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Mechanical and thermal properties of montmorillonite-epoxy nanocomposite
, Article International Journal of Modern Physics B ; Volume 22, Issue 18-19 , 2008 , Pages 3247-3253 ; 02179792 (ISSN) ; Bagheri, R ; Pearson, R. A ; Sharif University of Technology
World Scientific Publishing Co. Pte Ltd
2008
Abstract
In this investigation, the mechanical and thermal properties of the montmorillonite-epoxy nanocomposites were studied. The epoxy compounds were prepared by in situ polymerization and the intercalation dispersion were obtained as evidenced using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results reveal remarkable stiffening effect and slight toughening effect of the MMT in the epoxy resin and an insight about the crack tip and notch tip toughening mechanism. According to the DMA, the glass transition temperature increases as increasing the MMT content. © 2008 World Scientific Publishing Company
Study the effect of architectural modification on fracture behavior of Al-DRA composite [electronic resource]
, Article Mechanics of Advanced Materials and Structures ; September 2014, Volume 21, Issue 8, pages 662-668 ; Khalili, S ; Bagheri, R ; Simchi, A. (Abdolreza) ; Sharif University of Technology
Abstract
An architectural modification method was utilized to improve fracture toughness of discontinuously reinforced aluminum (DRA) composites. Al-DRA composites having a structure similar to that of reinforced concrete were fabricated. The number of reinforcing DRA rods within Al matrix and volume fraction of SiC particles in DRA were altered to evaluate their effect on fracture behavior of these materials. It was found that architectural modification does not have any destructive influence on elastic modulus and yield strength of the composite. Moreover, the success of this method on toughness improvement strongly depends on the occurrence of debonding between Al and DRA regions upon loading
The effect of aging on the fracture characteristics and ductility of self-compacting concrete
, Article Materials and Design ; Volume 55 , March 2014 , Pages 937-948 ; Kazemi, M. T ; Nikbin, I. M ; Vaseghi Amiri, J ; Sharif University of Technology
Abstract
Good knowledge of fracture parameters and cracking behavior of self-compacting concrete (SCC) from early ages until the SCC becomes mature plays an important role in design of SCC structure and also in evaluation of durability and consequently prevention of damage. In this paper, variation of fracture parameters and corresponding ductility behavior of SCC at different ages (e.g. 3days, 7days, 28days and 90days) for SCC mixes with w/c ratios of 0.45 and 0.65 have been experimentally studied. To do so, three-point bending tests were carried out on 120 notched beams. Then, size effect method (SEM) and work of fracture method (WFM) were applied to interpret the results. The results of analyses...
Mechanical and metallurgical properties of wide-gap aluminothermic rail welds
, Article Iranian Journal of Materials Science and Engineering ; Volume 8, Issue 4 , 2011 , Pages 27-33 ; 17350808 (ISSN) ; Kokabi, A.H ; Davami, P ; Sharif University of Technology
Abstract
The wide-gap aluminothermic rail welds with root opening of 50-70 mm were produced using plain carbon steel rail and non-alloy aluminothermic charge. Mechanical properties and micro-structure of the weld metal and HAZ as well as the impact energy and the fracture toughness of the welds were investigated. The yield and tensile strength of wide-gap welds were about 98% and 95% of the base metal, respectively. Both minimum and maximum hardnesses of the joint were seen in HAZ which were related to the grain coarsening and normalizing, respectively. The mean value of wide-gap weld fracture toughness is more than narrow-gap weld. Moreover, trans-granular cleavage indicated the brittle fracture...
Deformation, Yield and fracture of elastomer-modified polypropylene
, Article Journal of Applied Polymer Science ; Volume 90, Issue 14 , 2003 , Pages 3767-3779 ; 00218995 (ISSN) ; Bagheri, R ; Seyed Reihani, S. M ; Lazzeri, A ; Sharif University of Technology
2003
Abstract
In recent decades, great attention has been devoted to the toughening of isotactic poly(propylene) (PP) with elastomers such as ethylene-propylene rubber (EPR). The most important reasons for this interest are the moderate cost and favorable properties of PP. This article is focused on the role of EPR in the deformation and fracture mechanism of PP/EPR blends with different volume fractions of elastomer phase. Differential scanning calorimetry (DSC), tensile tests, and microscopy techniques were used in this study. The fracture mechanism of isotactic PP toughened by EPR (PP/EPR) has also been studied by three point bending (3-PB) and four point bending (4-PB) tests. Rubber particle...
