Arhona Bhadra
Age: 13 | Waterloo, Ontario
Regional Award at Waterloo-Waterloo Science and Engineering Fair
INTRODUCTION
Helmets are considered to be one of the most important protective equipment with a wide scope of individual customizations to prevent fatal head injuries. In a motorcycle traffic accident, the force impacted on the head is several times more than the natural capacity of the skull-bone to bear the force, thus resulting in a skull fracture. Such accidents account for 9% of road deaths. But the use of helmets is found to have reduced the risk of deaths by 50% (Bosch, 2006). As mentioned by Gregory et al. (Luna, Copass, Oreskovich and Carrico, 1981), the types and severity of injuries caused by motorcycle accidents can be standardized according to the Injury Severity Score (ISS). At most four safety tests were designed to ensure the safety standards for motorcycle helmets by comparing the irrelative performance under identical and realistic test-conditions on a flat surface. These tests could be arranged in an increasing order of level of performance as – Department of Transport (DOT) FMVSS No. 218, Economic Commission for Europe (ECE) No. 22.05, the British Standards Institution 6658-1985 (BSI) Type A, and Snell (Thom, 2006).
The two basic safety-components of a motorcycle helmet are an outer-helmet shell and an inner- impact liner system (acts as the shock absorber). Although the thickness of both the layers has direct relation with the force-bearing capacity during an impact (Dera & Goupy, 1978), the thickness of the inner shock-absorber has been considered in this study as researchers find this layer to be more efficient for impact prevention. Mills et al. have mainly reported the importance of the lower shock- absorption layer (Mills & Gilchrist, 2006). Moreover, the study performed by Shuaeib et al. corroborates the fact that describes the shock absorption layer as a critical part of the helmet in order to ensure safety. The researchers mentioned that the use of Expanded Polypropylene (EPP) makes the shock absorption layer more protective (Shuaeib, Hamouda, Wong, Umar, & Ahmed, 2007). Even Fernandes et al. have emphasized on the relation between the shock- absorption layer and the force of impact (Fernandes, Alves de Sousa, Ptak, &Migueis, 2019). They have brought up test results that indicate that agglomerated cork liners could replace the synthetic ones in protective gear for improving its capacity to withstand multi-impacts. Their results showed that the significant protection level was achieved for the 40mm thick shock- absorption layer of the helmet. Based on the studies performed on the 3D-printed helmet, newer design concepts of helmets are also approached. The present work offers an opportunity to conceptualize the relation between the protection benefit of the helmet designed with optimally thick shock absorbing layer and the impact-force. The material for the helmet is purposefully not taken into consideration as it is beyond the scope of this study. In the backdrop of the above discussion, the present project is inspired to reveal an optimal thickness of the shock-absorbing layer. Using the latest trend in 3D printing technology, the customized dimension of helmet has been fabricated; to which a varying thickness of SAL was later incorporated.
The prepared 3D printed helmet was used as a prototype for the experiment as it can be shaped and sized as per requirement. The experiment conducted and the results recorded can be used to give people an idea of what thickness of shock-absorbing layer should be present in the helmet in order to protect the skull during a particular activity. So the problem can be stated as what the helmet (shock-absorbing layer) thickness should be to prevent skull fracture due to the force of impact during an accident.
HYPOTHESIS
If the thickness of the helmet SAL is increased, then only a higher force of impact can damage the skull because an optimally thick helmet protects the skull better.
MATERIALS AND METHODS
The materials required for this experiment constitute of a 3D-printed helmet having spherical shape of diameter 9 cm without its SAL as shown in Figure 1.
Figure 1: Helmet being constructed inside the Ultimaker 2+ 3D printer
In addition, the experiment required a few eggs, loads of varying mass from 42.5 g (1.5 oz) to 255 g (9 oz) and SALs made of PlayDoh manufactured by Hasbro Inc. of four thicknesses 0.2 cm (1st thickness), 0.4 cm (2nd thickness), 0.6 cm (3rd thickness) and 0.8 cm (4th thickness). Also the experiment required a ruler to take measurements, supports to hold the egg and helmet and the last but not the least, a notepad and a pen for recording the mass at which the egg breaks for each of the thicknesses of the SALs for 3 times as per sample size. The impact on an egg under the helmet without the SAL when mass of 42.5 g (1.5 oz) was dropped on the egg from the height of 1 ft can be considered as the control group of the experiment. The significant constants include: material type for the SAL of each size, amount of force for each of the iterations of the experiment (i.e. 3), dropping height (i.e. 1 ft), helmet dimensions, type of eggs, surface/platform to conduct the experiment.
The SAL of the 1st thickness was temporarily attached underneath the helmet. The helmet along with the SAL was placed on top of the egg with the help of supports as depicted in Figure 2. The experimental loads simulate the force of impact, and the eggs simulate the impact on the skull during an accident. Each of the selected loads was dropped, in increasing order of mass, on the set-up helmet from the height of 1 ft as depicted in Figure 3. Results were recorded for the corresponding SAL when a particular mass broke the egg. The tested SAL was then replaced with the thicker layer. The steps were repeated until results were recorded for each of the four SALs as described by the flowchart in Figure 4.
