Introduction
Structures made of functionally graded materials (FGMs) have
attracted tremendous attention from research and engineering
communities due to their unique advantages offered by smooth
and continuously graded distribution of material composition
along one or more directions. Numerous studies have been conducted
on FGM beams, plates and shells in the past few decades.
One of the latest developments in FGMs is structures with graded
porosity which introduces pores into the microstructure to meet
the desired structural performance by tailoring the local density
of the structure. This represents an important opportunity in a
wide range of engineering applications. For example, the graded
metal foam offers unique potential for lightweight structures in
aerospace, automotive and civil engineering [1–12]. The excellent
energy-absorbing capability of porous FGMs also makes them the
perfect candidates for structures under dynamic or impact loading
[13–15]. Despite of its practical importance, research in this
emerging area is only at the beginning stage and is very limited
with most of the previous studies devoted to the compression