CAE-Companion-2018-2019

Safety WISSEN CAE

sure, brain deformation and skull deformation. Anatomical and structural analysis of the children head-neck systemas a function of age showed that the scaling downmethodwas applicable to children over 6 years old. For younger children, specific geometrical and structural specifications such as sutures, fontanels, skull homogeneity should be considered. Figure 2 reports the head-neckmodels developed for the 6 weeks, 6months, 1 , 3 and 6 years old childmodels. Model Based Head Injury Criteria and Applications In order to establish human head tolerance limits or head in- jury criteria, no less than 125 real world head trauma involving adults and children have been simulatedwith the above head models. Several cranial and intra-cranial mechanical parame- ters have been computed and correlatedwith the occurrence of skull fracture, subdural hematoma and neurological injuries respectively. It has been shown that a under 50% risk of subdural hematoma appears for maximal pressure of the CSF of about -135kPa, the 50% risk of neurological injury exists for an intra-cerebral vonMises shearing stress of around 37 kPa, both, for the adult and the child. Coming to skull fracture pre- diction it was shown that the relevant mechanical parameter is skull strain energy and that the critical value (50% risk) is strongly age dependent as it varies from0.5 J for the adult to 6 J for the youngest child.

Figure 4: Implementation of the head injury prediction tool into a full FE approach considering the coupled head-protective systemmodel in the framework of car bonnet or helmet optimization. Conclusion Background of head injury criteria based on single head acceleration and on advanced head FEmodels are presented. Further, the Strasbourg University Finite Element HeadModel (SUFEHM) has been presented and validated. In an attempt to developmodel based head injury criteria a total of 125 real world head trauma that occurred inmotorcyclist, American football and pedestrian accidents were reconstructedwith SUFEHM. Tolerance limits to specific injury have been computed for a 50% injury risk of skull fracture, SDH and neurological injuries Finally it is shown how the proposedmodel based head injury criteria can be applied to experimental and numerical head protection systems evaluation and optimization. References [1] Lissner H.R., LebowM., Evans F.G., Experimental studies on the relation between acceleration and intracranial pressure changes in man, Surgery, Gynecology and Obstetrics, vol. 111, 1960. [2] Gurdjian E.S., Webster A., Head Injury, Little Brown Company, Boston, 1958. [3] Gadd C.W., Use of a weighted – impulse criterion for estimating injury hazard, Proc. of the 10th STAPP Car Crash Conf., pp. 164-174, 1966. [4] Ward C.C., ChanM., NahumA.M., Intracranial pressure: a brain injury criterion, SAE, 1980. [5] Zhou C., Kahlil T.B., Dragovic L.J., Head injury assessment of a real world crash by finite element modelling, Proc. of the AGARD Conf., 1996. [6] Kang HS,, Willinger R., Diaw BM, Chinn B : Validation of a 3D human head model and replication of head impact in motorcycle accident by finite element modelling. Proceed. of the 41th Stapp Car Crash Conf. Lake Buena Vista USA, pp 329-338, 1997. [7] King A., Yang K., Zhang L., and Hardy W. Is head injury caused by linear or angular acceleration? IRCOBI Conference, pp 1–12, 2003 [8] Kleiven S (2007) Predictors for traumatic brain injuries evaluated through accident reconstructions. Proceedings 51th Stapp Car Crash Conference, SAE paper 2007-22-0003:81-114. [9] Deck C., Willinger R., (2008) Improved head injury criteria based on head FE model, International Journal of Crashworthiness, Vol 13, No 6, pp. 667-678. [10] Tinard V, Deck C, Willinger R.: Newmethodology for improve- ment of helmet performances during impacts with regards to biome- chanical criteria. J of Materials and Design 37 (2012) 79-88. CAEWissen by courtesy of Dr. Caroline Deck & Prof. Dr. RemyWillinger, University Strasbourg & CNRS, France

Figure 3: Implementation of the head injury prediction tool into a standard test method according to the coupled experimental versus numerical test method. The proposed headmodels and injury criteria transform thesemodels to numerical head injury prediction tools with a number of possible applications in the field of evaluation and optimization of head protection systems or advanced virtual testing. The coupled experimental versus numerical test procedure is illustrated in figure 3. Further, a full FE approach is possible as well when the protective systemhas been previous- lymodelled. In this case a virtual evaluation and optimization of the protective system is possible as reported by Tinard et al 2012 [10] and illustrated in figure 4 for a car bonnet and a motorcyclist helmet optimization.

111