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Advances in Functionally Graded Materials

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Advanced Composites".

Deadline for manuscript submissions: closed (31 October 2011) | Viewed by 42553

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Prof. Dr. Zengtao Chen

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Department of Mechanical Engineering, University of Alberta, Edmonton, AB T6G 1H9, Canada
Interests: characterization of materials; micromechanics modelling; finite element modelling; functionally graded materials; smart materials and structures; composite materials; multifield behaviour; manufacturing engineering; structural integrity; thermoelasticity; electromagnetic materials
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Dear Colleagues,

New metallurgy techniques make it possible to devise material structures. Particularly, material properties can be designed to vary continuously along structural geometry to prevent delamination and stress concentration in traditional multilayered structures. This will make so called functionally graded materials. Although they were first invented to be utilized as a thermal shield to sustain very high temperature gradients in thin structures, Functionally graded materials are currently being used for many other applications such as wear-resistant linings, heat exchanger tubes, thermoelectric generators, heat-engine components, and in some prostheses. In recent years, materials scientists are developing sophisticated methodologies to fabricate new functionally graded materials for emerging applications, while mechanical engineers and mechanicians are investigating the physical behaviour of these materials to push the application boundary of these materials. Functionally graded materials have been used in microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) under multiple physical fields such as electromagnetic fields, high frequency vibrations, and thermal shocks.

This special issue of Materials will focus on recent advances in functionally graded materials. Realizing the importance of integration of the research efforts in materials science and mechanical engineering to the further development of functionally graded materials, the objective of this issue is to provide a platform for materials scientists and mechanical engineers to share their research ideas and showcase their achievements in the general area of functionally graded materials.

Prof. Dr. Zengtao Chen
Guest Editor

Keywords

functionally graded materials
smart materials and structures
micro-constituents
composite materials
multifield behavior
manufacturing engineering
structural integrity
thermoelasticity
piezoelectricity
electromagnetic materials

Published Papers (7 papers)

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Research

158 KiB

Open AccessArticle

Exact Solution of a Constraint Optimization Problem for the Thermoelectric Figure of Merit

by Wolfgang Seifert and Volker Pluschke

Materials 2012, 5(3), 528-539; https://doi.org/10.3390/ma5030528 - 21 Mar 2012

Cited by 3 | Viewed by 5269

Abstract

In the classical theory of thermoelectricity, the performance integrals for a fully self-compatible material depend on the dimensionless figure of merit zT. Usually these integrals are evaluated for constraints z = const. and zT = const., respectively. In this paper we discuss the question from a mathematical point of view whether there is an optimal temperature characteristics of the figure of merit. We solve this isoperimetric variational problem for the best envelope of a family of curves z(T)T. Full article

(This article belongs to the Special Issue Advances in Functionally Graded Materials)

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330 KiB

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Stresses and Displacements in Functionally Graded Materials of Semi-Infinite Extent Induced by Rectangular Loadings

by Hong-Tian Xiao and Zhong-Qi Yue

Materials 2012, 5(2), 210-226; https://doi.org/10.3390/ma5020210 - 30 Jan 2012

Cited by 9 | Viewed by 5983

Abstract

This paper presents the stress and displacement fields in a functionally graded material (FGM) caused by a load. The FGM is a graded material of Si₃N₄-based ceramics and is assumed to be of semi-infinite extent. The load is a distributed loading over a rectangular area that is parallel to the external surface of the FGM and either on its external surface or within its interior space. The point-load analytical solutions or so-called Yue’s solutions are used for the numerical integration over the distributed loaded area. The loaded area is discretized into 200 small equal-sized rectangular elements. The numerical integration is carried out with the regular Gaussian quadrature. Weak and strong singular integrations encountered when the field points are located on the loaded plane, are resolved with the classical methods in boundary element analysis. The numerical integration results have high accuracy. Full article

(This article belongs to the Special Issue Advances in Functionally Graded Materials)

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543 KiB

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Generalized Fractional Derivative Anisotropic Viscoelastic Characterization

by Harry H. Hilton

Materials 2012, 5(1), 169-191; https://doi.org/10.3390/ma5010169 - 18 Jan 2012

Cited by 21 | Viewed by 6384

Abstract

Isotropic linear and nonlinear fractional derivative constitutive relations are formulated and examined in terms of many parameter generalized Kelvin models and are analytically extended to cover general anisotropic homogeneous or non-homogeneous as well as functionally graded viscoelastic material behavior. Equivalent integral constitutive relations, which are computationally more powerful, are derived from fractional differential ones and the associated anisotropic temperature-moisture-degree-of-cure shift functions and reduced times are established. Approximate Fourier transform inversions for fractional derivative relations are formulated and their accuracy is evaluated. The efficacy of integer and fractional derivative constitutive relations is compared and the preferential use of either characterization in analyzing isotropic and anisotropic real materials must be examined on a case-by-case basis. Approximate protocols for curve fitting analytical fractional derivative results to experimental data are formulated and evaluated. Full article

