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brittle-fracture
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Modeling Fracture Problems with X-FEM
, M.Sc. Thesis Sharif University of Technology ; Khoei, Amir Reza (Supervisor)
Abstract
Every year, fracture imposes high economic costs and casualties to all societies. Since the beginning of the twentieth century, scientific approach to this issue has lead to invention of a new branch in mechanics, called fracture mechanics. In general, fracture problems fall into two categories. Brittle fracture, like what happens in glass, in which, few plastic deformations and energy absorption occurs and ductile fracture, which is preceded by large plastic deformations and energy absorption. This kind of fracture is usual in ductile metals like low carbon steel. Finite Element which is considered as the most important numerical method in the mechanics of materials, is also, widely used in...
Numerical Modeling and Experimental Investigation of the Efficiency of the Laser-assisted Machining for Ceramics
, Ph.D. Dissertation Sharif University of Technology ; Movahhedy, Mohammad Reza (Supervisor) ; Shoja Razavi, Reza (Co-Supervisor)
Abstract
Laser-assisted machining is nowadays considered as an alternative to conventional machining processes including ceramics grinding, which has provided the basis for extensive experimental and numerical studies in this field. Since the main difference between laser-assisted machining and conventional machining is in the presence of lasers, the main purpose of this study was to investigate the effects of laser on the laser assisted machining process. In this regard, in the first step the process of laser heating to the ceramic workpiece has been studied experimentally and numerically by finite element method. The material used in this research is a slip cast fused silica ceramic. The...
An Investigation of Brittle Fracture of Composite Pressure Vessels with Metal Liner Using a Numerical Approach Based on XFEM
, M.Sc. Thesis Sharif University of Technology ; Hosseini Kordkhili, Ali (Supervisor)
Abstract
A metal cylinder tank with composite coating is a pressure vessel which is made of a thin metal layer and a composite layer; like Graphite, and most of the loading is carried by the composite layer. In this study the penny-shaped cracks in cylindrical pressure vessels with composite coating is studied. These kinds of cracks are mostly initiated in manufacturing processes and they have crucial rule in fatigue life and load carrying of the structure. Although there are numerous analytical and numerical methods, they have shortcomings in the case of penny-shaped cracks problems. The strain discontinuity in the interfaces of materials along with discontinuity and singularity due to the crack are...
Experimental and numerical simulation of the microcrack coalescence mechanism in rock-like materials
, Article Strength of Materials ; Volume 47, Issue 5 , September , 2015 , Pages 740-754 ; 00392316 (ISSN) ; Khaloo, A ; Marji, M. F ; Sharif University of Technology
Springer New York LLC
2015
Abstract
Rocks and rock-like materials frequently fail under compression due to the initiation, propagation and coalescence of the pre-existing microcracks. The mechanism of microcrack coalescence process in rock-like materials is experimentally and numerically investigated. The experimental study involves some uniaxial compression tests on rock-like specimens specially prepared from portland pozzolana cement, mica sheets and water. The microcrack coalescence is studied by scanning electron microscopy on some of the prepared thin specimens. It is assumed that the mica sheets play the role of microcracks within the specimens. Some analytical and numerical studies are also carried out to simulate the...
Analysis and characterization of the role of NI interlayer in the friction welding of titanium and 304 austenitic stainless steel
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; 2015 ; 10735623 (ISSN) ; Ashfaq, M ; Ashiri, R ; Muthupandi, V ; Sivaprasad, K ; Sharif University of Technology
Springer Boston
2015
Abstract
Joining of commercially pure Ti to 304 stainless steel by fusion welding processes possesses problems due to the formation of brittle intermetallic compounds in the weld metal, which degrade the mechanical properties of the joints. Solid-state welding processes are contemplated to overcome these problems. However, intermetallic compounds are likely to form even in Ti-SS joints produced with solid-state welding processes such as friction welding process. Therefore, interlayers are employed to prevent the direct contact between two base metals and thereby mainly to suppress the formation of brittle Ti-Fe intermetallic compounds. In the present study, friction-welded joints between commercially...
THE effect of T6 treatment on the tensile properties of hot extruded Al-15WT. %Mg 2Si metal matrix composite
, Article International SAMPE Technical Conference ; 2012 ; 9781934551127 (ISBN) ; Moghimi, F. M ; Emamy, M ; Soltani, N ; Hajaghasi, A ; Pech Canul M. i ; Sedghi, A ; Sharif University of Technology
SAMPE
2012
Abstract
This article investigates the effect of T6 heat treatment on microstructure and mechanical properties of hot extruded in-situ Al-15wt%Mg 2Si composite. This composite has already been introduced as a new class of light materials but the brittle structure of the primary Mg 2Si which is formed during solidification limits its application. As-cast composite was directly extruded as rod by using three different dies. Microstructure after this type of extrusion was studied by optical and scanning electron microscopy. Results demonstrated that extruded and heat treated composite possesses considerably higher strength and enhanced ductility in comparison with the as-cast samples. It was also found...
