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softening
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Interpretation of tensile softening in concrete, using fractal geometry
, Article Scientia Iranica ; Volume 15, Issue 1 , 2008 , Pages 8-15 ; 10263098 (ISSN) ; Mofid, M ; Sharif University of Technology
Sharif University of Technology
2008
Abstract
Concrete is a heterogeneous material with a wide variety of usage in structural design. Concrete under tension exhibits strain softening, i.e., a negative slope in the stress-deformation diagrams. Different softening curves have been proposed in the literature to interpret this phenomenon. In current research, a new softening curve for concrete has been proposed by using the newly introduced concept of fractal geometry. This new softening curve is denominated a 'Quasi-fractal' softening curve and consists of two parts, a linear portion at the beginning and an exponential portion in the rest of the curve. A comparison of a "Quasi-fractal" softening curve with a set of proposed experimental...
H-adaptive finite element analysis for localization phenomena with reference to metal powder forming
, Article Finite Elements in Analysis and Design ; Volume 38, Issue 6 , 2002 , Pages 503-519 ; 0168874X (ISSN) ; Lewis, R. W ; Sharif University of Technology
2002
Abstract
Standard finite element models, i.e. finite element methods that use standard constitutive models, suffer from excessive mesh dependence when strain-softening models are used in numerical analyses and cannot reproduce the size effect commonly observed in quasi-brittle failure. In this paper, an h-adaptive analysis for the mixed finite element solution of solid mechanics problems is presented with special reference to metal powder forming involving localization due to material instability. A remeshing strategy is employed to compute the distribution of required element size using the estimated error distribution. The numerical results are obtained for a Von-Mises yield criterion applied to a...
New method in characterizing tensile softenig procedure in concrete
, Article ISEC 2011 - 6th International Structural Engineering and Construction Conference: Modern Methods and Advances in Structural Engineering and Construction, 21 June 2011 through 26 June 2011 ; June , 2011 , Pages 1145-1150 ; 9789810879204 (ISBN) ; Mofid, M ; Yazdani S ; Cheung S. O ; Singh A ; Ghafoori N ; American Society of Civil Engineers (ASCE); Architectural Institute of Japan (AIJ); Chartered Institute of Building (CIOB); et al.; University of Nevada Las Vegas (UNLV), College of Engineering; Wayne State College of Engineering ; Sharif University of Technology
Research Publishing Services
2011
Abstract
Several investigators worked on various aspects of tensile behavior of concrete because of its wide usage in structural design. One of the observable phenomena during tensile failure of concrete is strain softening, i.e. a negative slope in the stress-deformation diagrams. There are many kinds of experiment-based softening curves for concrete. In current research, use of newly introduced concept of fractal geometry and a failure model yields to a new softening curve for concrete. This new curve is denominated "Quasi-fractal" softening curve, which is a theorybased softening model. Comparison of Quasi-fractal softening curve with a set of proposed experimental softening curves has been...
Geotechnical characterization and collapsibility of a natural dispersive loess
, Article Engineering Geology ; Volume 250 , 2019 , Pages 89-100 ; 00137952 (ISSN) ; Kiani, M ; Sadeghi, M ; Jafarzadeh, F ; Sharif University of Technology
Elsevier B.V
2019
Abstract
During preliminary investigation phase of the national Chabahar-Zahedan railway line, serious geotechnical problems including non-uniform settlements, tensile cracks, and local collapse were reported in parts of the path near the coastline. A follow-up field investigation revealed that the in-situ soil at construction site has a metastable structure being sensitive to saturation and loading. Therefore, a comprehensive series of physical, chemical, electro-chemical, and geotechnical tests were conducted to classify and characterize the soil properties and behavior in its natural state. The natural soil was classified as a clayey loess with moderately dispersive to dispersive characteristics....
