Search for: creep
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    Microstructural evaluation and fracture mechanisms of failed IN-738LC gas turbine blades

    , Article Case Studies in Engineering Failure Analysis ; Volume 1, Issue 2 , April , 2013 , Pages 85-94 ; 22132902 (ISSN) Attarian, M ; Khoshmanesh, R ; Nategh, S ; Davami, P ; Sharif University of Technology

    Concrete basic creep predi ction based on time-temperature equivalence relation and short-term tests

    , Article Arabian Journal for Science and Engineering ; Volume 35, Issue 2 A , 2010 , Pages 105-121 ; 13198025 (ISSN) Barani, O. R ; Mostofinejaad, D ; Saadatpour, M. M ; Shekarchi, M ; Sharif University of Technology
    Using temperature as an accelerator of reactions in short-term tests for the prediction of concrete creep is the main idea of this paper. The application of a time-temperature equivalence relation is examined with reference to creep in concrete under constant moisture conditions. A mathematical model is developed which uses short-term tests to predict long-term creep deformation of concrete under constant moisture conditions, taking into account aging of concrete and the influence of temperature. The thermal activation is assumed to be governed by the Arrhenius principle, and the activation energy of the viscosity of water is found to be applicable in the analysis of the experimental data.... 

    High performance of finite element method applied to plastic analysis of reinforced materials with application in optoelectronic devices

    , Article Journal of Optoelectronics and Advanced Materials ; Volume 17, Issue 9-10 , 2015 , Pages 1545-1548 ; 14544164 (ISSN) Monfared, V ; Daneshmand, S ; Fazaeli, D ; Sharif University of Technology
    National Institute of Optoelectronics  2015
    Finite element analysis of creeping short fiber composites is carried out in the second stage creep with application in microelectronic and optoelectronic/photonic devices. Prediction of the creep behavior is very significant for designing the optoelectronic and photonic composites with optical fibers. Study on the creep behavior is necessary for failure, fracture, fatigue, and creep resistance of the optoelectronic/photonic composites. The creep behavior of the short fiber composites is estimated by FEM. Study on the creep behavior is necessary for defect analysis and creep resistance of the short fiber composites. In this research work, prediction of the creep behavior of the short fiber... 

    Simulation of elasto-plastic deformations in composites by flow rules

    , Article Indian Journal of Science and Technology ; Vol. 7, issue. 2 , 2014 , pp. 180-184 ; ISSN: 09746846 Monfared, V ; Fazaeli, D ; Daneshmand, S ; Shafaghatian, N ; Sharif University of Technology
    In this paper, a novel model is proposed to predict stress behavior in the fibrous polymer composites under an applied tensile axial loading. Tangential stress is obtained by simulating between polymeric matrix flow (polyester) and fluid flow. In the other words, creep behavior of the petrochemical material or polymeric resin (matrix) is modeled using fluid flow theory. Furthermore, behavior of the shear stress is predicted by suitable mathematical functions. Finally, important relation is extracted by combining the solid and fluid mechanics formulations  

    Numerical study on the creep behavior of the metal matrix short fiber composites with application in optoelectronic and photonic devices

    , Article Optoelectronics and Advanced Materials, Rapid Communications ; Volume 9, Issue 9-10 , 2015 , Pages 1088-1092 ; 18426573 (ISSN) Monfared, V ; Daneshmand, S ; Fazaeli, D ; Sharif University of Technology
    FEM study is carried out for predicting the behavior of the short fiber composites in the steady state creep with application in optoelectronic and photonic devices. The study on the creep behavior is necessary in order for failure, fracture, fatigue, and creep resistance of the short fiber composites. In this article, the creep behavior of the short fiber composite is predicted under tensile axial loading by the numerical method. One of the significant applications of the work is in the short fiber composite designing and optimizing. Also, the available experimental results [10] are used for the FEM simulation  

    Study of microstructure and mechanical properties of high performance Ni-base superalloy GTD-111

    , Article Materials Science and Engineering A ; Volume 325, Issue 1-2 , 2002 , Pages 484-489 ; 09215093 (ISSN) Abdolkarim Sajjadi, S ; Nategh, S ; Guthrie, R. I. L ; Sharif University of Technology
    The Ni-base superalloy GTD-111 is widely used in manufacturing of the first stage blades of high power land-based gas turbines. In spite of its important role in increasing the performance of gas turbines, due to high temperature capability, there are little data on the microstructure, deformation mechanisms and mechanical properties of the alloy. The aim of present paper is to determine in details these properties. Microstructural characteristics of the alloy were assessed by means of optical, scanning and transmission electron microscopy. The tensile behaviour of GTD-111 has been studied in the temperature range 25-900 °C. The results showed abnormal variations in tensile properties with... 

