The mechanical response of metal-ceramic functionally graded materials: models and experiences

Functionally graded materials are composites with gradually varying material content. Especially envisaged for applications as thermal, wear and corrosion barriers, they can be profitably produced by the coupling of metals, which confer ductility, with hard, chemically stable and thermally insulating but brittle ceramics. Metal-ceramic composites are usually assumed to be isotropic at the macroscopic scale. Classical homogenization rules are mostly used either to predict their constitutive parameters or to recover the actual component distribution, which is not always easily controlled by the production process. The overall mechanical response of these materials has been investigated mostly in the elastic range, but the growing interest on applications for extreme loading and environmental conditions has fostered the development of several constitutive models apt to interpret the relevant inelastic phenomena. Unfortunately, several theoretical proposals lack of an adequate experimental validation. This contribution is intended to review the most commonly considered material idealizations and to discuss their reliability at the light of available laboratory results.