Scientists at NTU Singapore are developing more resistant and safer bicycle helmets made from new plastic

PICTURE: (from LR) Research Associate Goram Gohel, Associate Professor Leong Kah Fai and Research Associate Dr. Bhudolia Somen Kumar from NTU’s School of Mechanical and Aerospace Engineering with her … view their more

Photo credit: NTU Singapore

As cities around the world expand their cycle path networks and more and more cyclists take to the streets, the likelihood of bicycle accidents and possible collisions increases, underscoring the need for adequate bicycle safety in densely populated urban areas.

According to a 2020 report by the World Health Organization, more than 60 percent of reported bicycle deaths and long-term disabilities are due to accidents involving head injuries.

Researchers at Nanyang Technological University, Singapore (NTU Singapore), in collaboration with the French market leader in specialty materials Arkema, have developed a more robust and safer bicycle helmet that uses a combination of materials. The new helmet prototype has a higher energy absorption, which reduces the amount of energy that is transferred to the cyclist’s head in the event of an accident and reduces the risk of serious injuries.

Under the direction of Associate Professor Leong Kah Fai of the School of Mechanical and Aerospace Engineering, the team consisting of research fellow Dr Art developed thermoplastic acrylic resin reinforced with carbon fiber.

The new thermoplastic resin called Elium® was developed by Arkema, one of NTU’s industrial partners. The NTU team worked with Arkema engineers to develop a molding process for Elium® to make stronger bicycle helmets.

“Our partnership with Arkema is driven by a desire to develop a new type of helmet that is stronger and safer for cyclists,” said Assoc Prof. Leong. “Helmets have proven time and again to play a vital role in reducing the severity of injuries and the death toll. Our prototype helmet has undergone a variety of internationally recognized tests and has shown that it offers better protection compared to cyclists . to conventional helmets. ”

The results of the research team were published in May in the journal Composites Part B: Engineering.

More robust, stiffer outer shell absorbs more energy

Bicycle helmets consist of two components. The first is an outer shell, usually made from a mass-produced plastic such as polycarbonate. Underneath is a layer of expanded polystyrene foam – the same material used in product packaging and takeaway boxes.

The outer shell is designed to tear on impact to dissipate energy across the entire surface of the helmet. The foam layer then compresses and absorbs most of the impact energy, so less energy is transferred to the head.

The team’s composite helmet replaces the conventional outer shell made of polycarbonate with one made of carbon fiber-reinforced Elium®.

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

These properties enable the outer shell to absorb more impact energy over a longer period of time and at the same time to release it evenly through the helmet. This results in less force being applied to the head, reducing the risk of critical injury.

“When the helmet hits a surface at high speed, we have found that along with the scattering failure of the composite shell, there is a deformation, which means that the outer shell is taking more load and absorbing more energy,” said Dr. Somen. “That’s what you really want – the more impact the shell absorbs, the less the foam gets into the foam, and therefore the overall impact on the head is less. We found that with existing polycarbonate helmets, around 75 percent 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 percent of the impact energy, so the foam absorbed much less energy at around 35 percent.

Security forged on NTU’s anvils

Researchers tested their helmets by lowering them at high speed on three different types of anvils – flat, hemispherical (rounded), and curbs (pyramidal) – to simulate different road conditions.

These are the same tests used to certify the US Consumer Product Safety Commission (CPSC 1203), an internationally recognized safety standard for helmets. The team’s helmet prototype meets all CPSC 1203 guidelines.

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

In two flat anvil tests, the researchers’ helmets scored eye-to-eye with a polycarbonate control helmet and returned results of 194.7 G and 197.2 G versus 195.4 G and 198.2 G of the control.

However, tests on the hemispherical and curb anvils showed significant improvements in the team’s composite helmet over the polycarbonate helmet. In two hemispherical anvil tests, the composite helmet recorded 100.9 G and 103.1 G, while the control helmet had much higher peak acceleration of 173 G and 178.7 G.

In a single curb anvil test, the researchers’ helmets recorded 111.7 G, a remarkable improvement over the reference helmet, which returned a result of 128.7 G.

The researchers referenced the most widely used injury metric called the Head Injury Criterion (HIC) to calculate the likelihood of serious injuries and deaths while wearing the helmet. HIC values ​​are derived from a combination of peak acceleration values ​​and the acceleration duration.

The team’s analysis of the flat anvil and HIC test results showed that the composite helmet potentially reduced the critical and fatal injury rate from 28.7 percent and 6 percent to 16.7 percent and 3 percent, respectively, when compared to a polycarbonate helmet could lower.

Although the peak acceleration was roughly the same for both types of helmets, the harder outer shell of the composite helmet resulted in a longer acceleration time on impact. This allows the outer shell to absorb more energy, creating a lower HIC, which means less risk of critical and fatal injuries.

More efficient manufacturing could lead to cheaper, more resilient helmets

The prototype helmet is also easier to manufacture than a conventional helmet. The use of Elium® instead of other conventional thermoplastics simplifies the manufacturing process for composite helmets.

Elium® is liquid at ambient temperature, so it can be molded at room temperature, unlike other thermoplastic composite shells that require processing at higher temperatures.

The NTU researchers are working with Arkema to commercialize the helmet manufacturing process that would allow interested manufacturers to produce it. Assoc Professor Leong says helmets made using this method offer the same protection as current top-of-the-range helmets, but potentially at the price of mid-range helmets ($ 100 to $ 150).

The researchers are currently working on the development of composite helmets made from Elium® and polypropylene fabric, another thermoplastic. This is to overcome the only current compromise in composite helmets, which is that they weigh about 20 percent more than polycarbonate helmets.

Elium® and polypropylene fabric helmets may make them as light as polycarbonate helmets but offer better protection.

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The team’s research is supported by the Singapore Agency for Science, Technology and Research (A * STAR) as part of the nationwide Research Innovation Enterprise 2020 plan.

Notes to the editors:

Paper entitled “Development and Impact Characterization of Acrylic Thermoplastic Composite Bicycle Helmet Shells with Improved Safety and Performance”, published in Composites Part B: Engineering, May 25, 2021. DOI: 10.1016 / j.compositesb.2021.109008

Watch the NTU YouTube video about the investigation: https://www.youtube.com/watch?v=2hWTgrbDM3w

Media contact:

Mr. Lester Hio

Manager, media relations

Corporate communications office

Nanyang Technological University, Singapore

Email: [email protected]

About Nanyang Technological University, Singapore

Nanyang Technological University, Singapore (NTU Singapore), is a research-intensive public university with 33,000 undergraduate and graduate students in engineering, business, natural sciences, humanities, arts and social sciences, and graduate schools. It also has a medical school, the Lee Kong Chian School of Medicine, which was co-founded with Imperial College London.

The NTU is also home to world-class autonomous institutes – the National Institute of Education, the S Rajaratnam School of International Studies, the Earth Observatory of Singapore, and the Singapore Center for Environmental Life Sciences Engineering – and various leading research centers such as the Nanyang Environment & Water Research Institute ( NEWRI) and Energy Research Institute @ NTU (ERI @ N).

Counted among the best universities in the world by QS, the NTU has also been the best young university in the world for seven years. Often listed in the top 15 most beautiful university campuses in the world, the main university campus has 57 Green Mark (equivalent to LEED) certified construction projects, 95% of which are Green Mark Platinum certified. In addition to the main campus, NTU also has a campus in Singapore’s health district.

As part of the NTU Smart Campus vision, the university leverages the power of digital technologies and technology-enabled solutions to support better learning and life experiences, the discovery of new knowledge, and the sustainability of resources.

Further information is available at http://www.ntu.edu.sg

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