Hydrostatic Tube Cyclic Extrusion Compression as a Novel Severe Plastic Deformation Method for Fabricating Long Nanostructured Tubes

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.

Sodium-ion batteries: New opportunities beyond energy storage by lithium

Eftekhari, Ali,Kim, Dong-Won Elsevier 2018 Journal of Power Sources Vol.395 No.-

<P><B>Abstract</B></P> <P>Sodium has been recently attracted considerable attention as a promising charge carrier, but this sudden attention has made the strategy of research somewhat hazy, as most research reports are indeed the examination of typical materials rather than following a solid roadmap for developing practical cells. Although the history of sodium-ion batteries (NIBs) is as old as that of lithium-ion batteries (LIBs), the potential of NIB had been neglected for decades until recently. Most of the current electrode materials of NIBs have been previously examined in LIBs. Therefore, a better connection of these two sister energy storage systems can shed light on the possibilities for the pragmatic design of NIBs. The first step is to realise the fundamental differences between the kinetics and thermodynamics of Na as compared with those of Li. In fact, tiny differences between the electrochemical behaviours of these systems can lead us to new practical ideas for designing suitable materials. Furthermore, NIBs should be considered as new opportunities for energy storage rather than replacing LIBs. Hence, the subtle strategy of research is to learn from LIBs but not replicate them when designing NIBs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Sodium-ion batteries are reviewed from an outlook of classic lithium-ion batteries. </LI> <LI> Realistic comparisons are made between the counterparts (LIBs and NIBs). </LI> <LI> The challenges and potentials of NIBs are subtly highlighted. </LI> <LI> NIBs need a subtle strategy of research and a pragmatic roadmap. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Cathode materials for lithium-sulfur batteries: a practical perspective

Eftekhari, Ali,Kim, Dong-Won Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.34

<P>The most important challenge in the practical development of lithium-sulfur (Li-S) batteries is finding suitable cathode materials. Due to the complexity of this system, various factors have been investigated during the last years, but still, the roadmap for designing the best cathode candidates is not vivid. This review attempts to create a better picture of the cathode process to pave the path for developing more practical cathode materials. The most promising candidates as the host cathode material are porous carbon nanomaterials, which are highly conductive and lightweight while having the capability for fabricating freestanding electrodes. In this case, there is no need for a binder and current collector, and thus, a significantly higher energy density can be expected. Despite the good performance of these carbon-based sulfur cathodes, the presence of some additives anchoring the sulfur molecules to the electrode backbone seems necessary for practical performance. Metal oxides and sulfides are among the best options as additives, as they can act as mediators in the electrochemical redox system of Li/S. Despite their similarities, these additives might mediate in the battery system but <I>via</I> entirely different mechanisms. In addition to carbon nanomaterials, other porous materials, such as metal-organic frameworks, can also provide a cage-like architecture for the construction of the sulfur cathode.</P>

Influence of TBM operational parameters on optimized penetration rate in schistose rocks, a case study: Golab tunnel Lot-1, Iran

A. Eftekhari,A. Aalianvari,J. Rostami 사단법인 한국계산역학회 2018 Computers and Concrete, An International Journal Vol.22 No.2

TBM penetration rate is a function of intact rock properties, rock mass conditions and TBM operational parameters. Machine rate of penetrationcan be predicted by knowledge of the ground conditions and its effects on machine performance. The variation of TBM operational parameters such as penetration rate and thrust plays an important role in its performance. This study presents the results of the analysis on the TBM penetration rates in schistose rock types present along the alignment of Golab tunnel based on the analysis of a TBM performance database established for every stroke through different schistose rock types. The results of the analysis are compared to the results of some empirical and theoretical predictive models such as NTH and QTBM. Additional analysis was performed to find the optimum thrust and revolution per minute values for different schistose rock types.

Some factorization properties of idealization in commutative rings with zero divisors

Sina Eftekhari,Sayyed Heidar Jafari,Mahdi Reza Khorsandi 대한수학회 2024 대한수학회보 Vol.61 No.2

We study some factorization properties of the idealization $\idealztn{R}{M}$ of a module $M$ in a commutative ring $R$ which is not necessarily a domain. We show that $\idealztn{R}{M}$ is ACCP if and only if $R$ is ACCP and $M$ satisfies ACC on its cyclic submodules. We give an example to show that the BF property is not necessarily preserved in idealization, and give some conditions under which $\idealztn{R}{M}$ is a BFR. We also characterize the idealization rings which are UFRs.

Dynamic behavior of three-dimensional composite beam under flapwise excitation

Mojtaba Eftekhari 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.8

In this paper, dynamic response of a symmetrically laminated composite beam is studied under harmonic base excitation. The base is subjected to flapwise excitation tuned to the primary resonance in the presence of 2:1 internal resonance between the out-of-plane bending motion and the in-plane bending and torsional motions. In literature, modified modulation equations of composite beam have been derived and the stability of fixed points has been investigated in frequency and forced responses. However, post-critical behavior of the modulation equations is studied in this study. In bifurcation diagrams sketched near primary and internal resonances, it appears that detuning the flapwise excitation amplitude causes phenomena like jumps, period doubling, multi and quasi-periodic solutions to occur.