ETMB model investigation of flow softening during severe plastic deformation
, Article Computational Materials Science ; Volume 46, Issue 4 , 2009 , Pages 902-905 ; 09270256 (ISSN) ; Kazeminezhad, M ; Sharif University of Technology
2009
Abstract
In this study, the flow softening of FCC materials through severe plastic deformation (SPD) is investigated using ETMB (Y. Estrin, L.S. Toth, A. Molinari, Y. Brechet) model. To do so, using the model, the equal channel angular pressing (ECAP) processes of two FCC materials, aluminum and copper, are investigated. The correlation between the recovery parameters of ETMB model (the dynamic recovery exponents and coefficients) and the intrinsic characteristics of the materials (the stacking fault energy (SFE) and melting point) is described and compared with the previous claims. © 2009 Elsevier B.V. All rights reserved
Thermo-mechanical behaviours of light alloys in comparison to high temperature isothermal behaviours
, Article Materials at High Temperatures ; Vol. 31, issue. 1 , 2014 , pp. 12-17 ; ISSN: 09603409 ; Farrahi, G. H ; Winter, G ; Eichlseder, W ; Sharif University of Technology
Abstract
In this article, out-of-phase thermo-mechanical fatigue (TMF) behaviours of light alloys were investigated in comparison to their high temperature low cycle fatigue (LCF) behaviours. For this objective, strain based fatigue tests were performed on the A356 aluminium alloy and on the AZ91 magnesium alloy. Besides, TMF tests were carried out, where both strain and temperature changed. The fatigue lifetime comparison demonstrated that the TMF lifetime was less than that one under LCF loadings at elevated temperatures for both light alloys. The reason was due to severe conditions in TMF tests in comparison to LCF tests. The temperature varied in TMF test but it was constant under LCF loadings....
An enriched-FEM model for simulation of localization phenomenon in Cosserat continuum theory
, Article Computational Materials Science ; Volume 44, Issue 2 , December , 2008 , Pages 733-749 ; 09270256 (ISSN) ; Karimi, K ; Sharif University of Technology
2008
Abstract
The standard finite element models, i.e. the finite element methods that use the classical continuum models, suffer from the excessive mesh dependence when a strain-softening model is used. It cannot converge to a meaningful solution and the governing differential equation loses the ellipticity. This paper presents an enriched finite element algorithm for simulation of localization phenomenon using a higher order continuum model based on the Cosserat continuum theory. The governing equations are regularized by adding the rotational degrees-of-freedom to the conventional degrees-of-freedom and including the internal length parameter in the model. The extended finite element method (X-FEM) is...
Localization analysis in softening RC frame structures
, Article Earthquake Engineering and Structural Dynamics ; Volume 32, Issue 2 , 2003 , Pages 207-227 ; 00988847 (ISSN) ; Tariverdilo, S ; Sharif University of Technology
2003
Abstract
This paper discusses the sensitivity of softening reinforced concrete frame structures to the changes in input ground motion and investigates the possibility of localizations for this type of structure in static and dynamic analysis. A finite element model is used in which the sections resisting force are calculated using a proposed differential hysteretic model. This model is especially developed for modelling softening behaviour under cyclic loading. To obtain parameters of the differential model the moment-curvature of each section is evaluated using a microplane constitutive law for concrete and bi-linear elasto-plastic law for reinforcements. The capability of the procedure is verified...
Effect of surface energy on nano-resonator dynamic behavior
, Article International Journal of Mechanical Sciences ; Volume 119 , 2016 , Pages 51-58 ; 00207403 (ISSN) ; Nejat Pishkenari, H ; Meghdari, A ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
Presented herein is a comprehensive analysis on the size-dependent dynamic behaviors of electrostatically actuated nano-resonator including surface stresses effect. To this end, partial differential equation of nano-resonator based on Gurtin–Murdoch and Euler–Bernoulli theories is converted to ordinary differential equation utilizing assumed mode method. Effect of applied DC voltage on stability and bi-stability of nano-resonator is investigated and it revealed that surface elasticity and stress affect the bi-stability region of nano-resonator. By plotting frequency response of the resonator, hardening and softening behavior of nano-resonator are analyzed and it is shown that surface effect...
Design of Optimal Passive Energy Dissipation Systems Using Active Control Theory
, M.Sc. Thesis Sharif University of Technology ; Ahmadizadeh, Mehdi (Supervisor)
Abstract
In this paper, a methodology has been proposed for design of passive energy dissipation systems through active control theory. The passive control system is designed to achieve a structural response as close to that of active control system. It may be needed to reduce the stiffness of the original structure at some locations to reduce the acceleration response. Then, to compensate for the resulting increased interstory drifts, viscous fluid dampers are added to the structure at their optimum locations. The optimal distribution of dampers and the locations with reduced stiffness are obtained using the LQR active control algorithm. It is shown that the response of a properly-designed...