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459 KiB

Open AccessArticle

Novel Concept to Detect an Optimum Thixoforming Condition of Al-Al₃Ni Functionally Graded Material by Wavelet Analysis for Online Operation

by Noriyoshi Kumazawa, Yasuyoshi Fukui and Daisaku Nara

Materials 2011, 4(12), 2183-2196; https://doi.org/10.3390/ma4122183 - 14 Dec 2011

Cited by 2 | Viewed by 5650

Abstract

A novel technique to characterize the transition phenomenon from solid to melt of Al-Al₃Ni functionally graded material (FGM) through a wavelet analysis for the development of a thixoforming system is investigated. Identification of an optimum semi-solid condition for thixoforming is necessary not only for the construction of a system but also the fabrication of a near-net-shape product with fine microstructure. An online wavelet analysis system using Haar’s wavelet function, which is applied for its simplicity compared with Daubechies’ wavelet function, is developed to find the optimum operating condition. A thixoforming system, which is constructed adapting a threshold value as an index, monitors successfully a discontinuity of deformation of Al-Al₃Ni FGM with the temperature rise. Thus, the timing of an operation is not at pre-fixed temperature but at the time when the index related to a wavelet function is satisfied. The concept is confirmed to be suitable from the micro-structural observation of the Al-Al₃Ni FGM product, because the product under the optimum condition is found to have refined Al₃Ni grains, which change from coarse grains and are expected to improve the mechanical properties. Full article

(This article belongs to the Special Issue Advances in Functionally Graded Materials)

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501 KiB

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Thermo-Electro-Mechanical Analysis of a Curved Functionally Graded Piezoelectric Actuator with Sandwich Structure

by Zhi Yan, Mostafa Zaman and Liying Jiang

Materials 2011, 4(12), 2151-2170; https://doi.org/10.3390/ma4122151 - 12 Dec 2011

Cited by 14 | Viewed by 6855

Abstract

In this work, the problem of a curved functionally graded piezoelectric (FGP) actuator with sandwich structure under electrical and thermal loads is investigated. The middle layer in the sandwich structure is functionally graded with the piezoelectric coefficient g₃₁ varying continuously along the radial direction of the curved actuator. Based on the theory of linear piezoelectricity, analytical solutions are obtained by using Airy stress function to examine the effects of material gradient and heat conduction on the performance of the curved actuator. It is found that the material gradient and thermal load have significant influence on the electroelastic fields and the mechanical response of the curved FGP actuator. Without the sacrifice of actuation deflection, smaller internal stresses are generated by using the sandwich actuator with functionally graded piezoelectric layer instead of the conventional bimorph actuator. This work is very helpful for the design and application of curved piezoelectric actuators under thermal environment. Full article

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332 KiB

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Transient Thermal Stress Problem of a Functionally Graded Magneto-Electro-Thermoelastic Hollow Sphere

by Yoshihiro Ootao and Masayuki Ishihara

Materials 2011, 4(12), 2136-2150; https://doi.org/10.3390/ma4122136 - 12 Dec 2011

Cited by 11 | Viewed by 6112

Abstract

This article is concerned with the theoretical analysis of the functionally graded magneto-electro-thermoelastic hollow sphere due to uniform surface heating. We analyze the transient thermoelastic problem for a functionally graded hollow sphere constructed of the spherical isotropic and linear magneto-electro-thermoelastic materials using a laminated composite mode as one of theoretical approximation in the spherically symmetric state. As an illustration, we carry out numerical calculations for a functionally graded hollow sphere constructed of piezoelectric and magnetostrictive materials and examine the behaviors in the transient state. The effects of the nonhomogeneity of material on the stresses, electric potential, and magnetic potential are investigated. Full article

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318 KiB

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Heat Conduction in a Functionally Graded Plate Subjected to Finite Cooling/Heating Rates: An Asymptotic Solution

by Zhihe Jin

Materials 2011, 4(12), 2108-2118; https://doi.org/10.3390/ma4122108 - 08 Dec 2011

Cited by 4 | Viewed by 5290

Abstract

This work investigates transient heat conduction in a functionally graded plate (FGM plate) subjected to gradual cooling/heating at its boundaries. The thermal properties of the FGM are assumed to be continuous and piecewise differentiable functions of the coordinate in the plate thickness direction. A linear ramp function describes the cooling/heating rates at the plate boundaries. A multi-layered material model and Laplace transform are employed to obtain the transformed temperatures at the interfaces between the layers. An asymptotic analysis and an integration technique are then used to obtain a closed form asymptotic solution of the temperature field in the FGM plate for short times. The thermal stress intensity factor (TSIF) for an edge crack in the FGM plate calculated based on the asymptotic temperature solution shows that the asymptotic solution can capture the peak TSIFs under the finite cooling rate conditions. Full article

(This article belongs to the Special Issue Advances in Functionally Graded Materials)

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