Functionally graded porous structures: Analyses, performances, and applications - A Review

Structural innovation incorporating bio-inspired composites poses a fresh angle to develop novel lightweight forms with strengthened mechanical properties, among which a must-discuss topic is porous structures. The introduction of internal pores mimics the natural bones or timbers, makes the density a designable parameter, and opens a new world for researchers and engineers who have been obsessed in a variety of porous structural forms with desired aspects. One of the important trends is the development of functionally graded (FG) porous structures, where internal porosity gradations present significant potential to further enhance the already superior performances. This paper is aimed to review the recent research advances in this field by centring on the adopted mechanical analysis approaches, the obtained findings, and the application opportunities. We first elaborate on the general concepts of FG porous composites as well as the corresponding structural forms. The widely employed theoretical analysis method is subsequently looked at, touching on the nanofiller reinforcement and followed by the details and examples for numerical modelling and mechanical tests. The related artificial intelligence (AI) assisted calculations are also discussed. The fabrication techniques of FG porous specimens, e.g. additive manufacturing (AM), and the foam, lattice, and honeycomb based studies are strategically categorised. The later performance overview highlights the advantages originated from non-uniform cellular morphologies in the overall buckling, bending, vibration, and compressive energy absorption. Finally, the application perspectives in various sectors and future research directions are given. This synopsis enables the readers to grab the big picture of FG porous structures and possibly enlightens the path for future outlook in this scope.