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M. M. Najafizadeh,M. R. Isvandzibaei 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.8
In the present work, study of the vibration of thin cylindrical shells with ring supports made of a functionally gradient material (FGM) composed of stainless steel and nickel is presented. Material properties are graded in the thickness direction of the shell according to volume fraction power law distribution. Effects of boundary conditions and ring support on the natural frequencies of the FGM cylindrical shell are studied. The cylindrical shells have ring supports which are arbitrarily placed along the shell and which imposed a zero lateral deflection. The study is carried out using different shear deformation shell theories. The analysis is carried out using Hamilton’s principle. The governing equations of motion of a FGM cylindrical shells are derived based on various shear deformation theories. Results are presented on the frequency characteristics, influence of ring support position and the influence of boundary conditions. The present analysis is validated by comparing results with those available in the literature.
Behjati, P.,Kermanpur, A.,Najafizadeh, A.,Samaei Baghbadorani, H.,Jung, J.G.,Lee, Y.K. Elsevier Sequoia 2014 Materials science & engineering. properties, micro Vol.610 No.-
In this work, a specific thermomechanical treatment was used to enhance mechanical properties of a high-manganese austenitic steel. Simple uniaxial tension tests revealed that the treated steel exhibits an outstanding strength (yield strength: 970MPa and tensile strength: 1384MPa) and ductility (fracture strain: 37%) synergy. Microstructural studies showed that several strengthening mechanisms contribute to mechanical properties of the treated steel, including nano grains, nano twinned austenite grains, nano carbides and TRIP. Stacking fault energy and strain-induced martensitic transformation were found to have an important role in appropriate adjustment of the strengthening mechanisms to achieve the optimum properties.
Behjati, P.,Kermanpur, A.,Najafizadeh, A.,Samaei Baghbadorani, H.,Karjalainen, L.P.,Jung, J.G.,Lee, Y.K. Scientific and Technical Press ; Elsevier Science 2014 MATERIALS AND DESIGN Vol.63 No.-
A conceptual approach was used to design a new Ni-free austenitic stainless steel with a unique combination of ultrahigh strength and ductility. The concept was based on the alloying of the 0.05C-18Cr-12Mn (wt.%) steel by 0.39%N and heavy warm rolling (84% reduction) at 1173K (900<SUP>o</SUP>C) to achieve the yield strength of minimum 1GPa and high tensile strength and elongation due to a proper stability of the austenite as a result of the optimized stacking fault energy (SFE). The yield strength of 1010MPa, tensile strength of 1150MPa and high fracture strain of 70% were measured for the steel designed. Dislocation and solid solution hardening mechanisms are introduced as the main contributors for the ultrahigh yield strength of the steel. The strain hardening is gradual and the hardening rate reaches a high level of ~2400MPa at a high true strain of 40% due to slow α'-martensitic transformation and mechanical twinning. Consequently, the ductility of the designed steel is excellent.
Behjati, P.,Kermanpur, A.,Najafizadeh, A.,Baghbadorani, H.S.,Jung, J.G.,Lee, Y.K. Elsevier Sequoia 2014 Materials science & engineering. properties, micro Vol.614 No.-
In this work, the influence of precooling on deformation-induced α'-martensitic transformation and mechanical properties of Fe-16Mn-4Cr-0.1C (wt%) austenitic steel is investigated. It is shown that precooling in liquid nitrogen enhances the volume fraction of ε-martensite. During tensile testing, ε-martensite acts as a nucleation site for α'-martensite and promotes the strength and ductility of the steel. The precooled steel exhibits an excellent combination of mechanical properties (tensile strength of 1240MPa, uniform elongation of 35% and total elongation of 42%). Further, it is shown that tensile strength and elongation of the steel strongly depend on the deformation temperature. This is explained by the influence of temperature on stacking fault energy (SFE) and accordingly governing deformation mechanisms of the steel.
D. Rasouli,A. Kermanpur,E. Ghassemali,A. Najafizadeh 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.4
The martensite reversion treatment was conducted on two grades of Ni-free austenitic stainless steels interstitially alloyed withC and N. The hot rolled sheets of steels were cold rolled up to 80% thickness reduction to acquire strain-induced α′-martensiteand subsequently reversion annealed at temperatures from 700 to 850 °C for 1 to 1000 s to revert the α′-martensite to austenite. Microstructural evolution was investigated using optical microscopy, X-ray diff raction, electron backscatter diff raction,and magnetic measurement techniques. Mechanical properties were measured using tensile tests at room temperature. The resultant microstructures contained both reverted and recrystallized austenite when reverted at 700 and 750 °C withthe annealing time less than 100 s. A nonuniform grain structure was characterized under these conditions consisting ofnano/ultrafi ne grains formed via α′-martensite reversion and coarser grains by recrystallization of the retained austenite. However, a more uniform austenite grain size with average size of 1 μm was obtained at 850 °C for 1000 s. The specimenshaving nonuniform grain structure exhibited excellent combinations of strength and ductility. A variety of mechanical propertieswas achieved depending on the annealing condition. The work hardening behavior aff ected UTS and ductility of thestudied steels. The shift of the work hardening peaks to the higher strains was found suitable for ductility. Addition of C toN-containing Ni-free steels deteriorated mechanical properties. Best combination of strength and elongation was obtainedin the test material with lower C/N ratio.