Reactive friction stir processing of AA 5052-TiO2 nanocomposite: Process-microstructure-mechanical characteristics
, Article Materials Science and Technology (United Kingdom) ; Volume 31, Issue 4 , 2015 , Pages 426-435 ; 02670836 (ISSN) ; Simchi, A ; Kokabi, A. H ; Sadeghahmadi, M ; Gerlich, A. P ; Sharif University of Technology
Maney Publishing
2015
Abstract
Friction stir processing (FSP) is a solid state route with a capacity of preparing fine grained nanocomposites from metal sheets. In this work, we employed this process to finely distribute TiO2 nanoparticles throughout an Al-Mg alloy, aiming to enhance mechanical properties. Titanium dioxide particles (30 nm) were preplaced into grooves machined in the middle of the aluminium alloy sheet and multipass FSP was afforded. This process refined the grain structure of the aluminium alloy, distributed the hard nanoparticles in the matrix and promoted solid state chemical reactions at the interfaces of the metal/ceramic particles. Detailed optical and electron microscopic studies showed that the...
A fully coupled element-free Galerkin model for hydro-mechanical analysis of advancement of fluid-driven fractures in porous media
, Article International Journal for Numerical and Analytical Methods in Geomechanics ; Volume 40, Issue 16 , 2016 , Pages 2178-2206 ; 03639061 (ISSN) ; Pak, A ; Sharif University of Technology
John Wiley and Sons Ltd
Abstract
Hydraulic fracturing (HF) of underground formations has widely been used in different fields of engineering. Despite the technological advances in techniques of in situ HF, the industry uses semi-analytical tools to design HF treatment. This is due to the complex interaction among various mechanisms involved in this process, so that for thorough simulations of HF operations a fully coupled numerical model is required. In this study, using element-free Galerkin (EFG) mesh-less method, a new formulation for numerical modeling of hydraulic fracture propagation in porous media is developed. This numerical approach, which is based on the simultaneous solution of equilibrium and continuity...
The effect of water to cement ratio on fracture parameters and brittleness of self-compacting concrete
, Article Materials and Design ; Volume 50 , 2013 , Pages 267-276 ; 02613069 (ISSN) ; Kazemi, M. T ; Nikbin, I. M ; Amiri, J. V ; Sharif University of Technology
Elsevier Ltd
2013
Abstract
The paper describes an experimental research on fracture characteristics of self-compacting concrete (SCC). Three point bending tests conducted on 154 notched beams with different water to cement (w/c) ratios. The specimens were made from mixes with various w/c ratios from 0.7 to 0.35. For all mixes, common fracture parameters were determined using two different methods, the work-of-fracture method (WFM) and the size effect method (SEM). Test results showed that with decrease of w/c ratio from 0.7 to 0.35 in SCC: (a) the fracture toughness increases linearly: (b) the brittleness number is approximately doubled: (c) the effective size of the process zone cf in SEM and the characteristic...
Fracture properties of steel fiber reinforced high strength concrete using work of fracture and size effect methods
, Article Construction and Building Materials ; Volume 142 , 2017 , Pages 482-489 ; 09500618 (ISSN) ; Golsorkhtabar, H ; Beygi, M. H. A ; Gholamitabar, M ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
This paper deals with investigation of fracture behavior of steel fiber reinforced high strength concrete (SFRHSC) and compare it to plain high strength concrete (HSC). Based on an experimental program, a series of three point bending tests were carried out on 54 notched beams, as recommended by RILEM. The fracture parameters were measured by two methods: work of fracture method (WFM) and size effect method (SEM). Then the fracture parameters obtained from these two methods were compared. The results showed that with increase of steel fibers, fracture energy of GF in WFM and Gf in SEM increase but this increase in work of fracture method is more significant. The effective size of the process...
