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fracture-toughness
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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
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...
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
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...
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...
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....
Synthesis of Magnesium Aluminate Spinel Nanoparticles Using Chemical Method and Investigation of the Effect of Zirconia on Spinel Composites Properties
, M.Sc. Thesis Sharif University of Technology ; Nemati, Ali (Supervisor)
Abstract
In this research, a powder containing magnesium-aluminate spinel particles is prepared based on co-precipitation method and 5% , 10%, 15% and 20% zirconia-contained composites are produced as second phase from the synthesized powder. The raw materials used in the synthesis comprise hexa-hydrated magnesium nitrate, nona-hydrated aluminum nitrate, ammonium bicarbonate, 28% ammonium solution and distilled water. The properties of the powder is then investigated using STA, XRD and SEM tests. Also, XRD and SEM analyses as well as triple point flexural strength and Vickers hardness tests are carried out in order to investigate the effect of adding zirconia to the powders. The variations of the...
Large-scale testing on specific fracture energy determination of dam concrete
, Article International Journal of Fracture ; Volume 141, Issue 1-2 , 2006 , Pages 247-254 ; 03769429 (ISSN) ; Ghaemian, M ; Sharif University of Technology
2006
Abstract
The specific fracture energy of dam concrete is a basic material characteristic needed for the prediction of concrete dam behavior. Data on fracture properties of dam concrete are quite limited to date. A series of tests was carried out based on the size effect due to a number of geometrically similar notched specimens of various sizes. Experimental tests include three-point bending tests. The specimens were of square cross section with a span to depth ratio of 2/5. Three different specimens with depth of 200, 400 and 800 mm were considered for the purpose of testing. Concrete mixtures are provided from the Caroon 3 dam project site using river gravel or commonly crushed stones from...
Direct and indirect methods for determination of mode i fracture toughness using PFC2D
, Article Computers and Concrete ; Volume 20, Issue 1 , 2017 , Pages 39-47 ; 15988198 (ISSN) ; Haeri, H ; Shemirani, A. B ; Sharif University of Technology
Abstract
In this paper, mode I fracture toughness of rock was determined by direct and indirect methods using Particle Flow Code simulation. Direct methods are compaction tension (CT) test and hollow centre cracked quadratic sample (HCCQS). Indirect methods are notched Brazilian disk (NBD) specimen, the semi-circular bend (SCB) specimen, hollow centre cracked disc (HCCD), the single edge-notched round bar in bending (SENRBB) specimen and edge notched disk (END). It was determined that which one of indirect fracture toughness values is close to direct one. For this purpose, initially calibration of PFC was undertaken with respect to data obtained from Brazilian laboratory tests to ensure the...
Determination of Mechanical and Fracture Properties of Nanostructure of Severe Shot Peened A356.0 at Room Temperature
,
M.Sc. Thesis
Sharif University of Technology
;
Farrahi, Gholamhossein
(Supervisor)
Abstract
The most failures caused by wear, fatigue and corrosion are very sensitive to surface of material. Since the most failures starts or occurs at the surface of material, so control and improvement of the surface properties can have a significant effect on increasing the service life and improve the overall behavior of the material. Reforming of the structure and grain size is one of the methods to improve elastic properties, hardness, softness, toughness, etc. Also the macroscopic residual stresses in fracture toughness test specimens, can have tremendous effect on fracture toughness measurements. Many methods are used to modify the surface structure and to create a compressive residual stress...
Investigation of Toughening Mechanisms in Al/Al3Ti In-Situ Hot Extruded Composites
, M.Sc. Thesis Sharif University of Technology ; Madaah Hosseini, Hamid Reza (Supervisor)
Abstract
In this study in-situ Al/Al3Ti was fabricated by mechanical alloying, hot extrusion and subsequent heat treatment. First, initial pure powders of Al and Ti were mechanically alloyed with 5 weight percentages of Ti for 40 hours. The as-hot extruded samples containing 5 wt% of initial Ti particles, were exposed to heating at 600 oC for various time intervals up to 10 hours. Microstructure analysis by OM and SEM proved that in-situ Al3Ti phase was formed as a layer around Ti particles by solid reactive diffusion between Al and Ti particles. After 10 hours of heating, all the Ti particles were consumed and transformed to Al3Ti. Mechanical properties of samples were investigated by Brinell...
Processing and Characterization of Fracture Behavior of Hybrid Epoxy Nanocomposite Modified with Polycarbonate
, M.Sc. Thesis Sharif University of Technology ; Bagheri, Reza (Supervisor)
Abstract
Epoxy resins have good mechanical and thermal properties, high chemical resistance and low shrinkage during cure but in spite of these good properties,they are brittle and this limits the usage of them. Adding a second, soft or rigid, phase has been always an effective strategy to improve the toughness of epoxy. Rigid phase used in resins are divided into organic and inorganic. The aim of this study is to increase epoxy toughness, maintaining mechanical properties and study effect of silica and polycarbonate on fracture toughness simultaneously. Mechanical properties including yield strength and elastic modulus are evaluated by pressure test. Additionally fracture toughness and three...