Figure 2: Experimental setup
Figure 3: Experimental process diagram
Figure 4: Experimental process flowchart
RESULTS
As per Iteration 1, the egg-breaking mass for SAL thickness of 0.2 cm was 85 g, 0.4 cm was 101 g, 0.6 cm was 119 g and 0.8 cm was 135 g. During Iteration 2, the egg-breaking mass for SAL thickness of 0.2 cm was 85 g, 0.4 cm was 103 g, 0.6 cm was 118 g and 0.8 cm was 136 g. Finally, for Iteration 3, the egg-breaking mass for SAL thickness of 0.2 cm was 85 g, 0.4 cm was 102 g, 0.6 cm was 120 g and 0.8 cm was 137 g. Therefore, the mean egg-breaking mass for the SAL thickness of 0.2 cm was 85 g, 0.4 cm was 102 g, 0.6 cm was 119 g and 0.8 cm was 136 g. The median calculated was egg-breaking mass of 85 g for SAL thickness of 0.2 cm, 102 g for 0.4 cm, 119 g for 0.6 cm and 136g for 0.8 cm. Only the SAL thickness of 0.2 cm had a mode which was 85 g. Thus, as the thickness of the shock absorbing layer increases, the mass at which the egg breaks also increases. So, there is a positive correlation between the thickness of the SAL and the mass at which the egg breaks. Moreover, the graph in Figure 5 depicts a linear pattern.
Table 1: Summary table for mass vs. SAL thickness data from dropping height of 1 ft
Figure 5: Graph for egg-breaking mass for each SAL thickness
DISCUSSION
Helmets have inbuilt SALs beneath the outer shell and a restraint system which fixes the helmet to the head as shown in Figure 6.
Figure 6: Various parts of a helmet
When there is an accident, the shock waves are generated by the impact force as demonstrated in Figure 7. In the left diagram, shock waves pass through the helmet outer shell without SAL and then through the skull and the brain during an impact whereas in the right diagram, shock waves are blocked by the helmet’s SAL. As it travels it dampens by dissipating energy into the SAL. On the other hand, if the person is not wearing a helmet or the helmet is not protective enough, then these shock waves lead to concussion or skull fracture.
According to the current outcomes shown in Table 1, helmet with SAL thickness of 0.8 cm could bear greater mass than a helmet with SAL thickness of 0.2 cm. This happened because the thicker the SAL was, the more shock waves could it absorb. That is why there was a positive correlation between the SAL thickness and the egg-breaking mass.
Figure 7: Shock waves passing through the helmet outer shell without shock-absorbing layer (Left); shock waves blocked by the helmet shock-absorbing layer (Right) during an impact
FUTURE WORK
Due to unavailability of suitable material, it was not possible to make shock-absorbing layers of more controllable size and so the experiment had to be completed with only four thicknesses. If such material (e.g. Plasticine) is available, we could instead find the required shock-absorbing layer thickness for each egg-breaking mass. Such an experiment would have wider application. Moreover, a helmet can be designed according to the use-case. For example, a bicycle rider might need a helmet which can bear the mass of 136 g dropped from a height of 1 ft. So (s)he could wear a helmet with the shock-absorbing layer thickness of 0.8 cm.
CONCLUSIONS
A shock-absorbing layer with a smaller thickness needs less mass (force of impact) to break the egg under the helmet compared to a shock-absorbing layer with more thickness. Therefore, the results show that the hypothesis was justified to be correct. These tests suggest that shock-absorbing layers have promising potential as a critical dissipating component in personal protective equipment.
ACKNOWLEDGEMENTS
Author is grateful to her Science teacher, Ms. H. Fowler, for her guidance and encouragement. Author also acknowledges her parents’ support to get access to the materials required for the project. Moreover, Kitchener Public Library, ON, Canada helped the author to build the prototype of the helmet, using Ultimaker 2+ 3DPrinter.
REFERENCES
Bosch, H. V. (2006). Crash helmet testing and design specifications: University Press Facilities, Eindhoven, The Netherlands.
Dera, A., & Goupy, M. (1978). Enveloping helmet of composite structure: Google Patents.
Fernandes, F. A., Alves de Sousa, R. J., Ptak, M., & Migueis, G. (2019). Helmet design based on the optimization of biocomposite energy-absorbing liners under multi-impact loading. Applied Sciences, 9(4), 735.
Friess, M., & Bradtmiller, B. (2003, June 17). 3D Head Models for Protective Helmet Development. Retrieved from https://www.sae.org/publications/technical- papers/ content/2003-01-2176/.
Luna, G. K., Copass, M. K., Oreskovich, M. R., & Carrico, C. J. (1981). The role of helmets in reducing head injuries from motorcycle accidents: a political or medical issue?. The Western journal of medicine, 135(2), 89–92.
Mills, N. J., & Gilchrist, A. (2006). Bicycle helmet design. Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications, 220(4), 167-180. doi:10.1243/14644207jmda100
Ngo, T. D., Kashani, A., Imbalzano, G., Nguyen, K. T., & Hui, D. (2018). Additive manufacturing (3D printing): A review of materials, methods, applications and challenges. Composites Part B: Engineering, 143, 172-196.
Shuaeib, F. M., Hamouda, A. M. S., Wong, S. V., Umar, R. S. R., & Ahmed, M. M. H. M. (2007). A new motorcycle helmet liner material: The finite element simulation and design of experiment optimization. Materials & Design, 28(1), 182-195. doi: https://doi.org/10.1016/j.matdes.2005.04.015
Thom, D. R. (2006). Comparison tests of motorcycle helmets qualified to international standards. Paper presented at the Proceedings of the 2006 International Motorcycle Safety Conference.
Arhona Bhadra
Arhona Bhadra is a Grade 8 student at Centennial Public School, Waterloo, ON, Canada. She is passionate about Science and Technology. She likes to learn new Computer programming languages. She is always curious in various natural phenomena and is enthusiastic in finding innovative solutions to real-life problems. She has ranked top in various Science and Mathematics contests like Science Olympiad, Mathematics Olympiad, Caribou Contest, ASSET Talent Search, etc. Her hobbies include music and painting. She believes in the popular quote by Victor Hugo “Nothing is more powerful than an idea whose time has come.”