Search for: joining
Total 65 records
Interface formation and bond strength in 3Y-TZP/Cr composite bilayers produced by sinter–joining [electronic resource], Article Materials Science and Engineering: A ; Volume 527, Issue 3, 15 January 2010, Pages 449–453 ; Simchi, A. (Abdolreza) ; Hokamoto, K ; Tanaka, S ; Sharif University of Technology
The mechanism of interface formation during sinter–joining of nanostructured yttria stabilized zirconia (27 nm) compacts with chromium powder was investigated. The effect of sintering atmosphere, i.e. argon or vacuum, was studied. Microstructural evaluation and phase formation was examined by scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), and micro-focused X-ray diffraction (MFXRD) methods. It is shown that spreading and evaporation–condensation mechanisms are responsible for the interface formation. An improved joint shear-strength was obtained after sintering in vacuum (74 MPa) compared with argon (41 MPa). The result of MFXRD indicated formation of Cr-island at...
Article Thin-Walled Structures ; Vol. 85, issue , December , 2014 , p. 350-358 ; Kouchakzadeh, M. A ; Sharif University of Technology
Natural frequencies and mode shapes of two joined isotropic conical shells are presented in this study. The joined conical shells can be considered as the general case for joined cylindrical-conical shells, joined cylinder-plates or cone-plates, conical and cylindrical shells with stepped thicknesses and also annular plates. Governing equations are obtained using thin-walled shallow shell theory of Donnell and Hamilton's principle. The continuity conditions at the joining section of the cones are appropriate expressions among stress resultants and deformations. The equations are solved assuming trigonometric response in circumferential and series solution in meridional directions and all...
Article Carpathian Journal of Mathematics ; Volume 28, Issue 2 , 2012 , Pages 247-256 ; 15842851 (ISSN) ; Hosseinzadeh, M. A ; Diudea, M. V ; Ashrafi, A. R ; Sharif University of Technology
The modified eccentricity connectivity polynomial of a connected graph G is defined as Ξ(G; x)=Σ u∈V(G)d G(u)x ε′G (u), where ε′ G(u)=Σ v∈NG(u)εG(u)and d G(u) is the degree of u in G. In this paper modified eccentric connectivity polynomial is computed for several classes of composite graphs
The Effect of Temperature and Rotational Speed on Structure and Mechanical Properties of Cast Cu Base Alloy (Cu-Al-Si-Fe) Welded by Semisolid Stir Joining Method, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 46, Issue 12 , 2015 , Pages 5782-5788 ; 10735623 (ISSN) ; Aashuri, H ; Kokabi, A. H ; Shafizadeh, M ; Nikzad, S ; Sharif University of Technology
Semisolid stir joining has been under deliberation as a possible method for joining of copper alloys. In this study, the effect of temperature and rotational speed of stirrer on macrostructure evaluation and mechanical properties of samples were investigated. Optical microscopy and X-ray diffraction were performed for macro and microstructural analysis. A uniform micro-hardness profile was attained by semisolid stir joining method. The ultimate shear strength and bending strength of welded samples were improved in comparison with the cast sample. There is also lower area porosity in welded samples than the cast metal. The mechanical properties were improved by increasing temperature and...
Article Materials Today Communications ; Volume 22 , 2020 ; Eyvazian, A ; Simchi, A ; Sharif University of Technology
Elsevier Ltd 2020
Friction stir welding (FSW) of thermoplastic materials is an attractive but a challenging process due to inherent chemical and mechanical characteristics of polymeric materials. In the present work, thermo-mechanical models were employed to investigate the effect of processing parameters on of FSW of polycarbonate (PC). The heat flux during the joining process was localized around the PC join line and led to the formation of circular rings on the upper surface. According to the simulation results, increasing the tool rotational velocity reduced the temperature gradient and decfeased the suseptibelity of crack formation around the joint line. Cracks were formed at low frictional heats and...