On the origin of intermediate temperature brittleness in La-based bulk metallic glasses
, Article Journal of Alloys and Compounds ; Volume 770 , 2019 , Pages 535-539 ; 09258388 (ISSN) ; Tavakoli, R ; Aashuri, H ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
The effect of strain rate on the ductility of a La-based bulk metallic glass (BMG) over a wide temperature range, and the correlation between ductility and relaxation processes within this alloy are investigated in the present work. The three point bending test and dynamic mechanical analysis are employed to study these phenomena. It is found that the activation energies of the nearly constant loss (NCL) relaxation and intermediate temperature brittleness are almost identical. This observation reveals that the NCL relaxation, as a locally confined or caged dynamics, contributes as the main source of intermediate temperature brittleness in La-based BMGs. © 2018 Elsevier B.V
Effects of tool rake angle and tool nose radius on surface quality of ultraprecision diamond-turned porous silicon
, Article Journal of Manufacturing Processes ; Volume 37 , 2019 , Pages 321-331 ; 15266125 (ISSN) ; Akbari, J ; Yan, J ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
This paper presents an investigation of the effects of tool rake angle and nose radius on the surface quality of ultraprecision diamond-turned porous silicon. The results showed that as rake angle decreases, the high-stress field induced by the tool edge increases, causing microcracks to propagate extensively near the pore walls. As a result, the ductile-machined areas shrank under a negative tool rake angle. On the other hand, brittle fracture occurred around pores released cutting pressure significantly. These trends of rake angle effects are distinctly different from those in the cutting of non-porous silicon. Finite element simulation of stress in the cutting area agreed with the...
Effects of tool rake angle and tool nose radius on surface quality of ultraprecision diamond-turned porous silicon
, Article Journal of Manufacturing Processes ; Volume 37 , 2019 , Pages 321-331 ; 15266125 (ISSN) ; Akbari, J ; Yan, J ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
This paper presents an investigation of the effects of tool rake angle and nose radius on the surface quality of ultraprecision diamond-turned porous silicon. The results showed that as rake angle decreases, the high-stress field induced by the tool edge increases, causing microcracks to propagate extensively near the pore walls. As a result, the ductile-machined areas shrank under a negative tool rake angle. On the other hand, brittle fracture occurred around pores released cutting pressure significantly. These trends of rake angle effects are distinctly different from those in the cutting of non-porous silicon. Finite element simulation of stress in the cutting area agreed with the...
Room- and high-temperature torsional shear strength of solid oxide fuel/electrolysis cell sealing material
, Article Ceramics International ; Volume 45, Issue 2 , 2019 , Pages 2219-2225 ; 02728842 (ISSN) ; Kokabi, A. H ; Faghihi Sani, M. A ; Groß Barsnick, S. M ; Malzbender, J ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
The structural integrity of the sealant material is critical for the reliability of solid oxide fuel/electrolysis stacks. In the current study, a torsion test is implemented to evaluate and compare its shear strength with a partially crystallized glass sealant at room- and operation relevant high-temperatures. Hourglass-shaped specimens with different configurations of hollow- and full-halves are utilized for testing. The fracture surfaces are visualized via optical microscopy and complementary scanning electron microscopy. In addition, cyclic loading is used to investigate potential subcritical crack growth effects in the sealants. Both, the specimens with a hollow-half as well as the ones...
Fatigue fracture of friction-stir processed Al-Al3Ti-MgO hybrid nanocomposites
, Article International Journal of Fatigue ; Volume 87 , 2016 , Pages 266-278 ; 01421123 (ISSN) ; Khodabakhshi, F ; Simchi, A ; Kokabi, A. H ; Sharif University of Technology
Elsevier Ltd
Abstract
This paper presents experimental results on the fatigue properties of Al-matrix nanocomposites prepared by the friction stir processing (FSP) technique. An Al-Mg alloy (AA5052) with different amounts (∼2 and 3.5 vol%) of pre-placed TiO2 nanoparticles were FSPed up to 6 passes to attain homogenous dispersion of nano-metric inclusions. Microstructural studies by electron microscopic and electron back scattering diffraction (EBSD) techniques showed that nano-metric Al3Ti (50 nm), TiO2 (30 nm), and MgO (50 nm) particles were distributed throughout a fine-grained Al matrix (<2 μm). Consequently, a significant improvement in the tensile strength and hardness was attained. Uniaxial...
Similar and dissimilar friction-stir welding of an PM aluminum-matrix hybrid nanocomposite and commercial pure aluminum: Microstructure and mechanical properties
, Article Materials Science and Engineering A ; Volume 666 , 2016 , Pages 225-237 ; 09215093 (ISSN) ; Simchi, A ; Kokabi, A. H ; Gerlich, A. P ; Sharif University of Technology
Elsevier Ltd
Abstract
Friction stir welding (FSW) of dissimilar joints has recently attracted great interest for the fabrication of bimetallic and layered composite structures. In this paper, dissimilar joining of an aluminum-matrix hybrid nanocomposite to commercial pure aluminum is reported for the first time. An aluminum hybrid nanocomposite reinforced with Al2O3 (2 vol%; 15 nm) and SiC (2 vol%; 50 nm) nanoparticles was prepared by powder metallurgy routes including mechanical milling and hot powder consolidation techniques. Different joint designs at various ranges of rotational (w) and traverse velocities (v) were evaluated to determine process window for the dissimilar solid-state welding. Macro- and...
