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Journal of Materials Science & Technology 2014年第8期30卷 826-834页

作者： h.Barekatain M.Kazeminezhad a.h.kokabi Department of Materials Science and Engineering Sharif University of TechnologyAzadi AvenueTehranIran

In this study,AA 1050 aluminum alloy and commercially pure copper in annealed and severely plastic deformed conditions were *** technique used for imposing the severe strain to the sheets was constrained groove pressing（CGP） *** annealed and severely plastic deformed sheets were subjected to friction stir welding（FSW） at different rotation and traverse *** was placed in advancing *** offset of approximately 1 mm was used toward Al side for all welds.A range of welding parameters which can lead to acceptable welds with appropriate mechanical properties was *** the FSWed CGPed samples,it was observed that the welding heat input caused grain growth and decrease in hardness value at Al side of the stir *** was found that,generally the weakest parts of weld joints of annealed and CGPed samples were Al base metal and stir zone,*** investigations showed that several forms of intermetallic compounds were produced.

关键词： Friction stir welding Severe plastic deformation Aluminum Copper Intermetallics

Effects of heat input in friction stir welding on microstructure and mechanical properties of AA3003-h18 plates

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Transactions of Nonferrous Metals Society of China 2015年第7期25卷 2147-2155页

作者： B.ABNAR M.KAZEMINEZhAD a.h.kokabi Department of Materials Science and Engineering Sharif University of Technology

The non-heat-treatable AA3003-h18 plates were joined by friction stir welding（FSW） to achieve a proper joint by optimizing the welding *** this purpose,the effects of heat input on microstructure and mechanical properties of the welded samples were investigated by changing the ratios of rotational speed（800-1200 r/min） to travel speed（40-100 mm/min）（w/v）.It was revealed that the grain growth rate was strongly increased with the increase of the heat input by rotational speed at constant travel speed,while the grain growth rate was slightly increased with the increase of the heat input by travel speed at constant rotational ***,hardness reduction was observed in the stir zone at higher rotational speed compared with that at lower *** interesting observation was that various welding parameters do not have noticeable effect on the tensile strength of the FSW ***,it has been observed that the fracture location of tensile test specimens was placed in the heat-affected zone（hAZ）on the advancing side at lower travel speed,while at higher travel speed,it was placed at the hAZ/thermomechanical affected zone（TMAZ） interface on the retreating side.

关键词： AA3003-h18 alloy friction stir welding heat input microstructure mechanical properties

Improvement in the mechanical properties of Al/SiC nanocomposites fabricated by severe plastic deformation and friction stir processing

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International Journal of Minerals,Metallurgy and Materials 2017年第3期24卷 297-308页

作者： M.Sarkari Khorrami M.Kazeminezhad Y.Miyashita a.h.kokabi Department of Materials Science and Engineering Sharif University of Technology Department of Mechanical Engineering Nagaoka University of Technology

Severely deformed aluminum sheets were processed by friction stir processing(FSP) with Si C nanoparticles under different conditions to improve the mechanical properties of both the stir zone and the heat affected zone(hAZ).In the case of using a simple probe and the same rotational direction(RD) of the FSP tool between passes,at least three FSP passes were required to obtain the appropriate distribution of ***,after three FSP passes,fracture occurred outward from the stir zone during transverse tensile tests;thus,the strength of the specimen was significantly lower than that of the severely deformed base material because of the softening phenomenon in the *** improve the mechanical properties of the hAZ,we investigated the possibility of achieving an appropriate distribution of nanoparticles using fewer FSP *** results indicated that using the threaded probe and changing the RD of the FSP tool between the passes effectively shattered the clusters of nanoparticles and led to an acceptable distribution of Si C nanoparticles after two FSP *** these cases,fracture occurred at the hAZ with higher strength compared to the specimen processed using three FSP passes with the same RD between the passes and with the simple *** fracture behaviors of the processed specimens are discussed in detail.

关键词： friction stir processing plastic deformation aluminum silicon carbide nanocomposites mechanical properties

Effect of welding parameters on semisolid stir welding of Mg-9Al-1Zn magnesium alloy

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Transactions of Nonferrous Metals Society of China 2016年第10期26卷 2586-2594页

作者： V.A.hOSSEINI h.AAShURI a.h.kokabi Department of Engineering Science University West Materials Science and Engineering Department Sharif University of Technology

Semisolid stir welding of AZ91 was investigated with focus on the joining temperature and rotational speed. An Mg-25%Zn interlayer was located between two AZ91 pieces and the system was heated up to the semisolid state of base metal and interlayer. The weld seam was stirred using a drill-tip at different joining temperatures and rotational speeds. Optical and scanning electron microscopes were employedto study microstructure, cavity formation, and segregation. hardness profile and shear punch test werealso employed to rank the welds based on their quality and homogeneity. Results showed that the lowest cavity content （2.1%） withthemaximum ultimate shear strength （about 188 MPa） was obtained in weld with the joining temperatureof530℃ and the rotational speedof1600 r/min. Low quality welds and a reduction of ultimate shear strength were observed at very high orlow rotational speeds and joining temperatures. The process, in conclusion, produced close mechanical properties to those of thebase metal and homogenous quality throughout the joint, when the intermediate temperature and rotational speeds were employed.

