Yazar "Yildirim, Sefa" seçeneğine göre listele
Listeleniyor 1 - 9 / 9
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe A novel combined hardening rule for the brass cartridge case using crimping simulation and optimization(Sage Publications Ltd, 2025) Kacar, Ilyas; Yildirim, SefaA cartridge shell case, a critical component in the defence industry, undergoes a crimping process to form one end for the insertion of a bullet. The shell case is primarily composed of brass. The crimping process is simulated using a novel plasticity model that combines a hardening rule with the Hill48 yield criterion and the associated flow rule. This study focuses primarily on the hardening rule, where a bilinear isotropic hardening (BISO) and Chaboche's nonlinear kinematic hardening (CHAB) rules are combined to develop a novel hardening model. The raw parameters of the models are calculated by regression performed on the data from monotonic tensile test and low-cycle fatigue (LCF) test. A multi-objective genetic algorithm is used to calibrate the raw parameters by the inverse analysis. The performance of the models is evaluated on the diameter of the shell considering the work-hardening. The novelty of this study lies in the acquisition of calibrated hardening rule parameters for the crimping process, which involves a multi-axial deformation pattern, using only data from uniaxial tensile and LCF tests, which are simpler to conduct. The force-moment requirements, springback, and material flow path are also calculated. The results provide a valuable insight into the combined hardening model, its parameters, and their sensitivity for the crimping process. The calibration process results in significant improvements in material properties, particularly yield strength (YS) and tangent modulus (TM). For the crimping, YS is observed to increase by 37.82% and TM is observed to decrease by 13.84% while parameters { C 1 , gamma 1 , C 2 , gamma 2 , C 3 , gamma 3 } increase approximately 9% where Cm is hardening modulus, and gamma m is decrease rate. The model achives an absolute percent relative error (APE) of 0.18%.Öğe Calibrating the combined hardening rule parameters for burr-free forging simulation of the torque rod joint(Sage Publications Ltd, 2025) Kacar, Ilyas; Yildirim, SefaJoints used in the automotive industry are widely manufactured by forging. A cold upsetting process can provide burr-free forging which reduces economic loss by preventing material waste. In this study, finite element simulations for the upsetting of a torque rod joint made of 41Cr4 steel are performed. The novelty of the present study lies in the fact that the upsetting performance is investigated through simulation having hardening model in order to replace the existing forging process. The performance of hardening models is studied for an accurate simulation and optimum parameters are determined. A combination of the bilinear isotropic hardening rule and Chaboche's nonlinear kinematic hardening rule is employed with the associated flow rule and Hill48 yield criterion to set up a plasticity model of the upsetting process for the first time. The parameters of the bilinear isotropic hardening rule are determined from monotonic tensile tests. The Chaboche's parameters are determined by using hysteresis loops obtained from strain-controlled low-cycle fatigue tests. The parameters of both rules are combined. Furthermore, they are calibrated using inverse analysis based on the optimization method. Genetic algorithm is used for optimization. The experimental diameter and height measurements of the joint are compared with those obtained from the optimized model. The results show that the application of the combined hardening rule provides better prediction performance of the upset dimensions with minimum dimensional tolerance. The calibrated parameters are presented for the upsetting process. The calibrated parameters of the combined hardening model for the upsetting are YS = 446.64 MPa, TM = 3363.05 MPa, C-1 = 452.31 MPa, gamma(1) = 55.165, C-2 = 212.13 MPa, gamma(2) = 12.24, C-3 = 194.191 MPa, gamma(3) = 10.00 where YS, TM, C-1,C- gamma 1,C- C-2,C- gamma 2,C- C-3,C- gamma 3 are hardening models' parameters. Absolute percent true error (APE) is 0.19%. The parameters are YS = 1.93 MPa, TM = 6.98 MPa, C-1 = 580.79 MPa, gamma(1) = 1.08, C-2 = 597.23 MPa, gamma(2) = 0.98, C-3 = 565.05 MPa, gamma(3) = 2.87 in the case of cyclic load. APE is 1.66%. Also upsetting force requirement and material flow path are presented. The forging process can be replaced by the burr-free upsetting process with necessary changes in the die and press bench design. This replacement will save the 128-gr material per each one of the torque rod joint part.