Investigating the Effect of Softening Agent on the Performance Characterization of Asphalt Concrete Mixture with High RAP Content
, M.Sc. Thesis Sharif University of Technology ; Tabatatabee, Nader (Supervisor)
Abstract
Recycling of asphalt pavements has received much attention in recent years for its environmental and economical benefits. Because of increase in costs of raw materials and energy carriers, reuse of a high portion of reclaimed asphalt pavements (RAP) eliminates an enormous amount of waste and reduces the cost of hot-mix asphalt (HMA) mixtures. There are some problems in high-RAP mixtures such as high content of fine aggregate and filler, low temperature cracking potential because of higher stiffness of RAP binder, and low mixture workability. In this research, RAP fractionation was used to sort out and eliminate fine aggregate and filler. An organic-based softening agent was used to improve...
Modeling of inelastic mixed hinge and its application in analysis of the frames with reduced beam section
, Article International Journal of Steel Structures ; Volume 11, Issue 1 , 2011 , Pages 51-63 ; 15982351 (ISSN) ; Asl, M. H ; Sharif University of Technology
2011
Abstract
This paper represents new development of a previously introduced mixed shear-flexural (VM) link element, and its application in inelastic analysis of frames with reduced beam sections. The multi-surfaces concept with dissimilar yield surfaces is used in definition of link element. The yield surfaces are defined in deformation space and the element has the capability of modeling interactive axial-flexural-shear yielding. It is able to consider post yield softening behavior as well as flexibility and strength degradations. It is shown that the analysis results of the new mixed axial-shear-flexural (PVM) link have good agreement with the existing experimental and finite element results. Using...
A plasticity-based constitutive model for the behavior of soil-structure interfaces under cyclic loading
, Article Transportation Geotechnics ; Volume 14 , 2018 , Pages 41-51 ; 22143912 (ISSN) ; Toufigh, V ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
In this study, a new plasticity-based constitutive model is proposed for the behavior of soil-structure interfaces under monotonic and cyclic loadings. The features of the interface including the strain-softening behavior, phase transformation, steady-state, and dilatancy behavior were described by the proposed model with satisfactory accuracy. The proposed model does not require additional concepts such as damage or disturbance, and the model parameters can be obtained easily using straight-forward analyses of the results obtained from constant normal stress tests. Moreover, the results of the proposed model showed its capability in predicting the experimental results obtained from various...
Tensile fracture behavior of heterogeneous materials based on fractal geometry
, Article Theoretical and Applied Fracture Mechanics ; Volume 46, Issue 1 , 2006 , Pages 46-56 ; 01678442 (ISSN) ; Mofid, M ; Sharif University of Technology
2006
Abstract
Many of heterogeneous structural materials, like concrete, have different behavior under tensile stresses in comparison to their behavior under compressive stresses. The aim of this paper is to interpret behavior of such materials subjected to tensile stresses, by using newly introduced concept of fractal geometry. In the first part of this paper, tensile behavior of granular composites has been studied by using fractal geometry. It is shown that the fractality of the cross section in this kind of composites can be used to interpret the size effect on tensile strength. In fact, this work is a modification with innovations on the previous studies on fractal based size effect. This hypothesis...
Study on the dynamic and static softening phenomena in Al-6Mg alloy during two-stage deformation through interrupted hot compression test
, Article Measurement: Journal of the International Measurement Confederation ; Volume 77 , 2016 , Pages 50-53 ; 02632241 (ISSN) ; Pakbaz, M ; Firooz, S ; Jandaghi, M. R ; Khalaj, G ; Sharif University of Technology
Elsevier, B. V
2016
Abstract
The dynamic and static softening phenomena in Al-6Mg alloy were studied through interrupted two-stage hot compression test performed isothermally at 480°C and strain rate range of 0.001-0.1 s-1. The interruptions of 29 and 90 s were considered when the true strain reached 0.5. It was concluded that the effect of static softening on the flow stress was not highlighted by extending the interruption at a constant strain rate. Also, it was exhibited that softening rate highly enhanced with the strain rate decrement at a constant time. Moreover, the static and dynamic recrystallization was revealed as the dominant softening mechanisms at low and high strain rates, respectively
Finite Element Modelling of Damage in FRC using Microplane Method
, M.Sc. Thesis Sharif University of Technology ; Kazemi, Mohammad Taghi (Supervisor)
Abstract
In concrete which is a quasi-brittle material failure initially occurs between aggregate and mortars. Fibers of all orientations, randomly embedded in FRC, serve to restrict and delay the coalescence of micro-cracks, micro-voids and micro-slips into wide continuous cracks. While the fibers increase the uniaxial tensile and compressive strength only moderately, they are very effective for enhancing the ductility and energy absorption capability. This elevates structure resistance to impact, ground-shock and blast. One of the most successful efforts toward reaching a macroscopic model which can take micromechanical properties into account is the Microplane model. In this microscopic...
