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Journal of Hydrodynamics 2011年第3期23卷 302-313页

作者： HEJRANFAR Kazem FATTAH-HESARY Kasra Aerospace Engineering Department sharif university of technology

A numerical treatment for the prediction of cavitating flows is presented and assessed. The algorithm uses the preconditioned multiphase Euler equations with appropriate mass transfer terms. A central difference finite volume scheme with suitable dissipation terms to account for density jumps across the cavity interface is shown to yield an effective method for solving the multiphase Euler equations. The Euler equations are utilized herein for the cavitation modeling, because some certain characteristics of cavitating flows can be obtained using the solution of this system of equations with relative low computational effort. In addition, the Euler equations are appropriate for the assessment of the numerical method used, because of the sensitivity of the solution to the numerical instabilities. For this reason, a sensitivity study is conducted to evaluate the effects of various parameters, such as numerical dissipation coefficients and grid size, on the accuracy and performance of the solution. The computations are performed for steady cavitating flows around the NACA 0012 and NACA 66 （MOD） hydrofoils and also an axisymmetric hemispherical fore-body under different conditions and the results are compared with the available numerical and experimental data. The solution procedure presented is shown to be accurate and efficient for predicting steady sheet- and super-cavitation for 2D/axisymmetric geometries.

关键词： cavitating flows preconditioned multiphase Euler equations interface capturing method central difference FVM

Electrical annealing of severely deformed copper: microstructure and hardness

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International Journal of Minerals,Metallurgy and Materials 2017年第10期24卷 1158-1168页

作者： Saeed Nobakht Mohsen Kazeminezhad Department of Materials Science and Engineering Sharif University of Technology Azadi Avenue Tehran Iran

Commercial pure copper sheets were severely deformed after primary annealing to a strain magnitude of 2.32 through constrained groove pressing. After induction of an electrical current, the sheets were heated for 0.5, 1, 2, or 3 s up to maximum temperatures of 150, 200, 250, or 300℃. To compare the annealing process in the current-carrying system with that in the current-free system, four other samples were heated to 300℃ at holding times of 60, 90, 120, or 150 s in a salt bath. The microstructural evolution and hardness values of the samples were then investigated. The results generally indicated that induction of an electrical current could accelerate the recrystallization process by decreasing the thermodynamic barriers for nucleation. In other words, the current effect, in addition to the thermal effect, enhanced the diffusion rate and dislocation climb velocity. During the primary stages of recrystallization, the grown nuclei of electrically annealed samples showed greater numbers and a more homogeneous distribution than those of the samples annealed in the salt bath. In the fully recrystallized condition, the grain size of electrically annealed samples was smaller than that of conventionally annealed samples. The hardness values and metallographic images obtained indicate that, unlike the conventional annealing process, which promotes restoration phenomena with increasing heating time, the electrical annealing process does not necessarily promote these phenomena. This difference is hypothesized to stem from conflicts between thermal and athermal effects during recrystallization.

关键词： annealing severe plastic deformation copper microstructure hardness

Microstructure and Mechanical Properties in Dissimilar Butt Friction Stir Welding of Severely Plastic Deformed Aluminum AA 1050 and Commercially Pure Copper Sheets

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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

Microstructural evolution during ultra-rapid annealing of severely deformed low-carbon steel: strain, temperature, and heating rate effects

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International Journal of Minerals,Metallurgy and Materials 2016年第7期23卷 779-792页

作者： M.A.Mostafaei M.Kazeminezhad Department of Materials Science and Engineering Sharif University of Technology

An interaction between ferrite recrystallization and austenite transformation in low-carbon steel occurs when recrystallization is delayed until the intercritical temperature range by employing high heating rate. The kinetics of recrystallization and transformation is affected by high heating rate and such an interaction. In this study, different levels of strain are applied to low-carbon steel using a severe plastic deformation method. Then, ultra-rapid annealing is performed at different heating rates of 200–1100°C/s and peak temperatures of near critical temperature. Five regimes are proposed to investigate the effects of heating rate, strain, and temperature on the interaction between recrystallization and transformation. The microstructural evolution of severely deformed low-carbon steel after ultra-rapid annealing is investigated based on the proposed regimes. Regarding the intensity and start temperature of the interaction, different microstructures consisting of ferrite and pearlite/martensite are formed. It is found that when the interaction is strong, the microstructure is refined because of the high kinetics of transformation and recrystallization. Moreover, strain shifts an interaction zone to a relatively higher heating rate. Therefore, severely deformed steel should be heated at relatively higher heating rates for it to undergo a strong interaction.

关键词： low-carbon steel annealing microstructural evolution recrystallization phase transformation plastic deformation

Effects of non-liquefiable crust layer and superstructure mass on the response of 2×2 pile groups to liquefaction-induced lateral spreading

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第10期15卷 2701-2719页

作者： S.Mohsen Haeri Morteza Rajabigol Saman Salaripour Hiwa Sayaf Milad Zangeneh Department of Civil Engineering Sharif University of TechnologyTehranIran

In this research,two shake table experiments were conducted to study the effects of non-liquefiable crust layer and superstructure mass on the responses of two sets of 22 pile groups to liquefactioninduced lateral *** this regard,an inclined base layer overlain by a very loose liquefiable layer was constructed in both models;while only in one model,a non-liquefiable crust layer was built.A lumped mass,being representative of a superstructure,was attached to the cap of one pile group in both *** models were fully instrumented with various sensors,including acceleration,displacement,and pore water pressure ***,the piles were instrumented with pair strain gauges to measure pure bending moments induced by cyclic and monotonic loadings associated with ground shaking and lateral spreading,*** results showed that the existence of the non-liquefiable crust layer increases both the maximum and residual soil displacements at the free field and also the maximum bending moments in the *** results of the experiments indicated that the crust layer induces a high kinematic lateral soil pressure and force on the piles which are not present in the crustless *** crust layer increases the pile cap displacement before liquefaction,albeit decreases it after liquefaction,due to the elastic rebound of the piles in the liquefiable *** crust layer postpones both liquefaction triggering and dissipation of excess pore water *** existence of the superstructure mass on the pile caps decreases the acceleration amplitude of the pile caps,while increases their maximum displacement.