Electronic Structure and Half-Metallicity in the Zr2RuZ (Z = Ga, In, Tl, Ge, Sn, and Pb) Heusler Alloys

A. Eftekhari,F. Ahmadian 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.9

The electronic structures, magnetic properties and half-metallicity in Zr2RuZ (Z = Ga, In, Tl, Ge, Sn, and Pb) alloys with AlCu2Mn- and CuHg2Ti-type structures were investigated using firstprinciples density functional theory (DFT) calculations. The calculations showed that Zr2RuIn, Zr2RuTl, Zr2RuSn, and Zr2RuPb compounds with CuHg2Ti-type structures were half-metallic ferromagnets with half-metallic band gaps of 0.18, 0.24, 0.22, and 0.27 eV, respectively. The halfmetallicity originated from d-d and covalent hybridizations between the transition metals Zr and Ru. The total magnetic moments of the Zr2RuZ (Z = In, Tl, Sn, and Pb) compounds with CuHg2Titype structures were integer values of 1B and 2B, which is in agreement with Slater-Pauling rule (Mtot = Ztot 18). Among these compounds, Zr2RuIn and Zr2RuTl were half-metals over relatively wide regions of the lattice constants, indicating that these two new Heusler alloys are ideal candidates for use in spintronic devices.

Measurement of local strain: machine vision and finite element method

Seyyed Ehsan Eftekhari Shahri,Mohammad Lakhi,Sadegh Ranjbar 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.3

Determining the material deformation behavior including local strain data is very useful for analyzing the forming processes. In order to measure strain properties, the uniaxial tensile test was used. More than 10 important mechanical properties were obtained from the uniaxial tensile test. However, through this test, only one strain in the tensile direction can be reported. Obtaining strain at various points in the transverse and longitudinal directions can provide important information about anisotropy, the Poisson’s ratio and material heterogeneity. In this study, machine vision method along with graphical programming were used for automatic strain calculations. Also, an innovative numerical method was developed based on machine vision procedure. In this new method, a number of circles were carved as a matrix pattern on the finite element model. Removing the limitations of the machine vision method, including its sensitivity to vibration, is the most important advantage of this numerical model. The results of the finite element method were evaluated in comparison with the tensile test and the machine vision procedure.

A coupled Ritz-finite element method for free vibration of rectangular thin and thick plates with general boundary conditions

Seyyed A. Eftekhari 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.28 No.6

A coupled method, that combines the Ritz method and the finite element (FE) method, is proposed to solve the vibration problem of rectangular thin and thick plates with general boundary conditions. The eigenvalue partial differential equation(s) of the plate is (are) first reduced to a set of eigenvalue ordinary differential equations by the application of the Ritz method. The resulting eigenvalue differential equations are then reduced to an eigenvalue algebraic equation system using the finite element method. The natural boundary conditions of the plate problem including the free edge and free corner boundary conditions are also implemented in a simple and accurate manner. Various boundary conditions including simply supported, clamped and free boundary conditions are considered. Comparisons with existing numerical and analytical solutions show that the proposed mixed method can produce highly accurate results for the problems considered using a small number of Ritz terms and finite elements. The proposed mixed Ritz-FE formulation is also compared with the mixed FE-Ritz formulation which has been recently proposed by the present author and his co-author. It is found that the proposed mixed Ritz-FE formulation is more efficient than the mixed FE-Ritz formulation for free vibration analysis of rectangular plates with Levy-type boundary conditions.

A Simple and Robust Model-Based Loss Minimization Method for Direct Torque Control of Induction Motor

S. Rasul Eftekhari,S. Alireza Davari,Peyman Naderi,Cristian Garcia,Jose Rodriguez 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

Across the different variety of loss decreasing methods, the loss-model-based methods (LMM) show a fast response and a low torque pulsation. Despite all the mentioned advantages, the approach needs the precise loss model and the knowledge of the motor parameters. Furthermore, the application of the model-based method is direct torque, and flux control is more complicated because the magnetic coefficients of the motor should accurately identify. In this paper, To solve the LMM’s issues, a new model based approach has presented. The inaccuracy problem has fulfilled by dividing the homogenous parameters by each other. Via using this technique, the need for magnetic coefficient identification and the effect of inaccurate parameters have dwindled. Coupled with this, the requirement for computation of iron core loss coefficients have omitted by replacing of iron core loss resistance, which by this deed, in a manner, the estimation precision of iron core loss will enhance. At last, the proposed method had verified by simulation and the results are presented in table format, withal, the parameters of the simulated motor have identified by analyzing an induction motor (IM) in ANSYS Maxwell.