Three Years Old Child Neck Finite Element Modelisation

Despite of recent progresses in occupant safety, the protection of children are not still optimal. To offer a better understanding of child injury mechanisms, the present study proposes a humanlike finite element model of a three years old child’s neck. The subject was scanned with a medical scanner. The images were first semiautomatically segmented in order to extract the soft tissues and the bones. In the second step, we separate the different bones slice by slice on the geometry previously reconstructed. The anatomic structures are identified and each vertebra is reconstructed independently with special attention for the articular process. In a second step, we have generated a original meshing on the previous geometry to obtain a finite element model of the child’s neck. The anatomical structures incorporated are the head, the seven cervical vertebrae (C1–C7), the first thoracic vertebra (T1), the intervertebral discs and the principle ligaments which are modelled using non-linear shockabsorbing spring elements. The stiffness values used are taken from literature, and scaled down using scale factors from Irwin. This model incorporates 7340 shell elements to model the eight vertebrae, the head and 1068 solid 8-node elements to model the intervertebral discs. Contact between the articular surfaces is represented by interfaces permitting frictionless movement. Since this study does not aim to reproduce bone fractures, we have modelled the cervical vertebrae as rigid bodies. A scaling factor for the intervertebral discs modulus of 0,705 is supposed by Yoganandan for the 3 year old child, this values conduce to disc modulus of the order of 100 MPa. Given that validation data were not available, the model validation was conduced against Q3 dummy component sled tests. The accelerometric responses of the head model were similar with those recorded experimentally with a Q3 dummy neck in rearward, frontal and lateral impact direction. INTRODUCTION Each year, more than 700 children are killed on European roads and 80.000 are injured. The EC project CHILD (Child Injury Led Design) aims to improve the protection offered to children in cars by increasing the understanding about the injuries sustained and providing innovative tools and methods for improvement of Child Restraint Systems (CRS) in cars. One of the tools developed is a three year old child head and neck finite element model. If some models are existing in the literature like Van Ratingen’s [1] or Yoganandan’s [2] model, they differ largely in term of purpose and methodology. Multi-body Child Neck Model Child multi-body neck finite element models are mainly models developed under MADYMO. Thus, TNO developed 3, 4, 5, 6, 8, 10 and 12 year old child models usable in automotive crash test reconstruction. The models are carried out by the assembly of cylinders, ellipsoids, parallelepipeds connected to each other by joints with one or more degrees of freedom and different stiffness according to mobility. The models were validated by reproducing the tests carried out on Q serie dummies. A scaling was conduced on corridors resulting from the tests on volunteers and PMHS carried out by Mertz and Patrick [3] and Patrick and Chou [4]. Corridors of validation [1, 5] were then considered as the reference for the child (see figure 1). The three year old child MADYMO model is most recent child model. It was developed by TNO in parallel of the Q3 dummy. Its validation was conduced within the framework of the EC CREST project. The Q3 model is directly issued from the dummy CAD. The head/neck elements were similar to those of the dummy.