Functionally graded materials (FGM) are composite materials formed of two or more constituent phases with a continuously variable distribution. The variations in the phase distribution may be reflected in their volume or weight fraction, orientation, and shape. In the majority of studies of FGM in engineering, the authors aim to achieve their goals with only one of these factors, the volume fraction being a typical variable. The variation of the phase volume fractions may be exclusively through the thickness of the structure and/or in any other direction, such as in-surface coordinates of a plate or shell.