Search for: aging
Total 356 records
Article SAGE Open ; Volume 11, Issue 2 , 2021 ; 21582440 (ISSN) ; Gholampour, S ; Sharif University of Technology
SAGE Publications Inc 2021
Cheating is an academically dishonest behavior about which there has been a thrust of research. However, it has not been extensively researched in an Iranian context. Therefore, the current study was conducted with 310 Iranian students. A cheating questionnaire was devised and administered to the participants. Certain demographic variables were investigated. Both descriptive and inferential statistics were employed to analyze the obtained data. The results of the descriptive statistics revealed that cheating was common among participants, and most students did not harbor any negative attitude toward cheating or at least were neutral about it. The most common method of cheating was “letting...
Article Materials and Design ; Volume 24, Issue 5 , 2003 , Pages 325-330 ; 02641275 (ISSN) ; Asgari, S ; Sharif University of Technology
Elsevier Ltd 2003
In this research, results obtained on the growth kinetics of γ′ precipitates in superalloy IN-738LC are presented. It was found that when the coarsening of primary and secondary γ′ are considered together, the overall kinetic of coarsening followed a linear trend, as predicted by Lifshitz, Slyozov and Wagner (LSW) theory. However, when only the population of secondary γ′ was taken into account, growth rate for the secondary γ′ departed from the linear trend predicted by the theory. It is therefore suggested that the observed deviation of coarsening kinetics from linear behavior may be related to the short inter-particle distances in this system which caused elastic interaction energy to...
Article Journal of Materials Processing Technology ; Volume 205, Issue 1-3 , 26 August , 2008 , Pages 388-393 ; 09240136 (ISSN) ; Karimi Taheri, A ; Sharif University of Technology
In this paper, an Al-Mg-Si-Cu aluminum alloy was exposed to various heat treatment processes and the effect of precipitation hardening on hardness was investigated as a function of time and temperature. It was concluded that the variation in time and temperature can improve the hardness of the alloy. The work revealed that time and temperature play an important role in the precipitation hardening process of the alloy. To achieve the maximum hardness, an optimum aging cycle should be used which is heating at 180-190 °C for 15-18 h. Kinetics studies show an apparent activation energy of 58 kJ/mol. A relationship was derived which can be used to estimate the hardness at a given time and...
Article Iranica Antiqua ; Volume 48 , 2013 , Pages 147-174 ; 00210870 (ISSN) ; Emami, S. M ; Malekzadeh, M ; Hassanpour, A ; Davami, P ; Sharif University of Technology
In this paper, an analysis is presented of some bronze vessels from recent excavations at the first millennium BC site of Sangtarashan in eastern Luristan, Iran, according to metallography (OM), ICP-OES and SEM-EDS methods to identify alloying as well as manufacturing processes. This study provides new evidence for a better understanding of the bronze archaeometallurgy during the Iron Age in Iran. It concludes that the artifacts contain homogenous and single phase tin bronze (Cu-Sn) alloy. The Sn content in the artifacts also allowed to apply mechanical operations on the vessels without causing brittleness. Apart from tin, other elements that are classified as trace elements were present,...
The influence of thermal exposure on the γ′ precipitates characteristics and tensile behavior of superalloy IN-738LC, Article Journal of Materials Processing Technology ; Volume 147, Issue 3 , 2004 , Pages 343-350 ; 09240136 (ISSN) ; Asgari, S ; Sharif University of Technology
The effects of long term aging on γ′ size and distribution and its influence on tensile behavior of superalloy IN-738LC at room and in elevated temperatures were investigated. Samples were aged isothermally at 850 °C for different times up to 3000 h and tensile tests were performed on samples in both standard heat treatment (SHT) and aged conditions. For samples in SHT condition yield stress (σy) was independent of tensile temperature up to 550 °C, after which it decreased slightly and then reached a maximum at 650 °C. Also minimum ductility was observed in this temperature. For aged samples, results showed an initial decrease of σy up to 550 °C, followed by a subsequent increase in σy...
