Biomimetism of Brazil nutshell (Bertholletia excelsa)
Resumen
For thousands of years, nature has accumulated countless possibilities for optimized
solutions to engineering problems using limited raw material, room temperature,
aqueous solutions, solar energy and renewable resources. Recently,
this natural accumulated knowledge has increasingly being studied and applied
to solve technical problems in studies of biomimicry and bioinspiration.One from
many examples are the fruit walls of nuts and drupes which are of special interest
for the development of impact and puncture resistant bioinspired structures. This
project aims to identify and apply the principles responsible for the excellent mechanical
properties of Brazil’s nutshell (Bertholletia excelsa) to develop polymeric
composites with superior toughness and mechanical resistance. Firstly, the hierarchical
levels of organization of the nutshell structure were identified through
chemical analysis, optical microscopy, scanning electron microscopy (SEM) and
microtomography (MicroCT). Additionally, the mechanical properties of the nutshell
were evaluated in tensile, compression, hardness, and fracture toughness
tests, at different length-scales. Moreover, the analysis of fractured surface was
carried out by optical microscopy, SEM and MicroCT, identifying the fracture and
toughness mechanisms developed by Brazil’s nutshell. Finally, the principles responsible
for Brazil’s nutshell mechanical performance were applied to optimize
the mechanical performance of a bioinspired polymeric composite. The developed
composite is composed of a 3D printed structure of polylactic acid reinforced
with 30% of carbon fiber (PLA-30CF) which was impregnated with syntactic foam
(epoxy resin and hollow glass microspheres). The mechanical performance of the
bioinspired composite is promising. It has density of 0.96 g/cm3, flexural elastic
modulus of 2.52 GPa, and impact strength of 1.8 kJ/m2. However, adjustments
and improvements in the syntactic foam are still required.
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