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- MakaleYalnız künye2023Comparison of Mechanical Properties Obtained for Armor Steels: Conventional Methods vs. Nanoindentation
Ekmekci, Dursun; Cora, Ömer Necati
The mechanical properties of three armor steels, namely Ramor 500, Ramor 550, and Armox Advance, were acquired by nanoindentation and conventional methods, and then the results were compared. To this goal, samples were extracted from different (e.g., undeformed and deformed) zones of the ballistically tested armor plates. Then, nanoindentations were performed at 10-mN maximum load and different maximum indentation depths (50-150 nm). In addition to the hardness and modulus of elasticity values of the examined materials, residual stress values of the samples were calculated through the equations suggested in the literature. These values were then compared with the residual stress measurements obtained with the conventional x-ray diffraction (XRD) - sin2ψ method. Moreover, Charpy V-notch impact tests were performed to calculate the fracture toughness of armor steel samples. Microstructural analysis (e.g., optical microscope, scanning electron microscope, atomic force microscope), surface roughness, and micro-hardness (micro-Vickers) measurements were also obtained. It was noted that hardness values for the Ramor 500 and Ramor 550 armor steels were in the range of 5.5-9 GPa, whereas the hardness values of Armox Advance samples were obtained in the 8.6-10.2 GPa range at a 50-nm indentation depth. The residual stress values obtained with nanoindentation were found to be in quite good agreement with the one obtained through XRD. It was proven that nanoindentation can be used to acquire several mechanical properties through considerably less sample preparation procedure, in an automated, and a more representative manner because of the measurements obtained at multiple points.
- MakaleAçık Erişim2023Effect of aging time and temperature on properties of AA7075 alloy; [Yaşlandırma süresinin ve sıcaklığının AA7075 alaşımının özelliklerine etkisi]
Budak, Selahattin; Çolak, Harun; Yakut, Yusuf
In this study, the effect of aging at different temperatures and times on the properties of AA7075-T6 alloy was investigated. The samples prepared for the experimental studies were subjected to the solution, quenching, and then aging heat treatment at 100 °C and 200 °C for different periods (42-66-90 hours). The properties of the experimental samples were investigated by hardness, compression test, and scanning electron microscope (SEM). As a result of the studies, it was determined that the aging heat treatment had a positive effect on the microstructure and mechanical properties of the AA7075 alloy compared to the reference sample. Especially as a result of the heat treatments at 100 °C, higher results were obtained in hardness and compression strength compared to the initial values.
- MakaleYalnız künye2022Effect of Working Conditions on the Lubricated Wear Behavior of Zn-40Al-2Cu-2Si Alloy in the As- Cast and T6 Heat-Treated States
Savaskan, Temel; Hekimoglu, Ali Pasa; Azakli, Zeki; Calis, Merve
In order to determine the effect of working conditions on the lubricated wear behavior of Zn-40Al-2Cu-2Si alloy in the as-cast and T6 heat-treated states, its tribological properties were studied at different oil flowrates, contact pressures, and sliding speeds in comparison with SAE 660 bronze. It was observed that the friction coefficient, temperature, and wear volume of both materials decrease, but their average surface roughness increase with increasing oil flowrate. As the pressure increased, the friction coefficient and average surface roughness of the experimental materials decreased, but their temperature and wear volume increased. It was also found that the working temperature of these materials increased, but their wear volume showed a decrement and a subsequent increment with increasing sliding speed. In addition, their wear volume and average surface roughness showed opposite changes with the sliding speed. Zn-40Al-2Cu-2Si alloy in both as-cast and heat-treated conditions showed lower wear volume and friction coefficient than SAE 660 bronze. This indicates that Zn-40Al-2Cu-2Si alloy can be used to manufacture diesel engine crankshaft journal bearings.
- MakaleYalnız künye2020Effect of indentation loading type on the mechanical properties of advanced high strength steel grade DP 800
Ekmekci, Dursun; Cora, Ömer Necati
The goal of this study was to acquire mechanical properties of a dual-phase grade advanced high strength steel (AHSS) by means of different microindentation loading conditions. Conventional, cyclic, and multi-step indentations were performed on DP 800 sample; and Young’s modulus, hardness values were obtained by the depth-sensing indentation technique. Effects of different load levels (50–300 mN) and type of indentation on the results were also analyzed through ANOVA. The load levels experimented yielded overall material response rather than its constituents (e.g., martensite and ferrite). Both hardness and Young’s modulus tend to decrease with increasing maximum indentation load level, especially from 50 to 100 mN, which is regarded as indentation size effect.
- MakaleYalnız künye2016Effect of plasma nitriding treatment on structural, tribological and electrochemical properties of commercially pure titanium
Çelik, Ilhan; Karakan, Mehmet
In this study, plasma nitriding treatment was applied to commercially pure titanium (Grade 2). Structural properties, electrochemical and tribological behaviours of the nitrided pure titanium specimens were comparatively investigated. Microstructure and morphology of the plasma nitrided specimens were analysed by X-ray diffraction and scanning electron microscopy. Furthermore, corrosion tests were conducted in Ringer's solution, which represents a human body environment, to determine electrochemical properties. Then, tribological and frictional properties were investigated using pin-on-disc tribometer, and a micro-hardness tester was used to measure the hardness of the coatings. The results showed that plasma nitrided specimens exhibited higher surface hardness than the untreated specimens did. In addition, the plasma nitrided specimens at 700 °C presented significantly better performance than the other plasma nitrided specimens (at 500 °C and 600 °C) under dry wear conditions. Moreover, corrosion test results showed that corrosion behaviours of untreated and nitrided samples had similar characteristic.
- MakaleYalnız künye2016Investigation of structural and tribological properties of electroless Ni-B coated pure titanium
Çelik, Ilhan; Karakan, Mehmet; Bülbül, Ferhat
In the present study, the surface of commercial pure (Grade 2) titanium was coated with electroless Ni-B and, then, it was subjected to heat treatment for an hour at 400°. The surface morphology, microstructure and phase identification were analysed by X-ray diffraction and scanning electron microscope. Wear behaviour characterisation was carried out using a ball-on-disc tribometer. The results of the analyses showed that the electroless Ni-B coating had a significantly amorphous structure in the as-deposited condition. It was also determined that the coating structure crystallised after the heat treatment and wear resistance of pure titanium increased after electroless Ni-B coating. Particularly, upon the heat treatment, it was observed that wear resistance and surface hardness of pure titanium considerably increased.
- Derleme MakaleYalnız künye2015EXPERIMENTAL INVESTIGATION OF THE STRESS RELAXATION BEHAVIOURS OF EPDM SYNTHETIC RUBBERS
Mazlum, Ugur; Vahapoglu, Vahap; Karadeniz, Sami
Rubber type materials are preferred because they are suitable for use in many engineering applications besides their elasticity. EPDM rubber show outstanding heat, ozone and weather resistance and has excellent electrical properties. Therefore this rubber as an elastomer is an engineering material that has wide range of applications in industry such as door and window seals, radiator, garden and heating hoses, tubing, washers, belts, electrical insulation, roofing membrane and rubber mechanical goods. In this works, the stress relaxation behaviour of EPDM rubber at the room temperature were experimentally investigated. Applied to the hardness EPDM samples were subjected to different loading programs. In addition, for the loading programs that were implemented, it is shown that for the EPDM rubbers tested the stress relaxation curves obtained at different stretch ratios may be represented by a single representative curve for the specimens having the same hardnesses.