Article Transactions of Nonferrous Metals Society of China (English Edition) ; Volume 23, Issue 9 , September , 2013 , Pages 2585-2590 ; 10036326 (ISSN) ; Aashuri, H ; Kokabi, A ; Sharif University of Technology
Joining in the semisolid state is considered a possible method to join alloys to each other. The mechanisms taking part in semisolid stir welding of AZ91 alloys were investigated. Two 7.5 mm-thick AZ91 pieces and a 2 mm-thick Mg-25%Zn interlayer piece were placed in a heating plate. After holding for 3 min at a desired temperature, the weld seam was stirred by a rotational tool. The heating plate was travelled on a trolley at a constant speed of 4.6 cm/min. In addition, one sample was welded without interlayer. Evolution of welding as a function of stirring rate, tool shape and temperature was studied throughout this welding process with scanning electron and optical microscopes. Interlayer...
Article Semi-Solid Processing of Alloys and Composites 10 - Selected, peer reviewed papers from the 10th International Conference on Semi-Solid Processing of Alloy and Composites, S2P 2008, Aachen, 16 September 2008 through 18 September 2008 ; Volume 141-143 , 2008 , Pages 225-230 ; 10120394 (ISSN); 9771012039401 (ISBN) ; Aashuri, H ; Kokabi, A. H ; Khosravani, A ; Kiani, M ; Foroughi, A ; Sharif University of Technology
Trans Tech Publications Ltd 2008
A technique to achieve the globular weld structure using stirring the localized semisolid zone during butt-joining of zinc AG40A (Zamak-3) die cast alloy is reported. Since the semisolid temperature range of this alloy is very narrow, the accurate controlling of weld pool temperature must be considered. By presented process, globular microstructure of the weld zone can be achieved. Moreover the near weld zone would have the globular structure due to semisolid holding. A gas heating system was designed to heat up the nitrogen gas to desired temperature accurately. A heating element was embedded in a castable ceramic block while a stream of gas could pass closely around the hot element length....
Experimental and numerical investigation of the effect of laser input energy on the mechanical behavior of stainless steel and polyamide joint in the LAMP joining method, Article International Journal of Advanced Manufacturing Technology ; Volume 113, Issue 11-12 , 2021 , Pages 3585-3597 ; 02683768 (ISSN) ; Ranjbarnodeh, E ; Shoja Razavi, R ; Pircheraghi, G ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH 2021
The present study investigated the effect of laser input energy on the quality and mechanical behavior of a 304 stainless steel–polyamide 6 joint in the laser-assisted metal and polymer direct joining (LAMP) method experimentally and numerically. After the proposed heat transfer model was validated, it was determined whether there was an optimal amount of laser input energy that could produce a joint with favorable quality and mechanical behavior. Among different laser input energies used in this study, 28-J/mm energy can provide more uniform and extensive wetting of the metal surface by the polymer, while excessive polymer degradation in the joint zone was prevented. As a result, an optimal...
Article Materials Science and Engineering: A (Elsevier) ; 2014, 585, 222-232 ; Sharif University Of Technology
Solid-state joining of powder-metallurgy processed (P/M) Al–2 vol% Al2O3 (15 nm) nanocomposite by friction stir welding (FSW) was studied. The nanocomposite was prepared via high-energy mechanical milling followed by hot consolidation processes. The microstructure, mechanical properties and fracture behavior of the welds were evaluated and compared with FSWed wrought 1050 aluminum sheets (WAS). We have found that unlike WAS that can processed at various FSW conditions, the working window for the solid-state joining of P/M nanocomposite is narrow and only feasible at relatively high heating inputs. Microstructural studies showed the formation of melted zones with high hardness at the...
