Repercussions of quasi-isotropic behavior emerging in FGMs obtained via FAST/SPS

The increasing use of functionally graded materials (FGMs) has propounded their careful consideration for high performance engineering applications. This interest has been largely nurturing challenging applications and prospects in various scientific and technological fields due to the increasing number of available fabrication processes. Among all, field assisted sintering technology (FAST), also known as spark plasma sintering (SPS), has been demonstrated as an efficient method for their throughput fabrication. In this regard, understanding the properties of these advanced sintered materials is critical to serve as the baseline for their development and optimization. Recently, a few peculiar experimental correlations of FGMs to their monolithic equivalents, when exclusively obtained by FAST/SPS, have been documented in the literature. In particular, a moderate anisotropic behavior of sintered samples is observed, though the existing gradient structure due to the spatial variation of volume fraction of reinforcing particles. This paper primarily aims to establish a theoretical criterion by taking advantage of the claimed moderate anisotropy of FGMs and provide a quantitative assessment tool for their effective elastic properties. Repercussions are stated, theoretically formulated, discussed and validated with reference to a set of experimental measures. • FGMs are shown to behave peculiarly when obtained by FAST/SPS. • A quasi-isotropic behavior is surprisingly observed. • Theoretical repercussions are illustrated to predict effective elastic properties of FGMs. • The resulting criterion is validated against recent experimental measures.