  Bamboo has a functionally-graded microstructure that endows it with a
combination of desirable properties, such as high failure strain, high
toughness, and a low density. As a result, bamboo has been widely used in
load-bearing structures. In this work, we study the use of bamboo-inspired void
patterns to geometrically improve the failure properties of structures made
from brittle polymers. We perform finite element analysis and experiments on
3D-printed structures to quantify the effect of the shape and spatial
distribution of voids on the fracture behavior. The introduction of periodic,
uniformly distributed voids in notched bend specimens leads to a 15-fold
increase in the work of fracture relative to solid specimens. Adding a gradient
to the pattern of voids leads to a cumulative 55-fold improvement in the work
of fracture. Mechanistically, the individual voids result in crack blunting,
which suppresses crack initiation, while neighboring voids redistribute
stresses throughout the sample to enable large deformation before failure. In
addition, we conduct qualitative, low-energy impact experiments on PMMA plates
with laser-cut void patterns, illustrating the broader potential for this
strategy to improve damage tolerance and energy absorption in a wide range of
materials systems.