Spanning trees and spanning closed walks with small degrees
, Article Discrete Mathematics ; Volume 345, Issue 10 , 2022 ; 0012365X (ISSN) ; Sharif University of Technology
Elsevier B.V
2022
Abstract
Let G be a graph and let f be a positive integer-valued function on V(G). In this paper, we show that if for all S⊆V(G), ω(G∖S)<∑v∈S(f(v)−2)+2+ω(G[S]), then G has a spanning tree T containing an arbitrary given matching such that for each vertex v, dT(v)≤f(v), where ω(G∖S) denotes the number of components of G∖S and ω(G[S]) denotes the number of components of the induced subgraph G[S] with the vertex set S. This is an improvement of several results. Next, we prove that if for all S⊆V(G), ω(G∖S)≤∑v∈S(f(v)−1)+1, then G admits a spanning closed walk passing through the edges of an arbitrary given matching meeting each vertex v at most f(v) times. This result solves a long-standing conjecture...
Mixed mode I/II delamination analysis of rubber-modified glass-reinforced epoxy composites
, Article Journal of Reinforced Plastics and Composites ; Vol. 33, Issue 17 , September , 2014 , pp. 1634-1643 ; ISSN: 07316844 ; Dadfar, M. R ; Zeraati, A. S ; Sharif University of Technology
Abstract
In this study, the effect of carboxyl-terminated butadiene-acrylonitrile liquid rubber on fracture toughness of glass-reinforced epoxy composites has been investigated. Fracture toughness tests were conducted in modes I, II and different mixed mode ratios. The data obtained from these tests have been analyzed by using different methods. Results indicated that interlaminar fracture toughness of composite specimens improved considerably through addition of carboxyl-terminated butadiene-acrylonitrile in modes I, II and mixed mode. Interlaminar fracture surfaces of the specimens were also characterized by field emission scanning electron microscope
Toughness enhancement in roll-bonded Al6061-15 vol.% SiC laminates via controlled interfacial delamination
, Article Journal of Materials Engineering and Performance ; Volume 22, Issue 11 , 2013 , Pages 3414-3420 ; 10599495 (ISSN) ; Bagheri, R ; Reihani, S. M. S ; Sharif University of Technology
2013
Abstract
Researchers have examined different approaches to improve damage tolerance of discontinuously reinforced aluminum (DRA). In this study, three-layer DRA laminates containing two exterior layers of Al6061-15 vol.% SiCp and an interlayer of Al1050 were fabricated by hot roll bonding. Interfacial adhesion between the layers was controlled by means of rolling stain. The results of shear test revealed that, the bonding strength of laminates was influenced by number of rolling passes. Considering this effect, the role of interfacial bonding on the toughness of laminates was studied under three-point bending in the crack divider orientation. The quasi-static toughness of the laminates was greater...
Fracture toughness of a hybrid rubber modified epoxy. II. Effect of loading rate
, Article Journal of Applied Polymer Science ; Volume 125, Issue 3 , January , 2012 , Pages 2476-2483 ; 00218995 (ISSN) ; Kouchakzadeh, M. A ; Bagheri, R ; Sharif University of Technology
Wiley
2012
Abstract
Effect of loading rate on toughness characteristics of hybrid rubber-modified epoxy was investigated. Epoxy was modified by amine-terminated butadiene acrylonitrile (ATBN) and recycled tire. Samples were tested at various loading rates of 1-1000 mm/min. Fracture toughness measurements revealed synergistic toughening in hybrid system at low loading rates (1-10 mm/min); hybrid system exhibited higher fracture toughness value in comparison with the ATBN-modified resin with same modifier content. However, synergistic toughening was eliminated by increasing the loading rate. At higher loading rates (10-1000), the fracture toughness of hybrid system decreased gradually to the level lower than that...
An Investigation on the Microstructure and Hardness of Martensitic Stainless Steel in Repair Welding Method
, M.Sc. Thesis Sharif University of Technology ; Kokabi, Amir Hossein (Supervisor) ; Madah Hoseini, Hamid Reza (Co-Advisor)
Abstract
Repair welding is one of the important maintenance processes that include build-up welding and surfacing.In this study, investigation of repair welding parameters has been conducted to achieve desired microstructure with the appropriate toughness and minimum residual stress.In this research, local post-weld heat treatment has been performed by Tungsten electrode arc on weld zone. Performing this process with optimum parameters leads to the best heat cycle with the tempered Martensite microstructure. Residual stress of the sample will be reduced. HAZ coarse grains will be refined to finer grains which result in to improved toughness and reduced hardness to the acceptable limit.
