Kazuo Miki

Finite Element Analysis of Knee Injury Risks in Car-to-Pedestrian Impacts

In vehicle–pedestrian collisions, lower extremities of pedestrians are frequently injured by vehicle front structures. In this study, a finite element (FE) model of THUMS (total human model for safety) was modified in order to assess injuries to a pedestrian lower extremity. Dynamic impact responses of the knee joint of the FE model were validated on the basis of data from the literature. Since in real-world accidents, the vehicle bumper can impact the lower extremities in various situations, the relations between lower extremity injury risk and impact conditions, such as between impact location, angle, and impactor stiffness, were analyzed. The FE simulation demonstrated that the motion of the lower extremity may be classified into a contact effect of the impactor and an inertia effect from a thigh or leg. In the contact phase, the stress of the bone is high in the area contacted by the impactor, which can cause fracture. Thus, in this phase the impactor stiffness affects the fracture risk of bone. In the inertia phase, the behavior of the lower extremity depends on the impact locations and angles, and the knee ligament forces become high according to the lower extremity behavior. The force of the collateral ligament is high compared with other knee ligaments, due to knee valgus motions in vehicle-pedestrian collisions.

Analysis of traumatic brain injury due to primary head contact during vehicle-to-pedestrian impact

We developed a 50th-percentile American male pedestrian model including a detailed brain, and the mechanical responses and kinematic biofidelity predicted by this model were validated against the available cadaveric test data. Vehicle-to-pedestrian impact simulations were then performed to investigate a potential mechanism for traumatic brain injury resulting from a lateral blunt impact to the head. Due to inertia of the brain mass, it was found that the average traction force produced in the cervical spinal cord exceeded 50 N in the impact involving a sport utility vehicle and 25 N in the impact involving a sedan, when the striking vehicle was travelling at 40 km/h. This inertial loading may play a key role in a brainstem, or upper-cervical-cord, lesion occurring before head strike. Results of this study suggest that close attention should be paid to pedestrian kinematics during free flight even before the head makes primary contact with the striking vehicle.

Development of a Finite Element Model of the Human Lower Extremity for Assessing Automotive Crash Injury Potential

A finite element (FE) model of the human lower extremity has been developed and validated against published experimental data quasi-statically and dynamically. The calculated results indicate that the current FE model possesses reasonable biomechanical characteristics and adequate biofidelity in dorsiflexion behavior. In future work, it is hoped that the application of this model for realistic automotive crash analyses can increase not only better understanding of the injury mechanisms but also basic biomechanical data for further occupant protection.

Numerical Analysis of the Biomechanical Characteristics and Impact Response of the Human Chest

The mass density, Young’s modulus (E), tangent modulus (Et ) and yield stress (σy ) of the human ribs, sternum, internal organs and muscles play important roles when determining impact responses of the chest associated with pendulum impact. A series of parametric studies was conducted using a commercially available three-dimensional finite element (FE) model, Total HUman Model for Safety (THUMS) of the whole human body, to determine the effect of changing these material properties on the impact force, chest deflection, and the number of rib fractures and fractured ribs. Results from this parametric study indicate that the initial chest stiffness was mainly influenced by the mass density of the muscles covering the torso. The number of rib fractures and fractured ribs were primarily determined by E, Et and σy of the ribcage and sternum. Similarly, the E, Et and σy of the ribcage, which is defined as the bony skeleton of the chest, and sternum and E of the internal organs contributed to the maximum chest deflection in frontal impact, while the maximum chest deflection for lateral impact was mainly affected by the E, Et and σy of the ribcage.Copyright

Fundamental Study of Dynamic Analysis of Lumbar Vertebrae

This paper describes the results of fundamental study of dynamic analysis of the lumbar vertebrae for the accidental injury. A finite element model with linear brick elements and nonlinear truss elements is constructed for the study of dynamic responses of the fifth and fourth lumbar vertebrae. The results of the analyses show the folio wings: In case of the estimation of the global behavior of vertebrae, it is efficient method to treat the stiff parts of the bone as rigid elements and apply the 8-points integration to the other soft brick elements. To determine the stiffness of ligament for various modeling cases, response surface methodology using design of experiment is applied and the usefulness is verified. And this design of experiment is also applied to examine the influence of the disk properties on the lumbar vertebral stiffness. This bending stiffness of the lumbar vertebrae is rapidly increasing when Poisson’s ratio of nucleus pulposus is very close to 0.5. If Poisson’s ratio is close to 0.5, nucleus pulposus changes its characteristic from compressible to incompressible. In this case, the disk is expected to function as rotator in the extension or flexion of the lumbar vertebrae. To verify this function of rotator, the impact response analyses that dropped block comes into contact with the upper side of the lumbar vertebrae is performed and this function is verified quantitatively.

ANALYSIS OF HEAD AND NECK RESPONSE DURING SIDE IMPACT

This paper presents numerical analyses of head and neck response during side impact. A mathematical human model for side impact simulation was developed based on previous studies of other researchers. The effects of muscular activities during severe side impact were analyzed with the use of this model. Results show that the effect of muscular activities is significant, especially if the occupant is prepared to resist the impact. This suggests that the modeling of muscles is important for the simulation of real accident situations.