Hydroxyapaptite Coating on Zirconia Toughened Alumina Nanocomposite by Biomimetic Method
, M.Sc. Thesis Sharif University of Technology ; Nemati, Ali (Supervisor) ; Salahi, Esmaeil (Co-Advisor)
Abstract
Zirconia toughened alumina (ZTA) Nanocomposites were prepared using nano sized Zirconia (ZrO2) powders doped with 3% mol of yttria (Y2O3) nanopowders and the sintering behavior at different temperature (1450 °C, 1550 °C and 1650 °C) were studied. The ZTA composite with different amount of partially stabilized Zirconia (PSZ)(5, 10, 15 and 20% mol) were prepared via axial pressing and then sintered to achieve maximum densification. After that phase changes of the samples were monitored. SEM was used for microstructural study and hardness and fracture toughness were determined by means of Vickers indentation. X-ray diffraction pattern showed that at constant composition, tetragonal zirconia...
Production and Evaluation of Fracture Behavior of Al-Dra Laminated Composites
, M.Sc. Thesis Sharif University of Technology ; Bagheri, Reza (Supervisor) ; Seyyed Reihani, Morteza (Supervisor)
Abstract
Particulate ceramic reinforced aluminum matrix composites have high specific strength and stiffness; however, low fracture toughness and deformability have restricted their industrial applications. Among the methods introduced to overcome this shortcoming is fabricating the layered composites which contain alternative layers of aluminum (Al) and discontinuously reinforced aluminum (DRA). In this study, two different routes; i.e., "Powder extrusion - Casting - Rolling" and "Powder extrusion - Roll bonding" were employed to produce layered Al-DRA composites. After production of Al6061/SiCp composites via hot powder extrusion, mentioned processes were utilized to make DRA-Al-DRA laminate. In...
Toughening of Laminated Composites Composites Using Micro and Nano Particles
,
M.Sc. Thesis
Sharif University of Technology
;
Koochakzadeh, Mohammad Ali
(Supervisor)
Abstract
In this study, standard composite laminate specimens with micro and nano sized particle additives are made to study the effect of the additives on the fracture toughness of the specimens in standard tests. The composite laminates are made from epoxy resin and unidirectional glass fibers. The mode I and mode II fracture toughness of the specimens are measured under various loadings in standard tests. The fracture surface is then, fractogaphed by microscopic instruments. In conclusion, the fracture behavior of laminated composites, toughened by micro and nano particles is discussed. The results show that using rubber particles will improve fracture toughness of neat epoxy resin and laminated...
Characterization of Metallurgical and Geometrical Parameters on Fracture Behavior of Pure Titanium thin Sheets
, M.Sc. Thesis Sharif University of Technology ; Ekrami, Ali Akbar (Supervisor) ; Ziaei Moayyed, Ali Akbar (Supervisor)
Abstract
Commercially pure titanium (CP-Ti) is an important groups of titanium family and because of high strength, low density, high corrosion resistance and biocompatibility, this group of titanium is a suitable choice for application at chemical, petrochemical and medicine industry. Nowadays surgeons have a tendency toward use of CP-Ti instead of Ti-6Al-4V alloy. Moreover, because of body anatomy limitation, use of thick sheets result in high volume and damage soft tissue. Therefore, for sheet thickness reduction, study of the effects of metallurgical and geometrical parameter on fracture behavior of thin sheets is important. In this study, the fracture behavior of CP-Ti thin sheets investigated....
Study the effect of architectural modification on fracture behavior of Al-DRA composite
, Article Mechanics of Advanced Materials and Structures ; Vol. 21, issue. 8 , 2014 , Pages 662-668 ; ISSN: 15376494 ; Khalili, S ; Bagheri, R ; Simchi, A ; 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
synergistic toughening in ternary silica/hollow glass spheres/epoxy nanocomposites
, Article Polymer - Plastics Technology and Engineering ; Volume 54, Issue 6 , 2015 , Pages 581-593 ; 03602559 (ISSN) ; Bagheri, R ; Kouchakzadeh, M. A ; Abadyan, M ; Sharif University of Technology
Taylor and Francis Inc
2015
Abstract
Herein, the fracture toughness of ternary epoxy systems containing nanosilica and hollow glass microspheres (HGMS) is investigated. The experimental measurements reveal synergistic fracture toughness in some hybrid compositions: The incorporation of 10 phr of HGMS and nanosilica alone modify the fracture toughness of epoxy by 39% and 91%, respectively. However, use of 10 phr hybrid modifier can enhance the fracture toughness of the resin up to 120%. Observations reveal different toughening mechanisms for the blends i.e., plastic deformation for silica nanoparticles and crack bifurcation for HGMS. Both of these toughening mechanisms additively contribute to the synergism in ternary epoxies