical results validates the proposed method, demonstrating its accuracy in predicting the mechanical behaviour of the reinforced composite material.
Citation - WoS: 5
Citation - Scopus: 5
A Large-Deformation Gradient Damage Model for Single Crystals Based on Microdamage Theory
(Mdpi, 2020) Aslan, Ozgur; Bayraktar, Emin
This 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.
Citation - WoS: 2
Citation - Scopus: 2
Lifetime Prediction of Single Crystal Nickel-Based Superalloys
(Mdpi, 2025) Kasar, Cagatay; Kaftancioglu, Utku; Bayraktar, Emin; Aslan, Ozgur
Single crystal nickel-based superalloys are extensively used in turbine blade applications due to their superior creep resistance compared to their polycrystalline counterparts. With the high creep resistance, high cycle fatigue (HCF) and low cycle fatigue (LCF) become primary failure mechanisms for such applications. This study investigates the fatigue life prediction of CMSX-4 using a combination of crystal plasticity and lifetime assessment models. The constitutive crystal plasticity model simulates the anisotropic, rate-dependent deformation behavior of CMSX-4, while the modified Chaboche damage model is used for lifetime assessment, focusing on cleavage stresses on active slip planes to include anisotropy. Both qualitative and quantitative data obtained from HCF experiments on single crystal superalloys with notched geometry were used for validation of the model. Furthermore, artificial neural networks (ANNs) were employed to enhance the accuracy of lifetime predictions across varying temperatures by analyzing the fatigue curves obtained from the damage model. The integration of crystal plasticity, damage mechanics, and ANNs resulted in an accurate prediction of fatigue life and crack initiation points under complex loading conditions of single crystals superalloys.
Citation - WoS: 19
Citation - Scopus: 19
Modeling and Simulation of Coupled Phase Transformation and Stress Evolution in Thermal Barrier Coatings
(Pergamon-elsevier Science Ltd, 2020) Sait, Ferit; Aslan, Özgür; Gurses, Ercan; Aslan, Ozgur; Sait, Ferit; Aslan, Özgür; Sait, Ferit; Mechanical Engineering; Aerospace Engineering; Mechanical Engineering; Aerospace Engineering
The thermally grown oxide layer is known to be responsible for the failure of coating systems due to the generation of severely high stresses. In this work, oxidation induced stresses generated in thermal barrier coating (TBC) systems are investigated for high temperature isothermal oxidation. In that sense, a comprehensive model, where phase transformation is coupled with mechanics is developed for the life-time estimation of TBC systems and a modified version of the Allen-Cahn type phase field approach is adopted in order to model the generation of thermally grown oxide (TGO) in finite strain constitutive framework. The top-coat material behavior is modeled using a rate-dependent Gurson type plasticity for porous materials which also accounts for creep. The results for the isothermal phase transformation analysis and the model validation using experimental results are demonstrated. The capability of the model in predicting the local stresses which is the main variable in the analysis of possible delaminations and accurate lifetime estimation of TBC systems is shown.
Citation - WoS: 15
Citation - Scopus: 17
Numerical Modeling of Hydrogen Diffusion in Metals Accounting for Large Deformations
(Pergamon-elsevier Science Ltd, 2015) Aslan, Ozgur
While 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.
Citation - WoS: 10
Citation - Scopus: 16
A Review on Analysis of Reinforced Recycled Rubber Composites
(Mdpi, 2022) Kabakci, Gamze Cakir; Aslan, Ozgur; Bayraktar, Emin
Rubber recycling attracts considerable attention by a variety of industries around the world due to shrinking resources, increasing cost of raw materials, growing awareness of sustainable development, and environmental issues. Recycled rubber is commonly used in aeronautic, automotive, and transportation industries. In this study, recycled rubber composites designed with different reinforcements in the literature are scrutinized by means of toughening mechanisms, mechanical and physical properties, as well as microstructural and fracture surface analysis. Microscale reinforcements (glass bubbles, alumina fiber, etc.) and nanoscale reinforcements (nanosilica, graphene nanoplatelets, etc.) utilized as reinforcements in rubber composites are thoroughly reviewed. The general mechanical properties reported by previous studies, such as tensile, compressive, and flexural strength, are investigated with the main goal of optimizing the amount of reinforcement used. The majority of the studies on recycled rubber composites show that recycled rubber reinforced with microscale particles leads to the development of physical and mechanical properties of the structures and also provides low-cost and lightweight composites for several application areas. Moreover, recycled rubber containing composites can be suitable for applications where high toughness and high resistance to impact are desirable. The present review aims to demonstrate research on reinforced recycled rubber composites in the literature and prospective outcomes.
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, Emin
Within 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.
Citation - WoS: 9
Citation - Scopus: 10
Toughening Mechanism Analysis of Recycled Rubber-Based Composites Reinforced With Glass Bubbles, Glass Fibers and Alumina Fibers
(Mdpi, 2021) Kabakci, Gamze Cakir; Aslan, Ozgur; Bayraktar, Emin
Recycling 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.