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Öğe A new method for determining limit strains of materials that show post-uniform elongation behavior(SAGE PUBLICATIONS LTD, 2014) Turkoz, Mevlut; Halkaci, Huseyin S.; Yigit, Osman; Dilmec, Murat; Ozturk, FahrettinIn this study, a new method is proposed to determine limit strains at the onset of localized necking for ductile materials that show post-uniform elongations. The new method is first applied for AA 5754-O using the ISO 12004-2 forming limit diagram determination standard. The method is also applied for ductile materials of 7114 steel, 304 stainless steel, and CuZn37 brass and finally for AA 2024-T4 having brittle fracture behavior. The results indicate that the new proposed method is quite successful, easy, and accurate for ductile materials that show post-uniform elongations.Öğe A new methodology for ductile fracture criteria to predict the forming limits(SPRINGER, 2007) Ozturk, Fahrettin; Lee, DaeyongThe main objective of this study was to develop an improved method for an application of ductile fracture criteria to predict forming limit diagram (FLD) of the sheet metals. Neck initiation was studied experimentally and numerically for a tensile test. Based on the results, a new methodology regarding the ductile fracture criteria was proposed to estimate forming limits. The new methodology states that the fracture criteria constant could be calculated at a thickness strain in the range of 20-25%, and be considered as a critical value of the ductile fracture criteria for strain localization. The new proposed methodology was successful in predicting the left side of the FLD and more refinement is needed to predict the right side of the FLD.Öğe An Investigation of Use Biaxial Data in Sheet Metal Forming Simulations(WILEY-V C H VERLAG GMBH, 2010) Esener, Emre; Ozturk, Fahrettin; Yenice, MustafaThe use of biaxial data in sheet metal forming simulation of a DP600 steel sheet is investigated. The biaxial strain data is experimentally determined and the stresses are calculated by the inverse finite element method. Then the biaxial flow curve is formed by the Hill 48 material model. The simulation results using tensile and biaxial data are compared with experimental data for an industrial part. Results reveal that the finite element simulations performed by biaxial data display higher accuracy than the tensile data.Öğe Analysis of Forming Limit Diagrams of DP600 Steel at Various Deformation Speeds(WILEY-V C H VERLAG GMBH, 2010) Uysal, Emrah; Ozturk, FahrettinThe forming limit diagrams (FLDs) of DP600 steel at various deformation speeds are experimentally investigated. Results show that forming limit diagram of the material at various deformation speeds is not significantly different. The left side of the FLD is most rate insensitive than the right side of the FLD. The outcome of the research is used for finite element software to evaluate simulation results correctly.Öğe Analysis of tempering treatment on material properties of DIN 41Cr4 and DIN 42CrMo4 steels(ASM INT, 2007) Bayrak, Mustafa; Ozturk, Fahrettin; Demirezen, Mehmet; Evis, ZaferDIN 41Cr4 and DIN 42CrMo4 materials have been widely used in automotive driving elements. Although 42CrMo4 is more expensive than 41Cr4, it is more preferable in terms of material properties. In this study, these two materials were heat treated by austenitizing in a continuous furnace at 850 degrees C and quenched in oil at 90 degrees C. After they were tempered at various temperatures, mechanical properties were determined for each tempering temperature. The material properties for both materials were compared with each other. Results indicated that same mechanical properties for 41Cr4 and 42CrMo4 can be achieved by tempering 41Cr4 about 50 degrees C lower temperature than for 42CrMo4. In addition to the mechanical tests, fatigue tests were performed for both materials. Weibull distributions were plotted. Results indicated that 42CrMo4 had a longer life than 41Cr4 material.Öğe ARTIFICIAL-NEURAL-NETWORK PREDICTION OF HEXAGONAL LATTICE PARAMETERS FOR NON-STOICHIOMETRIC APATITES(INST ZA KOVINSKE MATERIALE I IN TEHNOLOGIE, 2014) Kockan, Umit; Ozturk, Fahrettin; Evis, ZaferIn this study, hexagonal lattice parameters (a and c) and unit-cell volumes of non-stoichiometric apatites of M-10(TO4)(6)X-2 are predicted from their ionic radii with artificial neural networks. A multilayer-perceptron network is used for training. The results indicate that the Bayesian regularization method with four neurons in the hidden layer with a tansig activation function and one neuron in the output layer with a purelin function gives the best results. It is found that the errors for the predicted data of the lattice parameters of a and c are less than 1 % and 2 %, respectively. On the other hand, about 3 % errors were encountered for both lattice parameters of the non-stoichiometric apatites with exact formulas in the presence of the T-site ions that are not used for training the artificial neural network.