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brittle-fracture
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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...
The influence of roll bonding parameters on the bond strength of Al-3003/Zn soldering sheets
, Article Materials Science and Engineering A ; Volume 487, Issue 1-2 , 25 July , 2008 , Pages 417-423 ; 09215093 (ISSN) ; Madaah Hosseini, H. R ; Kokabi, A. H ; Sharif University of Technology
2008
Abstract
Al-3003/Zn bi-layer soldering sheets were produced using roll bonding process at different reductions in both cold and hot conditions. The bond strengths of the bi-layer sheets were measured by peel test before and after supplemental annealing treatment. The peeled surfaces were examined using optical and scanning electron microscopy. The results indicate that by increasing the reduction in thickness during rolling and/or the annealing treatment the bond strength improves. Additionally, the decrease of initial sheet thickness and increase of rolling temperature can effectively improve the bond strength. Microscopic examinations show that the fracture type of Al-3003/Zn sheets is...
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...
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...
Correlation of production rate of ornamental stone with rock brittleness indexes
, Article Arabian Journal of Geosciences ; Volume 6, Issue 1 , 2013 , Pages 115-121 ; 18667511 (ISSN) ; Ataei, M ; Yousefi, R ; Sharif University of Technology
2013
Abstract
The prediction of production rate in ornamental stones sawing is very important in cost estimation and process planning of the rock sawing plants. The main aim of this paper is finding a mathematical correlation between production rate and rock brittleness indexes. The utilized data have been collected from several stone factories in Iran. Seventeen different granite and carbonate rocks have been experienced sawing conditions with large-diameter circular saws. The laboratory tests such as uniaxial compressive strength and tensile strength, were carried out on the rock samples which were collected from these factories. The ratio of compressive strength to tensile strength (B1), the ratio of...
Mechanical and microstructural characterization of A1-5083/St-12 lap joints made by friction stir welding
, Article Procedia Engineering, 5 June 2011 through 9 June 2011 ; Volume 10 , June , 2011 , Pages 3297-3303 ; 18777058 (ISSN) ; Kokabi, A. H ; Seyed Reihani, S. M ; Najafi, H ; Sharif University of Technology
2011
Abstract
Al-5083 and St-12 alloys sheets were friction stir lap welded at various travel and rotation speeds of the welding tool. Microscopic examinations indicate that the joint strength is due to the macroscopic and microscopic mechanical lockings and also atomic diffusion. The reaction zone of the welded joints consists of mixed layers of ultra-fine grains and the intermetallic compounds. The microhardness and nano indentation results prove that the intermetallic phase layer is more brittle in comparison to base metals and ultra-fine grain region. The fracture surfaces are a combination of brittle and ductile fractures. The fracture loads show that the joint strength improves significantly by...
Numerical simulation of multiple crack growth in brittle materials with adaptive remeshing
, Article International Journal for Numerical Methods in Engineering ; Volume 85, Issue 8 , August , 2011 , Pages 1017-1048 ; 00295981 (ISSN) ; Khoei, A. R ; Sharif University of Technology
Abstract
In this paper, an automated adaptive remeshing procedure is presented for simulation of arbitrary shape crack growth in multiple cracked bodies. The Zienkiewicz-Zhu error estimator is employed in conjunction with the modified superconvergent patch recovery (SPR) technique to obtain more accurate estimation of error. A stability analysis is performed to determine active cracks from a set of competitive cracks. Various crack growth criteria together with the respective crack trajectory prediction are compared. Several numerical examples are illustrated to demonstrate the efficiency, robustness and accuracy of computational algorithm in the simulation of multiple crack growth
The role of first non-singular stress terms in mixed mode brittle fracture of V-notched components: an experimental study
, Article Fatigue and Fracture of Engineering Materials and Structures ; Volume 40, Issue 4 , 2017 , Pages 623-641 ; 8756758X (ISSN) ; Saeidi Googarchin, H ; Aliha, M. R. M ; Sharif University of Technology
Blackwell Publishing Ltd
2017
Abstract
This paper investigates the effects of the first non-singular stress terms on the fracture assessment of sharp V-notches under mixed mode loading. First, numerical studies have been performed on a fracture test configuration called single V-notched ring (SVR) specimen. Then, the notch stress intensity factors as well as the coefficients of the first non-singular stress terms, which are vital parameters in brittle fracture of V-notched components, were calculated via a finite element over-deterministic algorithm for a wide range of loading and geometry conditions. The obtained results demonstrate that the SVR specimen is able to provide a complete range of mode mixities from pure mode I to...
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...
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...
The effect of SiC nanoparticles on the friction stir processing of severely deformed aluminum
, Article Materials Science and Engineering A ; Vol. 602, issue , April , 2014 , p. 110-118 ; ISSN: 09215093 ; Kazeminezhad, M ; Kokabi, A. H ; Sharif University of Technology
Abstract
The 1050 aluminum sheets are severely deformed by two passes of the constrained groove pressing (CGP) process to obtain the strain of 2.32. Friction stir processing (FSP) is then performed on these specimens at two conditions of with and without SiC nanoparticles. Microhardness measurements indicate that in the state of FSP without any particle, the microhardness of stir zone is decreased due to the recrystallization and grain growth occurrence because of high stored strain energy in the CGPed specimens. In order to enhance the mechanical properties of the stir zone, SiC nanoparticles are used during FSP. Also, the effect of FSP pass number on the distribution of nanoparticles is...
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...