Results...
Results...
Correlation between Microstructure with Wear and Toughness Properties of Martensitic Stainless Steel
, M.Sc. Thesis Sharif University of Technology ; Pouranvari, Majid (Supervisor) ; Kokabi, Amir Hossein (Supervisor)
Abstract
Fe-Cr-C hardfacing alloy is the most popular alloy used in severe abrasive condition such as mining and cement industries. One of the limitation of these hardfacing alloys is their low toghness, which reduce the application of these alloys under impact wear conditions. The purpose of this thesis is to investigate the effect of microstructure on the wear and toughness properties of AISI420 hardfaced martensitic stainless steel alloy. For this purpose, after deposition of the hardfaced alloy on a steel substrate, various heat treatments such as quench, quench temper, quench and partitioning and austenite reversion are designed to change the microstructure of the hardfaced alloy from fully...
Microstructure and mechanical properties of WC–10Co cemented carbide containing VC or (Ta, Nb)C and fracture toughness evaluation using different models [electronic resource]
, Article International Journal of Refractory Metals and Hard Materials ; March 2012, Volume 31, Pages 141–146 ; Abachi, P ; Simchi, A. (Abdolreza) ; Sharif University of Technology
Abstract
This article describes a study on WC–10Co cemented carbides with different percent of grain growth inhibitors. Samples were prepared by the conventional powder metallurgy method, using WC and Co powder and different concentrations of VC and (Ta, Nb)C powder. All samples were processed using a hot isostatic press (HIP) and the effect of grain growth inhibitors on the microstructure and mechanical properties were investigated. Additionally, microstructure and powder particle morphology were examined using scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS). The specimen's microstructure proved that the addition of VC is more effective at suppressing grain growth than...
Predictions of toughness and hardness by using chemical composition and tensile properties in microalloyed line pipe steels
, Article Neural Computing and Applications ; 2014 ; Khalaj, G ; Pouraliakbar, H ; Jandaghi, M. R ; Sharif University of Technology
Abstract
Artificial neural networks with multilayer feed forward topology and back propagation algorithm containing two hidden layers are implemented to predict the effect of chemical composition and tensile properties on the both impact toughness and hardness of microalloyed API X70 line pipe steels. The chemical compositions in the forms of "carbon equivalent based on the International Institute of Welding equation (CEIIW)", "carbon equivalent based on the Ito-Bessyo equation (CEPcm)", "the sum of niobium, vanadium and titanium concentrations (VTiNb)", "the sum of niobium and vanadium concentrations (NbV)" and "the sum of chromium, molybdenum, nickel and copper concentrations (CrMoNiCu)", as well...
Preparation of highly rubber-toughened nylons
, Article Iranian Polymer Journal (English Edition) ; Volume 16, Issue 7 , 2007 , Pages 459-468 ; 10261265 (ISSN) ; Yousefi, A. A ; Ramezani saadatabadi, A ; Sharif University of Technology
2007
Abstract
Nylon 6 and 66 were toughened with EPDM-g-MA and SEBS-g-MA and steadystate rheological behaviour of rubbers, nylons and their blends and mechanical properties of nylons and their rubber-toughened blends were investigated. The EPDM maleic grafting preparation was performed In the framework of this study where SEBS-g-MA was obtained from a commercial source. The results showed the ultratoughened SEBS-g-MA blends, whereas EPDM blends under the same blending conditions did not show a significant improvement in toughness. In case of EPDM toughened blends an average of some micrometers was observed for the dispersed EPDM particles. Impact and tensile properties of the toughened blend with 20% of...
Evaluation of the effect of maximum aggregate size on fracture behavior of self compacting concrete
, Article Construction and Building Materials ; Vol. 55 , 2014 , pp. 202-211 ; ISSN: 09500618 ; Kazemi, M. T ; Vaseghi Amiri, J ; Nikbin, I. M ; Rabbanifar, S ; Rahmani, E ; Sharif University of Technology
Abstract
This paper presents and discusses the effect of maximum size of coarse aggregate on fracture characteristics and brittleness of self-compacting concrete (SCC). Based on an experimental program, a series of three point bending tests were carried out on 86 notched beams, as recommended by RILEM. For all mixes, the parameters were analyzed by the work-of-fracture method (WFM) and by the size effect method (SEM) and consequently a correlation between these methods was obtained which is used to calibrate cracking numerical models. Test results showed that with increase of size of coarse aggregate, (a): fracture energies of GF in WFM and Gf in SEM increase which may be explained by the change in...
