In materials science functionally graded material (FGM) may be characterized by the variation in composition and structure gradually over volume, resulting in corresponding changes in the properties of the material. The materials can be designed for specific function and applications. Various approaches based on the bulk (particulate processing), perform processing, layer processing and melt processing are used to fabricate the functionally graded materials. The concept of FGM was first considered in Japan in 1984 during a space plane project. Where a combination of materials used would serve the purpose of a thermal barrier capable of withstanding a surface temperature of 2000 K and a temperature gradient of 1000 k across a 10 mm section. In recent years this concept has become more popular in Europe, particularly in Germany. A transregional collaborative research center (SFB Transregio) is funded since 2006 in order to exploit the potential of grading monomaterials, such as steel, aluminum and polypropylene, by using thermo mechanically coupled manufacturing processes. The basic structural units of FGMs are elements or material ingredients represented by maxel. The term maxel was introduced in 2005 by Rajeev Dwivedi and Radovan Kovacevic at Research Center for Advanced Manufacturing (RCAM). The attributes of maxel include the location and volume fraction of individual material components. A maxel is also used in the context of the additive manufacturing processes (such as stereo lithography, selective laser sintering, fused deposition modeling, etc.) to describe a physical voxel (a portmanteau of the words 'material' and 'voxel'), which defines the build resolution of either a rapid prototyping or rapid manufacturing process, or the resolution of a design produced by such fabrication means.
Fig 1.1 Fabrication of FGM
Types of Graded Structures
Stepwise Graded Structures
A stepwise graded structure is one which is formed by changing its composition from a refractory ceramic to a metal.
Continuous Graded Structures
Continuous Graded Structures is formed by its change in porosity and composition. An example is the human bone which .Change in porosity happens across the bone because of miniature blood vessels inside the bone.
Fig 1.2 (a) Continuous gradient of human bones Fig1.2 (b)
Advantages & Challenges of FGM’s
Provide ability to control deformation, dynamic response, wear, corrosion, etc. and ability to design for different complex environments. Provide ability to remove stress concentrations.
Provide opportunities to take the benefits (pros) of different material systems [e.g. ceramics and metals such as resistance to oxidation (rust), toughness, machinability, and bonding capability] 1.3.2
Challenges of FGMs
Areas of Application
Some of the applications of functionally graded materials are highlighted below:
Functionally graded materials can withstand very high thermal gradient, this makes it suitable for use in structures and space plane body, rocket engine component etc. If processing technique is improved, FGM are promising and can be used in wider areas of aerospace.
Living tissues like bones and teeth are characterized as functionally graded material from nature, to replace these tissues, a compatible material is needed that will serve the purpose of the original bio-tissue. The ideal candidate for this application is functionally graded material. FGM has find wide range of application in dental and orthopaedic applications for teeth and bone replacement.
One of the most important characteristics of functionally graded material is the ability to inhibit crack propagation. This property makes it useful in defence application, as a penetration resistant...
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