Introduction to Functionally Graded Materials

Modern efforts to develop new materials for applications related to: biomedical devices/prosthetics; metallurgy; solar panels; sensors; aerospace transport and ceramics require a metric to measure quality as a means of controlling performance specifications.  Spatial defects in the chemical composition or physical properties of a material volume will result in variability in the performance of said material. To compensate for this issue, industrial coatings are developed to generate a homogeneous surface with the goal of minimizing potential failure locations. This concept is the fundamental reasoning behind systematic efforts to characterize and define specifications for functionally graded materials (FGM).Of particular interest to this author is the development of novel materials that are designed to mimic fundamental processes in nature. The utility of nature’s solutions to appease the architectural muse is omnipresent in modern science. The FGM motif pulls from descriptive observations like the hardness of a seashell or the tensile strength of bamboo. When developing new materials, practical engineering considerations of the manufacturing process (e.g. blending or mixing techniques, machine temperatures etc.) are optimized to produce a product that can mimic these properties.

For commercial applications, the current challenge is the development of reproducible methods that can provide production scale throughput on a cost effective platform. In the laboratory, FGM are characterized by well reported microscopy methods to determine structural morphology. Performance tests vary depending on the intended application but may include differential measurements by a variety of spectrophotometric and electrochemical devices. Description of analytical methods could be found in textbooks on the subject of corrosion and failure analysis. Performance specifications of interest may include: temperature threshold; elasticity; conductivity; resistance to environmental degradation).  Thermal characterization methods (e.g. differential scanning calorimetry) may be applied to polymer materials.

The origins of the FGM concept have been traced to Japan but have since generated global interest. Active research for this topic includes joint efforts by industrial, government and academic collaboration. Funding for research in this field has been provided by a number of agencies including the National Institute for Standards and Technology (NIST) and National Science Foundation (NSF). Current research into the development of FGM has incorporated an automated nonlinear mathematics approach via software development and simulation. It is anticipated that the reduction of offline/manual heuristic efforts would reduce costs associated with sourcing chemical reagents and generating waste. For further information, readers of this work are directed to the current literature of academic journals. There are currently a number of textbooks related to this topic in press.