Article Journal of Alloys and Compounds ; Volume 368, Issue 1-2 , 2004 , Pages 144-151 ; 09258388 (ISSN) ; Asgari, S ; Sharif University of Technology
In this investigation, changes in γ′ characteristics in superalloy IN-738LC during aging are presented. The SEM studies revealed that coarsening kinetics of γ′ follows a linear law at different aging time for different temperatures. Whereas when coarsening of secondary γ′ is studied, it was found that at the early stage of aging, volume fraction of secondary γ′ is high, leading to short inter-particle distances. In this condition interfacial energy is dominant and variation of [r3-r03] as a function of aging time is linear. As the coarsening proceeds, volume fraction of secondary γ′ decreases and elastic interaction energy becomes dominant. In such case a deviation in variation of [r3-r03]...
Article Scientia Iranica ; Volume 11, Issue 4 , 2004 , Pages 392-397 ; 10263098 (ISSN) ; Seyed Reihani, S. M ; Sharif University of Technology
Sharif University of Technology 2004
In this work, the production and properties of Al 6061/SiC composites, made using a squeeze casting method, were investigated. SiC preforms were manufactured by mixing SiC powder, having a 16 and 22 pm particle size, with colloidal silica as a binder. 6061 Al melt was squeeze cast into the pores of the SiC preform to manufacture a DRA composite containing 30v/o reinforcement. The aging behavior, tensile properties and fracture mechanism of the cast material were studied. The results show that higher hardness, yield strength, tensile strength and Young's modulus can be obtained by the addition of SiC particles to 6061 Al alloy, whereas tensile elongation decreases. This is mainly caused by a...
Article Materials Science and Engineering A ; Volume 534 , 2012 , Pages 547-551 ; 09215093 (ISSN) ; Sharif University of Technology
Age hardening behavior of selected samples of AEREX ™ 350, a nickel-cobalt based superalloy, was investigated in this article. The relationship between the microstructure and mechanical properties was elucidated using hardness and compression testing methods and optical, scanning and transmission electron microscopy techniques. It was found that the microstructure is sensitive to the temperature of the solution and the aging treatments. This approach may be used to optimize the microstructure of the alloy for different applications
Article Journal of Alloys and Compounds ; Volume 781 , 2019 , Pages 945-983 ; 09258388 (ISSN) ; Taheri, A. K ; Taheri, K. K ; Sharif University of Technology
Elsevier Ltd 2019
Al-Zn-Mg-Cu alloys (7xxx series Al alloys) are extensively used for their superior mechanical and corrosion performance. These properties are microstructure-sensitive and highly dependent on the formation, growth and coarsening of precipitates. To date, a wide variety of ageing procedures have been developed to tailor the evolved microstructures so as to yield a good combination of mechanical capacity and corrosion resistance of 7xxx series Al alloys. Among these methods, isothermal ageing, multi-stage ageing, non-isothermal ageing, retrogression and re-ageing (RRA), and stress ageing (i.e. creep ageing) are the most significant. In the present review, all of these approaches are...
Investigation of Mechanical Milling Effects on Al-Cu and Al-CuO Powder Mixture Morphological and Structural Characteristic and Mechanical Properties Changes Resultant from Age Hardening, M.Sc. Thesis Sharif University of Technology ; Simchi, Abdolreza
In the present work, nanocrystalline Al-4wt%Cu alloy reinforced with nanometric Al2O3 particles was synthesized by in-situ reactive milling of Al and CuO powder mixture and hot extrusion. The effect of nanometric Al2O3 particles on the aging behavior and mechanical properties of this alloy was investigated. During mechanical milling, copper oxide were reduced and dissolved in the aluminum lattice. consequently, Al(Cu) solid solution matrix was produced. Also, nanometric Al2O3 particles were also distributed in the matrix uniformly. The powder blend was then pressed in an Al can at 100 MPa pressure and subsequently extruded at 450 0C at the extrusion ratio of 16:1. The density of the...