关键词： Mg-Al-Zn alloy mechanical stirring semisolidstir welding

Butt joining of Al-Cu bilayer sheet through friction stir welding

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Transactions of Nonferrous Metals Society of China 2012年第12期22卷 2925-2929页

作者： R.BEYGI M.KAZEMINEZhAD a.h.kokabi Department of Materials Science and Engineering Sharif University of Technology

Butt joining of Al–Cu bilayer sheet produced by cold roll bonding was studied through friction stir welding (FSW). A defect free joint was obtained. Flow patterns and mixing of two layers during FSW were investigated. Microstructural investigations and hardness profile measurements were carried out. It is shown that material flow in stir zone leads to the formation of banding structure in Cu layer at advancing side. Traces of Al particles along with Al–Cu intermetallic compounds exist in the fined grain region of this banding structure which leads to higher hardness values.

关键词： bilayer sheet Al-Cu sheet friction stir welding microstructure

Free vibration and buckling analysis of polymeric composite beams reinforced by functionally graded bamboo fbers

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Applied Mathematics and Mechanics(English Edition) 2024年第3期45卷 543-562页

作者： h.M.FEIZABAD M.h.YAS Department of Mechanical Engineering Razi UniversityKermanshah ***Iran

Natural fibers have been extensively researched as reinforcement materials in polymers on account of their environmental and economic advantages in comparison with synthetic fibers in the recent *** fibers are renowned for their good mechanical properties,abundance,and short cycle *** beams are one of the fundamental structural components and are susceptible to mechanical loads in engineering applications,this paper performs a study on the free vibration and buckling responses of bamboo fiber reinforced composite(BFRC)beams on the elastic *** different functionally graded(FG)layouts and a uniform one are the considered distributions for unidirectional long bamboo fibers across the *** elastic properties of the composite are determined with the law of *** hamilton’s principle,the governing equations of motion are *** generalized differential quadrature method(GDQM)is then applied to the equations to obtain the *** achieved outcomes exhibit that the natural frequency and buckling load values vary as the fiber volume fractions and distributions,elastic foundation stiffness values,and boundary conditions(BCs)and slenderness ratio of the beam ***,a comparative study is conducted between the derived analysis outcomes for BFRC and homogenous polymer beams to examine the effectiveness of bamboo fibers as reinforcement materials,demonstrating the significant enhancements in both vibration and buckling responses,with the exception of natural frequencies for cantilever beams on the Pasternak foundation with the FG-◇fiber ***,the obtained analysis results of BFRC beams are also compared with those for carbon nanotube reinforced composite(CNTRC)beams found in the literature,indicating that the buckling loads and natural frequencies of BFRC beams are lower than those of CNTRC beams.

关键词： bamboo fiber free vibration buckling analysis functionally graded(FG)beam elastic foundation generalized differential quadrature method(GDQM)

holographic dark energy in non-conserved gravity theory

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Communications in Theoretical Physics 2024年第4期76卷 126-133页

作者： h R Fazlollahi Institute of Gravitation and Cosmology Peoples Friendship University of Russia(RUDN University)6 Miklukho-Maklaya StMoscow117198Russia

Recently, reconsidering the Rastall idea T_(μ;νν)^(v)=α_(,μ) through relativistic thermodynamics gives a new form for the scalar field α which led us to construct modern modified theory of gravity debugged ‘non-conserved gravity theory’ Fazlollahi 2023 Euro. Phys. J. C 83 923. This theory unlike other modified theories of gravity cannot directly explain the current acceleration expansion in the absence of the cosmological constant and or existence of other forms of dark energy. hence, in this study we have reinvestigated holographic dark energy Ρ_(X)~h^(2) in the non-conserved theory of gravity. In this context, the density and pressure of dark energy depend on the non-conserved term and density of the dust matter field. As shown, due to non-conservation effects on large-scale structures, unlike the original holographic model, our model onsets an acceleration epoch for the current Universe satisfies observations. Moreover, the interaction and viscous scenarios are studied for this model.

