The origin of the method

Limitations in the
current regulations

Current regulations test helmets in a straight line, i.e. perpendicular to the impact surface. Certimoov adds oblique impacts to its tests, which better reflects the real conditions of collision (e.g. impact on a road with a component of horizontal speed).
For European regulations, the criteria for the acceptance of a helmet is based on the translational acceleration registered with a rigid headform which does not faithfully represent the human brain and considers pass/fail criteria which is not particularly representative of the  impact tolerance limits of brain. Certimoov works with a more complex mathematical head model and considers brain injury criteria drawn from over hundred real world head trauma. These elements enable bioengineers and Certimoov to base their tests on more realistic injury criteria which corresponds to the actual impact tolerance of the brain. 
The regulation’s pass/fail criteria for helmet acceptance is yes or no: either the helmet fulfils the regulation or it does not. Certimoov enables the addition of nuances to the tests with a score from 0 to 5.

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A tripartite project

Three entities are behind Certimoov: the MAIF Foundation, which co-financed the development of the test method, the University of Strasbourg, which developed the test method and as of today carries out the tests, and Mutuelle des Motards, which makes the project ongoing by financing test campaigns and notifying helmet users and manufacturers so that they can improve their manufacturing methods.

Modelling the mechanical behaviour of the brain

The model of the brain and the calculation of the
mechanical response

The Certimoov method applies techniques used in engineering to calculate the deformation of a bridge or an airplane wing. The use of these techniques enables the calculation of the mechanical response of the brain at the time of impact. 
These methods are computer-assisted. The brain is shown as a multitude of small brick elements with the solid mechanical properties of the skull and the soft properties of the brain. With these elements it is possible to calculate the internal pressure and shear stress in the brain (intra-cerebral stress). 

Illustration of the mechanical brain model, which enables the calculation of intra-cerebral stress at the time of impact

Simulating real
head trauma

Bioengineers have been gathering information concerning head injuries from real accidents for almost 15 years. The conditions in which the accidents happened and the descriptions of the injuries have made it possible to simulate the kinematics (the movement of the victims during accident) and to calculate the impact conditions of  the head at the time of the collision, for pedestrians, cyclists, bikers and athletes.

Depiction of the calculation of the victim’s kinematics, showing the speed of the head at the time of impact. This is the basis for the simulation of head trauma. 

Head injury criteria

After gathering information about the head impact conditions, bioengineers are able to theoretically simulate head injuries. 
By simulating over 120 real injuries, bioengineers are able to correlate the occurrence of a coma to the mechanical intracerebral parameters calculated. This enables the definition of the limits of tolerance to brain impact: this is what is known as injury criteria. 
Thanks to the mechanical parameters calculated and the injury criteria, the model of the human head has become a useful head injury prediction tool. It is a new tool for the evaluation and optimization of head protection systems!

NB: the severity of neurological injury taken into account is reversible. In other words, the bioengineers work on serious concussion and short-term loss of consciousness. 
 

The risk curve in accordance with numerous simulations of head injury. The higher the intracerebral stress, the greater the probability of coma.

Problems with rotational acceleration

In general, the mechanical loading of the brain is related to acceleration at the time of impact: this is what is known as inertial mechanical load. Impact is an acceleration pulse corresponding to a change in speed in a very short lapse of time. This acceleration could be:

  • Linear: when the impact falls exactly on the axis of the centre of gravity of the head
  • Rotational: when the impact is oblique and involves a tangential component

It has been known since 1943 that rotational acceleration has a harmful effect on the brain as it induces shear stress and that the soft “brain material” deforms easily under such stresses. If you wish to see an example, try shaking your head to say no very energetically, or look at a boxer who is trying to knock his opponent out by means of rotation.

Question : what about the snowball ????

