Search for: strain-rate
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    Modeling of the mutual effect of dynamic precipitation and dislocation density in age hardenable aluminum alloys

    , Article Journal of Alloys and Compounds ; Volume 683 , 2016 , Pages 527-532 ; 09258388 (ISSN) Khani Moghanaki, S ; Kazeminezhad, M ; Sharif University of Technology
    Elsevier Ltd  2016
    A model has been proposed to capture the complex strain rate effect on dynamic precipitation of GP zones in an age-hardenable aluminum alloy. The contributions of vacancies and dislocations to dynamically formed GP zones have been specified in the model. It has been demonstrated that the proposed model is capable for predicting the contribution of each dynamic precipitation mechanisms, accurately, which are acting during deformation. Furthermore, the vacancy and dislocation evolutions during deformation have been considered in this modeling. The effect of strain rate by considering different mechanisms of dynamic precipitation of GP zones has been studied and confirmed by experimental data... 

    Strain-rate dependent influence of adherend stiffness on fracture load prediction of BGA solder joints

    , Article Engineering Fracture Mechanics ; Volume 186 , 2017 , Pages 119-133 ; 00137944 (ISSN) Nourani, A ; Akbari, S ; Farrahi, G ; Spelt, J. K ; Sharif University of Technology
    Fracture experiments with ball grid array (BGA) specimens having different adherend rigidities were performed under bending loads at intermediate strain rates (0.2–1 s−1) and a high strain rate of 30 s−1. A cohesive zone model (CZM) was established and the predictive capability of the model was assessed for the specimens with different rigidities. The predicted fracture loads were within 12% of the measured forces when the CZM parameters were obtained using specimens with a similar degree of constraint. This suggests that in many practical cases, the effect of adherend stiffness can be neglected in predicting the strength of BGA solder joints. © 2017 Elsevier Ltd  

    A novel phenomenological constitutive model for Ti-6Al-4V at high temperature conditions and quasi-static strain rates

    , Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 235, Issue 13 , 2021 , Pages 1831-1842 ; 09544100 (ISSN) Ashrafian, M. M ; Hosseini Kordkheili, A ; Sharif University of Technology
    SAGE Publications Ltd  2021
    Phenomenological constitutive modeling of Ti-6Al-4V at temperatures between 923 and 1023 K under 0.0005–0.05 s−1 quasi-static rates is studied based on a phenomenological approach. For this purpose, the Johnson–Cook constitutive model is revisited. At low temperature conditions under moderate to high strain rates, the material’s stress–strain curves are the most similar to power-law function. Contrary to this, at high temperature conditions under low to moderate strain rates, the saturation-type function well describes the stress–strain curves. On the other hand, it is illustrated that the Johnson–Cook constitutive model is feeble to predict the material’s behavior correctly. Accordingly, in... 

    Effect of strain rate on tensile properties of sheep disc anulus fibrosus

    , Article Technology and Health Care ; Volume 12, Issue 4 , 2004 , Pages 333-342 ; 09287329 (ISSN) Kasra, M ; Parnianpour, M ; Shirazi Adl, A ; Wang, J. L ; Grynpas, M. D ; Sharif University of Technology
    IOS Press  2004
    We investigated the effect of loading rate on tensile properties of sheep bone-anulus-bone specimens in axial direction. Disc anulus Samples with adjacent bone attachments were prepared from lateral, posterior and anterior regions of sheep lumbar spinal segments. The specimens were then tested at different strain rates under non-destructive cyclic tensile loading followed by destructive tensile loading. Each specimen was prepared by embedding the bony parts in the polymethylmetacrylate (PMMA) exposing the anulus portion to support tension. The results of non-destructive cyclic tests indicated a decrease in the hysteresis energy loss as strain rate increased. In the destructive tests, no... 

    Modelling the flow behaviour of steel under non-isothermal conditions

    , Article Materials Science and Technology ; Volume 19, Issue 8 , 2003 , Pages 1065-1069 ; 02670836 (ISSN) Serajzadeh, S ; Zebarjad, S. M ; Sharif University of Technology
    A mathematical model is proposed for evaluating flow behaviour under hot deformation conditions. The effects of dynamic recovery and recrystallisation as well as temperature and strain rate variations are considered in the model by means of Bergstrom's approach and the additivity rule for strain. To verify the model, hot compression tests for three grades of steel together with upsetting experiments are carried out. Comparison between experimental and theoretical results confirms the reliability of the model. © 2003 IoM Communications Ltd. Published by Maney for the Institute of Materials, Minerals and Mining  