关键词： non-conserved gravity covariant form of thermodynamics holographic dark energy

Novel synthesis of stabilized Bi1-x-yGdxDyyO1.5 solid electrolytes with enhanced conductivity for intermediate temperature solid oxide fuel cells（SOFCs）

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Journal of Rare Earths 2024年第10期42卷 1903-1911页

作者： Ahmed h.Ibrahim Yehia M.Abbas h.A.Ayoub Marwa h.Ali Mustafa Aldoori Materials Science Laboratory Physics DepartmentFaculty of ScienceSuez Canal University Ministry of higher Education and Scientific Research Aliraqia University

herein,we report the synthesis of a Dy-Gd co-doped cubic phase-stabilized Bi2O3solid electrolyte system via solid-state processing under atmospheric *** with Dy3+and Gd3+has been observed to significantly enhance the densification process during sintering for stabilization purposes,thereby improving the electrical properties of δ-Bi2O3-type *** synthesized ceramics were characterized using X-ray diffraction（XRD）,field emission scanning electron microscopy-energy dispersive X-ray spectroscopy（FESEM-EDX）,thermal gravimetry/differential thermal analysis（TG/DTA）,and the four-point probe technique（4PPT）.XRD analysis reveals that the samples Bi1-x-yGdxDyyO1.5（y=0.05/x=0.05,0.10,0,15,and 0.20,and x=0.05/y=0.10,0.15,and 0.20） exhibit a stable face-centered cubic δ-phase and a mixed-phase crystallographic *** XRD analysis of the stabilized δ-phase suggests that the prepared oxides show a face-centered cubic（FCC） structure with a space group of *** micrographs reveal that the composition Bi0.90Gd0.05Dy0.05O1.5has no significant ***,an evident increase in the pore formation is observed as the amount of Gd2O3increases until it reaches 20%.This finding suggests that dense pellets are formed during the sintering process at 900-1000℃.The DTA analyses were performed to verify the phase stability,which agrees with the XRD *** electrochemical performance of the synthesized Dy-Gd co-doped Bi2O3solid electrolyte system was evaluated and analyzed in detail by using the electrochemical impedance spectroscopy（EIS） technique,Based on EIS and conductivity measurements,Bi0.75Gd0.20Dy0.05O1.5exhibits the lowest activation energy of 0.519 eV and the highest conductivity value of 0.398 S/cm at 627℃compared to the other samples;this composition can be used as a solid electrolyte for intermediatetemperature solid oxide fuel cells（SOFCs）.

关键词： Electrochemical impedance spectroscopy (EIS) Fast Fourier transform (FFT) Rare earths Rietveld Solid oxide fuel cells (SOFCs) Solid-state processing

Convexification of hybrid AC-DC Optimal Power Flow with Line-Commutated Converters

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CSEE Journal of Power and Energy Systems 2024年第2期10卷 617-628页

作者： hongyuan Liang Zhigang Li J.h.Zheng Q.h.Wu School of Electric Power Engineering South China University of TechnologyGuangzhou 510641China

Line-commutated converter (LCC)-based high-voltage DC (hVDC) systems have been integrated with bulk AC power grids for interregional transmission of renewable power. The nonlinear LCC model brings additional nonconvexity to optimal power flow (OPF) of hybrid AC-DC power grids. A convexification method for the LCC station model could address such nonconvexity but has rarely been discussed. We devise an equivalent reformulation for classical LCC station models that facilitates second-order cone convex relaxation for the OPF of LCC-based AC-DC power grids. We also propose sufficient conditions for exactness of convex relaxation with its proof. Equivalence of the proposed LCC station models and properties, exactness, and effectiveness of convex relaxation are verified using four numerical simulations. Simulation results demonstrate a globally optimal solution of the original OPF can be efficiently obtained from relaxed model.

关键词： AC-DC power system convex relaxation linecommutated converter optimal power flow second-order cone programming

Shell-model representations of the microscopic version of the Bohr-Mottelson collective model

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Communications in Theoretical Physics 2024年第8期76卷 79-90页

作者： h G Ganev Joint Institute for Nuclear Research DubnaRussia Institute of Mechanics Bulgarian Academy of SciencesSofiaBulgaria

The structure of the irreducible collective spaces of the group Sp(12,R),which many-particle nuclear states are classified according to the chain Sp(12,R)⊃U(6)⊃SO(6)⊃SU_(pn)(3)⊗SO(2)⊃SO(3)of the proton-neutron symplectic model(PNSM),is considered in *** chain of the PNSM was recently shown to correspond to a microscopic shell-model version of the Bohr-Mottelson collective *** construction of the relevant shell-model representations of the Sp(12,R)group along this chain is considered for three nuclei with varying collective properties and from different mass *** is shown that the SU_(pn)(3)basis states of the Sp(12,R)representations belonging to the SO(6)irreps with seniorityυ≥υ0,withυ0 denoting the maximal seniority SO(6)irrep contained in the Sp(12,R)bandhead,are always Pauli allowed,but organized in a different way into different SO(6)*** is in contrast to the case of filling the levels of the standard three-dimensional harmonic oscillator and using the plethysm *** the SU_(pn)(3)multiplets withinυhe present work are important for the practical application of the microscopic version of the Bohr-Mottelson collective model.

关键词： microscopic shell-model version of the Bohr-Mottelson model proton-neutron symplectic model Sp(12,R)dynamical algebra shell-model representations