نشریه مهندسی مکانیک مدرس
سال سیزدهم شماره 4 (تیر 1392)

In grinding operation، cutting fluid is utilized for lubrication، cooling، chip removal from contact zone and also cleaning of grinding wheel. Despite these advantages، grinding fluids make many economic and environmental issues. On the other hand، dry grinding generally leading to thermal damages and reduction of surface quality level. Minimum Quantity Lubrication (MQL) technique is a new approach to elimination or reduction of cutting fluids that improves grinding performance by efficient penetration to the cutting zone. In this paper، in order to investigate the effect of MQL on grinding of steels، raw and hardened High Speed Steel have been selected. Grinding performance such as tangential grinding force، friction coefficient، roughness and morphology of the ground surface and chip form in three states of dry، conventional fluid and MQL have been studied and compared. The results show that MQL technique in comparison with the others lead to improvement of surface quality and also reduction of tangential grinding force and friction coefficient in hardened steel، but in the case of raw steel despite of reduction of tangential grinding force and friction coefficient، the surface quality is worst.

In this paper، mass flow rate and location of leakage in natural gas pipeline has been estimated simultaneously using inverse analysis. For doing so، at first natural gas transient flow in pipeline has been simulated numerically; this simulation is named direct problem. In the direct problem، it is assumed that the mass flow rate and location of leakage is definite and the governing equations are inhomogeneous well-known Euler equations. In these equations، the leakage effect has been considered as a source term. Steger–Warming flux splitting method has been used for numerical analysis of these equations. Then the location and mass flow rate of gas leakage of pipeline have been estimated simultaneously using Levenberg-Marquardt method for parameter estimation. This method is an iterative algorithm and based on minimizing the sum of the squares of the errors which are difference between pressures computed by the direct problem and pressures measured by pressure gauges. The results of the direct problem have good agreement with Mac–Cormack method and characteristics method of specified time intervals. The results of the inverse analysis demonstrate that Levenberg-Marquardt algorithm is stable and efficient enough to estimate simultaneously the mass flow rate and location of leakage in natural gas pipeline.

Sandwich panels have high strength to weight ratio because of their special structure. The variables which are defined for designing sandwich panels should be determined with applying necessary strength and lowest weight. In this paper، the imperialist competitive algorithm (ICA) has been used for minimizing the weight of a sandwich panel with prismatic core based on yielding and buckling criteria. ICA is inspired of imperialist competitions and it is based on two special criteria as recruitment policy and stable imperialist competition. Arrays numbers، core and surface thickness and panel height are assumed as design variables for decreasing panel weight. The results were shown that core and surface thickness and the total height of panel has been increased by increasing loading for given number of arrays. Also the core and surface thickness has been decreased and the total height have been increased by increasing array number for a determined loading and so panel weight has been decreased. A panel with diamond core has highest structure efficiency. It was shown that ICA is useful and competitive than the other heuristic algorithms because of direct using of function values in some problems which was required to the total optimization.

Shearography has proved to be a highly effective nondestructive testing (NDT) method، especially when it comes to composite and polymer materials used in automotive، aerospace engineering، nuclear and oil industries. Although its application in material testing and material research already has achieved acceptance in research، its applications need a highly considerations in limitations and its parameters. In this paper the application of digital shearography in the defect detection of polymer materials is studied. In this regard، a proper set-up of shearography is presented. A polyethylene plate with several defects in different sizes and depths have been made and tested with the presented set-up. The shearograms then have been compared to evaluate the shearographic system in defect detection. The effects of shear size and system of thermal loading have also been studied.

In tube hydroforming process، due to friction condition، uniform wall thickness، as well as sharp corners may not be achieved. Use of ultrasonic vibration can improve the contact conditions at the tube-die interface. The current work studies the effect of applying ultrasonic vibration on wall thickness and corner filling of hydroformed tubes. Firstly، a numerical model based on geometric relationships and stress-strain state has been established by which wall thickness and corner radius of hydroformed tubes can be obtained. In this model، the ultrasonic vibrations affect the nonlinear friction conditions at the tube-die interface. By comparing the FEM models of tubes in two cases of with vibration and without vibration، it is possible to investigate the effects of vibration on wall thickness and corner filling. The results indicate superimposing ultrasonic vibrations to the process will increase corner filling ratio of the tube significantly، and more uniform tube wall thickness will be achieved.

The structural integrity of welded joints in natural gas transportation through large diameter steel pipes requires the experimental determination of material mechanical properties in seam weld via destructive and non-destructive testes. In this paper، the metallurgical and mechanical characteristics of multi-pass girth weld in seam weld، heat affected zone (HAZ)، and base metal of a pipe with 56 inch outside diameter، 0. 780 inch wall thickness is determined. To do this، chemical analysis، standard metallography، tensile and impact tests and hardness experiments were conducted. The metallographic results demonstrated that different sub-zones in welded joint had different microstructure. The existence of different chemical contents in different weld passes and the presence of hard phases (such as martensite due to uncontrolled heat cycles) had direct effects on mechanical properties of the seam weld and HAZ. From the hardness test result، it was found that HAZ and centerline of the seam weld had the minimum and maximum hardness levels، respectively. Furthermore، the minimum Charpy impact energy was found in the seam weld centerline.