Öğe EFFECT OF THE FINITE ELEMENT MODELING TECHNIQUES ON THE DYNAMIC ANALYSIS OF BEAMS(2022) Noori, Ahmad Reshad; Yildirim, SefaAnalysis of the free and forced vibration responses of beams is one of the most critical problems to be examined in the design step of these structural members. The finite-element method which solves boundary value problems can be applied efficiently to vibration problems. In this study, the natural vibration frequency and damped and undamped transient analyses of the pinned-pinned beams are investigated. The well-known finite-element software packages, ANSYS and SAP2000, are used. The 2-D elastic beam which is based on the Euler-Bernoulli Beam theory, 3-D two-node and 3-D three-node beam elements which are based on Timoshenko beam theory, and four-node shell elements are used in ANSYS and the frame member is utilized in SAP2000. The effect of these elements on the dynamic behaviors of the isotropic beam is discussed. The results are given in tabular and graphical form for the free and forced vibration, respectively.Öğe Free vibration of axially or transversely graded beams using finite-element and artificial intelligence(Elsevier, 2022) Yildirim, SefaThe effect of grading direction on the natural frequencies of heterogeneous isotropic beams is investigated and the artificial neural network approach is conducted to estimate the free vibration characteristics. The two-dimensional beam is graded in axial or transverse direction according to the power-law form. An artificial neural network model has been developed to estimate relationship between material properties and model, grading direction, slenderness ratio as an input layer and natural frequencies obtained by Finite-Element method as an output layer. The Levenberg-Marquardt back-propagation method is used as a training algorithm. The novelty of this study is that it deals with the estimation of free vibration characteristics of beams made of functionally-graded material using aforementioned input layer for the first time. The proposed artificial neural network model can predict the natural frequencies without the need for a solution of any differential equation or time-consuming experimental processes. The results show that artificial intelligence techniques can be efficiently adopted to free vibration problems of functionally graded beams. The influence of grading direction on the natural frequency is also demonstrated. (C) 2021 THE AUTHOR. Published by Elsevier BV on behalf of Faculty of Engineering, Alexandria University.Öğe Inertio-elastic instability of functionally graded nanotube-reinforced composite disks(Sage Publications Ltd, 2025) Yildirim, Sefa; Tutuncu, NakiRotational elastic instability of annular members is an important phenomenon which may lead to the destruction of structures. The instability analysis of rotating disks made of carbon nanotube reinforced composite (FG-CNTRC) has been presented. This study is the first to investigate the rotational instability of FG-CNTRC disks, providing new insights into the design of high-stability rotating structures. The rotating disk mounted to rigid shaft has variable-thickness and the function of CNT distribution along the radial coordinate may be uniform or functionally graded. The refined rule of mixture approach is used to obtain the material properties of composite where efficiency parameters are considered. The actual centrifugal force with radial displacement is taken into account and the burst velocities at which instability observed are obtained. The theory used in the analysis is plane elasticity and the governing differential equations of the problem have variable-coefficients where the analytical solution may not be available. Complementary Functions Method, which is a powerful numerical solution scheme, is implemented into the analysis and high accuracy with few collocation points are achieved using non-dimensional parameters. The influences of CNT distribution pattern, volume fraction of CNTs and variations of thickness profiles on the burst velocities of disk are examined. It is revealed that CNT addition to the isotropic polymer has a stabilizing effect on the rotating disk by increasing the burst velocity and the most effective parameter is the CNT distribution pattern. Considering all distribution patterns, the FG-V pattern yields the most stable disk design. Validation of the results is done using analytical solution which is only available for uniformly distributed CNTRC with the hyperbolic thickness profile.