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In this paper the creep behavior of a functionally graded (FG) rotating disc made of Aluminum 6061 and Silicon Carbide is investigated and the optimum volume fraction of FG disc and its profile has been obtained. For this purpose, the temperature gradiant along the disc radius is obtained by solving the govering heat transfer differential equation. All the thermal properties of the material are assumed to be the function of temperature and volume fraction. To obtain material properties, two models of Mori-Tanaka and Hashin-Schtrickman are used. To validate the results, they are compared with those given in the literature. Two solution methods: semi-analytical and closed form are employed and the results are compared. The optimum design is carried out with one, and multi-objective methods which are based on genetic algorithm. The objectives are increasing the factor of safety, reducing the weight of the disc and reducing the range between minimum and maximum safety factors. The design variables are percentage of volume fraction, the power of material distribution formula, and the thickness of the disc. The results show that two solution methods compare well. Also, it has been shown that high fraction of Silicon Carbide in the outer side the disc provide optimum results. Also, contradiction of the objectives is reviled, hence the results are presented as Pareto front.

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The forces due to the unbalance in a system cause undesired vibration and noise, and reduce the system life. One of the new and efficient methods used to reduce the unbalance is the use of automatic dynamic ball balancer. The automatic dynamic ball balancer is a typical passive balancer which doesn't need control systems to balance the rotor. Because these devices are used in the systems which have variable unbalance according to the operating conditions and the system may be switched on and off several times a day, therefore reducing the balancing time becomes a necessary task. In practice, the gyroscopic effect is created for several reasons, e.g. when the rotor is located offset from the shaft midspan. Previous studies have not determined the optimum values of the damping ratio and mass of balls of the automatic dynamic ball balancer under the gyroscopic effect. In this study, the effect of damping ratio and the mass of balls of the automatic dynamic ball balancer on the stability and balancing of the system under the gyroscopic effect have been investigated and, using the Nelder-Mead simplex algorithm, the optimum values of these parameters to minimize the time of balancing and converging the Euler angles to zero are obtained.

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In this paper a method has been developed to obtain an optimum material distribution for a cylindrical shell with Functionally Graded (FG) material and additional piezoelectric outer layer. The objective of the optimization is to satisfy full stress loading criterion. For this purpose; firstly, a solution method has been outlined in which, the governing equations are developrd by combining First order Shear Deformation Theory (FSDT) and Maxwell equations, with the use of Hamilton principle. Dynamic analysis is a major concern in this solution method because of the significant dynamic displacements, strains and stresses due to the effect of moving load. Hence, the time dependent transient responses of the structure and stress distribution have been obtained. At the next stage, a methodology has been introduced to obtain the optimum material distribution. In this method, instead of using pre-assumed material distribution functions which impose limitations to the manufacturing of the shell and also to the optimization solution, control points with Hermite functions are used. The thickness of the shell and volume fraction of the FG material at these points have been regarded as optimization variables. The optimization method is based on the genetic algorithm and to reduce the solution time, calculations are carried out using parallel processing in four cores. The results show that the developed method is capable of analyzing the FG structures and provide optimum solution. The major advantage of this method is its flexibility in providing volume fraction distribution of the material.

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Creep behavior of butt-welded joints in pressurized steel pipes operating at high temperature is one of the major concerns in industry. The creep behavior of 1.25Cr0.5Mo weldment has been investigated in this paper. Three different layers: Base Metal (BM), Heat Affected Zone (HAZ) and Weld Metal (WM) have been considered and the creep behavior of each layer has been modeled using constitutive equations. Constitutive parameters have been determined using the results of uniaxial constant load creep tests. A numerical approach based on least square method has been used to calculate optimum values of the constitutive parameters. The results have been compared with those provided in the literature for different alloys and good agreement has been observed. Creep tests have been carried out at 30, 35, 40 and 50 MPa and temperature levels of 670, 700, 725, 750 and 800 °C. Specimens have been machined out from Base and Weld Metal. Since machining specimens with appropriate size from HAZ is impossible, a method is proposed to obtain constitutive parameters for this layer. This method is validated by comparing the constitutive parameters which have been calculated for WM with those obtained using creep tests. Micrographical and microhardness tests show that there are significant differences in the microstructure of the layers. Consequently, the creep behavior of layers is different. The results show that steady state creep strain rate for WM is higher than the rates for BM and HAZ; also at low stress levels, creep strain rate of HAZ is larger than BM.