مجله مهندسی مکانیک
سال چهل و دوم شماره 2 (پیاپی 64، پاییز و زمستان 1391)

Lack of machining accuracy، at corners and corner radii، is one of the major problems in Wire-EDM process. The focus of investigation in this work was on corner radii errors through successive cuts of roughing and finishing operations. Effects of discharge frequency، inter-electrode average gap voltage، and feed-speed were investigated for finishing operations. Residual material left on straight path and over-cut on convex curved path were measured. Results indicated that the influence of the input variable parameters on the thickness of the residual material on straight paths is remarkable in comparison to curved corners. Ultimately، for corner radii، an optimum set of parameters could reduce the errors only by 12%. It was، then، concluded that the roughing operation is the most influential stage of cutting on corner radii

As Al-Mg alloys have a great usage in various industries and the microstructures of these alloys are very sensitive todefects formation during casting، it seems a meticulous investigation of their microstrutures can be beneficial for theseindustries. Although oxygen solubility in molten aluminium alloys is said to be negligible، since aluminum alloys melt arevery sensitive to oxidation during casting، when the surface of melt is exposed to air it oxidizes quickly and an oxide film isformed on the melt surface. Then this surface oxide film can be folded and entrained into the melt due to surface turbulence. In this research، sandwiches of oxide-metal-oxide formed on a short time within the cast during solidification were used tostudy the effect of magnesium content (i. e. 1wt% and 2wt %) on the oxide film thickness. To form sandwiches of oxidemetal-oxide within the cast a certain amount of air was blown into the melt every 3 seconds during casting time by means ofa compressor at 0. 5 atmosphere pressure. Where bubbles of air reached each other، they formed a sandwich which later wasused for investigating purpose. Both the thickness of oxide films and the surface of each layer were studied via SEM. Theresults showed that the thickness of the short time oxide film varies in the range of 150-200 and 200-300 nanometers for Al-1Mg and Al-2Mg alloys، respectively. This is a new finding for this type of alloys.

Hyperthermia is one of the known methods for curing tumours in medicine science. Successfulness of hyperthermia treatment depends on the accuracy of prediction and the controlling of temperature distribution in tissue. In this study، the relation between heat flux and temperature gradient has been studied by using dual phase lag (DPL) model. One dimensional transient energy equation with perfusion and metabolic heat generation terms in tissue has been solved by using the space-time conservation element and solution element (CESE) method. The CESE method unlike other conventional finite-volume methods treats with space and time coordinates equally. In this method both temperature and heat flux variables are estimated explicitly and simultaneously. Thus، the above method is more accurate in compare to other methods and decreases the run time. In this work، the result of CESE method has been compared with conventional finite-volume methods. One of the basic characteristic of this method is that it can capture large discontinuities without introducing numerical oscillations in temperature distribution of tissue while in pervious methods these oscillations are clearly observed. Transient thermal wave in hyperthermia treatment is studied in various places in tissue and effective elements on it، is surveyed.

In this article، the buckling of composite cylindrical shells is investigated under thermal and different mechanical loading consisting of the axial compression، torsion and external pressure. To achieve this، a semi-analytical finite element method is developed based on the First order Shear Deformation Theory (FSDT). The eigenvalue equation obtained is used to determine the critical load and its corresponding circumferential mode. In the mechanical loading، two methods are introduced to make the geometric stiffness matrix، the results of which are compared to each other and also to the references. For single layer composite cylindrical shells and each loading، the most strength ply angle against buckling are studied.

The main aim of this paper is to investigate experimentally the active flow control using plasma actuators over an airfoil. The method involved the application of single Dielectric Barrier Discharge (DBD) in order for changing the frequency of vortex-shedding and the turbulence characteristics concerning NACA4412 airfoil. The objective was also to reduce the control flaps noise in transporting aircraft via an effective body force generated by the actuators. The obtained results indicate that the use of plasma actuator led to a significant decrease in frequency of vortex-shedding around the flap whereas significant increase in turbulence levels were achieved at a distance far from the actuator، as well.

These days machinery، devices and tools that are used in industry، are very complex and costly. Therefore using producing and inspecting methods with maximum reliability that supply equipments، are required. Non-destructive testing is one of those methods that are used to inspect equipment that already have been mentioned. One of the non-destructive testing، which has more industrial application، is ultrasonic test. In this paper، examine of the ultrasonic guided waves in laminated isotropic plates has been discussed. With the assumption that there is not space between layers andthey are connected to each other and as boundary conditions، on the top and bottom of plate’s surfaces، tension is zero. The purpose of this study are extracting diagrams of frequency spectrum (frequency depending on the wave number)، phase velocity depending on frequency، group velocity depending on frequency and eventually the wave structure and stress distribution in a two-layers plate، the equations for multi-layer plates are solved and diagrams that discussed above are extracted. How to stimulate a particular mode at a probe frequency for two layers plate is investigated in continuance and graphs of radiation angle at frequency are plotted.