ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

[6,7]. In order to reproduce numerically that impacting device, a cylinder was built
numerically with brick elements. That cylinder is divided in two parts. One part behaves
like linear elastic aluminium:
Density = 2,700 kg/m 3 .
Young modulus = 70 GPa.
Poisson’s ratio = 0.33.
The contact second part, which is the contact part with the head, has the same
mechanical properties as human skin, that is to say a linear elastic behaviour:
Density = 1,000 kg/m 3 .
Young modulus = 16.7 MPa.
Poisson’s ratio = 0.42.
For each impact case, the experimental conditions have been adapted to the basic
numerical impact configuration:
The impactor mass and velocity.
The head circumference and mass.
The skin and bone thickness at the impact point.
The results for each numerical impact reconstruction were recorded in terms of:
Deleted elements on the skull. These elements allow predicting skull fractures.
Interaction force between the head and the impactor. That calculated force is
compared to the experimentally measured force.
4. RESULTS
4.1 Case NG04
The numerical impact simulation predicts fracture patterns on the frontal bone as
illustrated in Figure 2. The linear fracture through the right orbita is not predicted since
the face has only a linear elastic behaviour in the model. Therefore, the fracture pattern
stops on the frontier between the skull and the face. Nevertheless, a global fracture
region is predicted by the model even if the location is not as accurate as the one
observed in the experience. In terms of interaction force between the head and the
impacting mass, the numerically calculated amplitude in 2,000 N higher than the
experimentally measured one as illustrated in Figure 2. Nevertheless, the duration of the
first impact in numerical simulation and in the experimental impact are the same.
Moreover, the numerical simulation shows a second impact which is also observable in
the experience but with a lower amplitude. Eventually, the calculated global strain
energy of the skull reaches levels of 10,000 mJ and thus allows the model to predict
skull fracture since the limit relies on 833 mJ.
Figure 2: Skull deleted elements numerical prediction (left), and experimental (blue)
and numerical (pink) interaction force between the head and the impactor (right).