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Test and method

Horizontal anvil and
inclined anvil

Certimoov tests helmets with a linear impact i.e. a vertical drop onto a horizontal surface. Certimoov also studies oblique impacts with a vertical drop onto an anvil inclined at 45°. This test on an inclined surface leads to the rotation of the headform in addition to the translation deceleration.
In order for the test to be complete, helmets are tested in 6 different kinds of impact (each impact is repeated 3 times, which means there are 18 tests):

linear:

  • Frontal
  • Lateral
  • Occipital

Oblique:

  • RotY: administered in the frontal zone and causing rotation around the left-right axis
  • RotX: administered in the lateral zone and causing rotation around the front-back axis
  • RotZ: administered in the lateral zone and causing rotation around the vertical axis

Illustration of the 6 impact conditions (3 linear and 3 oblique)

Headform improved
with linear and rotational
accelerometers

The headform used by Certimoov makes tests more accurate. In fact, the headform used under current regulations are not adapated to the new kinds of impact tested by Certimoov because :

  • Inertia in rotation is not adapted to the impacts tested
  • The head-helmet friction is not realistic
  • The headform does not contain rotational acceleration sensors

The headform used in Certimoov not only enables helmet testing under realistic impact conditions but above all it permits the objective evaluation of the level of brain protection for each helmet. 

The ISO headform used under current regulations (right) and the HIII dummy head used by Certimoov.

Theoretical response of the
brain to a real impact

The most innovative aspect of Certimoov is to couple the experimental test and a digital head injury prediction tool. 
For this purpose, the linear and rotational acceleration registered within the helmeted headform for a given impact are included in the theoretical brain model. It calculates the maximum intra-cerebral shear stress in order to deduce the risk of injury by means of the risk curve.

Illustration of the coupled “experimental versus digital” method, for the assessment of brain injury risk for a given impact

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Understanding the points system

Calculating an average
risk level for suffering
a moderate neurological injury

In order to ensure the quality of results, each type of impact (3 on a horizontal surface and 3 on an inclined one) is repeated 3 times, leading to a total of 18 impacts (and so 18 simulations and 18 levels of brain stress). The average from these values is shown on a brain injury risk curve and leads to an overall risk of injury for a given helmet.. 
The mark is then calculated in accordance with the risk level: the lower the risk, the higher the mark.

The assignation of marks in accordance with the overall risk of injury obtained for 18 impacts.

6 kinds of mark

In order to enable a more profound analysis of the protection capacities of each helmet, a mark is given for each of the 6 types of impact according to the same methodology.
This information enables helmet manufacturers to better identify the strengths and weekness of their helmets and what they can do to improve them.

Contributing to the
evolution of regulations

Certimoov’s aim is to improve user safety by proposing a complementary test method to existing  regulations. If Certimoov is widely accepted, this will give credibility to the new test method, and in the long term this will make regulations evolve and include the same kind of approach in their methods. 

Helping helmet
manufacturers

The supplementary information provided by Certimoov means helmet manufacturers can better know the points they could improve on their products in the field of safety. By giving precise results, Certimoov aims to work directly with helmet manufacturers to help them to ?? improve the safety of their products by making innovative tools available for them. The bioengineers and Certimoov are at manufacturers’ disposal to answer any questions they may have, inform them about the test method and provide them with further details on the results via an e-mail account especially for this purpose.

Informing consumers about
the comparative level of
protection provided by
different helmets

As safety should be the first criterion of choice in ?? a helmet, Certimoov enables users to find more details about the level of brain protection provided by each helmet. The helmets tested are given a mark from 0 to 5, 0 being the worst result and 5 the best. It is essential to remember that all standardized helmets provide an appropriate level of protection. If some of them get a poor mark it is because they are not manufactured (optimized) to protect in cases of oblique impact, and also because the level of injury taken into account by Certimoov is reversible injury. Our purpose is to identify the best helmets and get them to evolve. 

Jet helmets

Please note that Certimoov tests the impact of a collision on the brain. This is why jet helmets might have a better mark than full-face helmets. Impact on the chin is not measured. 

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