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Effect of superheat and solidified layer on achieving good metallic bond between A390/A356 alloys fabricated by cast-decant-cast process

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Transactions of Nonferrous Metals society of China 2014年第3期24卷 665-672页

作者： M.MOHAMMADI RAHVARD M.TAMIZIFAR M.A.BOUTORABI s.gholami shiri school of Materials science and Engineering and Center of Excellence for High strength Alloys Technology Iran University of Science and Technology school of Materials science and Engineering Sharif University of TechnologyAzadi Ave. P.O. Box 11365-9466 Tehran Iran Damavand Petrochemical Company Phase 2 Pars Special Economic Energy Zone Asaloye Boshehr Iran

The cast-decant-cast is a new method for the preparation of the functionally graded components that has been developed in recent years. The functionally graded cylindrical shape component with a radial gradient, e.g. the first alloy （A390） with high wear resistance on the surface of the piece and toughness and the second alloy （A356） of low machining costs in the core of the piece can be produced via this melt process. The effect of the second alloy superheat at temperatures of 750, 820 and 860 ℃ as well as the effect of the first alloy solidified layer at 25, 35 and 45 s decanting time on achieving the perfect interface between the two alloys was investigated. The characterization of the interface was carded out by optical microscopy and scanning electron microscopy, and its width was measured by the microhardness test. The results showed that the best interface was obtained at 860 ℃ and 35 s decanting time with a width of 500 ~tm. Also, the wear resistance test was performed to measure and compare the surface wear resistance to the core.

关键词： A390 alloy A356 alloy functionally graded material cast-decant-cast process

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

Nonlinear forced vibration in a subcritical regime of a porous functionally graded pipe conveying fluid with a retaining clip

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Applied Mathematics and Mechanics(English Edition) 2025年第1期46卷 101-122页

作者： M.gholami M.EFTEKHARI Department of Mechanical Engineering Shahid Bahonar University of Kerman

This study examines the nonlinear behaviors of a clamped-clamped porous pipe made of a functionally graded material(FGM) that conveys fluids and is equipped with a retaining clip, focusing on primary resonance and subcritical dynamics. The nonlinear governing equations for the FGM pipe are derived by the extended Hamilton's principle, and subsequently discretized through the application of the Galerkin *** direct method of multi-scales is then used to solve the derived equations. A thorough analysis of various parameters, including the clip stiffness, the power-law index, the porosity, and the clip location, is conducted to gain a comprehensive understanding of the system's nonlinear dynamics. Through the analysis of the first natural frequency, the study highlights the influence of the flow velocity and the clip stiffness, while the comparisons with metallic pipes emphasize the role of FGM composition. The examination of the forced response curves reveals saddle-node bifurcations and their dependence on parameters such as the detuning parameter and the power-law index, offering valuable insights into the system's nonlinear resonant behavior. Furthermore, the frequency-response curves illustrate the hardening nonlinearities influenced by factors such as the porosity and the clip stiffness, revealing nuanced effects on the system response and resonance characteristics. This comprehensive analysis enhances the understanding of nonlinear behaviors in FGM porous pipes with a retaining clip, providing key insights for practical engineering applications in system design and optimization.

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Unexpected Effect of Nb Addition as a Microalloying Element on Mechanical Properties of δ-TRIP steels

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Journal of Iron and steel Research International 2016年第9期23卷 988-996页

作者： sajad gholami shiri seyed Ahmad Jenabali JAHROMI Yahya PALIZDAR Majid BELBAsI Department of Materials science & Engineering School of Engineering Shiraz University Shiraz 115019 Iran Nanotechnology and Advanced Materials Department Materials and Energy Research Center Karaj 128747 Iran Department of Materials Engineering Islamic Azad University Central Tehran Branch Tehran 009821 Iran

