Hot section gas turbine implements are subjected to fluctuating stresses and temperatures within aggressive environments. It results in combined fatigue, creep and oxidation of constituent materials. Studies of different types of high temperature fatigue of nickel base superalloys help us to understand the causes of failure and expectations for the prediction of life. Generally nickel base superalloys are used in the form of single crystal, directionally solidified, powder metallurgy products, and polycrystalline cast/wrought alloys for different applications. The high temperature properties of these various forms make interesting usage within different high temperature and aggressive environments under stressed conditions. Gas turbines of either aerospace, electricity or diesel engine sectors are the consumers of these alloys. Thermal profiles of gas turbines are zones of interest for application. Considerations of lightweight philosophies to the implements reduce the section thickness. Therefore evaluation of fatigue for these alloys under stipulation of simulation bears more attention. Creep interposition into fatigue theories has become the basis of interpretation. Experiences to date belong to empiricism, where the formulations require introduction of many suitable variables according to the system of exposure. Application of thermal barrier coatings improves the performances of previous designs. Key failure areas of thermal barrier coatings are thermally grown oxide growth and ceramic coat sinter induced buckling and spallations. These coatings in practice appear in the form of thick, thin, and duplex, laser surface re-melted, functionally gradient materials, and microlaminations. The composite system of materials evaluation corresponds to the requirement of fatigue experiments for life prediction. The objective is to study the comparative behavior of nickel base superalloys under different conditions of fatigue and the influence of the thermal barrier coating (TBC). Different typesof fatigue mechanisms experimentally simulate components exposed to services because the variable for interrelation of the physical-thermal-chemical-mechanical phenomenon that prevails in such systems appears to be deficient. been made in the past two intervening decades in the understanding of the physical mechanisms of fatigue in Ni-base superalloys. This will be the subject of concern in the present paper; a systematic approach has been made to disentangle the separate combinations of different types of fatigue leading to fracture particularly in Ni-base superalloys.
The first-order shear deformation theory (FSDT) was used to explore the natural frequency response of functionally graded piezoelectric plates subjected to static electrical and mechanical strain in this present study. A monomorph model for a functionally graded piezoelectric plate with material properties that change according to sigmoid law with respect to plate thickness has been considered. A three-dimensional finite element model with a free tetrahedral element mesh was created using COMSOL 4.2 Multiphysics® software, with each node having three degrees of freedom. Variations in the FGPM plate's free vibration boundary conditions, composition, and geometry have all been investigated. In free vibration analysis, non-dimensional natural frequency of FGPM plate initially decreasing considerably and then remaining almost constant with the increase in volume fraction index when material property graded by power law. When material properties are varied by sigmoid law, with an increase in volume fraction index, the non-dimensional natural frequency of FGPM plates remains virtually constant. FGPM plates have a lower non-dimensional natural frequency if the thickness to width ratio is greater. Non-dimensional natural frequencies of Clamped-Clamped FGPM plates (C-C-C-C) are greater compared to Clamped-Free FGPM (C-F-C-F) and Simply Supported Free FGPM (S-F-S-F).
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