Öğe Artificial-neural-network prediction of hexagonal lattice parameters for non-stoichiometric apatites(2014) Kockan, Umit; Ozturk, Fahrettin; Evis, ZaferIn this study, hexagonal lattice parameters (a and c) and unit-cell volumes of non-stoichiometric apatites of M10(TO4)6X2 are predicted from their ionic radii with artificial neural networks. A multilayer-perceptron network is used for training. The results indicate that the Bayesian regularization method with four neurons in the hidden layer with a tansig activation function and one neuron in the output layer with a purelin function gives the best results. It is found that the errors for the predicted data of the lattice parameters of a and c are less than 1 % and 2 %, respectively. On the other hand, about 3 % errors were encountered for both lattice parameters of the non-stoichiometric apatites with exact formulas in the presence of the T-site ions that are not used for training the artificial neural network.Öğe Assessment of Electrical Resistance Heating for Hot Formability of Ti-6Al-4V Alloy Sheet(TRANS TECH PUBLICATIONS LTD, 2011) Ozturk, Fahrettin; Ece, Remzi Ecmel; Polat, Naki; Koksal, Arif; Duflou, JR; Clarke, R; Merklein, M; Micari, F; SHirvani, B; Kellens, KTi-6Al-4V (Ti64) is the most commercially used heat treatable high strength/weight ratio, high corrosion, and thermal resistance alloy in titanium alloys. However, room temperature (RT) formability of this alloy is very poor and springback after forming is very severe due to the high yield strength and low elasticity modulus. In this research, the applicability of electrical resistance heating process which is a new and rapid heating process for hot forming application is investigated in order to improve formability and eliminate springback. The electrical resistance heating method is found to be effective for T64 alloy. Results reveal that the changes in hardness and grain size of the alloy have been found inconsiderable when the method is used. Springback compensation is achieved at high temperatures and springback free part is almost produced.Öğe Detailed Investigation of Forming Limit Determination Standards for Aluminum Alloys(AMER SOC TESTING MATERIALS, 2013) Dilmec, Murat; Halkaci, H. Selcuk; Ozturk, Fahrettin; Turkoz, MevlutIn this study, experimental studies were conducted to evaluate the differences between the ASTM E2218-02 and ISO 12004-2 standards that are used for construction of the forming limit curve (FLC) and that made various assumptions, which create dissimilar FLCs for the same material. The comparison was made for two materials which have moderate brittle and ductile characteristics, AA2024-T4 and AA5754-O alloys, respectively. The effects of a specimen's geometry, lubrication condition, and determination methods of limit strains on FLCs were considered and compared. Because the same strain evaluation method should be used for the standards, so as to be able to investigate the effect of only standards, a simple method in the computer grid analysis system was used. To test the validity and the reliability of the method, limit strains on the same specimens were also determined with using a real-time measurement method for the ISO experiments, and the results reveal that the method is reliable. Failure mechanisms were inspected for further investigation. The Nakajima specimens formed with the two standards showed different failure mechanisms. Finally, conducting the case studies, it was concluded that ISO 12004-2 yields more reliable and reproducible results than the ASTM standard.Öğe EFFECT OF PRE-STRAINING ON THE SPRINGBACK BEHAVIOR OF THE AA5754-0 ALLOY(INST ZA KOVINSKE MATERIALE I IN TEHNOLOGIE, 2011) Toros, Serkan; Alkan, Mahmut; Ece, Remzi Ecmel; Ozturk, FahrettinThis study presents the effect of pre-straining on the springback behavior of the AA5754-0 aluminum-magnesium (Al-Mg) alloy sheet under V bending by an experimental and finite-element simulation studies. Pre-straining ranges from 0 To to 11 % were applied to the samples, which were bent on a 60 degrees V-shaped die for the springback evaluation. Commercially available finite-element software, ETA/Dynaform, was used to simulate the 60 degrees V-die bending process. The dynamic explicit finite-element method for pressing and the static implicit finite-element method for the unloading phase were used for the simulations. The results from both the experiment and the simulation indicate that the pre-straining has no positive effect on the springback compensation.