مهندسی مکانیک مجلسی
سال:1392 | دوره: | شماره: |تعداد مقالات:11

Hydro-mechanical deep drawing (HDD) is one of the most convenient processes in which a sheet metal is drawn against a counter pressure rather than a rigid die in conventional stampings. This process has been increasingly used to produce aerospace and automotive components. More recently, aerospace industry is demanding new materials with capability to produce high strength to weight ratio products. Moreover on hydro-mechanical deep drawing investigations, numerical considerations are used in order to design the process parameters to produce a cost-effective with high quality components. While, this process has not been investigated for superalloy cups. Nickle-based superalloy sheet metals are more prominent in aviation and spaceflight industries. In this paper, numerical simulation of hydro-mechanical deep drawing for Haynes230 nickle based superalloy has been investigated. Moreover, the pressure paths which yield rupture and wrinkling have been realized. Furthermore, differences between applying uniform and gradual pressure into the pressure chamber have been detected to nominate a pressure path for successfully producing a superalloy cup made by HDD. Subsequent to that, chamber pressure against punch travel curves was depicted. For this investigation, 3-D finite element method was employed and the results obtained from numerical simulation were validated using experimental data already available in the literature.

Production and preparation of many parts of the aircraft body including wings with long length, smooth form, and large radius of curvature are amongst the most important challenges in this industry. In this paper, the effective factors in the rubber pad forming method on pieces containing curvature radius, have been investigated by finite element method. The effect of variables such as curvature radius, sheet thickness, rubber pad thickness, rubber hardness, lubrication condition, spring back phenomena have been analyzed. To validate the finite elements simulation, the experimental results were compared. Subsequently, other above-mentioned variants were studied. The obtained results indicate that there is a close differentiation between the numerical and experimental works. Moreover, the cited parameters have different effects on part quality as discussed.

Aluminium 7075- T651 alloys are widely used in the production of light weight structures requiring a high strength to weight ratio and high corrosion resistance. The effect of processing parameters on fatigue life of 7075-T651 aluminium joints produced by friction stir welding was investigated in the present study. Welding samples were made by employing rotating tool speed of 770, 900 and 1200 r.p.m, welding speeds of 70, 75 and 80 mm/min. After welding process, mechanical properties of samples were evaluated by means of fatigue testing machine at room temperature. Results clearly illustrated that as the tool speed decreases, fatigue life decreases. The highest fatigue life was obtained with 80mm/min welding feed and weld speed of 1200 r.p.m.

In this paper, a fully discretized bio-fidelity simulation model for biomechanical (kinematic) analysis of scoliosis for various patients was developed to analyze forces on vertebrae, loads acting on the intervertebral disc, corresponding angles between vertebrae, and tension in the spine muscles during lateral bending.It was further developed to study the movement limitation and muscle activation of a scoliotic subject. This system was built by using the commercial software Life MOD. The whole spine (pre-defined by the software) was discretized into individual vertebra segments with rotational joints representing intervertebral discs. In this study, two female subjects (with 40±1.0 kg weight and 154±3 cm height), one with normal spine and the other one with scoliotic spine, were asked to do lateral bending and bend as far as they can. Motion capture data of these two subjects was obtained. Next, motion capture data was assigned to the model using a motion agent set and the inverse dynamics simulation was performed to simulate the complicated multi-body motion of lateral bending. The mobility of the ribcage, activity of muscles which are important in the lateral motion of body, as well as joint angles were analyzed using the developed simulation model. According to the obtained results, the mobility of the ribcage in scoliosis model was less than that of the normal model with the same anthropometric data. This finding is in direct agreement with the qualitative experimental results done by other researchers.

Rayleigh-Taylor (RT) instability has a growing importance in many fields including aircraft industry and astrophysics. The development and the growth of RT instability were investigated using sinusoidal disturbances with different wavelength at the interface of the two fluids. Numerical simulations were performed by solving Navier-Stokes unsteady equations with the VOF formulation. Results of the 2D simulation are compared with experimental results.It is shown that beyond a critical time, not captured experimentally, the mushroom shape of RT instability turns into a helical path or breaks down into a patchy shape depending on the shape of disturbance. Nonlinear instabilities responsible for such behavior are apparent when the wavelength exceeds 10 times the length scale introduced in this study.

In this study, the time-average velocity in the near wake of a two dimensional Notch-Back car model located in the wake of a trailer has been investigated. Experiments were carried out in an open circuit low-speed wind tunnel made by FaraSanjeshSaba Ltd, in Iran. Results show that at close spacing, time-average velocity profile behind the car has a maximum peak due to the interaction of the jet fluid with the wake of the car, such that with increased vehicle spacing, the jet fluid effect creating the maximum velocity peak gradually fades. In addition, along with increasing vehicle spacing, the velocity in the wake of the car starts to grow quickly. To measure the drag coefficient it was preferred to use the wake-survey method combined with the equation recently derived by Van Dam.The dimensionless distance between vehicles derived is based on the length of the front vehicle ranging from 0.1 to 3. It was observed that the car drag coefficient experiences a rising trend at the beginning and then descending along dimensionless distance of 0.1 to 1.3, compared to the individual case. In farther distances it will be less pronounced than the individual case.