    Study of Morphology and Effectiveness Mechanism of Mg2Si Phase on Mechanical Properties of Magnesium Alloy AZ91

    , M.Sc. Thesis Sharif University of Technology Piryaee, Mohammad Mahdi (Author) ; Varahram, Nasser (Supervisor) ; Aashouri, Hossein (Supervisor)
    AZ91 alloy (Mg-9Al-1Zn-0.2Mn) is the most important Magnesium casting alloy and because of its high strength to weight ratio, is increasingly demanded in automobile and aerospace industry as the best alloy of the present century. Poor creep resistance of AZ91 alloy is attributed to poor elevated temperature properties of Mg17Al12, which has melting point of 437°C. The softening of the Mg17Al12 phase at elevated temperature is the main cause of grain boundary sliding. in this investigation, The effects of addition of Si element on the microstructure and mechanical properties of AZ91 alloy have been studied as a solution to produce high temperature resistant magnesium alloys. The results show... 

    Nanoindentation creep behavior of nanocomposite Sn-Ag-Cu solders

    , Article Journal of Electronic Materials ; Volume 41, Issue 8 , 2012 , Pages 2057-2064 ; 03615235 (ISSN) Roshanghias, A ; Kokabi, A. H ; Miyashita, Y ; Mutoh, Y ; Ihara, I ; Guan Fatt, R. G ; Madaah Hosseini, H. R ; Sharif University of Technology
    High-density, ultrasmall-pitch electronic applications require miniaturized solder bumps with improved thermomechanical performance. In addition, novel techniques which are able to precisely characterize these solder bumps are needed. One approach to meeting both of these requirements is to make use of recently developed nanocomposite solders with enhanced creep resistance, and to characterize these solders using a nanoindentation technique. In the present study, the creep behavior of ceria-reinforced nanocomposite solder foils fabricated by the accumulative roll-bonding process was characterized using a depth-sensing nanoindentation technique. It was found that the creep resistance of the... 

    A new analytical shear-lag based model for prediction of the steady state creep deformations of some short fiber composites

    , Article Materials and Design ; Volume 30, Issue 4 , 2009 , Pages 1075-1084 ; 02641275 (ISSN) Mondali, M ; Abedian, A ; Ghavami, A ; Sharif University of Technology
    A new analytical model based on the shear-lag theory is developed for stress analysis and prediction of the steady state creep deformation of short fiber composites subjected to an applied axial load. A perfect fiber/matrix interface is assumed and the steady state creep behavior of the matrix is described by an exponential law. The results obtained from the proposed analytical solution satisfy the equilibrium and constitutive creep equations. These analytical results are then validated by the FEM modeling. Interestingly, good agreements are found between the analytical and numerical predictions for all the stress and displacement rate components. © 2008 Elsevier Ltd. All rights reserved  

    An axisymmetric poroelastic model for description of the short-term and long-term creep behavior of L4-L5 intervertebral disc

    , Article 2011 1st Middle East Conference on Biomedical Engineering, MECBME 2011, Sharjah, 21 February 2011 through 24 February 2011 ; 2011 , Pages 308-311 ; 9781424470006 (ISBN) Nikkhoo, M ; Haghpanahi, M ; Parnianpour, M ; Wang, J. L ; Sharif University of Technology
    Understanding the relationship between different kinds of mechanical loading and the failure of the intervertebral disc is difficult to study in vivo and in vitro. Through finite element studies some of these issues may be overcome enabling more detailed assessment of the biomechanical behavior of the intervertebral disc. The objective of this paper is to develop a nonlinear axisymmetric poroelastic finite element model of intervertebral disc and show its capability for studying the time-dependent response of disc. After comparison of the response of different models in quasi-static analysis, the poroelastic model of intervertebral disc is presented and the results of a short-term and... 

