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Volume 8, Number 4, December 2019

Flexoelectric effect has a major role on mechanical responses of piezoelectric materials when their dimensions become submicron. Applying differential quadrature (DQ) method, the present article studies dynamic characteristics of a small scale beam made of piezoelectric material considering flexoelectric effect. In order to capture scale-dependency of such piezoelectric beams, nonlocal elasticity theory is utilized and also surface effects are included for better structural modeling. Governing equations have been derived by utilizing Hamilton's rule with the assumption that the scale-dependent beam is subjected to thermal environment leading to uniform temperature variation across the thickness. Obtained results based on DQ method are in good agreement with previous data on pizo-flexoelectric beams. Finally, it would be indicated that dynamic response characteristics and vibration frequencies of the nano-size beam depends on the existence of flexoelectric influence and the magnitude of scale factors.

Key Words
flexoelectricity; flexoelectric effect; response; piezoelectric; wave; beam

(1) Laith A. Hassan Kunbar, Nadhim M. Faleh:
Al-Mustansiriah University, Engineering Collage P.O. Box 46049, Bab-Muadum, Baghdad 10001, Iraq;
(2) Basim Mohamed Alkadhimi:
Wasit University, College of Engineering, Electrical Engineering Department, Iraq;
(3) Hussein Sultan Radhi:
University of Diyala, College of Engineering, Computer Engineering Department, Iraq.

The engine parts material used in gas turbines (GTs) should be resistant to high-temperature variations. Thermal barrier coatings (TBCs) for gas turbine blades are found to have a significant effect on prolonging the life cycle of turbine blades by providing additional heat resistance. This work is to study the performance of TBCs on the high-temperature environment of the turbine blades. It is understood that this coating will increase the lifecycles of blade parts and decrease maintainence and repair costs. Experiments were performed on the gas turbine blade to see the effect of TBCs in different combinations of materials through the air plasma method. Three-layered coatings using materials INCONEL 718 as base coating, NiCoCrAIY as middle coating, and La2Ce2O7 as the top coating was applied. Finite element analysis was performed using a two-dimensional method to optimize the suitable formulation of coatings on the blade. Temperature distributions for different combinations of coatings layers with different materials and thickness were studied. Additionally, three-dimensional thermal stress analysis was performed on the blade with a commercial code. Results on the effect of TBCs shows a significant improvement in thermal resistance compared to the uncoated gas turbine blade.

Key Words
materials; turbine blade; coatings; thermal analysis; finite element method; plasma spray

(1) Abdul Aabid, Jalal Mohammed Zayan, Sher Afghan Khan:
Department of Mechanical Engineering, Faculty of Engineering, International Islamic University Malaysia, P.O. Box No. 10, 50728, Kuala Lumpur, Malaysia;
(2) Jyothi:
Department of Aeronautical Engineering, Faculty of Engineering and Technology, Khaja Bandanawaz University, Rauza-I Buzurg, Kalaburagi (Gulbarga), 585104, Karnataka, India.

In this study, a three-dimensional Finite Element Model has been developed to estimate the size of the weakened zone in a bi-material a ceramic bonded to metal. The calculations results were compared to those obtained using Scanning Electron Microscope (SEM). In the case of elastic-plastic behaviour of the structure, it has been shown that the simulation results are coherent with the experimental findings. This indicates that Finite Element modeling allows an accurate prediction and estimation of the weakening effect of residual stresses on the bonding interface of Alumina. The obtained results show us that the three-dimensional numerical simulation used by the Finite Element Method, allows a good prediction of the weakened zone extent of a ceramic, which is bonded with a metal.

Key Words
bi-materials (ceramic/metal); damage; stress intensity factor; J integral; prediction

Department Faculty of Technology, LMPM, Mechanical Engineering, University of Sidi Bel Abbes, Algeria.

The objective of the present paper is to investigate the bending and free vibration behavior of functionally graded material (FGM) sandwich rectangular plates using an efficient and simple higher order shear deformation theory. Unlike other theories, there are only four unknown functions involved, as compared to five in other shear deformation theories. The most interesting feature of this theory is that it does not require the shear correction factor. Two common types of FGM sandwich plates are considered, namely, the sandwich with the FGM facesheet and the homogeneous core and the sandwich with the homogeneous facesheet and the FGM core. The equation of motion for the FGM sandwich plates is obtained based on Hamilton's principle. The closed form solutions are obtained by using the Navier technique. A static and free vibration frequency is given for different material properties. The accuracy of the present solutions is verified by comparing the obtained results with the existing solutions.

Key Words
sandwich; bending; free vibration; functionally graded plate; navier solution

(1) Nafissa Zouatnia:
Department of Mechanical Engineering, University of Tiaret, BP 78 Zaaroura, Tiaret, 14000, Algeria;
(2) Nafissa Zouatnia:
Laboratory of Structures, Geotechnics and Risks (LSGR), Hassiba Benbouali University of Chlef, BP 151, Hay Essalam, UHB Chlef, Chlef, 02000, Algeria;
(3) Lazreg Hadji:
Laboratory of Geomatics and Sustainable Development, University of Tiaret, 14000, Algeria;
(4) Lazreg Hadji:
Department of Mechanical Engineering, University of Tiaret, BP 78 Zaaroura, Tiaret, 14000, Algeria.

Shape Memory Polymer Composites (SMPC) have gained popularity over the last few decades due to its flexible shape memory behaviour over wide range of strains and temperatures. In this paper, non-linear bending analysis has been carried out for SMPC beam under the application of uniformly distributed transverse load (UDL). Simplified C0 continuity Finite Element Method (FEM) based on Higher Order Shear Deformation Theory (HSDT) has been adopted for flexural analysis of SMPC. The numerical solutions are obtained by iterative Newton Raphson method. Material properties of SMPC with Shape Memory Polymer (SMP) as matrix and carbon fibre as reinforcements, have been calculated by theory of volume averaging. Effect of temperature on SMPC has been evaluated for numerous parameters for instance number of layers, aspect ratio, boundary conditions, volume fraction of carbon fiber and laminate stacking orientation. Moreover, deflection profile over unit length and behavior of stresses across thickness are also presented to elaborate the effect of glass transition temperature (Tg). Present study provides detailed explanation on effect of different parameters on the bending of SMPC beam for large strain over a broad span of temperature from 273-373K, which encompasses glass transition region of SMPC.

Key Words
SMP; SMPC; HSDT; FEM; glass transition region

Mechanical Engineering Department, S.V. National Institute of Technology, Surat-395007, India.

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