Fundamentals of Functionally Graded Materials PDF

Structure and Scope of this Monograph

We provide in what follows a review of research on functionally graded materials, with focus on materials which contain at least one metallic constituent phase, and which serve at least partly a structural function. Our goals in providing this review are several.

• First, by its very nature, research on functionally graded materials, and on the general concept of functional grading, is multi-disciplinary. This was well understood in Japan when the concept was formulated and launched; however, much current research on the theme lacks the vertical integration that is expected of the concept once it enters engineering practice. One goal of this review is therefore to present the essential fundamentals which could serve as a common basis for communication between researchers across disciplinary lines .

• Published literature on the subject gives (paradoxically for a topic centered on unification of hitherto separate activities) an overall impression of immense activity in many seemingly disparate directions, reported in a large number of highly specialised conference proceedings, journals, and other venues (journals focused on composites, on metallurgy, on ceramics, on biomaterials, on structural materials and on device materials, and journals devoted to the mechanics of structures, to micromechanics, to biomechanics, to energy conversion, to joining, to design, and of course the patent and commercial literature, all provide relevant publication venues for FGlvl research and products). We have, therefore, sought to categorise, synthesise and unify, wherever possible, the wide multiplicity of processing and mechanical analysis methods employed in this field of research activity .

• The third goal is to seek to extend, wherever feasible, the acceptance of functionally graded materials, by calling attention to the fact that, widely used in structural material systems such as steels, this approach is both very well established and extensively practiced. Even though some novel issues (of modulus gradients, for example) are absent even in widely used steels, it may be fruitful to incorporate such established methods (e.g., graded steel) in current research efforts on FGMs.

This monograph comprises two main chapters. Chapter 2 deals with the processing of FGMs, and provides coverage of processes by which functionally graded metallic and metal/ceramic materials are produced. In doing so, we provide, after a few general considerations, a classification of FGM processes into two broad families: (i) processes where the graded material is constructed spatially, layer by layer and according to essentially any pre-chosen distribution, and (ii) processes wherein natural transport phenomena, such as fluid flow, atomic diffusion, or heat conduction, are exploited towards the creation of macroscopic gradients in composition and microstructure. For each process class, different subclasses exist; these are reviewed in turn, with emphasis on issues and phenomena of particular interest for each. In Chapter 3, attention is devoted to thermal and mechanical analysis of FGM structures, with a particular emphasis on issues such as thermal stresses, processing-induced internal stresses, geometry changes during thermomechanical deformation, onset and spread of plasticity and other forms of damage, as well as failure, which are highly relevant to metal-containing FGM structures. We then address the strategies for suppressing or minimising the propensity for inelastic deformation, crack initiation and subcritical fracture, for enhancing resistance to tribological damage, and for eliminating the deleterious effects of stress concentrations at free surfaces and edges. In each of these subtopics, an attempt is made to review the various levels of modelling where the link between quantitative analysis and microstructural size scales can be captured. This discussion also seeks to confront experiment with theory, to describe established successes of the approach, and to highlight progress in the unification of materials design, processing and performance. A separate list of symbols for all the chapters is also provided.

Edited by: S. Suresh, A. Mortensen