    Analytical solution for creeping motion of a viscoelastic drop falling through a Newtonian fluid

    , Article Korea Australia Rheology Journal ; Vol. 26, issue. 1 , 2014 , pp. 91-104 ; ISSN: 1226119X Vamerzani, B. Z ; Norouzi, M ; Firoozabadi, B ; Sharif University of Technology
    In this paper, an analytical solution for steady creeping motion of viscoelastic drop falling through a viscous Newtonian fluid is presented. The Oldroyd-B model is used as the constitutive equation. The analytical solutions for both interior and exterior flows are obtained using the perturbation method. Deborah number and capillary numbers are considered as the perturbation parameters. The effect of viscoelastic properties on drop shape and motion are studied in detail. The previous empirical studies indicated that unlike the Newtonian creeping drop in which the drop shape is exactly spherical, a dimpled shape appears in viscoelastic drops. It is shown that the results of the present... 

    An analytical model for stress analysis of short fiber composites in power law creep matrix

    , Article International Journal of Non-Linear Mechanics ; Volume 57 , 2013 , Pages 39-49 ; 00207462 (ISSN) Mondali, M ; Abedian, A ; Sharif University of Technology
    The creep deformation behavior of short fiber composites has been studied by an approximate analytical model. A perfect fiber/matrix interfacial bond is assumed and a power law function is considered for describing the steady state creep behavior of the matrix material. The results obtained from the proposed analytical solution satisfy the equilibrium and constitutive creep equations. Also, a parametric study was undertaken to define the effects of geometric parameters on the steady state creep strain rate of short fiber composites. The present model is then validated using the results of finite element method. The predicted strain rate and stress components by the proposed analytical... 

    Effect of reduced graphene oxide reinforcement on creep behavior of adhesively bonded joints

    , Article Mechanika ; Volume 23, Issue 5 , 2017 , Pages 646-652 ; 13921207 (ISSN) Marami, G ; Nazari, S. A ; Faghidian, S. A ; Vakili Tahami, F ; Sharif University of Technology
    Kauno Technologijos Universitetas  2017
    The creep behaviour of adhesively bonded joints is one of the major concerns in modern industry due to their application at relatively high temperature. In this re-search, the effect of added RGO on the creep behaviour of the Araldite 2011 adhesive is investigated. Uni-axial creep tests have been carried out on neat Araldite 2011 and RGO added adhesive at different stress and temperature levels. It has been shown that adhesive with RGO particles demonstrate higher creep resistance. Also, general time hardening models are developed for both materials and their constitutive coefficients have been determined using creep test data. Based on these models, the creep behavior of single lap joints... 

    Reliability assessment of cracked pipes subjected to creep-fatigue loading

    , Article Theoretical and Applied Fracture Mechanics ; Volume 104 , 2019 ; 01678442 (ISSN) Vojdani, A ; Farrahi, G. H ; Sharif University of Technology
    Elsevier B.V  2019
    The reliability analysis of defective pipes, which operate under creep-fatigue loading conditions has been studied. An austenitic stainless steel pipe containing an axially external semi-elliptical surface crack, subjected to variable internal pressure at elevated temperature has been considered as the benchmark problem. Different parameters in material behavior, geometry parameters, and operational condition have been assumed as random variables in the probabilistic assessments. The reliability of the cracked pipes have been evaluated at various operation times, using different reliability methods. Sensitivity analyses have been conducted to investigate the importance measure of the random... 

    Deformation behavior and cavitation of AA2017 at elevated temperatures

    , Article Metals and Materials International ; 2020 Vaghefi, E ; Serajzadeh, S ; Sharif University of Technology
    Korean Institute of Metals and Materials  2020
    In this work, deformation behavior of AA2017-T4 at elevated temperatures was studied employing uni-axial tensile and creep experiments. Tensile tests were carried out at temperatures varying 150–500 °C under different strain rates then, a combination of neural network and dynamic material modeling was utilized to construct the processing maps. Furthermore, creep experiments were conducted to assess inelastic deformation behavior of the alloy at temperatures between 150 and 225 °C and stresses in the range of 150 to 230 MPa. Microstructural evaluations were carried out for determination of microstructural changes and formation of voids and cavities within the samples. The results showed that... 

