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    Effects of production parameters and conditioning upon ballistic characteristics of para aramid light armors
    (SAGE PUBLICATIONS LTD, 2008) Akdemir, Ahmet; Candan, Can; Sahin, Oemer Sinan
    Composite materials are increasingly used in armors design due to their high strength to weight ratios and energy absorption capacities. It is very important to determine the best production parameters for armor production. On the other hand, the armors must show superior durability against harsh working conditions. So it is crucial to know the ballistic characteristics of such composite armors. In this study the effect of production parameters upon the terminal ballistic properties of para-aramid composite armor were examined under different conditionings. The composite armor plates were produced by hot pressing with four different pressing times. Before ballistic test, the armor plates conditioned at +21, +63, and -35 degrees C at 50% of relative humidity and +21 degrees C immersed into water temperature for 24 h, in which weapons, ammunition, and equipment designed for use in the battlefield, are expected to fully operate.
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    Fatigue Crack Growth Behavior of Filament Wound Composite Pipes in Corrosive Environment
    (SAGE PUBLICATIONS LTD, 2009) Sahin, Oemer Sinan; Akdemir, Ahmet; Avci, Ahmet; Gemi, Lokman
    The stress corrosion crack growth behavior of +/- 45 degrees, +/- 55 degrees, and +/- 75 degrees filament wound composite pipes with surface crack subjected to 0.6 M HCl acid under alternating internal pressure was investigated. E-glass/epoxy pipes consist of six layers with stacking sequences of (+45/-45)(3), (+55/-55)(3), and (+75/-75)(3). Dilute (0.6M) HCl acid was applied to the surface crack region by a corrosion cell mounted on the outer surface of the pipe. The specimens were tested at room temperature and exposed to open-ended fatigue tests in which the pipes can deform freely in the axial direction. The tests were performed in accordance with the ASTM D-2992 standard. The surface notches with different a/t and a/c forms were cut on the outer surface of the pipe parallel to the pipe axis. The internal pressure was generated by conventional hydraulic oil for fatigue loading. The low cycle tests were applied with 0.42 Hz frequency and R = 0.05 stress ratio. After the corrosion fatigue test, the fracture surfaces were examined and observed damage mechanisms discussed.
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    Fatigue crack growth of filament wound GRP pipes with a surface crack under cyclic internal pressure
    (SPRINGER, 2008) Samanci, Ahmet; Avci, Ahmet; Tarakcioglu, Necmettin; Sahin, Oemer Sinan
    In this study, fatigue damage behavior of (+/-75(3)) filament wound composite pipes with a surface crack under alternating internal pressure was investigated. The specimens were tested at room temperature and exposed to open ended fatigue tests in which the pipe can be deformed freely in the axial direction. The tests were carried out in accordance with the ASTMD-2992 standard. The alternating internal pressure was generated by conventional hydraulic oil. The low cycle tests were performed with 0.42 Hz frequency and R = 0.05 stress ratio. Glass reinforced polymer pipes (GRP) are made of E-glass/epoxy and have (+/-75(3)) configuration. Surface cracks were machined in the axial direction of the pipes which have depth-to-thickness ratios a/t = 0.25-0.38-0.50 and depth to length ratio of a/c = 0.2. Tests were performed at three different loads of 50%, 40%, and 30% of ultimate hoop stress strength of unnotched pipes. The failure behavior of GRP pipes during the test was observed and fatigue test results were presented by means of (S-N) Curves and delamination damage zone area-cycle (A-N) curves.
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    Mixed-mode Fracture Toughness and Kink Formation of Woven Glass Reinforced Epoxy Composites
    (SAGE PUBLICATIONS LTD, 2009) Colak, Fatih M.; Daghan, Behcet; Sahin, Oemer Sinan
    In this study the fracture behavior of woven glass fiber reinforced epoxy composites with trough thickness crack oriented at different angles were investigated. The composite plates consisting of five layers have a thickness of 1.2 mm. The trough cracks were formed at the center of the specimens with lengths of 5 mm, 7 mm and 9 mm. The fracture behavior of the composites, subjected to tensile loading and kink formation, were investigated. The fracture toughness of the composite specimens was determined by using both initial notch depth and the compliance method. The experimental results were presented in graphical form.