Optimization of Synthesis Method and Operational Improvement of High Temperature Water-gas Shift Catalyst, M.Sc. Thesis Sharif University of Technology ; Baghghalha, Morteza ; Kazemeini, Mohammad ; Bahmani, Mohsen
The water-gas shift reaction, as a vital reaction in industry especially as a source of hydrogen for the manufacture of ammonia, is influential for all of the scientists and researchers in chemical engineering all around the world. In this research, high temperature water-gas shift (HTS) catalysts were investigated in order to study synthesis parameters and improvement of their performance and catalytic activity. The two catalyst categories; non pre-active and pre-active (magnetite-based samples, not requiring a reduction step prior to use) were prepared by co-precipitation method, using chloride, sulfate and nitrate metal (Fe, Cr, Cu) precursors and NaOH as precipitating agent (the aging...
Fatal accident distribution by age, gender and head injury, and death probability at accident scene in Mashhad, Iran, 2006-2009, Article International Journal of Injury Control and Safety Promotion ; Volume 20, Issue 2 , 2013 , Pages 121-133 ; 17457300 (ISSN) ; Shafahi, Y ; Zangooei Dovom, M ; Sharif University of Technology
Several studies have investigated road traffic deaths, but few have compared by road user type. Iran, with an estimated 44 road traffic deaths per 100,000 population in 2002 had higher road traffic deaths than any other country for which reliable estimates can be made. So, the present study was conducted on road death data and identified fatal accident distribution by age, gender and head injury as well as the influences of age and gender on deaths at accident scenes for all road user groups. Data used in this study are on fatal road accidents recorded by forensic medicine experts of the Khorasan Razavi province in Mashhad, the capital of the province, the second largest city and the largest...
Upper bound analysis of deformation and dynamic ageing behavior in elevated temperature equal channel angular pressing of Al-Mg-Si alloys, Article Metals and Materials International ; Volume 16, Issue 3 , June , 2010 , Pages 363-369 ; 15989623 (ISSN) ; Karimi Taheri, A ; Seop Kim, H ; Sharif University of Technology
In the present study, the plastic deformation and dynamic strain ageing behavior of Al-6082 (Al-Mg-Si) alloy treated with elevated temperature equal channel angular pressing (ECAP) were investigated using upper bound analyses. Tensile tests were carried out over wide ranges of temperature and strain rate in order to evaluate the dynamic ageing conditions. ECAP processing was then experimentally performed at temperatures from room temperature up to 200 °C under various strain rates ranging between 10-4 s-1 and 10-1 s-1 . The upper bound analysis solutions and the experimental results are comparable. A theoretical dynamic ageing region was found to be in the temperature range of 90 °C to 260...
Article International Journal of Conservation Science ; Volume 9, Issue 2 , 2018 , Pages 277-290 ; 2067533X (ISSN) ; Dolati, A ; Emami, M ; Sharif University of Technology
Universitatea "Alexandru Ioan Cuza" din Iasi 2018
The corrosion process of two iron dagger handles decorated with bronze strips found from the Ziviyeh area, which is one of the important Iron Age sites in the northwest of Iran, is thoroughly investigated. X-ray radiography was used to obtain the damages and corrosion zones of the artifact. Optical and scanning electron microscopies were used to study the microstructure of cross sections and to achieve structural details about the metal matrix and corrosion layers. The X-ray diffraction method was used to study the chemical characterization of corrosion products. The results of studies have shown that severe stress on bronze strips is caused by the formation of goethite and lepidocrocite...
Cold-Briquetted iron and carbon (CBIC): investigation of the influence of environmental condition on its chemical and physical properties, Article Journal of Sustainable Metallurgy ; Volume 5, Issue 4 , 2019 , Pages 497-509 ; 21993823 (ISSN) ; Askari, M ; Shahahmadi, S. A ; Sharif University of Technology
In this study, a comprehensive investigation was carried out on the effects of environmental condition on physical and chemical properties of Cold-Briquetted Iron and Carbon (CBIC), Cold Direct Reduced Iron (CDRI), and Hot-Briquetted Iron (HBI). The results showed that cold briquetting of CDRI decreases its specific surface area by 51%, which has a significant effect on its oxidation resistance and mechanical strength. Microscopic observations revealed that the oxidation products are formed in near-surface porosities during aging, which protects the fresh material underneath from environmental oxidants, resulting in retarding further oxidation. The oxidation behavior of the samples showed...