A theory-driven organ donation campaign: a field intervention among university students in Iran
Marzieh Latifi,Sakineh Rakhshanderou,Katayoun Najafizadeh,Courtney A Rocheleau,Mohtasham Ghaffari 대한이식학회 2024 Korean Journal of Transplantation Vol.38 No.2
Background: This study conducted an empirical evaluation of an intervention derived from the theory of planned behavior (TPB) aimed at implementing a health campaign among medical students at Shahid Beheshti University of Medical Sciences. Methods: In this interventional study, a valid and reliable TPB-based questionnaire was administered before launching a health campaign titled “Organ Donation=Life Donation” among 260 medical students. The campaign was structured around nine steps: situation analysis, goal identification, target audience identification, strategy development, tactics establishment, media selection, timetable creation, budget planning, and program evaluation. Two months after the campaign, participants completed a posttest and were offered an organ donation card. Data analysis was conducted using SPSS ver. 16, employing descriptive statistics (frequency and percentage) and tests such as the Kolmogorov-Smirnov test and the paired-samples t-test. Results: All participants adopted more prodonation stances across all constructs measured, both immediately and 2 months after exposure to the health campaign, compared to their pretest scores. These results indicate that the health campaign had a significant impact on psychological variables such as attitudes (P<0.001), subjective norms (P<0.001), and perceived behavioral control (P<0.038), as well as on the actual acceptance of an organ donor card. Conclusions: Effective health education and promotion interventions, including health campaigns, are essential to encourage the use of organ donation cards. Additionally, current experiences indicate that the TPB serves as a suitable theoretical framework for designing organ donation interventions.
Kermanpur, A.,Behjati, P.,Han, J.,Najafizadeh, A.,Lee, Y.K. Scientific and Technical Press ; Elsevier Science 2015 Materials & Design Vol.82 No.-
Deformation mechanisms of the Ni-free Fe-18Cr-12Mn-0.05C (wt%) austenitic steels containing 0, 0.25 and 0.44N were investigated. Effects of N addition, strain and temperature on the formation of deformation-induced ε- and α'-martensite phases were determined using transmission electron microscopy and electron back-scattered diffraction techniques. Based on the microstructural evolutions, it is proposed that deformation mechanism of these steels includes the sequence of γ→ε-martensite→α'-martensite, in which the formation and stability of the ε-martensite is significantly enhanced by the N content. Increased deformation temperature from 298 to 373K reduces the formation of ε-martensite (more than 80%).
On the generalized principally injective modules
Fatemeh Gholami,Zohreh Habibi,Alireza Najafizadeh 대한수학회 2024 대한수학회보 Vol.61 No.2
Some results are generalized from principally injective rings to principally injective modules. Moreover, it is proved that the results are valid to some other extended injectivity conditions which may be defined over modules. The influence of such injectivity conditions are studied for both the trace and the reject submodules of some modules over commutative rings. Finally, a correction is given to a paper related to the subject.
Free vibration analysis of functionally graded coupled circular plate with piezoelectric layers
S. Jafari Mehrabadi,M. H. Kargarnovin,M. M. Najafizadeh 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.8
Based on classical plate theory (CLPT), free vibration analysis of a circular plate composed of functionally graded material (FGM) with its upper and lower surfaces bounded by two piezoelectric layers was performed. Assuming that the material properties vary in a power law manner within the thickness of the plate the governing differential equations are derived. The distribution of electric potential along the thickness direction in piezoelectric layers is considered to vary quadratically such that the Maxwell static electricity equation is satisfied. Then these equations are solved analytically for two different boundary conditions, namely clamped and simply supported edges. The validity of our analytical solution was checked by comparing the obtained resonant frequencies with those of an isotropic host plate. Furthermore, for both FGM plate and FGM plate with piezoelectric layers, natural frequencies were obtained by finite element method. Very good agreement was observed between the results of finite element method and the method presented in this paper. Then for the two aforementioned types of boundary conditions, the values of power index were changed and its effect on the resonant frequencies was studied. Also, the effect of piezoelectric thickness layers on the natural frequencies of FGM piezoelectric plate was investigated.