Öğe Multipart Die Design for Bladeless Fan Housing Using the Tube Deforming Simulation(Springer Heidelberg, 2025) Karacan, Kivanc; Kacar, Ilyas; Yildirim, SefaTube deforming is a sheet metal manufacturing process that requires significant plastic deformations. It offers a potential to produce fast and burr-free tube deformation for bladeless fan housing. In this study, a multipart die and punch have been designed to facilitate this process. Finite element method-based simulations are performed to analyze the tube deformation of AA7075-T6. To enhance the accuracy of the simulation, two hardening models are combined. The combined rule involves a bilinear isotropic hardening model, characterized by its linear nature, and Chaboche's kinematic hardening model, which exibits a nonlinear nature. The raw parameters are determined using regression on the uniaxial tensile test data and low cycle fatigue data. The raw parameters are calibrated using inverse analysis and multi-objective genetic algorithm to specialize them in the tube deformation process where the deformation path is cyclic. The plasticity model is constituted of Hill48 yield criterion, the combined hardening rule, and associated flow rule. The novelty of this study is that the model parameters for the tube deformation process, which has a more complex deformation pattern, are acquired using only the data obtained from tensile and low cycle fatigue tests which are simpler to conduct. Additionally, linear and nonlinear models are combined for more accuracy and the calibrated parameters are established. The force-moment requirement and material flow path are also presented.Öğe Nanosilika/ Sansevieria Trifasciata (Paşa Kılıcı) Doğal Fiber Katkılı Hibrid Epoksi Kompozitlerin Eğilme Performansının İncelenmesi(2024) Beylergil, Bertan; Ergin, Cihat Kerem; Yildirim, SefaBu çalışmada, Sansevieria Trifasciata (Paşa Kılıcı) bitkisinden elde edilen doğal lifler ve nanosilika katkılı hibrid epoksi kompozitlerin eğilme performansı araştırılmıştır. Çalışmanın ilk aşamasında, doğal lifler enzimatik havuzlama yöntemleri kullanılarak elde edilmiştir. Elde edilen lifler, alkali işlemden geçirilerek epoksi bağlanma kapasiteleri artırılmıştır. Bu aşamanın ardından, lifler uzunlamasına yerleştirilerek epoksi matrise nanosilika tozu ile eklenmiştir. Nanosilika oranı ağırlıkça %3 olarak belirlenmiştir. Ayrıca saf epoksiden referans numuneler üretilmiştir. Çalışma süresince üretilen kompozitlerin mekanik özellikleri ASTM D790 standartlarına uygun olarak üç nokta eğme testleri ile karakterize edilmiştir. Elde edilen sonuçlar, kompozit malzemenin yüksek mukavemet ve elastikiyet özelliklerine sahip olduğunu göstermektedir. Ancak homojen olmayan kırılma davranışları, malzemenin üretim sürecindeki varyasyonlardan kaynaklanabilir. Çalışma, çevresel sürdürülebilirlik ve endüstriyel uygulamalarda doğal kompozitlerin potansiyelini ortaya koymuştur.Öğe Parameter Calibration of a Novel Combined Hardening Model for a Wire Drawing Simulation of AA7075-T6(Springer, 2025) Kacar, Ilyas; Yildirim, SefaA novel combined hardening model integrating bilinear isotropic and nonlinear kinematic hardening rules is proposed to simulate the cold wire drawing process of AA7075-T6. The plasticity model is formulated using Hill48 yield criterion, the proposed hardening rule, and the associative flow rule. Firstly, the experiments of monotonic tensile and low cycle fatigue tests are carried out and true stress-true plastic strain data are obtained. The parameters of the hardening rules and anisotropy coefficients for yield criterion are determined using the obtained test data. An inverse analysis is performed to calibrate the parameters using optimization and the finite element-based wire drawing simulation. The hardening curves of a combined model, bilinear isotropic hardening rule, and Chaboche's nonlinear kinematic hardening rule are compared as their performance metric. Validation is achieved through experimental results, and the optimum and calibrated parameters for wire drawing of AA7075-T6 are proposed. The results offer an insight into the hardening model, its parameters, and their sensitivity for the wire drawing simulation. It is concluded that the prediction of the combined model is more accurate than those of bilinear isotropic and Chaboche's nonlinear kinematic hardening rules. The drawing force requirement and material flow path are also determined.Öğe Performance Analysis of Zhao and Durbin Numerical Inversion Methods of Laplace Transform(2023) Yildirim, SefaThe Laplace transform is essential to satisfy the independence of time for the analysis of the transient response of the composite or functionally-graded materials. The time independent boundary value problem may be solved then either by numerically or analytically. The solutions should be inverted to the physical plane using inverse Laplace transform. Therefore, the selected numerical inversion method may be crucial to obtain the high accuracy throughout the whole analysis steps. In the present study, Zhao’s Method I, Zhao’s Method II, Durbin’s Method and Modified Durbin’s Method are applied to dynamic loading conditions. The analysis results show that the accurate and stable solutions even for long time inversion have been obtained by Modified Durbin’s Method and Zhao’s Methods. However, compared with the methods of Zhao’s, the computational and programing load of Durbin’s Methods are minimum.