Fabrication of high strength in-situ Al-Al3Ti nanocomposite by mechanical alloying and hot extrusion: Investigation of fracture toughness
, Article Materials Science and Engineering A ; Volume 658 , 2016 , Pages 246-254 ; 09215093 (ISSN) ; Madaah Hosseini, H. R ; Seyed Reihani, S. M ; Sharif University of Technology
Elsevier Ltd
Abstract
High energy vibratiory mill was used to produce Nanocrystalline Al-20 wt% Ti powders by mechanical alloying. The milled powders were then consolidated by hot extrusion at 530°C. Produced bulk nanocomposite samples were studied by XRD analysis, optical microscopy (OM), Field Emission Scanning Electron Microscopy (FESEM), EDS spectroscopy, densitometry and hardness tests. Three point bending on SENB specimens was applied under quasi static condition to determine the fracture toughness and also investigate the fracture surface using SEM. The results indicated that after extrusion a fully dense Al-Al3Ti nanocomposite with the crystallite size of 200-400 nm is produced in which the Al3Ti...
Friction stir processing of an aluminum-magnesium alloy with pre-placing elemental titanium powder: In-situ formation of an Al3 Ti-reinforced nanocomposite and materials characterization
,
Article
Materials Characterization
;
Volume 108
,
October
,
2015
,
Pages 102-114
;
10445803 (ISSN)
; Simchi, A
; Kokabi, A. H
; Gerlich, A. P
;
Sharif University of Technology
Elsevier Inc
2015
Abstract
A fine-grained Al-Mg/Al3 Ti nanocomposite was fabricated by friction stir processing (FSP) of an aluminum-magnesium (AA5052) alloy with pre-placed titanium powder in the stirred zone. Microstructural evolutions and formation of intermetallic phases were analyzed by optical and electron microscopic techniques across the thickness section of the processed sheets. The microstructure of the nanocomposite consisted of a fine-grained aluminum matrix (1.5 μm), un-reacted titanium particles (<40 μm) and reinforcement particles of Al3 Ti (<100 nm) and Mg2 Si (<100 nm). Detailed microstructural analysis indicated solid-state interfacial reactions between the aluminum...
Friction stir welding joint of dissimilar materials between AZ31B magnesium and 6061 aluminum alloys: Microstructure studies and mechanical characterizations
, Article Materials Characterization ; Volume 101 , March , 2015 , Pages 189-207 ; 10445803 (ISSN) ; Behnamian, Y ; Mostafaei, A ; Izadi, H ; Saeid, T ; Kokabi, A. H ; Gerlich, A. P ; Sharif University of Technology
Elsevier Inc
2015
Abstract
Friction stir welding is an efficient manufacturing method for joining dissimilar alloys, which can dramatically reduce grain sizes and offer high mechanical joint efficiency. Lap FSW joints between dissimilar AZ31B and Al 6061 alloy sheets were made at various tool rotation and travel speeds. Rotation and travel speeds varied between 560-1400 r/min and 16-40 mm/min respectively, where the ratio between these parameters was such that nearly constant pitch distances were applied during welding. X-ray diffraction pattern (XRD), optical microscopy images (OM), electron probe microanalysis (EPMA) and scanning electron microscopy equipped with an energy-dispersive X-ray spectroscopy (SEM-EDS)...
Experimental study of the relationship between fracture initiation toughness and brittle crack arrest toughness predicted from small-scale testing
, Article Theoretical and Applied Fracture Mechanics ; Volume 110 , 2020 ; Mehmanparast, A ; Kulka, R ; Moore, P ; Xu, L ; Farrahi, G. H ; Sharif University of Technology
Elsevier B.V
2020
Abstract
It is vital to prevent brittle cracks in large structures. This is particularly important for a number of industry sectors including offshore wind, Oil & Gas, and shipbuilding where structural failure risks loss of human life and loss of expensive assets. Some modern steels exhibit high Charpy energy – i.e. high initiation fracture toughness, but poor resistance to crack propagation – i.e. low crack arrest toughness. The correlation between initiation and arrest toughness measured through small-scale testing is investigated in five different steels, which include S355 structural steel (with two different thicknesses), X65 pipeline steel, two high strength reactor pressure vessel steels and...