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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 - 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.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.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 - 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: 2Citation - Scopus: 2Lifetime Prediction of Single Crystal Nickel-Based Superalloys(Mdpi, 2025) Kasar, Cagatay; Kaftancioglu, Utku; Bayraktar, Emin; Aslan, OzgurSingle 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.Review Citation - WoS: 10Citation - Scopus: 16A Review on Analysis of Reinforced Recycled Rubber Composites(Mdpi, 2022) Kabakci, Gamze Cakir; Aslan, Ozgur; Bayraktar, EminRubber 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.Article Citation - WoS: 4Citation - Scopus: 5Assessing Cast Aluminum Alloys With Computed Tomography Defect Metrics: a Gurson Porous Plasticity Approach(Mdpi, 2023) Gul, Armagan; Aslan, Ozgur; Kayali, Eyuep Sabri; Bayraktar, EminAluminum 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.
