Showing 4 results for Karafi
, Mohammad. Sababi, Hasan. Foroghi, Mohammad. Reza. Karafi,
Volume 8, Issue 1 (10-2008)
Abstract
Blade is a sensitive and important part of turbines, and a few companies can produce it. Airfoil of blade has three-dimensional surfaces; therefore, it is necessary to have specific equipment for dimensional control of it. The purpose of this project is to design and manufacture a mechanical system for dimensional control of the airfoil. The foregoing device can produce two-dimensional contours of airfoil on the screen of the profile projector using fine pins. In the mentioned system, the blade is located on the table of device and two sets of pins approach it. In this situation pins are moved forward along their axis until their tips touch the surface of the blade, therefore the tips of pins, shape the contour of the airfoil. Then two sets of pins get away from each other and are moved to the focal area of lens of profile projector via a precision linear system. Then two sets of pins approach each other and reshape the previous contour again. In this situation, tips of pins are projected and contour of airfoil is made on the screen of the profile projector with a predefined scale. Produced contours can be compared with reference ones that have been printed on transparent sheets.
Ehsan Shakouri, Mohammad Hossein Sadeghi, Mehdi Maerefat, Mohammadreza Karafi, Mehdi Memarpour,
Volume 14, Issue 6 (9-2014)
Abstract
The problem of bone fracture in medicine due to an accident, aging or diseases, has existed from times when humans started to work and activity. The process of bone drilling is an essential part of internal immobilization in orthopaedic and trauma surgery. The force required to chip formation in drilling process, resulting in heat generation in drill site that leads to the occurrence of thermal necrosis. This research experimentally investigates the effect of ultrasonic vibration on thrust force in drilling of bovine femur bone. This method induces high-frequency and law-amplitude vibration in the feed direction during cutting, and has the potential to spread tiny cracks in bone and decrease friction leading to reduce of cutting forces and also increase the speed of chip disposal leading to reduction of machining forces, totally. Experimental results demonstrate that ultrasonic assisted drilling of bone produces fewer thrust force than conventional drilling and rotational speed of 1000 rpm is the optimal speed to achieve at minimum thrust force for all feed rates. Moreover, this method is due to the force independence of the feed rate in the rotational speed of 1000 rpm, is applicable in orthopedic surgery.
H. Vatanjou, Yousef Hojjat, M.r. Karafi,
Volume 19, Issue 11 (November 2019)
Abstract
In this paper nonlinear dynamic behavior of bending actuators of dielectric elastomer or Dielectric Elastomer Minimum Energy Structure (DEMES) is studied and the effects of viscoelasticity of dielectric film on system response are investigated. Considering hyper-elasticity and viscoelasticity of dielectric film, the equation of motion of the actuator is extracted using Euler-Lagrange method. The natural frequency of small amplitude oscillations around the equilibrium state is calculated by linearizing the original nonlinear equation and the effects of dielectric film pre-stretch and excitation amplitude on natural frequency is investigated. The numerical simulation of the nonlinear equation of motion for periodic excitation shows that the system possesses harmonic resonances as well as sub-harmonic and super-harmonic resonances. By increasing the damping ratio of the dielectric film, resonance frequency increases for all harmonics and their excitation amplitude decreases. The analytical results show that excitation amplitude of harmonic resonance in chaotic behavior changes to a quasi-alternate and then an alternative behavior by increasing damping ratio.
Saeed Ansari, Mohammad Reza Karafi,
Volume 24, Issue 9 (September 2024)
Abstract
This paper presents an innovative bulk magnetostrictive actuator made of a 2V-Permendur alloy rod, capable of functioning across multiple deformation modes—longitudinal, torsional, and flexural. In longitudinal mode, displacement is produced by the Joule effect, where a magnetic field applied along the rod’s axis, generated by a surrounding coaxial coil, induces deformation along its length. Torsional mode activation follows the Wiedemann effect, wherein an electric current passed directly through the rod produces a circumferential magnetic field that twists the material. Additionally, flexural deformation is achieved by a special designed magnetic core that directs a magnetic field to the rod’s surface, producing bending movements along the rod’s length. The actuator operates using controlled DC magnetic fields. Experimental results demonstrated outstanding performance, with maximum displacements reaching 12 microns in longitudinal mode, 7 microns in flexural mode, and 0.15 degrees in torsional mode. Such multi-functional performance highlights the actuator’s potential in precision positioning systems, with particular suitability for advanced microscopy, optical instrumentation, and other fields requiring sub-micrometer positioning accuracy.
