  In recent years, new flexible functional materials have attracted increasing
interest, but there is a lack of the designing mechanisms of flexibility design
with superstructures. In traditional engineering mechanics, the maximum bending
strain (MBS) was considered universal for describing the bendable properties of
a given material, leading to the universal designing method of lowering the
dimension such as thin membranes designed flexible functional materials.In this
work, the MBS was found only applicable for materials with uniformly
distributed Poisson's ratio, while the MBS increases with the thickness of the
given material in case there is a variation Poisson's ratio in different areas.
This means the MBS can be enhanced by certain Poisson's ratio design in the
future to achieve better flexibility of thick materials. Here, the inorganic
freestanding nanofiber membranes, which have a nonconstant Poisson's ratio
response on stress/strain for creating nonuniformly distributed Poisson's ratio
were proven applicable for designing larger MBS and lower Young's modulus for
thicker samples.
