نشریه مهندسی مکانیک ایران
سال هجدهم شماره 3 (پیاپی 44، پاییز 1395)

During the operation, the turbine blades of hot gas path suffer service induced degradation due to ýdifferent causes such as creep, fatigue, oxidation, corrosion and etc. The present study was carried ýout the effect of long-term service at the high temperature exposure to remaining life assessment gas ýturbine blade made of Inconel 792 nickel base superalloy. That is investigated by studying on ýmicrostructure by optical and scanning electron microscopy, mechanical properties such as high ýtemperature tensile and stress-rupture test and stress analyses of turbine blade. The result has been ýshown the gamma prime rafting and TCP phase formation has occurred at the microstructure. ýBecause of long-term service at high temperature, stress- rupture properties of blade reduced and ýý20% lower than new IN 792 alloys. The stress analyses with ANSYS software and creep life ýassessment results by use Larson-miller parameter, the safety factor of blade lower than 1 and life ýtime of turbine blade is finished.ý

In this paper, buckling and free vibration analysis of cylindrical panel reinforced by various distributions of carbon nanotubes (CNTs) on elastic foundation for two cases including uniform distributed (UD) and functionally graded (FG) is studied. Based on the first order shear deformation theory (FSDT), the equilibrium equations of cylindrical panel reinforced by CNTs are derived using energy method and Hamilton’s principle. Then, using Navier’s type solution, the governing equations of equilibrium for cylindrical panel reinforced by various distributions of CNTs are solved. Using the mixture rule, the material properties of cylindrical panel reinforced by CNTs are estimated. In this study, the effects of volume fraction, various distributions of CNTs, elastic foundation parameters on the critical buckling load and natural frequency of cylindrical panel reinforced with CNTs are investigated. The obtained results of this research indicate that the trend of increasing natural frequency leads to increase in the percentage of CNTs and elastic modulus parameters which the maximum natural frequency occurs for FG-X case. Also increasing the percentage of CNTs and elastic modulus parameters leads to increase the critical buckling load which the maximum and minimum values of this load take place for FG-X and FG-O, respectively. On the other hands, it can conclude that with suitable selecting of CNTs distributions and volume fraction, the stiffness of structures increases and then the critical buckling load and natural frequencies enhance. Thus this point is noticeable to design the optimum of structures at nanoscale.

In this paper, analyses of several finite cracks in bonded materials with a graded interfacial zone were studied. The distributed dislocation technique is used to carry out stress analysis for two elastic half planes bonded through a non-homogeneous interfacial zone under anti-plane loading. The solution is obtained by means of Fourier transform method. The stress components reveal the familiar Cauchy singularity at the location of dislocation. Finally several examples are solved and the numerical results for the stress intensity factor are obtained. The influences of the geometric parameters, the thickness of the functionally graded strip and the crack size have significant effects on the stress intensity factors of crack tips which are displayed graphically.

In recent years, Shape Memory Alloys have found a lot of interest among researchers and engineers. Material properties of SMA's change with temperature and stress. Also due to large strains that may occure in them, geometrical nonlinearities encountered in the analysis of SMA structures. These material and geometrical nonlinearities make difficulties in the analysis of SMA structures. In this thesis a numerical model based on the differential quadrature's method (DQM) is presented for the buckling analysis of circular cylindrical shells made of SMA material.

The present paper investigates vibration analysis of a functionally graded square plate integrated with two functionally graded piezoelectric layers as sensor or actuator resting on the elastic Visco-Pasternak foundation. All the mechanical and electrical properties except Poisson’s ratio can vary continuously and gradually along the thickness of the plate based on a power function. Electric potential was assumed as a quadratic function along the thickness direction and trigonometric function along the planar coordinate. Short circuited boundary conditions are considered on the top and bottom of functionally graded piezoelectric layers. The general constitutive relations in electromechanical systems are used for considering the effect of all mechanical and visco-Pasternak foundation parameters. These parameters are including the non-homogeneous indexes of core and piezoelectric layers, direct, shear and damping parameters of foundation. The obtained results present the effect of various mechanical and foundation parameters on the vibration responses of the system. The functionalities of two considered layers and core can be regarded independently and the effect of these indexes can be considered on the responses. The obtained results indicate that with increasing the non-homogeneous index of core and layers, the natural frequencies of the system decreases.