The effect of Ti on mechanical properties of extruded in-situ Al-15 pct Mg2Si composite
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 44, Issue 9 , September , 2013 , Pages 4366-4373 ; 10735623 (ISSN) ; Bahrami, A ; Pech Canul, M. I ; Sharif University of Technology
2013
Abstract
This work was carried out to investigate the effect of different Ti concentrations as a modifying agent on the microstructure and tensile properties of an in-situ Al-15 pctMg2Si composite. Cast, modified, homogenized small ingots were extruded at 753 K (480°C) at the extrusion ratio of 18:1 and ram speed of 1 mm/s. Various techniques including metallography, tensile testing, scanning electron microscopy were used to characterize the mechanical behavior, microstructural observations, fracture mechanisms of this composite. The results showed that 0.5 pctTi addition and homogenizing treatment were highly effective in modifying Mg2Si particles. The results also exhibited that the addition of Ti...
Vibration based algorithm for crack detection in cantilever beam containing two different types of cracks
, Article Journal of Sound and Vibration ; Volume 332, Issue 24 , November , 2013 , Pages 6312-6320 ; 0022460X (ISSN) ; Ghadami, A ; Maghsoodi, A ; Michael Hale, J ; Sharif University of Technology
2013
Abstract
In this paper, a simple method for detection of multiple edge cracks in Euler-Bernoulli beams having two different types of cracks is presented based on energy equations. Each crack is modeled as a massless rotational spring using Linear Elastic Fracture Mechanics (LEFM) theory, and a relationship among natural frequencies, crack locations and stiffness of equivalent springs is demonstrated. In the procedure, for detection of m cracks in a beam, 3m equations and natural frequencies of healthy and cracked beam in two different directions are needed as input to the algorithm. The main accomplishment of the presented algorithm is the capability to detect the location, severity and type of each...
The simultaneous effect of extrusion and T6 treatment on the mechanical properties of Al-15wt.%Mg2Si composite
, Article HTM - Journal of Heat Treatment and Materials ; Volume 67, Issue 6 , 2012 , Pages 378-385 ; 18672493 (ISSN) ; Bahrami, A ; Moghimi, F. M ; Pech-Canul, M. I ; Hajaghasi, A ; Sharif University of Technology
2012
Abstract
This article investigates the simultaneous effect of extrusion ratio and T6 heat treatment on microstructure and mechanical properties of in-situ Al-15wt.%Mg2Si composite. his composite has already been introduced as a new class of light materials but the brittle structure of the primary Mg2Si which is formed during solidification limits its application. As-cast composite was directly extruded as rod by using three different dies. After T6 heat treatment on extruded samples, microstructure 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...
Effect of oxide bifilms on the mechanical properties of cast Al-7Si-0.3Mg alloy and the roll of runner height after filter on their formation
, Article Materials Science and Engineering A ; Volume 548 , 2012 , Pages 99-105 ; 09215093 (ISSN) ; Varahram, N ; Davami, P ; Kim, S. K ; Sharif University of Technology
2012
Abstract
Oxide bifilms (double oxide films) are one of the most important defects that influence the mechanical properties of cast aluminum alloys. To investigate the formation of oxide bifilms, castings with different heights of runner were examined. SEM and EDX analysis were used to study the presence of oxide bifilms and fracture surface of tensile test samples. The fracture surface of the tensile test bars that were cast with lower height of runner revealed no oxide bifilm and features of ductile fracture mechanisms. On the other hand, the test bars that were cast with a higher height of runner showed a brittle fracture with areas covered by oxide bifilms. The results of tensile test were...
An investigation on the soldering of Al 3003/Zn sheets
, Article Materials Characterization ; Volume 60, Issue 5 , 2009 , Pages 441-446 ; 10445803 (ISSN) ; Kokabi, A. H ; Madaah Hosseini, H. R ; Sharif University of Technology
2009
Abstract
In this research, Al 3003/Zn sheets with different Zn layer thicknesses (as filler layer) have been soldered to the monolithic Al 3003 sheets. The effects of Zn layer thickness and soldering time at the peak temperature on the joint strength of soldered Al 3003 alloy by pure Zn filler (as the soldering sheets) have been evaluated. Furthermore, microstructure and fracture mechanism of Al 3003/Zn/Al 3003 soldered joints have been studied. The results indicate that by decreasing the Zn layer thickness and increasing the holding time at the peak temperature of soldering, the joint strength improves. Additionally, microscope examinations show that the fracture type of the Al 3003/Zn/Al 3003...
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...
Computational modeling of the interaction of two edge cracks, and two edge cracks interacting with a nanovoid, via an atomistic finite element method
, Article Computational Materials Science ; Volume 42, Issue 2 , 2008 , Pages 186-193 ; 09270256 (ISSN) ; Shodja, H. M ; Rafii Tabar, H ; Sharif University of Technology
2008
Abstract
The competition and interaction of two edge cracks within the triangular lattice of an fcc material are addressed. We have also examined the effect of presence of a nanovoid in the vicinity of one of the crack-tips, on the competition of the cracks. An atomic scale finite element method (AFEM) [B. Liu, Y. Huang, H. Jiang, S. Qu, K.C. Hwang, The atomic-scale finite element method, Comput. Methods Appl. Mech. Eng. 193 (2004) 1849-1864], based on the Morse interatomic potential, is employed to explore the events in the (1 1 1) plane. Particular attention is given to the phenomenon of brittle-to-ductile transition (BDT) that occurs during crack propagation. © 2007 Elsevier B.V. All rights...