    Finite element analysis of the fiber offsetting effects on the creep behaviour of MMC composites

    , Article 8th International Conference on Computational Structures Technology, CST 2006, Las Palmas de Gran Canaria, 12 September 2006 through 15 September 2006 ; Volume 83 , 2006 ; 17593433 (ISSN); 9781905088089 (ISBN) Mondali, M ; Abedian, A ; Pahlavanpour, M ; Sharif University of Technology
    Civil-Comp Press  2006
    It has been shown that FEM simulation of creep deformation of composites is somehow very challenging. The type of FEM model, mesh size, element type, internal defects (such as fibre/matrix debonding), and the type of mathematical creep law all affect the calculation of the creep strain rate. In the present study, the fibre offsetting which happens in the manufacturing phase of composites is added to the simulation. It is shown that this defect at some critical point can affect the calculation of creep deformation. Here, the quantification of this phenomenon is performed using 3-D FEM models. Since it has also been shown that the fibre/matrix debonding affects the creep strain rate, the... 

    Finite difference solution of steady state creep deformations in a short fiber composite in presence of fiber/matrix debonding

    , Article Materials and Design ; Volume 31, Issue 5 , 2010 , Pages 2616-2624 ; 02641275 (ISSN) Ghavami, A ; Abedian, A ; Mondali, M ; Sharif University of Technology
    A finite difference technique is developed to predict the second stage creep displacement rates and stress analysis of a short fiber metal matrix composite subjecting to a constant axial load through a micromechanical approach. The technique is capable to take into account the presence of interfacial debonding as one of the main factors affecting the creep performance of short fiber composites. The exponential law is adopted to describe the matrix creep behavior. Also, a model for prediction of interfacial debonding at fiber/matrix interface is developed using a stress based method. The obtained results could greatly help to better understand the flow pattern of matrix material and the load... 

    Microstructure evolution and its influence on deformation mechanisms during high temperature creep of a nickel base superalloy

    , Article Materials Science and Engineering A ; Volume 499, Issue 1-2 , 2009 , Pages 445-453 ; 09215093 (ISSN) Safari, J ; Nategh, S ; Sharif University of Technology
    The interaction of dislocation with strengthening particles, including primary and secondary γ′, during different stages of creep of Rene-80 was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). During creep of the alloy at 871 °C under stress of 290 MPa, the dislocation network was formed during the early stages of creep, and the dislocation glide and climb process were the predominant mechanism of deformation. The density of dislocation network became more populated during the later stages of the creep, and at the latest stage of the creep, primary particles shearing were observed alongside with the dislocation glide and climb. Shearing of γ′... 

    Effect of applied stress and bar characteristics on the short-term creep behavior of FRP bars

    , Article Construction and Building Materials ; May , Volume 171 , 2018 , Pages 960-968 ; 09500618 (ISSN) Pournamazian Najafabadi, E ; Bazli, M ; Ashrafi, H ; Vatani Oskouei, A ; Sharif University of Technology
    Elsevier Ltd  2018
    This paper presents the creep behavior of various FRP (GFRP, CFRP, and hybrid) bars in order to investigate the effects of different parameters, including the applied stress levels, bar diameter, and the type of fiber and resin in the creep behavior of FRP bars. The creep strains versus time curves were experimentally obtained for 83 days. Moreover, a statistical study, including analysis of variance (ANOVA) and linear Bayesian regression was conducted to investigate the contribution of the studied parameters. The results showed that in GFRP bars the ratio of ultimate creep strain to the initial elastic strain decreased when the applied stresses on the bars exceeded 30% of their ultimate... 

    Atomistic simulation of creep deformation mechanisms in nickel-based single crystal superalloys

    , Article Materials Science and Engineering A ; Volume 809 , 2021 ; 09215093 (ISSN) Khoei, A. R ; Tolooei Eshlaghi, G ; Shahoveisi, S ; Sharif University of Technology
    Elsevier Ltd  2021
    In this paper, the creep deformation mechanisms are investigated in nickel-based single crystal superalloys. Two-dimensional molecular dynamics (MD) simulations are conducted to model various temperatures, stress conditions, and phase interface crystal orientations. Ni-based single-crystal superalloys are of great importance in the aircraft industry due to their excellent high temperature creep resistance. This characteristic mainly originates from two features considered in their structure; firstly, their two-phase micro-structure comprising gamma γ and gamma prime γ′, and secondly the nature of this superalloy itself, which is a single-crystal. MD is a powerful tool to gain insight into...