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Tarlochan2012-FGMs.pdf
ISSN: 2168-9873
Journal of Applied Mechanical Engineering
The International Open Access
Journal of Applied Mechanical Engineering
Executive Editors
Ping Zhang
Indiana University, USA
Chuan-Chiang Chen California State Polytechnic University, USA
Krzysztof J Kubiak
University of Leeds, UK
Manosh C Paul
University of Glasgow, UK
Zhou Yufeng
Nanyang Technological University, Singapore
Available online at: OMICS Publishing Group (www.omicsonline.org)
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Digital Object Identifier: http://dx.doi.org/10.4172/2168-9873.1000e115
Tarlochan, J Appl Mech Eng 2012, 1:5
http://dx.doi.org/10.4172/2168-9873.1000e115
Applied Mechanical
Engineering
Editorial
Open Access
Functionally Graded Material: A New Breed of Engineered Material
Faris Tarlochan*
College of Engineering, Universiti Tenaga Nasional, Kajang, Selangor, 43009, Malaysia
Introduction and History of FGM
Materials have always been a crucial part of humans from the time
the first man was created. As time progressed, so did the enhancement
of technology and knowledge. Man started to engineer their own
materials from existing raw materials. These engineered materials go
back to 1000 BC in the form of composites of straw and mud. These
composite improved over time and in the last four decades, the world
was introduced with more sophisticated composites such as fiber
reinforced plastics. However due to the limitations of delamination in
such composites materials, another breed of composite material has
given birth in the form of Functionally Graded Material (FGM). FGM
is not new to us. Our nature is surrounded with FGMs. For example,
the bone, human skin and the bamboo tree are all different forms of
FGM. These breed of materials are the advanced materials in the family
of engineering composites made of two or more constituent phases
with continuous and smoothly varying composition [1]. FGMs are
engineered based on different gradients of composition in the preferred
material axis orientation. Due to this flexibility, FGMs are superior to
homogeneous material composed of similar constituents.
Applications of FGM
So where do FGM fit in? FGMs have good potential as a substitute
material where the operating conditions are severe. Examples includes
coatings, heat exchanger tubes, flywheels, biomedical implants and
turbine blades, no name a few. Usually coatings are just a layer sprayed
over the substrate. Overtime due to severe operating conditions and
abrupt transition of material properties from the coating to the substrate,
high interlaminar stresses will exist, causing the spray to be worn or
peeled off from the substrate. These sudden abrupt changes can be
overcome by smooth spatial grading of the material constituents [2,3].
FGM is also findings its way into new applications such as nuclear fuel
pellets, plasma wall of nuclear reactor, rocket space frame components,
artificial bones, dentistry, artificial skins, building materials, sport
goods, thermoelectric generators, optical fibers and lenses [4].
Effective Material Properties for FGM
In principle FGMs are fabricated by continuously fusing two
discrete phases of materials together for an example, a distinct mixture
of ceramic and metal. To estimate the effective material properties
via shape and distribution of particles may be a challenging task. The
effective properties such as elastic modulus, shear modulus, density, etc.
can be evaluated or estimated only on the volume fraction distribution.
Several models have been developed over the years to calculate the
effective properties of macroscopically homogeneous graded materials.
Some of these models are the self estimates models [5-7], Mori-Tanaka
method [8,9], the simplified strength of material method [10,11], and
the micromechanics model [12,13]. The micromechanics model is
perhaps the most accurate method, since the microstructure under
consideration is directly modeled via three-dimensional finite elements.
It is very important to assume the FGMs as heterogeneous material.
To be able to understand the smooth changing of the material properties
with respect to the spatial coordinates, the FGM has to undergo
some homogenization schemes. The material properties are generally
J Appl Mech Eng
ISSN:2168-9873 JAME, an open access journal
assumed to follow gradation through the thickness in a continuous
manner. In the literature, the most commonly used analytical models
are the exponential law and power law [14].
Research Studies and Future works on FGM
In the literature, there has been a lot of research work that has been
done on the analysis of FGM; in particular FGM subjected to thermo
elastic conditions, vibration and stability issues. Most of these works
focus on 2D models. There is a need to develop 3D models to understand
the out of plane response due to thermo-mechanical loadings. There is
also a need to use higher order theories combined with non local stress
analysis. In general, FGM holds a good potential in many applications.
Research work should now slowly progress beyond the elastic limit,
especially in the understanding of crack propagation due to fatigue.
Modelling would not be sufficient here. It has to be supported with
substantive experimental work.
References
1. Koizumi M (1993) The concept of FGM. Ceram Trans Funct Grad Mater 34:
3-10.
2. Finot M, Suresh S (1996) Small and large deformation of thick and thin-film
multilayers: effect of layer geometry, plasticity and compositional gradients. J
Mech Phys Solids 44: 683-721.
3. Krell T, Schulz U, Peters M, Kaysser WA (1999) Graded EB-PVD alumina–
zirconia thermal barrier coatings-an experimental approach. Mater Sci Forum
311: 396-401.
4. Miyamoto Y, Kaysser WA, Rabin BH, Kawasaki A, Ford RG (1999) Functionally
graded materials: design, processing, and applications. Kluwer Academic
Publications, USA.
5. Hill R (1965) A self-consistent mechanics of composite materials. J Mech Phys
Solids 13: 213-222.
6. Hashin Z (1968) Assessment of the self consistent scheme approximation:
conductivity of Particulate composites. J Compos Mater 4: 284-300.
7. Bhaskar K, Varadan TK (2001) The Contradicting Assumptions of Zero
Transverse Normal Stress and Strain in the Thin Plate Theory: A Justification.
J Appl Mech 68: 660-662.
8. Mori T, Tanaka T (1973) Average stress in matrix and average elastic energy of
materials with misfitting inclusions. Acta Metall Mater 21: 571-574.
9. Benveniste Y (1987) A new approach to the application of Mori–Tanaka’s theory
in composite materials. Mech Mater 6: 147-57.
10.Chamis CC, Sendeckyj GP (1968) Critique on theories predicting thermoelastic
properties of fibrous composites. J Compos Mater 2: 332-358.
*Corresponding author: College of Engineering, Universiti Tenaga Nasional,
Kajang, Selangor, 43009, Malaysia, E-mail: [email protected]
Received November 20, 2012; Accepted November 22, 2012; Published
November 24, 2012
Citation: Tarlochan F (2012) Functionally Graded Material: A New Breed of
Engineered Material. J Appl Mech Eng 1:e115. doi:10.4172/2168-9873.1000e115
Copyright: © 2012 Tarlochan F. This is an open-access article distributed under
the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and
source are credited.
Volume 1 • Issue 5 • 1000e115
Citation: Tarlochan F (2012) Functionally Graded Material: A New Breed of Engineered Material. J Appl Mech Eng 1:e115. doi:10.4172/21689873.1000e115
Page 2 of 2
11.Gibson RF (1994) Principles of composite material mechanics. CRC Press,
USA.
12.Reiter T, Dvorak GJ, Tvergaard V (1997) Micromechanical models for graded
composite materials. J Mech Phys Solids 45: 1281-302.
13.Charnis CC, Caruso JJ, (1986) Assessment of simplified composite
micromechanics using three dimensional finite element analysis. J Compos
Tech Res 8: 77-83.
14. Suresh S, Mortensen A (1998) Fundamentals of functionally graded materials.
(1st edn), UK.
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J Appl Mech Eng
ISSN:2168-9873, an open access journal
Volume 1 • Issue 5 • 1000e115
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