Article ISIJ International ; Volume 44, Issue 11 , 2004 , Pages 1867-1873 ; 09151559 (ISSN) ; Sharif University of Technology
Iron and Steel Institute of Japan 2004
In this work, the effects of dynamic strain aging and dynamic recovery on metal flow during warm working are studied. Compression experiments are utilized to assess the flow behavior of a low carbon steel under warm deformation conditions. Then, a two dimensional finite element routine is coupled with dynamic recovery and dynamic strain aging models. In this way, the temperature and the velocity fields are predicted during warm working operations with regard to the effects of dynamic recovery and dynamic strain aging. Warm rolling tests are performed in order to verify the modelling results. Comparison between the predicted and measured roll forces shows reliability of the employed model
Article Scripta Materialia ; Volume 52, Issue 4 , 2005 , Pages 253-257 ; 13596462 (ISSN) ; Mahmudi, R ; Khomamizadeh, F ; Sharif University of Technology
The structure, age hardening response, precipitate type and hardness of A319 cast aluminum alloy without and with zirconium addition were investigated. The as-solutionized and artificially-aged hardness values were higher for the Zr-containing alloy. This is believed to be a consequence of the precipitation of Al3Zr particles produced during sufficiently long solutionizing treatments. © 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
Article Materials Science and Technology ; Volume 26, Issue 2 , Jul , 2010 , Pages 169-175 ; 02670836 (ISSN) ; Karimi Taheri, A ; Sharif University of Technology
In this study both the quench aging and static strain aging kinetics of a 6082 Al alloy were investigated at a temperature range of 130-200°C using the Vickers hardness and tensile test. The activation energy and dislocation density were determined at different stages of the aging phenomenon. The former was used to analyse the kinetics of aging and the latter to interpret the competition of strengthening and recovery mechanisms during aging. It is shown that different activation energies are achieved depending on the aging time and temperature relating to formation of appropriate precipitates at different stages of aging. Moreover, it is revealed that prestrain reduces the activation energy....
M.Sc. Thesis Sharif University of Technology ; Serajzadeh, Siamak ; Kokabi, Amir Hossein
In this study, temperature and Thermo-mechanical stress Distributions during and after TIG welding operations of AA2024 have been investigated by means of numerical simulation and experimental observations. Different geometries and initial microstructures, i.e. artificially and naturally aged alloys, have been selected. The model can determine the effect of welding parameters as well as mechanical fixtures on temperature and stress fields developed within metal being welded. Furthermore the subsequent aging behaviour of welded alloy (up to 70 days) has been evaluated employing hardness measurement and tensile testing. In addition, microstructural evolutions have been made utilising Scanning...
Discrimination of bilateral finger photoplethysmogram responses to reactive hyperemia in diabetic and healthy subjects using a differential vascular model framework, Article Physiological Measurement ; Volume 34, Issue 5 , 2013 , Pages 513-525 ; 09673334 (ISSN) ; Aghajani, H ; Zahedi, E ; Sharif University of Technology
Endothelial dysfunction assessment has received considerable attention due to its potential in early screening of cardiovascular diseases. Since the seminal work by Celermajer in flow-mediated dilation (FMD) based on B-mode ultrasound measurement of the brachial artery dilation following limb ischemia, many attempts have been made toward applying this method to clinical, non-invasive endothelial dysfunction assessment. One major obstacle toward achieving this objective has been the relative high cost of the required setup and skilled manpower. Such limitations have prompted the investigation of other non-invasively accessible signals such as the photoplethysmogram (PPG) in relation to FMD....