SAMPE Journal - March/April 2023 - 19

representative NCF-FH9 sample show extensive
matrix damage diffusion and a lower extent of fiber
failure compared to NCF-FQI (see Figure 3). This
has resulted in NCF-FH9 achieving a 21% increase
in perforation energy compared to NCF-FQI (see
Figure 4a). Note that both the NCF conventional
QI laminates in NFRP and GFRP performed better
under LVI than their counterpart manufactured
via prepreg and autoclave. This is related to the
microstructural change between the use of a UD
thin-ply tape and the NCF fabric with higher ply
thickness. In fact, the lower ply thickness results
in an embrittlement of the composite due to the
ability of thin-ply materials of inhibiting matrix
micro-cracking and, in turn, delamination. Under
impact, this leads to premature fiber failure and
overall lower impact performance23,24
.
CONCLUSIONS
We investigated the use of Helicoid technology
to improve impact performance of conventional
NFRP and GFRP QI laminates and their hybrids.
We conducted LVI tests on samples manufactured
using prepreg and autoclave for both GFRPs, NFRPs
and their hybrids. LVI tests show that, compared to
monolithic conventional QI NFRP, Helicoid NFRP
achieves a simultaneous increase in:
*peak load - 21%;
*delay of catastrophic failure - 69%;
*energy dissipated before catastrophic failure
- 104%; and
*perforation energy - 43%.
Compared to monolithic conventional QI
GFRP, Helicoid GFRP can lead to a simultaneous
increase in:
*peak load - 32%;
*delay of catastrophic failure - 73%;
*energy dissipated before catastrophic failure
- 145%; and
*total dissipated energy - 48%.
Helicoid applied to hybrid GFRP/NFRP
laminates shows a continuous increase in
performance over monolithic Helicoid NFRPs with
an increasing GFRP content. Furthermore, at equal
hybrid content, the Helicoid hybrid laminates
consistently outperformed the conventional
QI hybrid laminates. Specifically, compared to
monolithic GFRP QI laminates, it is shown that by
hybridizing a Helicoid NFRP laminate with 50%
by mass of GFRP, it is possible to achieve a similar
peak load while also a simultaneous increase in:
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*delay of catastrophic failure - 60%;
*energy dissipated before catastrophic failure
- 105%; and
*total dissipated energy - 32%.
We conducted LVI tests on NCF samples
manufactured via VA-RTM. LVI tests show that,
compared to monolithic conventional QI NFRP,
Helicoid NFRP achieves a simultaneous increase
in:
*peak load - 14%;
*delay of catastrophic failure - 38%;
*energy dissipated before catastrophic failure
- 74%; and
*perforation energy - 21%.
The performance improvement achieved via
Helicoid fiber architectures is related to the ability
of Helicoid laminates to delay the occurrence of
fiber failure. This is achieved via activating subcritical
diffused matrix damage that allows to
dissipate energy while preserving the structural
integrity and load-bearing capability of the
composite. On the contrary, the brittle behavior
of conventional QI laminates results in localized
damage, characterized by extensive fiber failure.
We have demonstrated the potential of
leveraging Helicoid fiber architectures to enable
a more extensive use of low carbon footprint
materials such as natural fiber composites (NFRP)
in high performance, load-bearing applications.
This
aims at providing an avenue for new
applications and market opportunities currently
not accessible to NFRPs due to the inherent
lower performance compared to the high carbonfootprint
counterparts (namely, carbon fiber and
glass fiber). We have shown how the Helicoid
technology can be tailored to greatly enhance the
mechanical performance and damage resistance
to out-of-plane loads of conventional NFRP and
GFRP QI laminates and their hybrids using two
different
manufacturing
processes
suitable
to
both high-end, low-rate manufacturing (prepreg
and autoclave) and high-rate, high-volume
manufacturing (NCF and VA-RTM). In future work,
we will further explore NCF GFRP/NFRP Helicoid
hybrids and the effect of different hybridization
strategies (e.g., blocked plies instead of dispersed
plies).
MARCH APRIL 2023
|
SAMPE JOURNAL |
19
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SAMPE Journal - March/April 2023

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