Article Czechoslovak Mathematical Journal ; Vol. 64, Issue. 2 , 2014 , pp. 433-446 ; ISSN: 00114642 ; Aliakbarpour, M ; Ghanbari, N ; Nategh, E ; Shahmohamad, H ; Sharif University of Technology
Let G be a graph, and λ the smallest integer for which G has a nowherezero λ-flow, i.e., an integer λ for which G admits a nowhere-zero λ-flow, but it does not admit a (λ − 1)-flow. We denote the minimum flow number of G by Λ(G). In this paper we show that if G and H are two arbitrary graphs and G has no isolated vertex, then Λ(G ∨ H) ⩽ 3 except two cases: (i) One of the graphs G and H is K2 and the other is 1-regular. (ii) H = K1 and G is a graph with at least one isolated vertex or a component whose every block is an odd cycle. Among other results, we prove that for every two graphs G and H with at least 4 vertices, Λ(G ∨ H) ⩽ 3
Microstructure-property characterization of a friction-stir welded joint between AA5059 aluminum alloy and high density polyethylene, Article Materials Characterization ; Vol. 98, issue , December , 2014 , p. 73-82 ; Haghshenas, M ; Sahraeinejad, S ; Chen, J ; Shalchi, B ; Li, J ; Gerlich, A. P ; Sharif University of Technology
Aluminum alloys and high density polyethylene are utilized in a wide variety of industrial applications. In the present work the feasibility of friction stir butt welding between AA5059 alloy and high density polyethylene sheets is examined. The bonding mechanism, joint strength, and microhardness are considered in this study. Various welding parameters and tool alignment were investigated until sound joints were achieved by positioning approximately 85% of the rotating tool in the aluminum material on the advancing side (1.4 mm offset) at constant spindle speed and traverse speed of 710 rpm and 63 mm/min, respectively. The results indicate that AA5059 aluminum and high density polyethylene...
Article Transactions of the Indian Institute of Metals ; Volume 68, Issue 5 , October , 2015 , Pages 991-998 ; 09722815 (ISSN) ; Ghasemi, A ; Pouraliakbar, H ; Jandaghi, M. R ; Sharif University of Technology
Springer India 2015
Dissimilar Al/Cu joints were produced through simple cold compression technique. The influence of different reductions (40, 53 and 66 %) on the joint strength was studied. Also, the effect of heat treatment on the joints’ mechanical characteristics was investigated using a modified miniature shear test. Microscopical examinations by means of optical and scanning electron microscopes were conducted and results confirmed that acceptable joints produced through 53 and 66 % deformations. According to the shear test results, it was revealed that post-weld heat treatment influenced the joint’s strength and caused strength enhancement in the samples which were not subjected to annealing prior to...
M.Sc. Thesis Sharif University of Technology ; Nemaney Pour, Alireza
This research presents an efficient group key management protocol, CKCSS (Code for Key Calculation in Single and Simultaneous join/leave) for secure multicast. In this research, we propose a new protocol to reduce the key management overheads for single join/leave at first and then use the development of this technique for simultaneous one. This protocol is based on logical key hierarchy. In this protocol, when new members join the group, server sends only the group key to those new members. Then, current members and the new members calculate all the necessary keys by node codes and one-way hash function. A node code is a random number assigned to each key to help users calculate the...
M.Sc. Thesis Sharif University of Technology ; Ashuri, Hossein
Today, Mg and Al as the widely used metals, make a special contribution to automotive, electronics and aerospace industries. Increasing the application of alloys of these metals, has extended the demand for reliable joint between alloys of these two metals. The main problem with the dissimilar joining of A356 alloy and AZ91 alloy is hard and brittle intermetallic compounds formation such as Mg17Al12 and Mg2Si which brings about welding strength reduction. By far, a large number of researches about dissimilar joining of AZ91 alloy and A356 alloy in semi-solid condition have not accomplished. In this method two fragments, one from AZ91 alloy and another from A356 alloy among which was a 2...
