Showing 4 results for Mahdavi
J. Mahdavi and A Emaadi,
Volume 16, Issue 1 (7-1997)
Abstract
Power electronic converters are non-linear time-dependent systems whose exact analysis without the use of computers is very difficult, and even using computer softwares requires a long time. Use of the state space averaging method, as will be mentioned, in addition to simplifying the analysis procedure which is a result of converting a time-dependent system to a time-independent one, reduces the required computation time considerably. But this method is not applicable to circuits for which small variations of state variables does not apply, since it is not able to follow rapid and large changes. Therefore, we make use of a developed method in which we consider the average of the state variables as well as adding the harmonics. This more general method can basically be adjusted to various arbitrary wave forms, and is based upon a Fourier series time-dependent display for a sliding window of the given waveform. In this paper, after introducing the developed state space averaging method, results of applying this method to various basic DC/DC and DC/AC converters will be mentioned, and also effects of some parameters on the quality of model will be discussed.
M. Tafreshi, S. R. Allahkaram, S. Mahdavi,
Volume 37, Issue 3 (Journal of Advanced Materials-Fall 2018)
Abstract
In this research, Zn-Ni and Zn-Ni/PTFE coatings were electrodeposited from sulfate-based electrolytes. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were used to investigate the corrosion properties of the coatings. Hardness and tribological behavior of the coatings were examined by the Vickers microhardness testing machine and the pin-on-disc method, respectively. Chemical composition and morphology of the as-deposited and worn surfaces of the coatings were studied by a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). According to the results, the corrosion current density of the Zn-Ni film was about 30% of that of the composite coating. Hardness of the alloy film was partially decreased by the incorporation of Polytetrafluoroethylene (PTFE) particles. However, the wear loss and coefficient of friction of the Zn-Ni/PTFE coating were, respectively, about 43% and 57% of those of the Zn-Ni film. Moreover, wear mechanism was changed from plastic deformation and adhesive wear to slight abrasion by the co-deposition of PTFE particles.
R. Amirarsalani, M. Morakabati, R. Mahdavi,
Volume 40, Issue 1 (Journal of Advanced Materials-Spring 2021)
Abstract
In this research, the hot deformation behavior of W360 tool steel was investigated using hot compression test at 1000-1200°C and strain rates of 0.001, 0.01, 0.1, and 1 s-1. According to the results, dynamic recrystallization was found the most important restoration factor of this alloy during hot deformation. Recrystallization was enhanced with an increase in temperature and strain rate. Also, the hot working process was optimized by drawing the processing map of this steel. Microstructural images obtained from the hot compression test showed that recrystallization started at 1000°C and the strain rate of 0.01 s-1 and developed with increasing temperature and strain rate due to an increase in the stored energy and suitable regions for nucleation. The results of drawing the processing map showed that the best hot deformation region was the temperature range of 1050-1150°C and strain rates of 0.1-1 s-1.
H. Saki, M. Morakabati, R. Mahdavi,
Volume 40, Issue 3 (Journal of Advanced Materials-Fall 2021)
Abstract
Metastable beta titanium alloys have the ability to achieve different microstructures as a result of various heat treatment cycles. The aim of the present study was to create a combination of fine spherical and needle-shaped alpha phase in a metastable beta Titanium alloy (Ti-3Al-8Mo-7V-3Cr) using two-phase solution annealing and aging to improve tensile properties. In this regard, one strip of the alloy was solution annealed in the two-phase region (α+β) at 750°C. Then, some of the solution treated specimens were aged in one step and the others in two steps. The microstructural observation and phase analysis were studied by scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively followed by investigating tensile properties using tensile test. The results exhibited that the microstructure of the alloy after annealing in the two-phase region (α+β) consisted of a spherical primary alpha phase of 1 μm in the beta matrix. One-step aging at 600°C resulted in a microstructure without secondary alpha layers. This heat treatment cycle resulted a yield strength of 980 MPa and fracture strain of 13.9%. Two-step aging at 300°C and 600°C led to formation of the secondary alpha layers with 0.1 μm thickness and increased the yield strength and fracture strain to 1007 MPa and 15.8%, respectively.
