Browsing by Author "Salahi, Salar"

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Fabrication and mechanical characterization of polypropylene clay nanocomposites
(Trans Tech Publications Ltd, 2021) Zakaria, A. Z.; Salahi, Salar; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven
Investigating the influence of process parameters is vital to enhance the mechanical properties of nanoparticle reinforced polymer composites. Nanocomposites of polypropylene/nanoclay are prepared by the extrusion method. To characterize the mechanical response of nanocomposites over different compounding ratios, samples are prepared with 5 and 10 wt%. Effects of re-extrusion and (PP-g-MA) compatibilizer on the tensile performance of nanocomposites were evaluated at different strain rates. X-ray diffraction evaluation of compounds indicated that re-extrusion is an important factor in increasing the exfoliation degree. Results show that improvement in the exfoliation degree enhances the tensile modulus, without significant influence on the tensile strength.
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Fatigue behavior of friction stir welded joints of pure copper with ultra-fine grains
(Elsevier, 2015) Salahi, Salar; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Salahi, Salar
In order to determine the long term durability of friction stir welded joints with ultra-fine grained microstructure, investigation of the mechanical response with specific emphasis on fatigue behaviour is critical. In this paper, fatigue behavior of friction stir welded joints of pure copper in low cycle; strain-controlled regime was investigated. Microstructural characterizations indicated the formation of recrystallized ultrafine-grained microstructure in the nugget zone (NZ) after friction stir welding. Fatigue properties were specified at a strain ratio of 0.1 with total strain amplitudes of 0.01, 0.1, and 0.2%. The results attained from the experiments demonstrated cyclic hardening effect at high strain amplitudes, while softening was observed in low strain amplitude of 0.01%. The hysteresis loops indicated the concavity along with the small portion of linear behavior after the reversal point. Localized deformation in the form of shear bands along with equiaxed cells and noticeable misorientation were observed on the fracture surface.
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Low temperature behavior of ZK60 magnesium alloy after thermo-mechanical processing
(2017-08) Salahi, Salar; Yapıcı, Güney Güven; Yapıcı, Güney Güven; Bundur, Zeynep Başaran; İpekoğlu, M.; Department of Mechanical Engineering; Salahi, Salar
Due to its low weight and good combination of mechanical strength and formability, wrought magnesium alloys containing zinc and zirconium are widely used in automotive and aerospace industries. Since mechanical properties of pure magnesium are weak, the addition of alloying elements is used to improve the mechanical response of magnesium alloys. In this study, ZK60 wrought alloy was selected to improve its mechanical properties using thermo-mechanical processes. A systematic combination of heat treatment and warm rolling was applied for this purpose. The solution treated sample was exposed to rolling followed by annealing treatment for enhancing the formability. Static and under stress regimes of aging were performed to form fine precipitates in the Mg matrix. The low temperature tensile behavior of samples was investigated at temperatures of -60℃, -20℃ and ambient temperature at a quasi-static strain rate of 10-3 s-1. The effect of processing parameters including heat treatment, deformation and aging on the microstructure, texture and mechanical behavior of samples were characterized as well. It was shown that systematic thermo-mechanical processes can significantly refine the microstructure and enhance the mechanical properties of static and stress aged samples. The fine grained structure along with equiaxed and uniform grains were achieved for the stress aged samples, while bimodal structure with coarse grains was observed for the solution treated sample. It was shown that rolling and stress aging can form strong basal texture aligned with the normal direction. It was also observed that in solution treated sample few number of coarse precipitates were formed, while high density of fine precipitates was observed for the static aged sample. The stress aged sample possessed higher density of precipitates relative to the solution treated and static aged samples. The results obtained from the tensile tests proved that the mechanical properties of both static and stress aged samples were higher than that of the solution treated sample. While the tensile strength and elongation to failure of solution treated sample was 255 MPa and 11.2% respectively, the tensile response for best condition of static aged sample was improved up to 304 MPa and 25%. The rolling and stress aging processes under the load of 50 MPa for 3 hours improved the tensile strength of samples up to 353 MPa and ductility up to 12.5%. At -60℃, the mechanical response of solution treated sample is limited to strength of 262 MPa and ductility of 2.6%. The mechanical properties of stress aged sample are significantly improved at the same temperature up to strength of 338 MPa and ductility of 9.2%.
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Low-cycle fatigue behavior of friction stir-welded copper joints
(Springer, 2021-11) Ghobadlou, Ali Hosseinzadeh; Salahi, Salar; Radi, Amin; Sajadifar, Seyed Vahid; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Ghobadlou, Ali Hosseinzadeh; Salahi, Salar; Radi, Amin; Sajadifar, Seyed Vahid
Investigation of the fatigue response of friction stir-welded (FSWed) joints is especially important in the design and manufacturing of components with exposure to cyclic loading. In this study, cyclic response of FSWed pure copper joints is investigated in the low-cycle fatigue regime. Microstructural characterizations revealed that FSW introduced a severely deformed microstructure in the nugget zone (NZ). Fatigue response was determined at a strain ratio of 0.1 by varying the total strain amplitude from 0.1 to 0.6%. Cyclic softening was observed for the low strain amplitude of 0.1%, whereas hardening was detected at higher strain amplitudes. The hysteresis loops demonstrated symmetricity along with noticeable linear behavior after the reversals. Typical fractures occurred in the heat affected zone (HAZ) rather than the NZ or the base metal due to grain coarsening of the HAZ. Improved cyclic properties of the NZ along with stable behavior up to 1000 cycles at a total strain amplitude of 0.3% were attributed to its fine and homogeneous microstructure. Moreover, fracture surface analysis demonstrated a ductile behavior represented by dimples in the sample strained at 0.1% in contrast with a brittle fracture surface of the sample fatigued at 0.5% strain amplitude.