JEC COMPOSITES MAGAZINE - Special Issue Composites for Sports, Health & Leisure - November 2020 - 53

Future of sprinting: spikeless CFRTP sprinting shoe

Key benefits of the innovation
-	 Revolutionary spikeless structure designed for efficient power transmission
-	 Randomly-oriented ultra-thin CFRTP tapes
-	 New CFRTP material providing the finest detailed mouldability and material
waste reduction
-	 Reduced production costs without sacrificing any mechanical property
-	 Well-balanced combination between light weight and bending stiffness

Benefits for sprinters
Sprinting shoes play an important
role for athletes to provide traction
and efficiently transmit their power
to the ground because they are the
only interface between the athlete and
the ground. Therefore, they need to
be lightweight while keeping an ideal bending stiffness distribution and
sufficient traction. In general, a sprinting shoe has several metal spike pins
on the bottom of the sole. However,
based on the available data and the
insights from various athletes, Asics
Corporation hypothesized that if the
penetration and pull-out behaviour
of spike pins were minimized, sprinting performance could be improved
because 1) when sprinting in spike
shoes, it may take too long to generate
sufficient traction by penetrating the
spike pins into the track surface, 2) the
traction generated by the penetration
of spike pins can be excessive, and
3) increasing traction without spike
pins can be possible by increasing the

contact area of the shoe sole with the
ground.
When developing the new sprinting shoe, the challenge was twofold.
The first challenge was to develop a
CFRTP spikeless sole structure. In
the prototyping process, all the metal
spike pins were replaced with a set of
hexagonal-shaped "gripper" elements
made of carbon fibre-reinforced
thermoplastics. It was impossible
to manufacture this complex structure with traditional sheet moulding
compounds (SMC) due to their lower flexibility. Thus, a CFRTP made
from randomly-oriented ultra-thin
UD tapes was used to reinforce the
"grippers" from base to top effectively.
The second challenge was to maintain
a good balance of light weight and
bending stiffness distribution for the
new sprinting shoe. Utilizing parametric design, computer simulations, and
3D printing technology, the CFRTP
was employed over the whole area of
the sole and the prototypes were engi-

Typical photograh of world-class athletes wearing the prototypes in competition

neered for the best balance of bending
stiffness distribution and lightweight
properties that current sprinting shoes
ever achieved.
Tested by world-class athletes
The spikeless sprinting shoe prototype was first introduced at the event
celebrating the 100th anniversary of
ASICS founder Kihachiro Onitsuka
on 15 May 2018. The current development stage is the product testing phase
by world-class athletes. Many athletes
have been wearing the prototypes of
the spikeless CFRTP sprinting shoe
at their trainings for several months,
and some of them already used the
prototypes at their races, including
the World Athletics Championships
2019 at Doha. The company is now
collecting wear-out, fatigue strength
and traction property data from the
wear tests, especially the traction
properties under various weather and
surface conditions as well as, most
importantly, feedback from the athletes regarding the perception of the
spikeless sprinting shoes. Thanks to
the unique preforming technology
for ultra-thin carbon-fibre chopped
tapes, the mouldability of this CFRTP
random sheet involves much less restrictions than typical SMC composites. This made it possible to flexibly
design the geometry and direction
of the "grippers" and to fabricate the
complex three-dimensional structure.
Additionally, the bending stiffness
distribution of the spikeless sprinting
shoe sole can be modified flexibly by
controlling the amount of CFRTP. As
the next step, combining the mechanical/performance data and the athletes'
feedback will be considered to make
the sprinting shoes even better and
further optimized for each athlete.
A growing market
The global sports shoes market was
valued at close to USD 19.0 billion in
2018 and is anticipated to witness significant growth in future. Many sports
shoe companies are focusing on the

SPECIAL ISSUE Sports, Health & Leisure / November 2020 /

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