A custom-made nonlinear viscoelastic damper is designed for several industrial applications. The damper is structurally similar to typical commercial dampers and the design is solely based on the choice of the viscoelastic material used as damping agent in the damper. With rheological parameters of a selected material from experiment, the coefficients of Johnson-Segalman constitutive equation model are evaluated by fitting the data. The problem was first formulated by introducing the governing equations for the flow over flat plate. A numerical scheme of finite difference method is applied to solve the governing equations in the time domain. The model is capable of predicting the nonlinear amplitude dependent behavior of viscoelastic dampers under single and multiple-frequency excitations.

This paper is a computational study of the behavior of aerodynamic characteristics of an airfoil with blunt trailing edge and investigates the effects caused by modifications made to the trailing edge, on aerodynamic performance.Blunt trailing edge airfoils are of interest in the engineering of large wind turbine blades because they allow for a strong structure with a high aerodynamic lift to structural weight ratio. Blunt trailing edge airfoils would not only provide a number of structural benefits, such as decreased structural volume and ease of fabrication and handling, but they have also been found to improve the lift characteristics of thick airfoils. The incorporation of blunt trailing edge airfoils would allow blade designers to more freely address the structural demands without having to sacrifice aerodynamic performance. These airfoils do have the disadvantage of generating high levels of drag as a result of the low-pressure steady or periodic flow in the near-wake of the blunt trailing edge. Also vortex shedding in these airfoils induces fluctuating loads and radiated noise. In the present investigation, we tested the effects of two cavities on the base drag and wake of an airfoil with blunt trailing edge. In two-dimensional subsonic flows, any method that increases the base pressure of the airfoil with blunt trailing edge consequently reduces the base drag. The base pressure increases subsequent to the introduction of the cavity to the trailing edge. Moreover the cavity causes the trapping and stabilizing of the vortex.

This work presents a numerical study to investigate the heat transfer characteristics of a 2-D rectangular composite porous radiant burner (CPRB). In the construction of porous burner, the porous layer is considered to be composite consisting of upstream and downstream layers with equal thickness but with different physical and radiative properties. In the present work, a two dimensional rectangular model is used to solve the governing equations for porous medium and gas flow. In order to analyze the thermal characteristics of the CPRB, the coupled energy equations for the gas and porous medium are solved numerically and the discrete ordinates method is used to obtain the distribution of radiative heat flux in the porous media. Finally, the effects of the various factors on the performance of CPRB are determined. Computational results show that the high porosity and low scattering coefficient for downstream porous layer are desirable for maximizing the CPRB efficiency in comparison to homogeneous one. Comparison between the present results with those obtained by other investigators indicates a good agreement.

Pulsed Current Micro Plasma Arc Welding (PCMPAW) is one of the most widely used welding processes in sheet metal manufacturing industry. In any fusion arc welding process, the weld bead geometry plays an important role in determining the mechanical properties of the weld, which helps to improve the weld quality. Moreover, the geometry of weld bead involves several simultaneous quality characteristics, such as front width, back width, front height and back height, which must closely be monitored, controlled and optimized. This paper presents the optimization of the PCMPAW process by using the grey relational analysis considering the aforementioned quality characteristics, which are of maximum front width and back width, also minimum front height and back height.In relation to this, experiments were performed under different welding conditions such as peak current, back current, pulse rate and pulse width using AISI 304L stainless steel sheets of 0.25mm thickness using Response Surface Method (RSM) based on Central Composite Design (CCD) experimental design. It was observed that optimal welding parameters were determined by the grey relational grade from the grey relational analysis and they were also verified through confirmation experiments.

In this paper, a FEM-based Taguchi method is used to determine the effects of forming parameters on the quality of part formability in the process of hydrodynamic deep drawing assisted by radial pressure. Four important forming parameters, fluid pressure, friction coefficient at blank/punch interface, die entrance radius and the amount of gap (g) between die rim block and blank holder are considered in this investigation. In order to have more comprehensive study, three different workpieces are used as the case studies. Three-dimensional FE models are developed for simulating the forming process. After experimental validation, these models are used for performing the set of experiments designed by Taguchi’s L-9 orthogonal array. The signal-to-noise (S/N) ratio and the analysis of variance (ANOVA) techniques are used to calculate the contributions of each of the mentioned parameters to the output characteristic. The results indicate that fluid pressure and friction coefficient are the most influential parameters. Also, die entrance radius and the amount of gap (g) have considerable effect on the part formability. The obtained results may provide useful guidance on determining forming parameters.