SUFEHM Model

The *Strasbourg University Finite Element Head Model* (SUFEHM) is actively developed at the Strasbourg University since 1997. It represents a finite element model of the human head and can be used in real-world head impact conditions to evaluate the injury risk of the skull and the brain.

The geometry of the SUFEHM model was obtained from a scan of an adult human male skull. Its main anatomical features are the skull, falx, tentorium, subarachnoid or cerebrospinal fluid (CSF), scalp, cerebrum, cerebellum and brainstem. The finite element model consists of approx 13,200 elements and has a total weight of 4.7kg.

The validation of the SUFEHM model is based on the reconstruction of a total of 125 head impact scenarios, obtained from motorcyclist, American football and pedestrian accidents using the SUFEHM model in LS-DYNA simulations. In contrast to conventional statistical-based injury criteria, not only the translational acceleration of the head/brain was considered, but also the important rotational acceleration occuring during an impact situation.

This finally leads to model-based injury criteria and the SUFEHM model is able to predict three main injury probabilities
- skull fracture
- subdural hematoma (SDH)
vascular injuries with bleeding between the brain and skull
- diffuse axonal injuries (DAI)
neurological injuries like concussions, unconcsiousness and coma.
Separation into mild and severe levels according to coma duraction
(<24h for moderate, >24h for severe DAI)

The SUFEHM model can be used in stand-alone simulations, where the head model may be impacted against the vehicle structure to simulate a pedestrian impact scenario or impacted against the vehicle interior for occupant safety simulations. In this case, the acceleration curves obtained from a conventional human to vehicle simulation can be applied to the SUFEHM model to get a more detailed injury assessment of the human head in the specific impact situation.

Another approach may be to couple the SUFEHM model to human models like the THUMS. In this case, the SUFEHM model rather than the original model is used and the improved injury criteria of the SUFEHM model can be evaluated. This of course needs some modelling work, but already has been done by some customers.

The postprocessing, i.e. the evaluation of the injury probabilities is done using the Injury Risk Assessment (IRA) tool, also provided along with the SUFEHM model. The IRA tool extracts the injury relevant data from the LS-DYNA d3plot file database and calculates the probabilities for the three injury types (skull fracture, SDH and DAI). The resulting probabilities are visualized inside the IRA tool as depicted in Fig. [SUFEHM-IRA.png]. Additionally, the location of the maximum brain stress and the temporal  development of the injury-relevant values can be visualized using the IRA tool.

References
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Sahoo D., Deck C. and Willinger R. (2015): Axonal strain as brain injury
predictor based on real world head trauma simulations. IRCOBI 2015

Deck C. and Willinger R. (2009): Head injury prediction tool for protective
systems optimization, 7th European LS-Dyna Conference, Salzburg 2009

Deck C. et al (2008): Improved head injury criteria based on head FE model,
International Journal of Crashworthiness, Vol 13, No 6, pp. 667-678