Damage-plasticity model for mixed hinges in steel frames
, Article Journal of Constructional Steel Research ; Volume 67, Issue 8 , 2011 , Pages 1272-1281 ; 0143974X (ISSN) ; Asl, M. H ; Sharif University of Technology
2011
Abstract
A damage-plasticity based mixed axial-shear-flexural (PVM) link element for the inelastic analysis of frames is introduced in this paper. The multi-surfaces yield concept is utilized in the definition of the element. The yield surfaces are defined in deformation space and interaction of axial-shear-flexural deformations is considered by defining non-rectangular yield surfaces. The element is capable of considering damage and post-peak softening behavior. The analytical results of introduced element are verified by existing experimental results of steel beam to column connection and it is indicated that the analytical results have reasonable agreement with the test results. Nonlinear dynamic...
Laser-assisted friction stir processing of IN738LC nickel-based superalloy:stir processing of IN738LC nickel-based superalloy: Stir zone characteristics.tir zone characteristics
, Article Science and Technology of Welding and Joining ; Volume 21, Issue 5 , 2016 , Pages 374-380 ; 13621718 (ISSN) ; Pouranvari, M ; Ghaini, F. M ; Fujii, H ; Chung, Y. D ; Sharif University of Technology
Taylor and Francis Ltd
Abstract
Friction stir processing (FSP) of high softening-temperature materials such as nickel-based superalloys is considered to be difficult. Laser heating of a localised area ahead of the FSP tool was used to provide sufficient plasticity during the FSP of IN738LC nickel-based superalloy. The stir zone (SZ) microstructure of the friction stir processed and laser-assisted friction stir processed were characterised. Laser-assisted friction stir processing (LAFSP) produced a defect-free pass, but FSP resulted in generation of a discontinuity in the SZ. Both lower volume fraction of partially dissolved γ′ precipitates and coarser grain structure of SZ in LAFSP led to more ductility of the SZ material...
A nonlocal computational homogenization of softening quasi-brittle materials
, Article International Journal for Numerical Methods in Engineering ; Volume 119, Issue 8 , 2019 , Pages 712-736 ; 00295981 (ISSN) ; Saadat, M. A ; Sharif University of Technology
John Wiley and Sons Ltd
2019
Abstract
In this paper, a computational counterpart of the experimental investigation is presented based on a nonlocal computational homogenization technique for extracting damage model parameters in quasi-brittle materials with softening behavior. The technique is illustrated by introducing the macroscopic nonlocal strain to eliminate the mesh sensitivity in the macroscale level as well as the size dependence of the representative volume element (RVE) in the first-order continuous homogenization. The macroscopic nonlocal strains are computed at each direction, and both the local and nonlocal strains are transferred to the microscale level. Two RVEs with similar geometries and material properties are...
Modelling dynamic softening processes during hot working
, Article Materials Science and Engineering A ; Volume 404, Issue 1-2 , 2005 , Pages 130-137 ; 09215093 (ISSN) ; Sharif University of Technology
2005
Abstract
This paper models the kinetics of dynamic recovery and recrystallization under hot working conditions. For doing so, the first-order kinetics equation is coupled with a thermo-viscoplastic finite element analysis to determine the kinetics of dynamic softening processes at different points of deforming metal. The proposed model can consider the effects of macro parameters, such as temperature and strain rate variations as well as the influences of microparameters as initial grain size on the rate of dynamic softening processes. © 2005 Elsevier B.V. All rights reserved