مهندسی مکانیک مجلسی
سال:1394 | دوره: | شماره: |تعداد مقالات:10

A plain strain analysis of frictional rolling contact on an elastic graded coating is presented in this paper. Finite element method is applied to gain an understanding of the stresses and contact zone properties caused during rolling contact. The effects of friction, material stiffness ratio and coating thickness on stresses in contact zone and coating/substrate interface are studied. Shear modulus of softening and stiffening graded coatings change with exponential, power law and linear functions. The substrate is homogenous and the rigid cylindrical roller moves in a steady state condition with constant velocity. The coating is modeled in multi layers and a 2-D hard contact of rolling surfaces is considered. The analytical results verify the present method and show a good agreement. It is shown that thinner thicknesses have more effects on stresses and energy density, but these effects are not seen for thicknesses larger than a specific limit.

Ultrasonic Vibration assisted Single Point Incremental Forming (UVaSPIF) process is an attractive and adaptive method in which a sheet metal is gradually and locally formed by a vibrating hemispherical-head tool. The ultrasonic excitation of forming tool reduces the average of vertical component of forming force and spring-back rate of the formed sample. The spring-back phenomenon is one of the most important geometrical errors in SPIF process, which appear in the formed sample after the process execution. In the present article, a statistical analysis and optimization of effective factors on this phenomenon is performed in the UVaSPIF process based on DOE (Design of Experiments) principles. For this purpose, RSM (Response Surface Methodology) is selected as the experiment design technique. The controllable factors such as vertical step size, sheet thickness, tool diameter, wall inclination angle, and feed rate is specified as input variables of the process. The obtained results from ANOVA (Analysis of Variance) and regression analysis of experimental data, confirm the accuracy of mathematical model. Furthermore, it is shown that the linear, quadratic, and interactional terms of the variables are effective on the spring-back phenomenon. To optimize the spring-back phenomenon, the finest conditions of the experiment are determined using desirability method, and statistical optimization is subsequently verified by conducting the confirmation test.

this paper aim to presents a simple and efficient approach for modeling and solving the equations of a rotor with any number of disks, bearings and mass unbalances using the assumed modes method. This model consists of a continuous shaft, arbitrary number of mass unbalances in any axial location and phase angle, and any number of rigid disks and bearings. This arrangement is extensively used in diverse applications. In this study, final governing differential equations are not derived because the assumed modes method is directly inserted to solving process. Some examples in both cases of free and forced vibration have been dealt with. The results show the accuracy of this approach and its prediction of vibration behavior of the rotor in a complex combination of shaft, disk and bearing. This study also shows the results are as accurate as the results of the most popular approach, i.e. the Finite Element Method.

Forging of gas turbine blades needs a close control of the process parameters. These parameters require a suitable optimization method to achieve the best process conditions. This paper presents a hybrid method for the optimization of forging process of an aerofoil blade. Forging process of the aerofoil blade was simulated using 3-dimentional finite element method. Preform shape and die parting-line angle are optimized in order to minimize the volume of the unfilled die cavity, material waste, forging forces. The overall optimization scheme used in this research work includes a multi-objective approach that is combination of response surface and finite element methods. The results show that the proposed optimization approach accrued to decrease the flash volume and the forging force of the aerofoil forging process. Therefore the proposed algorithm is a suitable method for optimization of the gas turbine blade forging processes.

This paper describes a modified structural dynamics model for aeroelastic analysis of high-aspect-ratio wings undergoing large deformation behavior. To achieve this objective, a moderate deflection beam model is modified with some important large deflection terms and then coupled with a state space unsteady aerodynamics model. Finite element method is used to discretize the equations of motion. A dynamic perturbation equation about a nonlinear static equilibrium is applied to determine the flutter boundary. The obtained results show good agreement in comparison with the other existing data such as high-altitude long-endurance (HALE) wing and Goland wing. It is found that the present aeroelastic tool have a good agreement in comparison with valid researches and also considering the effect of the geometric structural nonlinearity and higher order nonlinear terms on the flutter boundary determination is very significant.

