Personal tools

Session 7

The use of different CSF representations in a numerical head model and their effect on the results of FE head impact analyses
To gain better insight in the mechanopathogenesis of brain and skull lesions and to improve the design of protective devices like helmets, finite element (FE) head models are used. Current FE head models have a detailed geometrical description of the anatomical components of the head but often lack an accurate description of the behavior of the cerebrospinal fluid (CSF). Different material properties, mesh resolutions and numerical implementations are used to represent the CSF in those head models. To examine the effect of those different CSF representations on the brain mechanical responses such as strain energy, Von Mises stress, strain and intracranial pressure, this paper starts with the development of a simplified head model and small adaptations are made to the representation of the CSF, both in mesh resolution and constitutive modeling. From this study it follows that depending on which material definition is used for modeling the CSF, the mesh resolution of the CSF can have an important effect on the brain mechanical responses. The study also highlights the need for a more accurate description of CSF material, since the CSF material properties, both material definition and property values, have a significant effect on the results of a head impact analysis.
Session7_Paper2_Abstract.pdf
Implementation of a Strain Rate Dependent Human Bone Model
Strain rate dependency of mechanical properties of cortical bone has been well demonstrated in literature studies. Nevertheless, the majority of these studies have been done on nonhuman bone and at lower magnitudes of strain rates. The need for a mathematical model which can describe the mechanical behavior of bone at lower strain rates as well as higher ones is essential. A human finite element model THUMS (Total Human Model for Safety) [1], developed by Toyota R&D Labs and the Wayne State University, USA has been applied for this study. This work proposes an isotropic elastic-plastic material model of cortical bone where rate effects have also been considered.
A pregnant woman model to study injury mechanisms in car crashes
Based on statistical analysis it has been estimated that 3 to 7% of pregnant women experience trauma, 2 third of those trauma are caused by car accidents. According to one epidemiologic study, the frequency of foetal losses could exceed the death frequency of children aged 0 to 4. Some numerical and experimental tools have recently been developed so as to better understand injury mechanisms leading to foetal losses, nevertheless shortcomings regarding the anatomy of the models must be outlined. Indeed they lack internal organs whereas there is a direct interaction with the uterine wall. Moreover the simplified amniotic fluid model (lagrangian) often implemented is not validated. To fulfil the need of an anatomically precise pregnant woman model, a first finite element model of a 9 month pregnant woman has been developed and validated via a PMHS experimental approach. This model was based on the Humos 50th centile male model and a simplified model of the amniotic fluid was used (Lagrangian). This paper will present the development and validation of the second generation of this model using the LS Dyna software. The geometry of the Humos 50th centile male model was adapted to the anatomy of a 50th centile woman using scaling techniques with a special focus on the pelvis. The model integrates the uterine wall, the foetus, the placenta and an Euler model for the amniotic fluid and represents the anatomy of a 7 month pregnant woman. The uterus is surrounded with main internal organs and bones. An improved PMHS approach was used for validation purpose. Some belt loading of the abdomen and crash tests were realized and compared to the numerical response of the model in similar loading conditions. The pregnant numerical model exhibited a response in agreement with the PMHS tests and will be used to investigate mechanisms leading to fetal losses. A study on parameters influencing the risk of fetal loss is also projected and could ultimately lead to specific safety systems designs.
Development of a thorax finite element model for thoracic injury assessment
Kinetic energy non-lethal weapons (KE-NLW) are now widely used by law enforcement, by military forces, by the police in situations where the use of lethal arms is not required or suitable. Unfortunately, their effects are still not well known. Therefore, there is a need to better understand the injury mechanism induced by such projectiles for a better prediction of the risk of injury. This may be beneficial for the manufacturer, the deciders or the end-users. Numerical simulations are being increasingly used for that purpose. This paper describes first steps in the development of finite element model for thoracic impacts. All the simulations were performed with Ls-Dyna code. For validation purpose, the results were compared to the results of tests made on Post-Mortem Human Subjects (PMHS) published in literature. The sensitivity of contact option and the use of two sets of parameters for the lung material model were examined.