Öğe Effect of pre-straining on the springback behavior of the AA5754-0 alloy(2011) Toros, Serkan; Alkan, Mahmut; Ece, Remzi Ecmel; Ozturk, FahrettinThis study presents the effect of pre-straining on the springback behavior of the AA5754-0 aluminum-magnesium (Al-Mg) alloy sheet under V bending by an experimental and finite-element simulation studies. Pre-straining ranges from 0 % to 11 % were applied to the samples, which were bent on a 60°V-shaped die for the springback evaluation. Commercially available finite-element software, ETA/Dynaform, was used to simulate the 60°V-die bending process. The dynamic explicit finite-element method for pressing and the static implicit finite-element method for the unloading phase were used for the simulations. The results from both the experiment and the simulation indicate that the pre-straining has no positive effect on the springback compensation.Öğe EFFECT OF SHEET THICKNESS ON THE ANISOTROPY AND THICKNESS DISTRIBUTION FOR AA2024-T4(INST ZA KOVINSKE MATERIALE I IN TEHNOLOGIE, 2013) Dilmec, Murat; Halkaci, Huseyin Selcuk; Ozturk, Fahrettin; Turkoz, MevlutIn this study, the effect of sheet thickness on the anisotropy and thickness distribution at room temperature (RT) was investigated for AA2024-T4 sheets. The anisotropy was determined using automated strain measurement with a grid analysis and profile-projector methods. The results indicate that the effects of the thicknesses of 0.8 mm, 1 mm, and 2 mm on the anisotropy were insignificant. In addition to the anisotropy measurement, the thickness variation of the specimens was also monitored. Besides the anisotropy values, no significant differences were observed between various thicknesses and directions.Öğe Effect of sheet thickness on the anisotropy and thickness distribution for AA2024-T4(2013) Dilmec, Murat; Halkaci, Huseyin Selcuk; Ozturk, Fahrettin; Turkoz, MevlutIn this study, the effect of sheet thickness on the anisotropy and thickness distribution at room temperature (RT) was investigated for AA2024-T4 sheets. The anisotropy was determined using automated strain measurement with a grid analysis and profile-projector methods. The results indicate that the effects of the thicknesses of 0.8 mm, 1 mm, and 2 mm on the anisotropy were insignificant. In addition to the anisotropy measurement, the thickness variation of the specimens was also monitored. Besides the anisotropy values, no significant differences were observed between various thicknesses and directions.Öğe Effect of Warm Temperature on Springback Compensation of Titanium Sheet(TAYLOR & FRANCIS INC, 2010) Ozturk, Fahrettin; Ece, Remzi Ecmel; Polat, Naki; Koksal, ArifIn the present study, the effect of warm temperature on springback compensation of commercially pure grade 2 (CP2) titanium sheet is investigated. The results reveal that the springback is substantially reduced with increasing temperature. The elastic energy and the ratio of tensile strength/yield strength (TS/YS) of the material are measured at various temperatures under tensile loading condition. A gradual decrease of elastic energy is observed with increasing temperature. The change in the ratio of TS/YS is left diminutive with increasing temperature.Öğe Effects of aging parameters on formability of 6061-O alloy(ELSEVIER SCI LTD, 2010) Ozturk, Fahrettin; Esener, Emre; Toros, Serkan; Picu, Catalin R.6XXX series aluminum-magnesium-silicon (Al-Mg-Si) alloys are medium strength alloys widely used as automotive body materials. The mechanical properties of these alloys are adjusted by performing age hardening heat treatments. In this research, the effect of aging time on formability of 6061-O alloy is investigated. The formability of the material is evaluated by tensile. Erichsen, and hole expansion tests. Results reveal that formability decreases with increasing aging time. The evolution of the anisotropy, r, with the aging time depends on the direction of probing relative to the texture direction. Yield surfaces predicted using the Hill-90 and Barlat-89 models are plotted using experimental r values for several aging times. Since r changes, these surfaces deform slightly and expand with increasing aging time. (C) 2010 Elsevier Ltd. All rights reserved.Öğe Effects of Aging Temperature, Time, and Pre-Strain on Mechanical Properties of AA7075(Univ Fed Sao Carlos, Dept Engenharia Materials, 2019) Kilic, Suleyman; Kacar, Ilya; Sahin, Mevlut; Ozturk, Fahrettin; Erdem, OguzAluminum alloys of the 7xxx series (AA7075) are preferred in the aerospace and automotive industries due to their low densities, high strength, good corrosion resistance properties. Additionally, these alloys show the most effective aging properties among aluminum alloys. For this reason, it is very important to determine the most appropriate aging parameters for microstructural development. Literature review reveals that the effect of pre-strain on springback has not been studied yet. In this study, the effects of aging temperature, time, and pre-strain on mechanical properties are investigated for AA7075. Precipitates present in solid solutions of AA7075 and their effects are examined. Results reveal that MgZn2 precipitation is not observed at aging temperatures of 120 and 160 degrees C. After the formation of MgZn2 precipitates, microstructure becomes softer when aging continues at a higher temperature or longer period of time. It is clearly seen that pre-strain causes Portevin-Le Chatelier (PLC) effect after aging at 120 and 160 degrees C for aging times of 30 and 90 minutes.