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    Effects of the number of fatigue cycles on the impact behavior of glass fiber/epoxy composite tubes
    (ELSEVIER SCI LTD, 2017) Kara, Memduh; Kirici, Muhammed
    This paper investigates the impact damage behaviors of filament wound glass reinforced plastic (GFRP) tubes that were fatigued under internal pressure. Damage to the GFRP tubes was investigated, and the tubes' bursting pressures were determined. (+/- 55 degrees)(3) E-glassfepoxy composite specimens were manufactured using the filament winding method. Fatigue tests were applied to the specimens at a stress rate of 0.05 and frequency of 0.42 Hz in accordance with the ASTM-D 2992 standard. The specimens were subjected to fatigue tests at a stress level of 35% static burst pressure. Fatigued and non-fatigued composite tube specimens were pre-stressed by applying 32 bar internal pressure. After applying internal pressure, low velocity impact tests at various energy levels (5 J, 10 J and 15 J) were performed on the GFRP tubes. Plots of contact force-time history were obtained. For impact characteristics, such as deflection, absorbed energies were calculated based on the force time histories. The damaged areas that developed on the specimens were also evaluated. The specimens that fatigued and impacted at the 10 J energy level burst in accordance with the ASTM D 1599 standard. It was concluded that for all of the energy levels employed in this work, as the number of fatigue cycle increases, the rigidity of the tubes decreases. (C) 2017 Elsevier Ltd. All rights reserved.
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    Impact behavior of carbon fiber/epoxy composite tubes reinforced with multi-walled carbon nanotubes at cryogenic environment
    (ELSEVIER SCI LTD, 2018) Kara, Memduh; Kirici, Muhammed; Tatar, Ahmet Caner; Avci, Ahmet
    This paper investigates the impact behaviors of filament wound carbon fiber/epoxy (CFRP) nanocomposite tubes at cryogenic temperatures. As nanofiller, multi-walled carbon nanotubes (MWCNT) were introduced to epoxy resin. (+/- 55 degrees)(4) carbon fiber/epoxy nanocomposite specimens were manufactured using the filament winding method. Low velocity impact tests at 15 J energy level were performed on the neat and MWCNT added CFRP tubes at different temperatures (23 degrees C, 0 degrees C, - 50 degrees C, -100 degrees C, -196 degrees C). The contact force-time, contact force displacement histories and absorbed energy values by the specimens were obtained from the low velocity impact tests for each test samples. The effects of temperature change to impact response of neat and MWCNT added CFRP tubes were evaluated. Damage zones on the specimens were also examined in detail. It was observed that damages on the specimens increased when the temperature decreased for all test samples. Furthermore, the addition of nanoparticles to the specimens resulted in higher contact force values for the same temperature and less damage in the sample sections.