Article Transactions of Nonferrous Metals Society of China (English Edition) ; Volume 22, Issue 12 , 2012 , Pages 2925-2929 ; 10036326 (ISSN) ; Kazeminezhad, M ; Kokabi, A. H ; 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
Article Transactions of Nonferrous Metals Society of China (English Edition) ; Volume 20, Issue 9 , September , 2010 , Pages 1792-1798 ; 10036326 (ISSN) ; Aashuri, H ; Kokabi, A ; Beygi, R ; Sharif University of Technology
A method to reach the globular weld structure of A356 aluminum alloy using stirring the localized semisolid zone during butt-joining is developed. Since the heat conductivity of this alloy is very high, the accurate controlling of temperature during joining must be considered. A gas heating system was used to heat up the nitrogen gas up to the required temperature. A dried and free oxygen gas was prepared when a stream of nitrogen gas could pass closely around a hot element. Hot and pure nitrogen gas flow through a precise ceramic nozzle was used to create a localized semisolid pool. At this stage a fine stirrer was introduced into the weld seam in order to mix the two sides into a single...
Article Transactions of Nonferrous Metals Society of China (English Edition) ; Volume 26, Issue 10 , 2016 , Pages 2586-2594 ; 10036326 (ISSN) ; Aashuri, H ; Kokabi, A. H ; Sharif University of Technology
Nonferrous Metals Society of China 2016
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 employed to study microstructure, cavity formation, and segregation. Hardness profile and shear punch test were also employed to rank the welds based on their quality and homogeneity. Results showed that the lowest cavity content (2.1%) with the maximum ultimate shear strength (about 188 MPa) was...
Article Science and Technology of Welding and Joining ; Volume 22, Issue 2 , 2017 , Pages 120-126 ; 13621718 (ISSN) ; Movahedi, M ; Kokabi, A. H ; Sharif University of Technology
Taylor and Francis Ltd 2017
Joining feasibility of aluminium alloy to polypropylene sheets via friction stir lap joining was examined. Effects of heat-input on microstructure and mechanical behaviour of the joints were investigated. A covering plate was used to confine flow of molten polymer. The results showed a distinctive interaction layer at polymer/aluminium interface, consisted mainly of C, O and Al. Shear strength of the joints decreased by enhancement of the heat-input due to increase in the thickness of the interaction layer as well as the gap width between this layer and both aluminium and polymer matrices. Maximum shear-tensile strength of 5.1MPa (∼20% of polymer shear strength) was obtained, which was...
Multi-join query optimization in bucket-based encrypted databases using an enhanced ant colony optimization algorithm, Article Distributed and Parallel Databases ; Volume 36, Issue 2 , 2018 , Pages 399-441 ; 09268782 (ISSN) ; Amini, M ; Sharif University of Technology
Springer New York LLC 2018
One of the organizations’ main concerns is to protect sensitive data in database systems, especially the ones outsourced to untrusted service providers. An effective solution for this issue is to employ database encryption methods. Among different encryption approaches, Bucket-based method has the advantage of balancing security and performance of database operations. However, generating false-positive results in executing queries is the main drawback of this method. On the other hand, multi-join queries are one of the most critical operations executed on these stored sensitive data. Hence, acceptable processing and response time in executing multi-join queries is required. In this paper, we...
Microstructural evolution and mechanical properties of semisolid stir welded zinc AG40A die cast alloy, Article Journal of Materials Processing Technology ; Volume 209, Issue 8 , 2009 , Pages 4112-4121 ; 09240136 (ISSN) ; Aashuri, H ; Kokabi, A. H ; Khosravani, A ; Sharif University of Technology
A high quality joint of zinc based pressure die cast alloys can be hardly achieved by conventional fusion welding. In this study, a novel technique to achieve the globular weld structure using stirring the localized semisolid zone during butt joining of Zamak-3 pressure die cast alloy is proposed and effect of welding parameters on mechanical and microstructural properties are investigated. A gas heating system was designed to heat up the nitrogen gas to desired temperature accurately to create a localized semisolid pool. At this stage a fine stirrer was introduced into the weld seam in order to mix the two sides into a single uniform joint. By presented process, globular microstructure of...