A numerical study for the simulation of induced-flow by a two-room compartment fire has been accomplished using a fully-coupled Large Eddy Simulation (LES) model which incorporates Smagorinsky and One-Equation Sub-Grid Scale (SGS) turbulence models. Also، modified Eddy Dissipation Concept (EDC) and Discrete Ordinate Methods (DOM) are used for incorporating combustion and radiation، respectively. The models are applied for a range of total heat release rate (HRR) for fire source in the center and corner of the fire room. Numerical results of prediction by each SGS model are validated and compared against well-known available experimental data. The predicted time-averaged temperature profiles at different location of the compartment for each case have been calculated and found to be in good agreement with the experimental data. The results also show that the accuracy of One-Equation SGS model for the prediction of the characteristics of fire is higher than those obtain by Smagorinsky SGS model. The air mixture at the fire room opening is higher for the centrally located fire source than the corner one.

In this paper، a unit cell based micromechanical model is presented to predict the elastic-viscoplastic response of aligned short fiber titanium matrix composites subjected to combined axial loading in the presence of fiber/matrix interfacial damage. The effects of manufacturing process thermal Residual Stress (RS) are also included in the analysis. The representative volume element (RVE) of the short fiber composites consists of c×r×h cells in three dimensions in which a quarter of the short fiber is surrounded by matrix sub-cells. In order to obtain elastic-viscoplastic curves، the fiber is assumed to be linear elastic، while the matrix exhibits elastic-viscoplastic behavior. The Evolving Compliance Interface (ECI) model is employed to analysis interface damage. This model allows debonding to progress via unloading of interfacial stresses even as global loading of the composite continues. Results revealed that for more realistic predictions، in comparison with available experimental and the other models results، both interfacial damage and thermal residual stress effects should be considered in the analysis.

In this paper، the influence of nanoclay Closite 30B on ballistic impact behavior of 2D woven E- Glass/Epoxy laminated composite has been investigated experimentally. The glass/epoxy/nanoclay hybrid laminate nanocomposites are manufactured by layup method under pressure. The nanoclay particles are Closite 30B and are dispersed into the epoxy system in a 0%، 3%، 5%، 7% and 7% ratio in weight with respect to the matrix. In additional to tensile test، ballistic impact test is carried out on the samples by flat-ended projectile with 8. 9gr mass and 10mm diameter in 134m/s and 169m/s velocities. The results have shown that not only the mechanical properties، but also ballistic impact resistance can be improved with adding nanoclay.

In this research، the phenomenon of vortex-induced vibrations and the effect of control cylinders usage with different configurations on vortex formation، lift and drag coefficients، and fluctuations amplitude at the back of an elastically supported rigid circular cylinder subjected to a uniform fluid flow are studied. Results obtained in the absence of control cylinders are validated with experimental and numerical results of other researchers and a good conformity is reached. After ensuring simulation accuracy and precision، control cylinders of equal diameter with master cylinder are placed as linear and triangular arrangements at the back of master cylinder and the optimal configuration and location of control cylinders are defined. In linear arrangement، at first the effect of a control cylinder usage at 5 different distances from 1. 5 to 3. 5 times diameter of master cylinder and then two control cylinders with ratios of 1. 5، 2 and 2. 5 times diameter of master cylinder are studied. At the end، in triangular arrangement، control cylinders are located at intervals of 1، 1. 5 and 2 times diameter of master cylinder.

Changing the trajectory of a projectile can be accomplished by unbalancing the pressure distribution on the body surface and this usually is achieved by surface spreading techniques. The major drawbacks of such techniques are high drag force; fins aerodynamic heating، high time response and etc. To overcome these difficulties، recently application of plasma actuators has been evaluated numerically and experimentally. It is known that the time response of a projectile to control commands is a key factor to its CEP. In the present paper، unsteady flow around a supersonic projectile was calculated using Fluent software and its time response to a control command was analyzed. In this investigation، it is shown that using plasma actuator in comparison with aerodynamic fins can reduce the time response of a projectile about one order of magnitude. This reduction in time response can improve the performance of a projectile significantly.

In this paper a method for online identification of satellite moment of inertia tensor parameters based on recursive least squares method، is presented. It is assumed that the satellite actuators are three orthogonal reaction wheels. Dynamic equations of the satellite are extracted in a special manner. The only available sensor is a three axes rate gyro which measures the angular velocity of satellite in the body coordinate system. Due to existence of noise in this sensor، the regressor matrix used in least squares method، changes stochastically. So in this case، the classic least squares method is not useful، and it cannot converge. For solving this problem، a modified least squares method with robust scheme is presented and its stability is proved using Lyapunov stability theory. The presented method can be used online in presence of measurement noise and other sensor imperfections. Simulation results have shown that this method can identify inertia parameters of the satellite with less than 3 percent error comparing to real parameters before and after changes.

In this research the effect of both calcium carbonate nanoparticles and PP-g-MA ones on impact strength and Young’s modulus of Polypropylene (PP) are investigated experimentally. Two kinds of CaCO3 nanoparticles (monolayer-coated and uncoated) are used to investigate the effect of surface treatment of nanoparticles on the mechanical properties of these composites. All samples are mixed in a co-rotating twin screw extruder and are formed into standard tensile and impact bars using the injection molding method. The effect of surface modification of nanoparticles and presence of PP-g-MA on the dispersion of calcium carbonate nanoparticles in polypropylene matrix are studied by field emission scanning electron microscopy (FESEM). The results show a good agreement between the TGA analysis and the related theory. The results also show that surface modification of calcium carbonate nanoparticles and also the PP-g-MA are affective in improving the distribution and dispersion of nanoparticles in the PP matrix. Increasing of the calcium carbonate nanoparticles improves both the impact strength and the Young''s modulus of polypropylene. The more the PP-g-MA is added to PP matrix the more the impact strength of the samples increases and the less their Young''s modulus decreases.