SAMPE Journal - March/April 2023 - 14

FEATURE / HELICOID FIBER ARCHITECTURES
infusion process. After infusion, compression
molding was used to consolidate the panels. The
pressure was increased to 4 bars (10mins) and held
for 1 hour, the pressure was then increased to 7
bar (10 mins) and held for 2 hours. Afterwards, the
pressure was decreased to atmospheric pressure
over 1 hour. The samples were subsequently kept
in the sealed vacuum bag for at least 8 hours before
demolding and cutting. An abrasive disc saw was
used to cut the laminates to shape (100 x 100
mm). The resulting flax specimens and glass fiber
specimens had an average ply thickness of 0.23
mm and 0.12 mm respectively.
The manufactured samples had an overall areal
weight of 0.87-0.92 g/cm2. The fiber volume fraction
was maintained in a range of 41% - 45% across
the different configurations and processing. We
manufactured up to 5 samples per configurations.
We designed one conventional QI for monolithic
GFRP and NFRP along with two Helicoid NFRP
and one Helicoid GFRP. Furthermore, we designed
four different types of hybrids in conventional
and Helicoid configurations with progressively
increasing percentage by mass of GFRP, including
21%, 30%, 50% and 74% of GFRP. For the NCF
laminates, we will report here only on the results
obtained for NCF-GFRP conventional QI, NCFNFRP
conventional QI and one NCF-NFRP
Helicoid. Manufacturing and testing of hybrid NCF
configurations is currently undergoing, and it will
not be included in this paper.
The design of the stacking sequence of
the Helicoid configurations aims at achieving
performance enhancement to out-of-plane loads.
The selection of the mismatch angle between
adjacent plies is driven by several microstructural
parameters including the interface/matrix strength
and toughness, and ply thickness8,12
. These are
selected aiming at the activation of complex failure
mechanisms characterized by highly diffused subcritical
matrix damage which consists of several
matrix cracks growing parallel to the local fiber
orientation. This generates twisting crack patterns
that dissipate energy through matrix damage,
hence delaying fiber failure9,16,18
. The hybrid
configurations are characterized by a variable
inter-ply angle. This design strategy was adopted
in order to 1) accommodate the various degree of
hybridization while obtaining the same structural
weight; and 2) to maximize the performance of the
laminate for compression stresses on the impact
side and tensile stresses on the back side15
.
Testing Methods: Low Velocity Impact (LVI)
We performed full-penetration LVI tests using a
custom-made test rig. Each specimen was simply
Table 2. Mean and max/min values (at full perforation) of the peak load, displacement at the peak
load, energy dissipation at the peak load along with perforation energy of LVI tests.
14 | 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