Influence of martensite volume fraction on impact properties of triple phase (TP) steels
, Article Journal of Materials Engineering and Performance ; Volume 22, Issue 3 , 2013 , Pages 823-829 ; 10599495 (ISSN) ; Ekrami, A ; Sharif University of Technology
2013
Abstract
Ferrite-bainite-martensite triple phase (TP) microstructures with different volume fractions of martensite were obtained by changing heat treatment time during austempering at 300 C. Room temperature impact properties of TP steels with different martensite volume fractions (VM) were determined by means of Charpy impact testing. The effects of test temperature on impact properties were also investigated for two selected microstructures containing 0 (the DP steel) and 8.5 vol.% martensite. Test results showed reduction in toughness with increasing VM in TP steels. Fracture toughness values for the DP and TP steels with 8.5 vol.% martensite were obtained from correlation between fracture...
Effects of pozzolans together with steel and polypropylene fibers on mechanical properties of RCC pavements
, Article Construction and Building Materials ; Volume 26, Issue 1 , January , 2012 , Pages 102-112 ; 09500618 (ISSN) ; Azizkhani, R ; Torki Harchegani, M. E ; Sharif University of Technology
Abstract
Effects of pozzolans and fibers on mechanical properties of RCC are addressed. The mechanical properties were evaluated using optimum moisture with different amounts of pozzolans, steel and polypropylene fibers. Using pozzolans, maximum increase in compressive strength was observed to occur between 28 and 90 days of age, rupture modulus was found to decrease; but toughness indices did not change considerably. The influence of steel fibers on compressive strength was often more significant than that of PP fibers; but neither steel nor PP fibers did contribute to increase in the rupture modulus independently from pozzolans. Also, the toughness indices increased when steel fibers were used
Microwave-assisted sintering of Al2O3-MWCNT nanocomposites
, Article Ceramics International ; Volume 43, Issue 8 , 2017 , Pages 6105-6109 ; 02728842 (ISSN) ; Ebadzadeh, T ; Sadeghian, Z ; Barzega Bafrooei, H ; Nemati, A ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
Alumina-MWCNT composite was densified by microwave sintering. CNTs were coated with boehmite nanoparticles to enhance their distribution in composite samples. Calcination temperature of composite powder was determined by TGA analysis (5 °C/min). Samples containing 0 and 1vol%CNT were produced by cold isostatic pressing at 180 MPa. Microwave sintering (1520 °C for 45 min) was conducted under the flow of argon. Phase analysis of the calcined composite powder showed complete transformation of boehmite into gamma-alumina. The relative densities were 99.3% and 98.1% for monolithic alumina and composite, respectively. CNT addition improved the fracture toughness of alumina by ~37%. SEM images...
Investigation of Fracture Toughness of Epoxy Resins by Addition of CNT and Rubber Microparticles
, M.Sc. Thesis Sharif University of Technology ; Bagheri, Reza (Supervisor)
Abstract
Epoxy resins are relatively brittle and have low resistance to crack propagation. It is common to add rubber particles to improve crack resistance in epoxies, although these particles may deteriorate the strength of the matrix. Different nanomaterials are used to overcome the inherent brittleness of epoxies and to keep the mechanical properties. Among them, carbon nanotubes has been attracted many attentions. Fractue behavior and mechanical properties of two kind of novel nanocomposites, i.e, epoxy/carbon nanotube and epoxy/rubber/carbon nanotube are investigated in current study. Electron microscopy investigations were done to assure the CNTs distribution and fracture mechanisms as well....
Study the Toughening Mechanisms in Hybrid Epoxy/Rubber/CNT Nanocomposites
, M.Sc. Thesis Sharif University of Technology ; Bagheri, Reza (Supervisor) ; Pircheraghi, Gholamreza (Supervisor)
Abstract
Epoxy resins are used for a wide number of application due to good stiffness, chemical resistant and dimensional stability. This is the reason of their use as matrix in composite material. The incorporation of a small amount of carbon nanotubes (CNTs) in epoxy increases mechanical properties if nanocomposite have strong interfacial interaction between epoxy and CNTs, fine dispersion of CNTs and high final aspect ratio CNTs. In Noncovalent functionalization by polymer surfactant, CNTs are dispersed in a solvent/surfactant solution by ultra-sonication and then added to epoxy. In this thesis a novel study of toughening and mechanical properties of epoxy/ rubber/ CNT nanocomposite is presented....