The concept of microalloying was applied to the δ-TRIP （transformation-induced plasticity） steel to inves- tigate the feasibility of increasing the mechanical properties and understanding the effect of microalloying on the morphology and structure of the steel. A hot rolled δ-TRIP steel with three different contents of Nb （0, 0.03, 0.07 mass%） was subjected to the microstructural and mechanical examination. The high Al and si concentration in these steels guaranteed the presence of the considerable δ-ferrite phase in the microstructure after the casting and the subsequent hot rolling. The obtained results showed that Nb dramatically affects the microstructure the dynamic re- covery and recrystallization behavior, as well as the grain shape and thus the stability of austenite after the thermo- mechanical process of hot rolling. The results also revealed an unexpected effect of Nb on the mechanical properties. The addition of Nb to the δ-TRIP steel led to a significant decrease in the ultimate strength （from 1144 to 917 MPa） and an increase in ductility （from 24% to 28%）. These unconventional results could be explained by the change in the steel microstructure. The work-hardening＇behaviors of all samples exhibit three stages of the work-hardening rate evolution. At the stage 2, the work-hardening rate of the studied steels increased, being attributed to the TRIP effect and the transformation of austenite to martensite.

关键词： δ-TRIP steel Nb microalloying high Al steel mechanical property work-hardening

Fatigue Reliability Analysis of Fiber-Reinforced Laminated Composites by Continuum Damage Mechanics

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Acta Mechanica solida sinica 2023年第3期36卷 469-476页

作者： Peyman gholami Aerospace Research Institute Ministry of ScienceResearch and TechnologyTehranIran

This paper investigates the reliability of composite laminates with various lay-ups under fatigue *** prediction of failure probability of composite laminates subjected to different loads involves many uncertainties associated with mechanical properties,loading,and boundary *** in the composite material is truly hard to trace because there are individual faults in each ply,and we face a stochastic process due to the scatter in the mechanical *** continuum damage mechanics(CDM),as a powerful approach,is applied to model the damage of fiber,matrix,and fiber/matrix *** method defines criteria for damage detection and determines safe *** material constitutive equations are executed using a subroutine *** first-order reliability method and second-order reliability method have been applied to examine the reliability of laminated *** results are compared with those of the Monte Carlo *** composite laminates under different stress levels are considered for the failure probability *** limit state functions and random variables have been determined based on the CDM ***,the effects of the number of cycles,applied stress,and stacking sequence of the laminate on the reliability and fatigue life in fiber-reinforced laminated composites are assessed.

关键词： Composite laminate Continuum damage mechanics Fatigue damage First-order reliability method second-order reliability method Monte Carlo simulation

Gas tungsten arc welding of CP-copper to 304 stainless steel using different filler materials

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Transactions of Nonferrous Metals society of China 2012年第12期22卷 2937-2942页

作者： sajjad gholami shiri Mohsen NAZARZADEH Mahmood sHARIFITABAR Mehdi shafiee AFARANI Materials science and Engineering Division School of Engineering University of Sistan and Baluchestan Zahedan Iran Department of Materials science and Engineering Ferdowsi University of Mashhad Mashhad Iran

The dissimilar joining of CP-copper to 304 stainless steel was performed by gas tungsten arc welding process using different filler materials. The results indicated the formation of defect free joint by using copper filler material. But, the presence of some defects like solidification crack and lack of fusion caused decreasing tensile strength of other joints. In the optimum conditions, the tensile strength of the joint was 96% of the weaker material. Also, this joint was bent till to 180° without any macroscopic defects like separation, tearing or fracture. It was concluded that copper is a new and good candidate for gas tungsten arc welding of copper to 304 stainless steel.

关键词： gas tungsten arc welding CP-copper 304 stainless steel dissimilar joint microstructure mechanical properties

synthesis and characterization of niobium-promoted cobalt/iron catalysts supported on carbon nanotubes for the hydrogenation of carbon monoxide

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燃料化学学报 2016年第7期44卷 815-821页

作者： Zahra gholami Noor Asmawati Mohd Zabidi Fatemeh gholami Mohammadtaghi Vakili Centralized Analytical Laboratory Universiti Teknologi PETRONAS Department of Fundamental and Applied sciences Universiti Teknologi PETRONAS Department of Mechanical Engineering Faculty of EngineeringUniversity of Malaya school of Industrial Technology Universiti Sains Malaysia