Öğe Effects of anisotropic yield functions on prediction of forming limit diagrams of DP600 advanced high strength steel(ELSEVIER SCIENCE BV, 2014) Ozturk, Fahrettin; Toros, Serkan; Kilic, Suleyman; Ishikawa, T; Mori, KIIn recent years, numerous researchers have reported that the predicted forming limit diagrams strongly depend on the method of determining the material parameters used in the yield functions and the corresponding the shape of the yield surface. In this study, the capability of different yield functions to predict the forming limit diagram of DP600 advanced high strength steel sheet is investigated. Additionally, the effects of determination method of the anisotropic parameters on the forming limit diagram are studied. The yield functions proposed by Hill-48, Barlat-89, and YLD2000-2d are considered and the forming limit diagrams are constructed using the Marciniak Kuczynski model. Results reveal that predictions using different yield functions are lower than the experimental forming limits. In terms of shape and tendency, the YLD2000-2d curve is best suited for representing experimental curve. (C) 2014 Published by Elsevier Ltd.Öğe Effects of sheet thickness and anisotropy on forming limit curves of AA2024-T4(SPRINGER LONDON LTD, 2013) Dilmec, Murat; Halkaci, H. Selcuk; Ozturk, Fahrettin; Livatyali, Haydar; Yigit, OsmanIn this study, the effects of sheet thickness and anisotropy of AA2024-T4 on forming limit curve (FLC) are experimentally investigated according to ISO 12004-2 standard. A new limit strain measurement method is proposed by using the grid analysis method so as to determine limit strains conveniently and reliably. In addition to the regular test specimens, various widths are added to enhance the FLC's accuracy at the plane strain condition (PSC). The accuracy and reliability of the proposed method are verified for different materials. Results illustrate that an increase in the sheet thickness increases the FLC level. The additional experiments for additional widths improve the accuracy of the FLC at the PSC, and the position of the lowest major strain value differs from the literature. However, the effect of anisotropy on the FLC is found to be insignificant. Finally, experimental and numerical case studies are carried out for conventional deep drawing, stretch drawing, and hydraulic bulge processes. Results reveal that different FLCs are necessary for different thicknesses for accurate predictions.Öğe EFFECTS OF THE ARTIFICIAL-AGING TEMPERATURE AND TIME ON THE MECHANICAL PROPERTIES AND SPRINGBACK BEHAVIOR OF AA6061(INST ZA KOVINSKE MATERIALE I IN TEHNOLOGIE, 2015) Polat, Aytekin; Avsar, Mustafa; Ozturk, FahrettinIn this study, the effects of the artificial-aging temperature and time on the mechanical properties and springback behavior of AA6061 are investigated. The results reveal that the yield strength, the tensile strength and the elongations decreased with the increasing artificial-aging temperature, but increased with the increasing artificial-aging time up to the peak age. The springback of the alloy increased significantly with the increasing artificial-aging time at the artificial-aging temperature ranging from 160 degrees C to 180 degrees C and decreased with the artificial-aging time at 200 degrees C. The springback angle in the as-received condition is lower than in all the aged conditions.Öğe Effects of the artificial-aging temperature and time on the mechanical properties and springback behavior of AA6061(Institute of Metals Technology, 2015) Polat, Aytekin; Avsar, Mustafa; Ozturk, FahrettinIn this study, the effects of the artificial-aging temperature and time on the mechanical properties and springback behavior of AA6061 are investigated. The results reveal that the yield strength, the tensile strength and the elongations decreased with the increasing artificial-aging temperature, but increased with the increasing artificial-aging time up to the peak age. The springback of the alloy increased significantly with the increasing artificial-aging time at the artificial-aging temperature ranging from 160 °C to 180 °C and decreased with the artificial-aging time at 200 °C. The springback angle in the as-received condition is lower than in all the aged conditions.