    Temperature dependence of serrated flow, strain-rate sensitivity and activation volume in a Ti-based bulk metallic glass

    , Article Journal of Non-Crystalline Solids ; Volume 553 , 2021 ; 00223093 (ISSN) Asadi Khanouki, M. T ; Tavakoli, R ; Aashuri, H ; Sharif University of Technology
    Elsevier B. V  2021
    In this study, the influence of temperature on serrated flow behavior, strain rate sensitivity (SRS) and effective activation volume in a Ti-based bulk metallic glass (BMG) bent at different strain rates has been investigated. Results reveal that the fundamental origin of shear deformation is related to the time-dependent structural relaxations, which occur during deformation at special temperatures and strain rates. Furthermore, the localized structural relaxation processes at intermediate temperatures cause an inelastic shuffling within cages and mitigate the activation of STZs. The main reason of negative SRS at intermediate temperatures is due to the insufficient time for structural... 

    Obtaining strain-rate dependent traction-separation law parameters of epoxy adhesive joints and predicting fracture for dissimilar bonding adherends

    , Article International Journal of Adhesion and Adhesives ; Volume 118 , 2022 ; 01437496 (ISSN) Darvishi, I ; Nourani, A ; Sharif University of Technology
    Elsevier Ltd  2022
    This study investigated the mode I fracture behavior of double cantilever beam (DCB) epoxy adhesive joints with similar adherends on the both sides (i.e., aluminum-aluminum or copper-copper) at different strain rates; i.e., quasi-static (∼10−3 s−1), low (∼7 s−1) and intermediate (∼14 s−1) rates. The fracture energy of the DCB joint in Al-adhesive-Al specimens decreased (i.e., by ∼62%, p = 0.0013) with an increase in the applied strain rate from quasi-static to low values, while it remained almost unchanged with further increase of stain rate to intermediate range (p > 0.05). For Cu-adhesive-Cu cases, however, the fracture energy was found to be almost insensitive to the applied strain rate... 

    Flow behavior and mechanical properties of a high silicon steel associated with dynamic strain aging

    , Article Journal of Materials Engineering and Performance ; Volume 21, Issue 9 , September , 2012 , Pages 1919-1923 ; 10599495 (ISSN) Akhgar, J. M ; Serajzadeh, S ; Sharif University of Technology
    Springer  2012
    Flow behavior of two grades of steel including a high silicon (HS) steel and a plain low carbon steel as the reference were considered in this work. Tensile testing at temperatures varying between 25 and 550 °C and different strain rates in the range of 4×10-5 to 0.1 s-1 were conducted and the mechanical properties, such as elongation at fracture point and strain rate sensitivity were then determined. It is observed that for both steels, dynamic strain aging occurs in the employed deformation conditions, however, the region of serrated flow and the type of the serration were somehow different. For the case of the HS steel, the serrated flow region is shifted to the higher temperatures and... 

    Deformation mode dependency of stable orientations: From plane strain compression to equibiaxial tension

    , Article Philosophical Magazine ; Volume 95, Issue 7 , Feb , 2015 , Pages 794-803 ; 14786435 (ISSN) Hajian, M ; Khajeh Salehani, M ; Assempour, A ; Mehdigholi, H ; Sharif University of Technology
    Taylor and Francis Ltd  2015
    Prediction of stable orientations is a key subject in the crystal plasticity literature. This work deals with the effects of deformation mode on the resulted stable orientations and texture evolution of FCC materials. The simulations are based on the numerical procedure developed by the authors in previous works in which, a rate-sensitive crystal plasticity model with Secant hardening law was employed. The resulting non-linear system of equations is solved by the modified Newton-Raphson method. In order to obtain the stable orientations for a deformation mode, initial orientations evenly spaced in the Euler space are selected and their evolution into the stable orientations is tracked. The... 

    Flow stress evolution in further straining of severely deformed Al

    , Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 50, Issue 5 , 2019 , Pages 2371-2380 ; 10735623 (ISSN) Charkhesht, V ; Kazeminezhad, M ; Sharif University of Technology
    Springer Boston  2019
    To investigate the flow stress evolution in further straining of severely deformed Al sheets, a comprehensive model which considers both mechanical and metallurgical alterations is needed. In this study, constrained groove pressing (CGP) as a severe plastic deformation method, and a flat rolling process for further straining are utilized. Using basic mechanical models, strain and strain rate were calculated for this process. Dislocation density and flow stress evolutions were predicted by utilizing initial mechanical data, considering the ETMB (Y. Estrin, L. S. Toth, A. Molinari, and Y. Brechet) dislocation density model. Based on these model predictions, the combination of the CGP process... 