In this study, changes in velocity, turbulence intensity and drag coefficient in the wake of a notch-back car modelling steady and Unsteady Flow is Measured and evaluated. The blow open circuit wind tunnel to simulate fluid flow. intensity and nominal maximum speed of the device is Measured to be 0.01% and 30 m/s respectively. the speed Has been continuously increased by an inverter Causing changes in rotational speed of the electromotor. In the near location to the model, the results showed three different regimes in the velocity profile of the model’s wake. with increasing distance from the model and with increasing the Speed, three regimes in the wake are close to each other. drag coefficient for several velocities is measured, where the result shows that decreasing in drag coefficient is proportional with increasing velocity. In addition, the changing trends of higher order velocity of parameters like flatness and skewedness are depicted.

Strip tearing during cold rolling process has always been considered among the main concerns for steel companies, while several works have been done so far regarding the examination of this issue. In this paper, experimental data from cold rolling tandem mill is used for detecting strip tearing. Sensors are placed across the cold rolling tandem mill, to collect information on parameters (such as angular velocity of the rolls, voltage and the electrical current of electrical motors driving rolls, roll gap, and strip tension force between rolls) directly from the cold rolling tandem mill. The information includes two modes: perfect rolling and ruptured rolling. A neural network is designed by means of MATLAB software and, then, trained using the information from the related data files. Finally, the neural network is examined by new data. It is concluded that the neural network has good accuracy in distinguishing between perfect and defected rolling.

The occurrence of chatter vibrations in boring operation has a great influence in improving workpiece dimensional accuracy, surface quality and production efficiency. In this paper instability analysis of machining process is presented by dynamic model of boring machine. This model, which consists of the machine tool’s structure, is provided by finite element method and ANSYS software. The model is evaluated and corrected with experimental results by modal testing on boring machine in which the natural frequencies and the shape of vibration modes are analyzed. The natural frequencies of this modal testing are extracted through Pulse Labshop and ME'scope modal analysis software. Finally, the stability lobes obtained from this model are plotted and compared with experimental results.

In this research, compositing the surface of AZ31B magnesium alloy with CNT was studied by FSP. The investigated parameters were rotational speed (500-1500rpm), transverse speed (12-44mm/min), number of passes (1-4), and CNT weight fraction (0-2%). Microhardness testing, optical metallography, FESEM, and EDS analysis were used for the characterization of the samples. The suitable limits for the transverse speed and rotational speed were 12-24mm/min and 870-1140rpm, respectively. The highest hardness in the FSP without compositing was observed at the transverse speed of 24mm/min, rotational speed of 870rpm with a hardness of about 60Vickers, and the stir region grain size of less than 5mm. The Zener-Holman parameter was calculated and the least value was related to the conditions of the transverse speed of 12-24mm/min and rotational speed of 870rpm; as a result, the samples with the finest grain size were theoretically and experimentally marked. The most homogenous structure with the highest hardness was related to the three-pass processed sample with a hardness of 69Vickers. The best rate of CNT weight was 2%, enjoying the highest hardness. The FESEM images confirmed the suitable distribution of CNTs in matrix after the performance of the three-pass processing.

In this paper the effect of block shape Vortex Generators (VGs) on an air-water finned-tube heat exchanger has been studied experimentally using exergy analysis method. Also the effect of these VGs on increasing heat transfer rate has been simulated numerically and the results indicate a good agreement with the experiments. In this research a wind tunnel is used to produce wind flow over heat exchanger in the range of 0.054 kg/s to 0.069 kg/s. The steady volume flow rate of hot water is 240 L/h with the temperature of 44oC to 68oC. These experiments have been carried out with and without VGs on the heat exchanger. Results demonstrate that using the VGs has reduced Air Side Irreversibility to Heat transfer Ratio (ASIHR). To reveal the effect of VGs on heat exchanger performance with respect to reducing ASIHR, a quantity is used namely Performance of Vortex Generator (PVG). The calculated PVG values are less than 15% to over 35% which confirm the satisfactory effects of VGs on heat exchanger performance.