Bimetallic Co /Fe catalysts supported on carbon nanotubes( CNTs) were prepared,and niobium( Nb) was added as promoter to the 70 Co ∶30Fe /CNT catalyst. The physicochemical properties of the catalysts were characterized,and the catalytic performances were analyzed at the same operation conditions( H_2 ∶CO( volume ratio) = 2 ∶1,p = 1 MPa,and t = 260 ℃) in a tubular fixed-bed microreactor system. The addition of Nb to the bimetallic catalyst decreases the average size of the oxide nanoparticles and improves the reducibility of the bimetallic catalyst. Evaluation of the catalyst performance in a Fischer-Tropsch reaction shows that the catalyst results in high selectivity to methane,and the selectivity to C_(5+) increased slightly in the bimetallic catalyst unlike that in the monometallic catalysts. The addition of 1% Nb to the bimetallic catalyst increases CO conversion and selectivity to C_(5+). Meanwhile,a decrease in methane selectivity is observed.

关键词： Fischer-Tropsch synthesis bimetallic catalyst niobium promoter carbon nanotubes

Determination of Parameters Affecting the Estimation of Iceberg Draft

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China Ocean Engineering 2023年第1期37卷 62-72页

作者： Hamed AZIMI Masoud MAHDIANPARI Hodjat shiri Civil Engineering Department Faculty of Engineering and Applied ScienceMemorial University of NewfoundlandA1B 3X5St.John’sNLCanada Department of Electrical and Computer Engineering Faculty of Engineering and Applied ScienceMemorial University of NewfoundlandA1B 3X5St.John’sNLCanada C-CORE A1B 3X5St.John’sNLCanada

Recent offshore oil and gas loading facilities developed in the Arctic area have led to a considerable awareness of the iceberg draft approximation, where deep keel icebergs may gouge the ocean floor, and these submarine infrastructures would be damaged in the shallower waters. Developing reliable solutions to estimate the iceberg draft requires a profound understanding of the problem’s dominant parameters. As such, the dimensionless groups of the parameters affecting the iceberg draft estimation were determined for the first time in the present study. Using the dimensionless groups recognized and the linear regression(LR) analysis, nine LR models(i.e., LR 1 to LR 9) were developed and then validated using a comprehensive dataset, which has been constructed in this study. A sensitivity analysis distinguished the premium LR models and important dimensionless groups. The best LR model, as a function of all dimensionless parameters, was able to estimate the iceberg draft with the highest level of precision and correlation along with the lowest degree of complexity. The ratio of iceberg length to iceberg height as the “iceberg length ratio” and the ratio of iceberg width to iceberg height as the “iceberg width ratio” was detected as the important dimensionless groups in the estimation of the iceberg draft. An uncertainty analysis demonstrated that the best LR model was biased towards underestimating the iceberg drafts. The premium LR model outperformed the previous empirical ***, a set of LR-based relationships were derived for estimating the iceberg drafts for practical engineering applications, e.g., the early stages of the iceberg management projects.

关键词： dimensional analysis iceberg draft subsea assets linear regression(LR) sensitivity analysis

Edge Coloring of Graphs with Applications in Coding Theory

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China Communications 2021年第1期18卷 181-195页

作者： Ghaffar Raeisi Mohammad gholami Department of Mathematical sciences Shahrekord UniversityShahrekordP.O.Box 115Iran

In this paper,a new type of edge coloring of graphs together with an algorithm for such an edge coloring is presented to construct some columnweight three low-density parity-check(LDPC)codes whose Tanner graphs are free of *** kind of edge coloring is applied on some well-known classes of graphs such as complete graphs and complete bipartite graphs to generate some column-weight 3 LDPC codes having flexibility in terms of code length and ***,the constructed(3;k)-regular codes with regularities k=4;5;:::;22 have lengths n=12;20;26,35;48;57;70;88;104;117;140;155;176;204;228;247;280;301;330;having minimum block length compared to the best known similar codes in the *** addition to linear complexity of generating such parity-check matrices,they can be considered as the base matrices of some quasi-cyclic(QC)LDPC codes with maximum achievable girth 18,which inherit the low-complexity encoder implementations of QC-LDPC *** results show that the QC-LDPC codes with large girth lifted from the constructed base matrices have good performances and outperform random codes,progressive edge growth LDPC codes,some finite fields and group rings based QC-LDPC codes and also have a close competition to the standard IEEE 802.16e(WiMAX)code.

关键词： low-density parity-check code edge coloring Quasi-cyclic LDPC code girth AWGN channel