Impact attenuation of customized user-centered bicycle helmet design

Bicycle helmets are currently available to cater to general head sizes, ranging from S/M and L/XL, but there is also a universal model that can fit all sizes through adjustable helmet strap. Numerous surveys addressed that wearing helmet is not comfortable and the current sizing did not accommodate various range of users, because the human head shapes and dimensions are different according to ethnic groups, age and gender. This paper describes impact attenuation of user-centred design approach, i.e by modifying the shape of the liner to improve fit of bicycle helmet in accordance to AS/NZS 2063:2008. Head scans of 15 participants from a selected control group were captured using Artec3D portable scanner, while bicycle helmets and J headform were scanned using Flexscan 3D scanning equipment. These participants were selected based on a grouping method referring to selected 37 landmarks on human head shape. A new headform for the control group was developed by aligning and combining all the involved head scans in Geomagic Studio 12. Several new helmets with different liner thickness were designed based on the new headform. A validated drop impact simulation model, developed using Abaqus FEA software, was used to conduct drop impact simulation of each customized helmet design. Thickness of each user-centred helmet models at 37 landmarks was also recorded and the peak linear acceleration (PLA) of the helmet at impact locations such as top, side and front area were measured. Results revealed that the PLA increases as the thickness of helmet liner decreases. The rate of increase of PLA as the helmet liner thickness decreases is different at each impact location; it was greater at front and side location compared to top impact location.