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    Analysis of tempering treatment on material properties of DIN 41Cr4 and DIN 42CrMo4 steels
    (ASM INT, 2007) Bayrak, Mustafa; Ozturk, Fahrettin; Demirezen, Mehmet; Evis, Zafer
    DIN 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.
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    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, Zafer
    In 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.
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    Artificial-neural-network prediction of hexagonal lattice parameters for non-stoichiometric apatites
    (2014) Kockan, Umit; Ozturk, Fahrettin; Evis, Zafer
    In 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.
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    Finite Element Simulation of Diametral Strength Test of Hydroxyapatite
    (AMER INST PHYSICS, 2010) Ozturk, Fahrettin; Evis, Zafer; Toros, Serkan; Chinesta, F; Chastel, Y; ElMansori, M
    In this study, the diametral strength test of sintered hydroxyapatite was simulated by the finite element software, ABAQUS/Standard. Stress distributions on diametral test sample were determined. The effect of sintering temperature on stress distribution of hydroxyapatite was studied. It was concluded that high sintering temperatures did not reduce the stress on hydroxyapatite. It had a negative effect on stress distribution of hydroxyapatite after 1300 degrees C. In addition to the porosity, other factors (sintering temperature, presence of phases and the degree of crystallinity) affect the diametral strength of the hydroxyapatite.
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    Mechanical and microstructural evaluations of hot formed titanium sheets by electrical resistance heating process
    (ELSEVIER SCIENCE SA, 2013) Ozturk, Fahrettin; Ece, Remzi Ecmel; Polat, Naki; Koksal, Arif; Evis, Zafer; Polat, Aytekin
    In this study, effect of temperature in the electrical resistance heating process on mechanical properties and microstructures of commercially pure titanium grade 2 (CP2) and Ti-6Al-4V (T64) alloy sheets was investigated. Sheets were successfully heated by the electric resistance heating process, and their mechanical properties and microstructures were evaluated. Ductilities of both materials were increased significantly after 400 degrees C. Results indicate that no significant change was observed in grain sizes and microhardness of the materials. XRD analysis revealed that presence of secondary phases regarding oxidation of Ti was observed for 164 alloy above the manufacturer specified temperature ranges. However, no secondary phase was observed even above the manufacturer specified temperature ranges for CP2. (c) 2013 Elsevier B.V. All rights reserved.