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- 검색키워드
- 저자 : M. Eftekhari (검색결과 4 건)
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M. Eftekhari,G. Faraji,M. Bahrami,M. Baniassadi 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.7
In this study, hydrostatic cyclic extrusion compression (HTCEC) is introduced as a novel severe plastic deformation techniquefor producing the relatively long and large ultrafine grained (UFG) and nano-grained tubes. In HTCEC technique, the utilizationof pressurized hydraulic fluid between the piece and the die leads to the reduction of the friction force and the requiredprocessing load. All of these conditions facilitate the processing of the long and large tubes. Also, during HTCEC process,a movable mandrel is placed inside the hollow tube, which plays a main role in the reduction of the required hydrostaticpressure. To investigate the efficiencies of HTCEC process, aluminum 5052 alloy tubes were processed by HTCEC up totwo passes. Then, the mechanical properties and microstructure evolution were examined. After the first pass of HTCEC,tangled and diffused arrangements of dislocations were formed. Then, the second pass of HTCEC resulted in a more refinedand more homogeneous UFG microstructure with an average subgrain size of 636 nm, while the average grain size of theinitial sample was ~ 360 μm. Tensile tests and hardness measurements revealed that two passes of HTCEC led to an increasein the yield strength from 98 MPa to 254 MPa (~ 2.6 times higher), the ultimate strength from 178 MPa to 306 MPa (~ 1.72times higher) and the microhardness from ~ 56 to ~ 120 Hv (~ 2.14 times higher). Simultaneously, a decrease in the elongationto failure from 31.6 to 15.4% was observed, which is a small amount compared to the results of other studies. Also, incomparison to one-pass, a more homogeneous microhardness distribution through the thickness was detected in the two-passprocessed tube. Fractography evaluations by SEM indicated that predominantly ductile fracture occurred in all samples. Furthermore, the equivalent strain and the pressing load of HTCEC process was evaluated by FEM simulation. It seems thatHTCEC process, by utilizing its potentials, can produce the relatively long and large UFG tubes having a simultaneous highstrength and good ductility.
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M. Motallebi Savarabadi,G. Faraji,M. Eftekhari 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.6
A newly introduced severe plastic deformation process for the production of relatively long ultrafine-grained (UFG) tubes,hydrostatic tube cyclic expansion extrusion (HTCEE), was applied up to two passes on commercially pure copper tubes tostudy the mechanical characteristics and microstructure of the HTCEE processed samples. In HTCEE process, the pressurizedhydraulic fluid around the piece has a main role in the reduction of the friction load leading to a decrease in the requiredpressing force. After the second pass of HTCEE, a UFG microstructure with an average grain size of ~ 127 nm was observed. In two-pass HTCEE processed tub, more refined and also more homogeneous microstructure was achieved compared to theone-pass HTCEE processed and annealed samples. This type of microstructure caused the increment of yield strength from75 to 310 MPa, (~ 4.13 times higher), ultimate tensile strength from 207 to 386 MPa (~ 1.86 times higher) and microhardnessfrom ~ 59 to ~ 143 Hv (~ 2.42 times higher). Simultaneously, elongation to failure was lessened from ~ 55 to 37%. In otherwords, a remarkable increase in the strength and hardness was attained besides a low loss of ductility. Also, microhardnessmeasurements revealed a more homogeneous distribution of hardness in the two-pass processed sample. SEM fractographyanalysis demonstrated that mostly ductile fracture happened in the HTCEE processed samples. Also, the influence of theHTCEE process on the equivalent plastic strain and also the required force was examined via FEM simulation using Abaqussoftware. It seems that HTCEE process, by applying low deforming force, possesses the potential of production of tubeswith long length having a simultaneous good ductility and strength.
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The Diversity of BoLA-DRB3 Gene in Iranian Native Cattle
Nassiry, M.R.,Eftekhari Shahroudi, F.,Tahmoorespur, M.,Javadmanesh, A. Asian Australasian Association of Animal Productio 2008 Animal Bioscience Vol.21 No.4
This study describes genetic variability in the BoLA-DRB3 gene in Iranian native cattle (Bos Indicus and Taurus) and relationships between these breeds. This is the first study of genetic polymorphism of the BoLA-DRB3 gene in Iranian native cattle. We examined exon 2 of the major histocompatibility complex (MHC) class II DRB3 gene from 203 individuals in four populations of Iranian native cattle (52 Sarabi, 52 Najdi, 49 Sistani, 50 Golpayegani cattle) using the hemi-nested PCR-RFLP method. We identified the 36 previously reported alleles and one novel pattern (*eac). Analysis of the frequencies of the various BoLA-DRB3.2 alleles in each breed indicated that DRB3.2*52 in Sarabi cattle (23%), DRB3.2 *14 and *24 alleles in Najdi cattle (13%), DRB3.2 *8 allele in Sistani cattle (22%) and DRB3.2*16 allele in Golpayegani cattle (14%), were the most frequent alleles. Allelic frequencies ranged from 1 to 23% among the 36 alleles and there were some alleles that were found only in Iranian cattle. Effective number of alleles in the four breeds was estimated to be 7.86, 11.68, 7.08 and 3.37 in Sarabi, Najdi, Sistani and Golpayegani, respectively. Observed heterozygosities were the highest in Sarabi (94%) and Najdi (94%). A population tree based on the frequency of BoLA-DRB3.2 alleles in each breed suggested that Najdi, Sarabi and Golpayegani cattle clustered together and Najdi and Sarabi were the closest breeds. Sistani cattle differed more from these three breeds. These new data suggest that allele frequencies differ between Iranian cattle breeds.
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Estimation of calcite wettability using surface forces
Mirhossein Taheriotaghsara,Maria Bonto,Hamid M. Nick,Ali Akbar Eftekhari 한국공업화학회 2021 Journal of Industrial and Engineering Chemistry Vol.98 No.-
The shift in the wetting conditions during injection of modified salinity water (MSW) in carbonatereservoirs has been interpreted in several recent works through the DLVO extended theory. Twosimplifications are usually adopted when applying the DLVO extended theory: (i) the electrostatic energyinteraction is quantified by an analytical solution developed for systems containing only monovalent ionsand (ii) the structural forces are independent of the type of brine. We address those by prioritizing thebrine chemistry. We initially calculate the potential at the mineral and oil surfaces using two differentsurface complexation models implemented in Phreeqc and then we quantify the electrostatic forces bysolving numerically the Poisson Boltzmann (PB) equations for non/symmetrical electrolytes. We observethat not only the identity of the ions, but also, more importantly, the boundary conditions (constantsurface charge or constant surface potential) considered for the solution of PB can drastically modify thecalculated electrostatic energy profile. We then calculate the total interaction energy and estimate amicroscopic contact angle that is consistent with measured values. Our calculations show that increasingthe concentration of salts such as MgCl2, CaCl2, and MgSO4 leads to more water-wet conditions, whereassalts like NaCl, KCl, and Na2SO4 show the opposite effect.
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