Browsing by Author "Elaldi, Faruk"

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Ballistic performance of unidirectionally oriented carbon fiber reinforced composite armor with high-velocity impact
(2020) Kacan, Yelda O.; Elaldi, Faruk
For the last few decades, composite materials have been more popular than other conventional metal materials in the aircraft industry. Having better mechanical properties (strength, fatigue life, impact strength, corrosion resistance, etc.) and being lighter than conventional engineering materials, composites have become very important in defense industry as well. In spite of the fact that some of the composite materials such as aramid-based composites have been effectively used in body protection, they have not been so successful in heavy armored vehicles which are generally equipped with different types of add-on armor blocks for protecting against threats. These add-on armors are mostly composed of armor steels and ceramics. This study specifically aims to investigate high-velocity impact behavior of unidirectionally oriented carbon fiber reinforced/epoxy layer sandwiched with armor steel plates that are exposed to kinetic energy projectile. Carbon fibers are normally very brittle to transverse loading direction, contrarily, to its axial tension or compression direction. This is the reason why it is claimed that this high compression strength property of carbon fibers could be used for manufacturing a layer in order to replace ceramics in add-on multilayer composite armor. In order to prove this hypothesis, an experimental analysis has been carried out by performing impact tests on these manufactured add-on armor test samples. Testing was carried out in accordance with the STANAG 4569 level-4 standard. The results indicated that the multilayer carbon fiber reinforced epoxy composite-armor steel hybrid panels can provide level-4 protection with a lower areal density compared to Rolled Homogenous Armor.
Effects of Repair Techniques and Scarf Angles on Mechanical Performance of Composite Materials
(2023) Karaduman, Beyza Naz; Elaldi, Faruk; https://orcid.org/0000-0003-0592-6868; AAG-5060-2019
Today, composite materials, which have the advantage of strength and lightness ratio, have gained great importance especially in the aeronautical industry and automotive sector. With widespread use of composites, the repair of damages caused by external factors has also become an important research topic. In this study, the effects of different repair methods and scarf angles on the mechanical performance of the material were investigated. Scarf angles of 20 degrees, 30 degrees, and 45 degrees have been selected in order not to create too many scarf areas and to find a quick repair method. Also, a comparison of single scarf and double scarf repair was made to find a more robust solution. The samples were produced from carbon fiber prepreg and with the [45/0/90/0/45](2s) fiber orientation. Tensile, compression, and flexural (3-point bending) tests according to ASTM standards were applied to composite samples prepared with single scarf and double scarf repair configurations at different angles. The stress-strain curves obtained as a result of the tests showed that the specimens repaired at 20 degrees had the highest strength. In addition, it has been determined that the samples repaired with double scarf withstand higher forces compared to the samples repaired with single scarf at the same angle.
Experimental Analysis for the Effect of Impactor Geometry on Carbon Reinforced Composite Materials
(2017) Elaldi, Faruk; Baykan, Busra; Akto, Can; 0000-0003-0592-6868; AAG-5060-2019
For the last three decades, composites have become very preferable materials to be used in the automotive industry, structural parts of aircraft and military systems and spacecraft, due to their high strength and modulus. Composite materials are sometimes exposed to invisible or visible damage due to impact loading during their service life. In this study, the effect of impactor geometry with four different contact surfaces on woven carbon fibre-reinforced composite plates having three different thicknesses are investigated. In the first stage, composite plates were manufactured with the ply orientations of [45/-45/0/90/45/-45](2s), [45/-45/0/90/45/-45](3s), [45/-45/0/90/45/-45](4s) based on conventional usage. In the second stage, carbon fibre-reinforced composite test panels were exposed to low velocity impact tests to obtain force-time, energy-time and force-displacement curves. Finally, semi and full penetration of composite panels and damage magnitude were determined. It was found that the impactor geometries with lower contact surfaces such as conical mid ogive types were much more penetrative on composite plates than the other geometries, but they caused larger damage area in the vicinity of the impact point.
A numerical model for analysis of layer thicknesses on ballistic resistance of a multilayer armor
(2023) Kacan, Yelda Ozdil; Elaldi, Faruk; 0000-0001-8009-9335
The interest in composite materials, which are lighter and have better mechanical properties (strength, fatigue resistance, corrosion resistance, etc.) than traditional engineering materials, is increasing day by day. In particular, their responses to low or high-velocity impact loads have been among the important research topics of recent years. In this study, unlike the traditional ceramic-based composite armor structures used in the defense industry, the effect of total carbon fibers specifically parallel oriented into impact direction on penetration resistance has been investigated, and penetration resistance of a multilayer hybrid composite armor which is composed of carbon fiber composite blocks sandwiched by two armor steel plates exposed to high-velocity impact has been analyzed numerically. Carbon fibers are normally very brittle to the transverse loading direction, contrarily, to their axial tension or compression direction. This is the reason why it is claimed that this high compression strength property of carbon fibers could be used as a layer in order to replace ceramics in add-on multilayer composite armor. The numerical model created in the ANSYS LS-DYNA program was verified by using the experimental data obtained in an earlier study. The verified numerical model was used to analyze high-velocity impact simulations of multilayer hybrid composite armor for different thicknesses of armor steel to reduce the areal density. By these simulations, minimum areal density compared to Rolled Homogeneous Armor steel for equivalent protection was finally achieved, and thus the hypothesis saying that carbon fibers parallel oriented to impact direction can give high penetration resistance was proved by showing that developed multilayer carbon fiber reinforced epoxy composite-armor steel hybrid panels have indicated a better protection level than STANAG 4569 Level-4 with a lower areal density.
An optimization for milling operation of Kevlar fiber-epoxy composite material using factorial design and goal programming methods
(2019) Ic, Yusuf Tansel; Elaldi, Faruk; Kececi, Baris; Uzun, Gozde Onder; Limoncuoglu, Nur; Aksoy, Irem; 0000-0003-0592-6868; 0000-0002-2730-5993; AAI-1081-2020; AAG-5060-2019; F-1639-2011; AAC-4793-2019
Kevlar fiber-epoxy composite material is extensively used in manufacturing areas because of the advantages of composite material's characteristics. It is usually processed by traditional machining methods but the drawbacks for determination of optimum cutting parameters might cause some material deformations during machining process. In this study, the cutting parameters are concurrently optimized by using the integrated 2k factorial design and goal programming methods for minimum delamination and minimum surface roughness of Kevlar fiber-epoxy composite and the best machining parameters have been obtained for the material. The results were compared with the results of the multi-criteria decision-based Taguchi methods.
Topsis Based Taguchi Optimization of Machining Characteristics in End Milling Operation of Kevlar-Epoxy Composites
(2016) Ic, Yusuf Tansel; Elaldi, Faruk; Kececi, Baris; 0000-0001-9274-7467; 0000-0003-0592-6868; 0000-0002-2730-5993; AGE-3003-2022; AAG-5060-2019; AAC-4793-2019
In this study, the surface quality of an end milling operation on Kevlar-epoxy composite material has been investigated. This article presents a study on design of experiment for optimized cutting parameters in the end milling operation of Kevlarepoxy composites using TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) based Taguchi method. In this paper, quality characteristics such as surface roughness and delamination have been selected for evaluation of the milling performance. Four major control parameters namely, feed rate, depth of cut, slope of the cut, and spindle speed have been analyzed for experimentation. From the application of combined TOPSIS-Taguchi method, the optimal combination levels of milling parameters are obtained. It was found that lower feed rate, lower depth of cut, higher slope of cut, and higher spindle speed is desirable for better surface finish.