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    EXTRUSION FORMING OF A DOUBLE BASE SOLID ROCKET PROPELLANT BY FINITE ELEMENT METHOD
    (Pamukkale Univ, 2007) Kalaycioglu, Baris; Dirikolu, M. Husnu; Celik, Veli
    In this study, three dimensional modelling of extrusion forming of a double base solid rocket propellant is performed on Ansys (R) finite element simulation package. For the purpose of initial model construction and later comparisons with elastoviscoplastik model, the solid propellant is assumed to obey the elastic-plastic material response during the direct extrusion process. Taking into account the contact surface behavior with Coulomb friction and geometric and material nonlinearities, an incremental large large strain solution methodology has been adapted in the simulation. The hydrostatic pressure, stress, strain, and displacement values during extrusion of the solid rocket propellant are obtained from the simulation.
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    The minimization of absolute deviation from common due date in two machine flowshop scheduling with learning effect
    (Gazi Univ, Fac Engineering Architecture, 2009) Isler, Mesut Cemil; Celik, Veli; Toklu, Bilal
    The phenomenon of the learning effect has been extensively studied in many different areas of operational research. However, there have been a few studies in the general context of production scheduling; also there have been fewer studies in flow-shop. Until the beginning of 1990 Earliness/Tardiness (E/T) problem was known as weighted absolute deviation problem. Not only tardiness but also earliness is very important performance criteria for scheduling problem. While total tardiness criteria provides adaptation for due date (ignoring results of earliness done jobs), it deals with only cost of tardiness. However this phenomenon has been started to change with Just in Time (JIT) production concept. Earliness is as important as tardiness on JIT production. In this study, the integer programming was suggested to take in to consideration "weighted E/T performance criteria and learning effect process property at the two machine flow-shop scheduling" and solution results was evaluated with sample problems by us.
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    Sliding Friction and Wear Behavior of Pack-Boronized AISI 1050, 4140, and 8620 Steels
    (Taylor & Francis Inc, 2008) Soydan, Yavuz; Koksal, Sakip; Demirer, Ahmet; Celik, Veli
    This paper describes the dry sliding friction and wear performance of boronized AISI 1050, 4140, and 8620 steels with the Fe(2)B phase coating on the surface. The studies were carried out using a pin-on-disc arrangement. The disc material was made of carburized AISI 1020 steel. For the normalized (untreated) steels, two basic wear regimes were observed; namely, oxidative and severe metallic wear. In the oxidative regime, a low wear rate of 1E-5 mm(3)/Nm was found. The worn surfaces of the pins and discs were smooth and covered with patchy oxides. In severe wear, the wear rate was very high (1 E-3 mm(3)/Nm). The worn specimens were characterized by rough surfaces, plastic deformation, and metallic wear debris. Boronizing changed the wear mechanisms of steels. The test results showed that the boronized steels underwent oxidative fatigue wear with very low wear rate of 2 E-6 mm(3)/Nm. In addition, boronized steels exhibited lower friction coefficient than normalized steels at a sliding speed of 2 m/s.
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    Theoretical and experimental investigation of acoustic performance of multi-chamber reactive silencers
    (ELSEVIER SCI LTD, 2020) Arslan, Hakan; Ranjbar, Mostafa; Secgin, Erkan; Celik, Veli
    The acoustic attenuation and performance analysis for blast flow field inside a silencer is investigated. In this regard, a silencer system is designed to reduce the exhaust noise. The effect of position and the number of the baffles for each design on sound transmission loss have been investigated using theoretical, numerical and experimental studies. Three prototypes are manufactured for the experimental studies. Using the measured results, insertion loss graphics have been obtained. The silencer performances are dependent on the baffle geometry, number and the positions. The experimental results are in a good agreement with the simulation results. It is observed that by considering the same number of baffle numbers but located at various locations, the model which shows the best sound transmission loss performance has also the best insertion loss performance and has the least value of peak sound pressure level. (C) 2019 Elsevier Ltd. All rights reserved.