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Conference Object Citation - WoS: 2Fem-Based Design Modifications and Efficiency Improvements of a Brushed Permanent Magnet Dc Motor(Ieee, 2017) Tarvirdilu-Asl, Rasul; Zeinali, Reza; Ertan, H. BulentThis paper describes design modifications of a brushed permanent magnet DC motor. Test motor is modeled using a Finite Element Method (FEM) based software. Model accuracy is investigated by comparing measurement and simulation results. Reducing material consumption in motor fabrication while the motor develops the desired torque at a higher efficiency is aimed in this paper. Modifications are done in three stages and simulations results are also presented. These results are also compared to simulation results of the test machine.Article Citation - WoS: 29Citation - Scopus: 37A Guide for Validation of Fe-Simulations in Bulk Metal Forming(Springer Heidelberg, 2005) Tekkaya, AE; Manufacturing EngineeringNumerical analysis of metal forming processes is an everyday practice in industry. Forming loads, material flow, forming defects such as underfills, laps, and even cracks, stresses in dies and punches, as well as product properties like new hardness distribution, dimensional accuracies, and residual stresses are predicted by numerical analysis and used for technology generation. Most of the numerical analysis is done by the finite element method made available for engineers and technicians by numerous powerful commercial software packages. These software packages act as black-boxes and usually hide the complicated numerical procedures and even their crucial parameters from the applier. Therefore, the question arises during industrial applications: how accurate is the simulation, and how can the results be assessed? The aim of this paper is to provide a guideline to assess the results of metal forming simulations. Although some ideas are valid for any metal forming process, bulk forming is the primary concern. The paper will address firstly the possible sources of error in a finite element analysis of bulk forming processes. Then, some useful elementary knowledge will be summarized. Various levels of validation such as result and ability validation and assessment will be discussed. Finally, interpretation of results will be treated. In this content also some suggestions will be given.Article Citation - WoS: 15Citation - Scopus: 21Comparison of Various Preforms for Hot Forging of Bearing Rings(Elsevier Science Sa, 2005) Arbak, M; Tekkaya, AE; Özhan, FProduction of bearing rings by hot forging is investigated in this study. The aim of the study is to determine a feasible preform at the first station of the forming process such that the tool wear is prolonged and tool fracture is prevented. For this purpose, it is assumed that the contact pressure at the interface between tools and workpiece is the predominant process parameter. The contact pressures are determined by precise thermo-mechanical coupled finite element analyses based on elastic-plastic material description. Material flow curves for various temperatures and strain-rates are determined in velocity controlled upsetting tests. Cooling experiments are used to determine the heat transfer coefficients. Accuracy of the numerical models has been verified by extensive numerical convergence studies and finally by comparing with experimental measurements. The analysed preforms are evaluated using a scheme of weight-factors for the various tool parts. Finally, a preform is suggested for which the weighted total tool pressure could be reduced by 15%. (c) 2005 Elsevier B.V. All rights reserved.Article Citation - WoS: 1Citation - Scopus: 1Prediction of the Onset of Shear Localization Based on Machine Learning(Cambridge Univ Press, 2023) Akar, Samet; Ayli, Ece; Ulucak, Oguzhan; Ugurer, DorukPredicting the onset of shear localization is among the most challenging problems in machining. This phenomenon affects the process outputs, such as machining forces, surface quality, and machined part tolerances. To predict this phenomenon, analytical, experimental, and numerical methods (especially finite element analysis) are widely used. However, the limitations of each method hinder their industrial applications, demanding a reliable and time-saving approach to predict shear localization onset. Additionally, since this phenomenon largely depends on the type and parameters of the constitutive material model, any change in these parameters requires a new set of simulations, which puts further restrictions on the application of finite element modeling. This study aims to overcome the computational efficiency of the finite element method to predict the onset of shear localization when machining Ti6Al4V using machine learning methods. The obtained results demonstrate that the FCM (fuzzy c-means) clustering ANFIS (adaptive network-based fuzzy inference system) has given better results in both training and testing when it is compared to the ANN (artificial neural network) architecture with an R-2 of 0.9981. Regarding this, the FCM-ANFIS is a good candidate to calculate the critical cutting speed. To the best of the authors' knowledge, this is the first study in the literature that uses a machine learning tool to predict shear localization.Article Citation - Scopus: 1Assessment and Improvement of Elementary Force Computations for Cold Forward Rod Extrusion(Springer Heidelberg, 2005) Öcal, M; Egemen, N; Tekkaya, AE; Manufacturing EngineeringTwo commonly used analytical force computation methods for cold forward rod extrusion are evaluated by means of precise finite element computations. The upperbound model by Avitzur based on the spherical velocity field and the model by Siebel based on a quasi-upper-bound solution are considered. It has been found that the pure deformation forces obtained by summing the ideal force and shear force terms deviate between +25% and -20% from the finite element solutions. Larger deviations, however, occur for the Coulomb-friction term in the container. A new model based on an elasto-static analysis combined with numerical analysis is suggested to compute this term. This new model supplies also the accurate pressure distribution within the container.Article Citation - WoS: 3Citation - Scopus: 5Higher Order Isoparametric Finite Element Solution of Stokes Flow(Elsevier Science inc, 2005) Eid, RA finite element method of the penalization type, using higher order shape functions with rectangular elements, is presented for the solution of the Stokes flow. The fluid is viscous and the flow is slow, steady and incompressible. The solution has been obtained in terms of velocity field while the pressure terms are eliminated using the penalty function approach. The degree of the finite element approximation can be increased as much as one needs with this higher order shape function formulation. The method is tested in a lid-driven square cavity and it is found that there is a relationship between the viscosity and penalty parameter. From one solution one can obtain all the other solutions only by arranging one of the parameters since the product of these parameters has been shown that is a fixed constant. Selected graphs of the velocity field are given showing these behaviors. (C) 2004 Elsevier Inc. All rights reserved.