    Modelling flow stress behaviour of aluminium alloys during hot rolling

    , Article Materials Science and Technology ; Volume 22, Issue 6 , 2006 , Pages 713-718 ; 02670836 (ISSN) Serajzadeh, S ; Sharif University of Technology
    A mathematical model is proposed to predict the flow stress behaviour of aluminium alloys under hot rolling conditions. To do so, a dislocation model for evaluating flow stress during deformation is coupled with a finite element analysis to access metal behaviour under non-isothermal and variable strain rate conditions. Then, with the aid of the proposed model, a hot strip rolling process was simulated. In order to verify modelling results, flow stress behaviour of an aluminium alloy is studied employing hot compression tests in various temperatures and strain rates and the model was examined on this material. Non-isothermal hot rolling experiments were carried out and good agreement was... 

    Influence of aluminide diffusion coating on low cycle fatigue properties of René 80

    , Article Materials Science and Engineering A ; Volume 486, Issue 1-2 , 2008 , Pages 686-695 ; 09215093 (ISSN) Rahmani, Kh ; Nategh, S ; Sharif University of Technology
    Low cycle fatigue is one of the most important phenomena affecting the lifetime of jet engine blades. In this paper, the effect of aluminide diffusion coating (CODEP-B) on low cycle fatigue properties of René 80 has been studied at temperature of 871 °C, R = 0 and strain rate of about 2 × 10-3 s-1. Experimental results show that the applied cyclic strain is lower than 0.8%, the presence of aforesaid coating increases the fatigue lifetime. In coated specimens, while the total cyclic strain is lower than 0.8%, the nucleation of the cracks occurs merely in substrate, but in cyclic strain more than 1%, as a result of simultaneous nucleation of cracks in the coating surface, diffusion layer and... 

    A study on strain ageing during and after warm rolling of a carbon steel

    , Article Materials Letters ; Volume 62, Issue 6-7 , 2008 , Pages 946-948 ; 0167577X (ISSN) Serajzadeh, S ; Akhgar, J. M ; Sharif University of Technology
    In this study, strain ageing during and after warm rolling of a carbon steel has been investigated. At the first step, the occurrence of serrated flow was studied by means of tensile tests at different temperatures and strain rates. In the next stage, warm rolling experiments were performed under different rolling conditions and then the samples were aged at the room temperature for a period of 3 months. For both aged and non-aged samples, tensile tests were employed to evaluate their mechanical properties. The results show that static strain ageing is possible to happen in the utilized ageing period and increases the yield stress of the aged steel. However, the samples that experience both... 

    Effect of building direction on high strain-rate compressive behavior of heat-treated LPBF-maraging steels using Split Hopkinson pressure bar apparatus

    , Article Materials Science and Engineering A ; Volume 835 , 2022 ; 09215093 (ISSN) Dehgahi, S ; Pirgazi, H ; Sanjari, M ; Seraj, P ; Odeshi, A ; Kestens, L. A. I ; Mohammadi, M ; Sharif University of Technology
    Elsevier Ltd  2022
    Rod-shaped samples of maraging steel were additively fabricated in vertical and horizontal directions using laser powder bed fusion technique. The samples were first aged at 490 °C for 6 h and then subjected to dynamic compressive tests using Split Hopkinson Pressure Bar apparatus. The dynamic compression tests were conducted on vertical samples at strain rates of 190, 460, 810, 1100, 1300 s−1. However, the high strain rate tests were performed at strain rates of 120, 615, 745, 890, 2200 s−1 on horizontal samples. After applying the compressive impact loads on the samples, it was found that although horizontally built samples exhibit higher dynamic strength, vertically built samples show... 

    Analysis of strain rate sensitivity of ultrafine-grained AA1050 by stress relaxation test

    , Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 45, Issue 12 , November 2014 , Pages 5442-5450 Mohebbi, M. S ; Akbarzadeh, A ; Kim, B. H ; Kim, S. K ; Sharif University of Technology
    Commercially pure aluminum sheets, AA 1050, are processed by accumulative roll bonding (ARB) up to eight cycles to achieve ultrafine-grained (UFG) aluminum as primary material for mechanical testing. Optical microscopy and electron backscattering diffraction analysis are used for microstructural analysis of the processed sheets. Strain rate sensitivity (m-value) of the specimens is measured over a wide range of strain rates by stress relaxation test under plane strain compression. It is shown that the flow stress activation volume is reduced by decrease of the grain size. This reduction which follows a linear relation for UFG specimens, is thought to enhance the required effective (or... 

