Yusuke Miyazaki

Effects of whole spine alignment patterns on neck responses in rear end impact

ABSTRACT Objective: The aim of this study was to investigate the whole spine alignment in automotive seated postures for both genders and the effects of the spinal alignment patterns on cervical vertebral motion in rear impact using a human finite element (FE) model. Methods: Image data for 8 female and 7 male subjects in a seated posture acquired by an upright open magnetic resonance imaging (MRI) system were utilized. Spinal alignment was determined from the centers of the vertebrae and average spinal alignment patterns for both genders were estimated by multidimensional scaling (MDS). An occupant FE model of female average size (162 cm, 62 kg; the AF 50 size model) was developed by scaling THUMS AF 05. The average spinal alignment pattern for females was implemented in the model, and model validation was made with respect to female volunteer sled test data from rear end impacts. Thereafter, the average spinal alignment pattern for males and representative spinal alignments for all subjects were implemented in the validated female model, and additional FE simulations of the sled test were conducted to investigate effects of spinal alignment patterns on cervical vertebral motion. Results: The estimated average spinal alignment pattern was slight kyphotic, or almost straight cervical and less-kyphotic thoracic spine for the females and lordotic cervical and more pronounced kyphotic thoracic spine for the males. The AF 50 size model with the female average spinal alignment exhibited spine straightening from upper thoracic vertebra level and showed larger intervertebral angular displacements in the cervical spine than the one with the male average spinal alignment. Conclusions: The cervical spine alignment is continuous with the thoracic spine, and a trend of the relationship between cervical spine and thoracic spinal alignment was shown in this study. Simulation results suggested that variations in thoracic spinal alignment had a potential impact on cervical spine motion as well as cervical spinal alignment in rear end impact condition.

Effects of the Mechanical Properties of the Shell and Liner on the Shock Absorption of Helmets

A combination of the characteristics of the shell and liner of a helmet, that makes it possible to improve the shock absorption capacity was investigated by constructing the finite element model of the helmet modeling both the bottoming of the liner and the fracture of the shell. The material model of the shell was defined as an elasto-plastic material, taking into account brittle fracture. The liner was modeled as a non-linear visco-elastic material, expressing both energy absorption by buckling of the cell foam, and the extreme increase of the stiffness caused by bottoming. The results of the parametric study, where the foaming ratio of the liner and the shell-thickness were varied, indicated that there is an optimum combination where the shell part fails without the liner bottoming, improving the shock absorption ability of a helmet.

Influence of the head shape variation on brain damage under impact

The influence of the head shape on intracranial responses under impact was investigated by using Finite Element Method. Head shape models of 52 young adult male Japanese were analyzed by Multi Dimensional Scaling (MDS), and a 2 dimensional distribution map of head shapes was obtained. Five finite element models of the Japanese head were constructed by a transformed finite element model of an average European adult male (H-Head model) using Free Form Deformation (FFD) technique. The constructed models represent the 5 th and 95 th percentile of the first 2 scales obtained by MDS. The same acceleration pulse was applied to the H-Head model and the five finite element models. The cause of the difference was considered to be differences in pressure distribution in the brain caused by the differences in the head shape. Variation in the head shape should be taken into account in simulating the effects of impact using a finite element model.

Dynamic Response and Damage Estimation of Infant Brain for Vibration

The purpose of this paper is to clarify the mechanical generation mechanism of acute subdual hematoma, which is a severe injury in infants, by performing experiments and finite element analysis. The acute subdural hematoma in infants is caused by accidents such as falling or abuse such as shaking. This paper describes the shaking events.