关键词： Soil liquefaction Lateral spreading 1g shake table test Pile group Crust layer Superstructure

Preparation of in-situ Cu/NbC nanocomposite and its functionally graded behavior for electrical contact applications

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Transactions of Nonferrous Metals Society of China 2015年第3期25卷 863-872页

作者： S.GHOLAMI SHIRI P.ABACHI K.POURAZARANG M.MOHAMMADI RAHVARD Department of Materials Science and Engineering Sharif University of Technology Damavand Petrochemical Company Phase 2Pars Special Economic Energy Zone School of Materials Science and Engineering and Center of Excellence for High Strength Alloys technology Iran University of Science and Technology

Cu–15%NbC (volume fraction) powder was synthesized using the starting powders of Cu, Nb and graphite in a high energy vibratory disc mill for 7 h of milling under argon atmosphere. A composite sample and a Cu/NbC functionally graded material (FGM) sample were produced by using the two-step press and sintering at 900 °C for 1 h under vacuum. The microstructure and physical and mechanical properties of the specimens were investigated. The field emission scanning electron microscopy, energy dispersive X-ray and X-ray diffraction analysis confirmed the synthesis of the nanostructure matrix of 18–27 nm with the nanoparticles reinforcement of 42 nm after sintering, verifying the thermal stability of this composite at high temperature. The hardness of Cu–15%NbC was five times greater than that of the pure Cu specimen. The volume reduction of the sample after the wear test decreased in comparison with the pure Cu specimen. The electrical conductivity of the composite specimen decreased to 36.68% IACS. The FGM specimen exhibited high electrical conductivity corresponding to 75.83% IACS with the same hardness and wear properties as those of the composite sample on the composite surface. Thus, Cu/NbC FGM with good mechanical and electrical properties can be a good candidate for electrical contact applications.

关键词： Cu/NbC nanocomposite in-situ composite mechanical alloying electrical contact wear behavior

Microstructural evolution,mechanical properties,and corrosion resistance of a heat-treated Mg alloy for the bio-medical application

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Journal of Magnesium and Alloys 2019年第1期7卷 80-89页

作者： Mohammad Janbozorgi Kimia Karimi Taheri Ali Karimi Taheri Department of Materials Science and Engineering Sharif University of TechnologyAzadi Ave.TehranIran School of Medicine Shahid Beheshti University of Medical ScienceTehranIran

During the recent years,some Mg based alloys have extensively been considered as a new generation of degradable and absorbable bio-medical *** this work,the Mg-2Zn-1Gd-1Ca(wt%)alloy as a new metallic bio-material was produced by the casting process followed by the heat *** samples of the alloy were solution treated at temperatures of 500,550,and 600°C and then quench aged at temperatures of 125,150,and 175°*** results of SEM-EDS examinations indicated that the alloy microstructure consists ofα-Mg matrix and the Ca_(2)Mg_(6)Zn_(3)and Mg_(3)Gd_(2)Zn_(3)secondary *** regard to the results of Vickers hardness test,the temperatures of 500°C and 150°C were selected as the optimum solutionizing and aging temperatures,***,the dissolution of casting precipitates and production of lattice distortion occurring after the solution treatment led to the reduction in ultimate shear strength up to 21%.But,the precipitation hardening and morphological changes taking place during the aging treatment improved the ultimate shear strength up to 32%.Furthermore,the results of electro-chemical and weight-loss measurements in a simulated body fluid indicated that the heat-treated alloy is a promising candidate for the Mg based alloys recently considered for the bio-medical applications.

关键词： Mg alloys Bio-medical applications Microstructural evolution Mechanical properties Corrosion resistance

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

Effects of non-isothermal annealing on microstructure and mechanical properties of severely deformed 2024 aluminum alloy

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Transactions of Nonferrous Metals Society of China 2017年第1期27卷 1-9页

作者： Saeed KHANI MOGHANAKI Mohsen KAZEMINEZHAD Department of Materials Science and Engineering Sharif University of TechnologyAzadi Avenue 11155-9466TehranIran

Microstructure and mechanical properties of AA2024 after severe plastic deformation （SPD） and non-isothermal annealing were investigated. The non-isothermal treatment was carried out on the severely deformed AA2024, and the interaction between restoration and precipitation phenomena was investigated. Differential scanning calorimetry, hardness and shear punch tests illustrate that static recovery and dissolution of GPB zones/Cu-Mg co-clusters occur concurrently through non-isothermal annealing. Scanning electron microscope and electron backscatter diffraction illustrate that non-isothermal annealing of deformed AA2024 up to 250 ℃ promotes the particle-free regions and also particle stimulated nucleation. Results show that through heating with the rate of 10 ℃/min up to 250 ℃, the ultimate shear strength and the hardness are maximum due to the presence of S＇/S phases which have been detected during non-isothermal differential scanning calorimetry experiment. Also, recrystallization phenomenon occurs in temperature range which includes the dissolution of S＇/S phases. The concurrent recrystallization and dissolution of S＇/S phase at 380 ℃ have been verified by differential scanning calorimetry, mechanical properties, and optical microscope.

关键词： AA2024 alloy severe plastic deformation non-isothermal annealing microstructure mechanical properties

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