    An energy-based approach for analysis of dynamic plastic deformation of metals

    , Article International Journal of Mechanical Sciences ; Volume 66 , January , 2013 , Pages 94-100 ; 00207403 (ISSN) Khayer Dastjerdi, A ; Naghdabadi, R ; Arghavani, J ; Sharif University of Technology
    An energy-based ordinary differential equation is derived for a plastic wave propagating through a Taylor impact test specimen. Using the definition of true strain, an analytical equation is presented to calculate the strain rate across the plastic wave front. Having considered a Johnson-Cook plasticity model for the projectile material, the derived energy equation accompanied by a governing kinematics relation and the strain rate equation is numerically integrated to obtain the final deformed profile of the specimen. The results of the energy based model are then compared with those of the commonly used momentum-based approach as well as the existing experimental data in literature for... 

    Deformation behavior of AA2017-SiCp in warm and hot deformation regions

    , Article Materials and Design ; Volume 67 , February , 2015 , Pages 318-323 ; 02613069 (ISSN) Serajzadeh, S ; Ranjbar Motlagh, S ; Mirbagheri, S. M. H ; Akhgar, J. M ; Sharif University of Technology
    Elsevier Ltd  2015
    In this work, the flow stress behavior of a metal matrix composite AA2017-10% SiCp was studied by means of the uni-axial compression test. The composite was first produced by stir casting technique and then, hot extrusion with the ratio of 18:1 was carried out to achieve a microstructure with a homogeneous distribution of SiC particles. In the next stage, the isothermal compression tests were conducted on the cylindrical specimens up to the true strain of 0.6. The experiments were performed at temperatures between room temperature to 400°C and strain rates of 0.003, 0.03 and 0.3s-1. Negative strain rate sensitivity was observed in the temperatures less than 250°C indicating the occurrence of... 

    Dynamic strain aging of a commercial Al-Mg-Si-Cu alloy during equal channel angular extrusion process

    , Article Journal of Alloys and Compounds ; Volume 502, Issue 1 , July , 2010 , Pages 59-62 ; 09258388 (ISSN) Tabatabaei, N ; Karimi Taheri, A ; Vaseghi, M ; Sharif University of Technology
    In this research, the occurrence of dynamic strain aging (DSA) phenomenon during equal channel angular extrusion (ECAE) of a commercial air cooled Al-Mg-Si-Cu alloy is investigated. In order to detect the negative strain rate sensitivity behaviour associated with DSA, samples were ECAE-ed at various temperatures and strain rates. Subsequently, the extruded billets were subjected to mechanical and physical tests and it was found that at a certain ECAE temperature range there is a critical strain rate above which DSA occurs. The implication of the results to strengthening of dilute solid solutions is discussed  

    Investigation into dynamic strain aging behaviour in high carbon steel

    , Article Ironmaking and Steelmaking ; Volume 37, Issue 2 , Jul , 2010 , Pages 155-160 ; 03019233 (ISSN) Kohandehghan, A. R ; Sadeghi, A. R ; Akhgar, J. M ; Serajzadeh, S ; Sharif University of Technology
    In this work, the phenomenon of dynamic strain aging in a high carbon steel is studied and different initial microstructures including fine and coarse pearlite structures are considered. Tensile tests at different temperatures and strain rates are performed to evaluate the occurrence of dynamic strain aging and mechanical properties as well as to calculate apparent activation energies for onset and termination of dynamic strain aging. The results show that dynamic strain aging occurs for both microstructures while the initial microstructures alters the activation energies for appearance and termination of this phenomenon. The microstructural studies illustrate that a combination of cementite... 

    Mechanical characterization of brain tissue in compression

    , Article ASME 2016 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, 21 August 2016 through 24 August 2016 ; Volume 3 , 2016 ; 9780791850138 (ISBN) Shafiee, A ; Ahmadian, M. T ; Hoviat Talab, M ; Computers and Information in Engineering Division; Design Engineering Division ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME) 
    The biomechanical behavior of brain tissue is needed for predicting the traumatic brain injury (TBI). Each year over 1.5 million people sustain a TBI in the United States. The appropriate coefficients for modeling the injury prediction can be evaluated using experimental data. In the present paper, using an experimental setup on bovine brain tissue, unconfined compression tests at quasi-static strain rates of ϵ 0.0004s-1, 0.008s-1 and 0.4s-1 combined with a stress relaxation test under unconfined uniaxial compression with ϵ 0.67s-1 ramp rate are performed. The fitted viscohyperelastic parameters were utilized by using obtained stressstrain curves. The finite element analysis (FEA) is...