SAMPE Journal - March/April 2023 - 12

FEATURE / HELICOID FIBER ARCHITECTURES
Figure 1. Photograph of creatures featuring Helicoid microstructures (mantis shrimp, scarabaei,
beetle and lobster); SEM of a coronal corss section of an impacted mantis shrimp dactyl club; and a
schematic of Helicoid layup sequence.
architectures with NFRPs offers the opportunity to
deliver performance improvement independently
of the raw material adopted.
Biomimicry is an effective way to greatly increase
performance of composite structures starting from
constituents with relatively low performance, if
taken individually. This is achieved by designing
the microstructure of the resulting composite
aiming at activating a wide range of failure
mechanisms, including crack arrest, fiber pullout,
crack deflection, subcritical crack diffusion.
These allow a structure to dissipate energy while
preserving its structural integrity, hence leading
to solutions with outstanding damage tolerance9
.
By leveraging on the microstructural design
rather than on specific material constituents,
several bioinspired strategies can be applied to
improve a wide range of FRPs, including NFRPs.
Helicoidally arranged laminated structures are
particularly recurring in natural microstructures
to withstand impact (out-of-plane loading). These
can be found on the highly mineralized club of
the
mantis
shrimp (odontodactylus
scyllarus)
as well as in the exoskeleton of other creatures
including, lobster, beetles and scarabei9
. Helicoid
architectures are characterized by plies of parallel
fibers laid up to result in stacking sequences
with helicoidal distribution of fiber orientations.
This results in highly multidirectional laminates
where large interplay angles (>30°) conventionally
used in composite engineering are replaced by
smoother transitions in ply orientation. Such
fiber arrangement results in reduced interlaminar
stresses at the ply interface and the activation of
complex, tortuous fracture patterns dominated
by matrix damage10-15
. This mechanism delays
fiber failure and it allows to dissipate energy while
preserving structural integrity.
While Helicoid architectures have proven
successful in enhancing the impact resistance of
several FRPs9,16, including monolithic NFRPs17
, a
direct performance comparison of Helicoid NFRPs
against conventional GFRPs is still missing. This
is key to understanding the potential of Helicoid
NFRPs to replace high-carbon footprint materials
for high volume transport solutions. Furthermore,
the combined effect of Helicoid architectures and
fiber hybridization remain unexplored.
To this end, we designed, manufactured, and
tested under low velocity impact several Helicoid
NFRP laminates, GFRP laminates and their
hybrids to measure the energy required to achieve
perforation of such components. For the first time
in the published literature:
*Helicoid NFRP laminates are designed,
manufactured, and tested against GFRP
Helicoid and conventional QI laminates;
*Helicoid NFRP laminates are designed,
manufactured, and tested using NonCrimped
Fabrics (NCF) and vacuum assisted
resin transfer molding (VA-RTM) to test the
performance for high-volume and high-rate
manufacturing applications; and
*Helicoid hybrid NFRP/GFRP laminates
are designed, manufactured, and tested to
identify optimal laminate design strategies to
maximize impact performance.
MATERIALS AND METHODS
Materials and Manufacturing Methods
The NFRP laminates were made using flax fiber
and epoxy resin. For the prepreg and autoclave
processing we used a pre-impregnated (prepreg)
material made of unidirectional flax fibers and
epoxy resin, FLAXPREG-T-UD-110 provided by
Eco-Technilin. The prepreg consists of 50% flax
fibre and 50% Huntsman XB3515 epoxy resin by
mass, resulting in an area density of 220 g/m2
the NCF and infusion process, we used AmpliTex
. For
12 | SAMPE JOURNAL | MARCH APRIL 2023
www. sampe.org

http://www.sampe.org

SAMPE Journal - March/April 2023

Table of Contents for the Digital Edition of SAMPE Journal - March/April 2023