Browsing by Author "Evci, Celal"

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Citation Count: Evci, C., Gülgeç, M. (2012). An experimental investigation on the impact response of composite materials. International Journal of Impact Engineering, 43, 40-51.
An experimental investigation on the impact response of composite materials
(Pergamon-Elsevier Science Ltd, 2012) Evci, Celal; Gülgeç, Müfit; 243247; 4168
Due to the improved impact performance characteristics, composites are widely used in engineering and military applications to absorb the impact energy. Determination of impact response of composite materials provides the engineer and the manufacturer with critical knowledge to understand the failure criteria, initiation of the first failure and damage growth through the laminates. This study covers the investigation of impact damage growth and determination of Hertzian failure and maximum force thresholds in three different types of composites. Unidirectional E-Glass, woven E-Glass and woven Aramid composite samples with dimensions of 100 x 100 mm are subjected to low velocity impact with an instrumented impact test system. Rebound, on-set of perforation and perforation limits of composites are found out. Also, energy profile diagrams of both unidirectional and plain weave E-Glass composites are obtained. According to test results, woven composites are found to be superior to unidirectional composites in the protection limit of low velocity impact. It is also observed that damage growth in woven composites is restricted within a smaller area. Impact tests conclude that strength of the composite materials under dynamic loading increases considerably compared to static loading case as a result of strain rate sensitivity.
Citation Count: Evci, C., Gülgeç, M. (2014). Effective damage mechanisms and performance evaluation of ceramic composite armors subjected to impact loading. Journal Of Composite Materials, 48(26), 3215-3236. http://dx.doi.org/10.1177/0021998313508594
Effective damage mechanisms and performance evaluation of ceramic composite armors subjected to impact loading
(Sage Publications Ltd, 2014) Evci, Celal; Gülgeç, Müfit; 243247; 4168
Researches on the armor systems composed of composite materials with ceramic frontal face and polymer-based back-support are continuously developing further. This study, which mainly covers the impact behavior of ceramic composite armors, is a two-stage research. The first stage involves the investigation of component-level impact characteristics and failure mechanisms of the ceramic composite armors. At this stage, low-velocity impact behavior of ceramics and fiber-reinforced composites is investigated. Impact test results revealed that impact loading is of dynamic nature and strength of the composite materials under dynamic loading increases considerably as a result of strain rate sensitivity, which makes them the right choice to be used in conjunction with ceramics in armor systems. The second stage examines the ballistic impact behavior and ballistic performance of the armor systems. The extent and pattern of impact damage related to projectile velocity are determined for the armor components and the armor itself.
Citation Count: Gulgec, Mufit; Evci, Celal, "Functionally Graded Hollow Cylinder Under Pressure and Thermal Loading: Effect of Material Parameters on Stress and Temperature Distributions", International Journal of Engineering Science, 123, pp. 92-108, (2018).
Functionally Graded Hollow Cylinder Under Pressure and Thermal Loading: Effect of Material Parameters on Stress and Temperature Distributions
(Pergamon-Elsevier Science LTD, 2018) Evci, Celal; Gülgeç, Müfit; 4168
This study presents an analytical solution of stresses and displacements in a long functionally graded (FGM) hollow cylinder subjected to uniform heat generation and internal pressure. Thermo-elastic material properties of FGM cylinder continuously vary in radial direction along the thickness with a power function. The temperature distribution is assumed to vary as a function of the radial coordinate and in steady state. Stress formulation approach is employed using the Airy stress function to derive the analytical solution. In the failure analysis of FGM cylinder, Coulomb-Mohr theory is applied for the ceramic phase whereas Tresca yield criterion is used for the metal phase. The stress analysis reveals that stresses in FGM cylinder decrease considerably, compared to the homogenous one, for a particular interval of material parameters. Radial displacement analysis in FGM cylinder supports the results obtained from stress analysis. (C) 2017 Elsevier Ltd. All rights reserved.