This thesis evaluates, by means of finite element methods the possible head injuries that
might occur during an EN 1078 standard impact setting, as well as the energy percentage
absorbed by the helmet in the same conditions.
In this thesis, the geometry of a commercially available bicycle helmet has been modelled
using CATIA. The helmet model geometry has then been meshed with quadrilateral and
hexahedral elements using Hypermesh software. The last step of the thesis was
performing helmeted head impact simulations using LS-DYNA software.
The impacts upon which this thesis is based on are the EN 1078 flat anvil and curbstone
anvil shock absorbing capacity tests, which are the EU standards for bicycle helmet safety
evaluations. To validate the results, a comparison between the resultant acceleration and
impact time between this study and previous studies was made. The EN 1078 flat anvil
test has been validated and the set-up for the EN 1078 curbstone anvil test has been
deemed correct. The acceleration results deemed the helmet safe by the EN 1078 standard.
The head injury criteria assessed for the EN 1078 flat anvil test suggest 50% probability
of skull fracture and a 75% concussion probability. A HIC value of 970.2 was obtained,
indicating an 88% probability of moderate injury and 49% of serious injury. It was also
found that DAI injuries are in the threshold of reaching a 50% probability of occurrence.
The head injury criteria assessed for the EN 1078 curbstone anvil test indicates a 50%
probability of concussion. A HIC value of 224.2 was obtained, which associates to 7%
probability of moderate injury and 3% of serious injury. It was also found that DAI
injuries are 11.1 kPa away from the 50% probability threshold.
Regarding the additional tests made, the following results were obtained: the PU Foam
has little effect on the absorption properties of the helmet and its main use is rider comfort.
The importance of the modeling the straps in the simulation is demonstrated, since they
keep the head attached to the helmet at all times. Depending on impact speed the helmet
can absorb up to 50% of the impact energy. It is proposed that bicycle helmets must be
mandatory for all people regardless of age, since the effectiveness of the helmet has also
been demonstrated at low impact speeds. An analysis made to the different densities of
the EPS Foams showed that in order to achieve a more distributed impact, with a low HIC
value and low maximum acceleration it is recommended to use an EPS Foam with a larger
density. Curves of injury probability against impact speed were developed showing that
minor injuries start to happen at 10 km/h, severe at 15 Km/h and the most extreme injuries
at 20 Km/h. The critical value for untreatable damage in the impact is 29.4 Km/h. Even
though the effectiveness of the helmet has been proven in this study, it has also been
found that at high speeds the cyclist can suffer untreatable damage; therefore, new
research on helmets and cyclist safety is required to increase the likelihood of survival.
It is proposed to lower the bicycle speed limits to 20 km/h in city shared pathways, and
to limit the speed of electric bikes to reach a maximum of 20 km/h without rider input to
keep extreme injury modes within reasonable values in the worst-case-scenario impact.Ingeniería Mecánic
