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    Thermomechanical behavior of work rolls during warm strip rolling

    , Article Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science ; 2012 , Pages 1-11 ; 10735615 (ISSN) Khalili, L ; Serajzadeh, S ; Koohbor, B ; Sharif University of Technology
    Abstract
    A mathematical model was developed to assess thermomechanical behavior of work rolls during warm rolling processes. A combined finite element analysis-slab method was first developed to determine thermal and mechanical responses of the strip being rolled under steady-state conditions, and then, the calculated roll pressure and temperature field were utilized as the governing boundary conditions for the thermomechanical problem of the work roll. Finally, the thermomechanical stresses within the work rolls were predicted by a thermoelastic finite element approach. The results of the model indicate that, in warm strip rolling, thermal and mechanical stresses developed in the work rolls are... 

    Investigations of the failure in boilers economizer tubes used in power plants

    , Article Journal of Materials Engineering and Performance ; Volume 22, Issue 9 , 2013 , Pages 2691-2697 ; 10599495 (ISSN) Moakhar, R. S ; Mehdipour, M ; Ghorbani, M ; Mohebali, M ; Koohbor, B ; Sharif University of Technology
    2013
    Abstract
    In this study, failure of a high pressure economizer tube of a boiler used in gas-Mazut combined cycle power plants was studied. Failure analysis of the tube was accomplished by taking into account visual inspection, thickness measurement, and hardness testing as well as microstructural observations using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD). Optical microscopy images indicate that there is no phase transformation during service, and ferrite-pearlite remained. The results of XRD also revealed Iron sulfate (FeSO4) and Iron hydroxide sulfate (FeOH(SO4)) phases formed on the steel surface. A considerable amount of Sulfur was also... 

    The effect of dynamic strain aging on room temperature mechanical properties of high martensite dual phase (HMDP) steel

    , Article Materials Science and Engineering A ; Volume 550 , 2012 , Pages 325-332 ; 09215093 (ISSN) Shahriary, M. S ; Koohbor, B ; Ahadi, K ; Ekrami, A ; Khakian Qomi, M ; Izadyar, T ; Sharif University of Technology
    Elsevier  2012
    Abstract
    AISI 4340 steel bars were heated at 900 °C for one hour, annealed at 738 °C for different durations and oil-quenched in order to obtain dual phase steels with different ferrite volume fractions. A 3% prestrain at the temperature range of 150-450 °C was then imposed to the samples, and room temperature tensile tests were carried out, afterwards. Results indicate that the maximum values for both yield and ultimate tensile strength would exist for the samples pre-strained at the temperature range of 250-300 °C. Also, a sudden drop of the ductility was observed at the mentioned temperature range. The observed behavior might be attributed to the occurrence of dynamic strain aging taken place at... 

    A generalized semi-analytical solution for the dispersive henry problem: effect of stratification and anisotropy on seawater intrusion

    , Article Water (Switzerland) ; Volume 10, Issue 2 , 2018 ; 20734441 (ISSN) Fahs, M ; Koohbor, B ; Belfort, B ; Ataie Ashtiani, B ; Simmons, C. T ; Younes, A ; Ackerer, P ; Sharif University of Technology
    MDPI AG  2018
    Abstract
    The Henry problem (HP) continues to play a useful role in theoretical and practical studies related to seawater intrusion (SWI) into coastal aquifers. The popularity of this problem is attributed to its simplicity and precision to the existence of semi-analytical (SA) solutions. The first SA solution has been developed for a high uniform diffusion coefficient. Several further studies have contributed more realistic solutions with lower diffusion coefficients or velocity-dependent dispersion. All the existing SA solutions are limited to homogenous and isotropic domains. This work attempts to improve the realism of the SA solution of the dispersive HP by extending it to heterogeneous and...