Scientists develop tougher, safer bicycle helmets using new plastic
material

Date:
July 22, 2021
Source:
Nanyang Technological University
Summary:
Researchers have developed a tougher, safer bicycle helmet using
a combination of materials. The new helmet prototype has higher
energy absorption, reducing the amount of energy transferred to
a cyclist's head in the event of an accident and likely lowering
the chances of serious injury.



FULL STORY ==========================================================================
As cities worldwide expand their networks of cycling paths and more
cyclists take to the streets, the chances of cycling accidents and
potential collisions increase as well, underscoring the need for proper
cycling safety in dense urban areas.


========================================================================== According to a World Health Organisation report in 2020, more than 60 per
cent of the reported bicycle-related deaths and long-term disabilities
are a result of accidents with head injuries.

Researchers from Nanyang Technological University, Singapore (NTU
Singapore), in collaboration with French specialty materials leader
Arkema, have developed a tougher, safer bicycle helmet using a combination
of materials. The new helmet prototype has higher energy absorption,
reducing the amount of energy transferred to a cyclist's head in the
event of an accident and lowering the chances of serious injury.

Led by Associate Professor Leong Kah Fai from the School of Mechanical
and Aerospace Engineering, the team, comprising research fellow Dr
Bhudolia Somen Kumar, research associate Goram Gohel and MSc student
Elisetty Shanmuga, created the composite helmet with an outer shell made primarily of a new type of acrylic thermoplastic resin, reinforced with
carbon fibre.

The new thermoplastic resin, named Elium(R), was developed by Arkema, one
of NTU's industry partners. The NTU team worked with Arkema engineers
to develop a moulding process for Elium(R) to manufacture stronger
bicycle helmets.

"Our partnership with Arkema is driven by the desire to develop a new type
of helmet that is stronger and safer for cyclists," said Assoc Prof Leong.

"Helmets have been proven time and time again to play a critical role in reducing the severity of injuries and number of fatalities. Our prototype helmet has been subjected to a barrage of internationally benchmarked
tests and has demonstrated the ability to provide greater protection
for cyclists compared to conventional helmets." The findings by the
research team were published in the peer-reviewed journal Composites
Part B: Engineering in May.



========================================================================== Tougher, stiffer outer shell absorbs more energy Bicycle helmets are
made up of two components. The first is an outer shell, usually made
from a mass-produced plastic like polycarbonate. Beneath it is a layer of expanded polystyrene foam -- the same material used in product packaging
and takeaway boxes.

The outer shell is designed to crack on impact in order to dissipate
energy across the entire surface of the helmet. The foam layer then
compresses and absorbs the bulk of impact energy so that less energy is transferred to the head.

The team's composite helmet replaces the conventional polycarbonate
outer shell with one using Elium(R) reinforced with carbon fibre.

This reinforcement makes the outer shell tougher, stiffer, and less
brittle than a polycarbonate shell. It also increases the helmet's contact time, which is the total time of impact in which the helmet experiences
impact load.



========================================================================== These properties allow the outer shell to absorb more impact energy
over a longer period, while also dissipating it evenly throughout the
helmet. This results in less overall force reaching the head, thereby
reducing the chances of critical injury.

"When the helmet hits a surface at high speed, we noticed that there is a deformation along with the spread failure of the composite shell, which
means the outer shell is taking more load and absorbing more energy,"
said Dr Somen.

"This is what you really want -- the more impact absorbed by the shell,
the less of it that reaches the foam, and so there is less overall impact
to the head. We found that in existing polycarbonate helmets, about
75 per cent of the energy is absorbed by the foam. This is not ideal
as the foam is in direct contact with the human head." In contrast,
the team's composite helmet shell absorbed over 50 per cent of impact
energy, leaving the foam to absorb much less energy at about 35 per cent.

Safety forged on the anvils of NTU The researchers tested their helmets
by driving them down at high speeds on three different types of anvils
-- flat, hemispherical (rounded), and curbstone (pyramid-shaped) --
to simulate different road conditions.

These are the same tests used for the U.S. Consumer Product Safety
Commission standard (CPSC 1203) certification, an internationally
recognised safety standard for helmets. The team's helmet prototype
meets all CPSC 1203 guidelines.

The researchers paid particular attention to peak acceleration forces,
which is a measure of how much force a helmet takes based on how fast it
is moving at the point of impact. A helmet must have a peak acceleration
of less than 300G (g-force) to be deemed fit for use under CPSC 1203,
with lower g-force values being safer.

On two flat anvil tests, the researchers' helmets performed on par with
a control polycarbonate helmet, producing results of 194.7G and 197.2G
to the control's 195.4G and 198.2G.

However, tests on the hemispherical and curbstone anvils showed
substantial improvements of the team's composite helmet over the
polycarbonate one. On two hemispherical anvil tests, the composite helmet recorded 100.9G and 103.1G, while the control helmet had a much higher
peak acceleration of 173G and 178.7G.

On a single curbstone anvil test, the researchers' helmets recorded
111.7G, a notable improvement over the reference helmet that produced
a result of 128.7G.

The researchers referred to the most widely used injury metric called
the Head Injury Criterion (HIC) to calculate the probability of serious
injury and fatality while using the helmet. HIC values are derived from a combination of peak acceleration values and the duration of acceleration.

The team's analysis of the flat anvil test results and the HIC showed
that the composite helmet could potentially reduce critical and fatal
injury rates from 28.7 per cent and 6 per cent to 16.7 per cent and 3
per cent respectively, compared to a polycarbonate helmet.

Even though peak acceleration was roughly equal between both types
of helmets, the composite helmet's tougher outer shell led to longer
duration of acceleration during impact. This allows the outer shell to
absorb more energy, therefore generating a lower HIC which means a lower
chance of critical and fatal injuries.

More efficient manufacturing could lead to cheaper, tougher helmets The prototype helmet is also easier to produce than a conventional helmet.

Using Elium(R) instead of other conventional thermoplastics simplifies
the composite helmet manufacturing process.

Elium(R) is liquid at ambient temperature, allowing it to be moulded
at room temperature as opposed to other thermoplastic-based composite
shells that require higher temperature processing.

The NTU researchers are working with Arkema to commercialise the helmet's manufacturing process, which would allow interested manufacturers to
produce them. Assoc Prof Leong says that helmets produced through their
method would offer the same protection of current top-tier helmets,
but potentially at the price of mid-tier helmets ($100-$150).

The researchers are currently working on developing composite helmets
made from Elium(R) and polypropylene fabric, which is another type
of thermoplastic. This is to overcome the composite helmet's one
current trade-off which is that they weigh about 20 per cent more than polycarbonate helmets.

Helmets made from Elium(R) and polypropylene fabric will potentially
make them just as light as polycarbonate ones but offer better protection.

========================================================================== Story Source: Materials provided by
Nanyang_Technological_University. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Goram Gohel, Somen K. Bhudolia, Shanmuga Bala Subramanyam Elisetty,
Kah
Fai Leong, Pierre Gerard. Development and impact characterization of
acrylic thermoplastic composite bicycle helmet shell with improved
safety and performance. Composites Part B: Engineering, 2021; 221:
109008 DOI: 10.1016/j.compositesb.2021.109008 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/07/210722112908.htm

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