Yazar "Halkaci, Huseyin Selcuk" seçeneğine göre listele

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    Comparison of Flow Curves of AA 5457-O Sheet Material Determined by Hydraulic Bulge and Tensile Tests at Warm Forming Temperatures
    (AMER SOC TESTING MATERIALS, 2016) Sukur, Emine Feyza; Turkoz, Mevlut; Dilmec, Murat; Halkaci, Huseyin Selcuk; Halkaci, Mehmet
    The deformation behavior of sheet materials changes according to temperature. It is possible that the formability of a material for different temperatures is investigated and the flow curves are obtained by using a hydraulic bulge test. Generally, biaxial stress state occurs in real forming processes. Flow curves can be derived from the hydraulic bulge test for the biaxial stress state, and the higher strain values can be achieved in comparison to the tensile test without extrapolation. Hydraulic bulge tests are preferred instead of tensile tests on account of presuming the problems can occur during the formation process of sheet material, being informed about the formability of material at the current pressure and temperature states, and obtaining flow curves to perform more accurate process simulations. In this study, the flow curves for the material AA5754-O were obtained using the warm bulge test and by considering the strain rates. The sections of the curves that can be used in simulation were identified, and these curves were comparatively investigated with respect to the curves obtained from the tensile test. In addition, case studies were performed in order to conduct more realisitic simulations using the results of the flow curves obtained from the bulge and tensile tests.
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    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, Mevlut
    In 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.
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    Effects of Heat Treatment Conditions on the Mechanical Properties of AA 2024 Alloy
    (TRANS TECH PUBLICATIONS LTD, 2012) Halkaci, Huseyin Selcuk; Turkoz, Mevlut; Yigit, Osman
    Aluminum alloys have good properties such as high strength-to-weight ratio, corrosion resistance and relatively low cost. Nowadays they are primarily used as wrought and cast in many industries such as automotive, aviation and aerospace because of these properties. Aluminum alloys are classified into two categories as non-heat-treatable and heat-treatable. The mechanical properties of the heat-treatable alloys are improved by solution heat treatment and controlled ageing. While mechanical properties of some heat-treatable alloys, especially 2XXX series, become stable with natural ageing at room temperature within a few days, some of them are unstable and exhibit significant changes in properties even after many years. Heat treatment process of AA 2024 is very sensible and critical and therefore should be carefully performed. In this research, effects of the solution temperature, soaking time, heating rate and quenching delay condition of AA 2024 on the mechanical properties were investigated.
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    Enhancing formability in hydromechanical deep drawing process adding a shallow drawbead to the blank holder
    (ELSEVIER SCIENCE SA, 2014) Halkaci, Huseyin Selcuk; Turkoz, Mevlut; Dilmec, Murat
    In this paper, a new method was proposed in order to enhance the limiting drawing ratio (LDR) of AA5754-O in the hydromechanical deep drawing process (HDD). In the proposed method, a shallow drawbead was added to the blank holder to increase LDR so as to provide strain hardening of a large region on the flange of the sheet material in addition to pre-bulging process which affects particularly only the initial stage but not the later ongoing process. So the LDR of the AA5754-O was increased from 2.65 to 2.787 by enlarging the region of strain hardening in the flange and partially reducing wrinkling tendency due to occurred tensile stresses using the convenient pressure and blank holder force profiles. The importance levels and their convenient values for height of drawbead, pre-bulge height and pressure, surface roughness of the punch were determined with analysis of variance (ANOVA) is a statistical method. ANOVA analysis illustrated that adding a shallow drawbead to the blank holder is the most effective factor between the investigated factors for the HOD process. While the effects of the pre-bulging pressure and pre-bulging height were determined as quite small, the surface roughness of the punch was found unimportant compared to the effect of the shallow drawbead. The highest LDR value was obtained with 1 mm drawbead height, 5 mm pre-bulging height, 10 MPa pre-bulging pressure and 2.8 mu m surface roughness of the punch. (C) 2014 Elsevier B.V. All rights reserved.
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    Experimental investigation on feasibility of using spherical-tip tool electrodes in EDM for rough machining-machining of rectangular pockets
    (GAZI UNIV, FAC ENGINEERING ARCHITECTURE, 2019) Avlar, Engin; Dilmec, Murat; Halkaci, Huseyin Selcuk
    In this study, feasibility of widely used spherical tip tool electrode for machining rectangular pockets instead of a model to form cavity on the work piece for rough machining in Electric Discharge Machining (EDM) was investigated. In CNC EDM machine, two alternative tool paths which gives the changes of the tool electrode geometry were examined using rough machining parameters provides minimum tool wear and maximum material removal rate. Electrode tools have been measured with optoTOP-HE 3B optical measurement system before and after manufacturing with EDM. Center coordinates of spherical electrodes, tool wear and deviation of machined cavities from expected surfaces have been determined from 3D data using Rapidform 2004 PPS software. Moreover, a basic algorithm of a CNC EDM CAM program is proposed for machining rectangular pockets. The accuracy of the algorithm which can find the electrode radius and the tool compensation deviations has been verified with comparing simulation and experimental results.
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    INVESTIGATION INTO REASONS FOR MINIMUM MAJOR STRAIN OFFSETTING OF FORMING LIMIT CURVE OBTAINED WITH NAKAJIMA TEST FOR AA 2024-T4
    (GAZI UNIV, FAC ENGINEERING ARCHITECTURE, 2014) Dilmec, Murat; Halkaci, Huseyin Selcuk; Ozturk, Fahrettin
    In a typical forming limit curve (FLC), the minimum major strain where the minor value is equal to zero is located at y axes. In many forming processes, failure occurs at this region. Many studies in literature indicates that minimum major strain value is obtained about at y axis. In this study, the minimum major strain value is not determined on the y axes and it was found to be offsetted from the y axes to the right about 0.04 strain for AA 2024-T4. This value could be important for evaluations of sheet metal forming processes. In this study, the reasons for the minimum major strain of setting of the forming limit curve for AA 2024-T4 were investigated. It was found that drawbead and heat treatment were most effective parameters for this offsetting. It is observed that offsetting result from pre-strain which occur for conducted tests with using draw-bead and residual stress arising from T4 heat treatment.
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    Investigation on Earing Behavior of AA 2024-T4 and AA 5754-O Aluminum Alloys
    (TRANS TECH PUBLICATIONS LTD, 2011) Turkoz, Mevlut; Dilmec, Murat; Halkaci, Huseyin Selcuk
    Deep drawn parts usually have different wall heights because of earing behavior. This behavior is due to the planar anisotropy (Delta r) of sheet metals. A measure of the variation of normal anisotropy with the angel to the rolling direction in sheet plane is known as planar anisotropy. If the magnitude of the planar anisotropy is relatively large as absolute value, the earing behavior becomes more effective so larger ears occur. Furthermore, the orientation of the sheet with respect to the die or the part to be formed will be important. In addition, cutting of scraps in the parts which have ears leads to material waste. The scope of this study is to determine the planar anisotropy of AA 5754-O and AA 2024-T4 aluminum alloys and to investigate the earing behavior by the way of deep drawing of cylindrical cups.