Susumu Ejima

Ribcage characterization for FE using automatic CT processing

Standard medical chest and abdominal computed tomography (CT) scans of 46 subjects were analyzed to characterize aspects of human ribcage geometry and bone density. A semi-automatic algorithm was developed to define framework curves for individual ribs. Measurements of this framework were taken to record anthropometric properties of the ribcage such as overall ribcage dimensions and individual rib lengths and angles. Furthermore, the ribcage framework was used to explore the voxel space of the CT images, recording local rib bone cross-sectional density properties. Proposals are made for the use of these measurement techniques to inform and improve human finite element (FE) chest models in terms of global geometry, material properties, and individuality.

Age-Dependent Factors Affecting Thoracic Response: A Finite Element Study Focused on Japanese Elderly Occupants

Objectives: The ultimate goal of this research is to reduce thoracic injuries due to traffic crashes, especially in the elderly. The specific objective is to develop and validate a full-body finite element model under 2 distinct settings that account for factors relevant for thoracic fragility of elderly: one setting representative of an average size male and one representative of an average size Japanese elderly male. Methods: A new thorax finite element model was developed from medical images of a 71-year-old average Japanese male elderly size (161cm, 60 kg) postmortem human subject (PMHS). The model was validated at component and assembled levels against original series of published test data obtained from the same elderly specimen. The model was completed with extremities and head of a model previously developed. The rib cage and the thoracic flesh materials were assigned age-dependent properties and the model geometry was scaled up to simulate a 50th percentile male. Thereafter, the model was validated against existing biomechanical data for younger and elderly subjects, including hub-to-thorax impacts and frontal impact sled PMHS test data. Finally, a parametric study was conducted with the new models to understand the effect of size and aging factors on thoracic response and risk of rib fractures. Results: The model behaved in agreement with tabletop test experiments in intact, denuded, and eviscerated tissue conditions. In frontal impact sled conditions, the model showed good 3-dimensional head and spine kinematics, as well as rib cage multipoint deflections. When properties representative of an aging person were simulated, both the rib cage deformation and the predicted number of rib fractures increased. The effects of age factors such as rib cortical thickness, mechanical properties, and failure thresholds on the model responses were consistent with the literature. Aged and thereby softened flesh reduced load transfer between ribs; the coupling of the rib cage was reduced. Aged costal cartilage increased the severity of the diagonal belt loading sustained by the lower loaded rib cage. Conclusions: When age-specific parameters were implemented in a finite element (FE) model of the thorax, the rib cage kinematics and thorax injury risk increased. When the effect of size was isolated, 2 factors, in addition to rib material properties, were found to be important: flesh and costal cartilage properties. These 2 were identified to affect rib cage deformation mechanisms and may potentially increase the risk of rib fractures.

Effect of aging on brain injury prediction in rotational head trauma-a parameter study with a rat finite element model

Objective: The aim of this study was to investigate the possible effects of age-related intracranial changes on the potential outcome of diffuse axonal injuries and acute subdural hematoma under rotational head loading. Methods: A simulation-based parametric study was conducted using an updated and validated finite element model of a rat head. The validation included a comparison of predicted brain cortex sliding with respect to the skull. Further, model material properties were modified to account for aging; predicted tissue strains were compared with experimental data in which groups of rats in 2 different lifecycle stages, young adult and mature adult, were subjected to rotational trauma. For the parameter study, 2 age-dependent factors—brain volume and region-specific brain material properties—were implemented into the model. The models young adult and old age were subjected to several injurious and subinjurious sagittal plane rotational acceleration levels. Results: Sequential analysis of the simulated trauma progression indicates that an increase in acute subdural hematoma injury risk indicator occurs at an early stage of the trauma, whereas an increase in diffuse axonal injury risk indicators occurs at a later stage. Tissue stiffening from young adult to mature adult rats produced an increase in strain-based thresholds accompanied by a wider spread of strain distribution toward the rear part of the brain, consistent with rotational trauma experiments with young adult and mature adult rats. Young adult to old age brain tissue softening and brain atrophy resulted in an increase in diffuse axonal injuries and acute subdural hematoma injury risk indicators, respectively. Conclusions: The findings presented in this study suggest that age-specific injury thresholds should be developed to enable the development of superior restraint systems for the elderly. The findings also motivate other further studies on age-dependency of head trauma.

Analysis of Intervertebral Strain Response during Rear Impact Using Head-Neck Finite Element Model

Minor neck injuries in rear collision accidents have become a huge problem in many countries. Therefore, it is urgent to develop a suitable criterion for assessing neck injury risk. In this study, a detailed head-neck finite element (FE) model was developed. Skull and vertebrae models were created based on CT images of a typical Japanese male. Models of intervertebral discs, ligaments and muscles were also created according to literatures. Furthermore, material properties were taken from the published data. In order to evaluate intervertebral soft tissue strain due to translational rotational coupled motion of vertebrae, a 2D strain analysis method was also proposed. The method was applied to cervical vertebral motion data obtained from previous rear impact tests using human volunteers and from test reconstruction using the head-neck model. A potential correlation between intervertebral strain and neck injury was clarified from the comparison between the intervertebral strain level and existence of neck discomforts. The model’s response is also in good agreement with the volunteers’ response, indicating that the head-neck model is suitable for minor neck injury analysis and that it is possible to analyze the intervertebral strain with a head-neck model.

Sound Insulation Analysis of a Resin Composite Material Using the Homogenization Method

We propose a numerical method to predict the noise transmission loss of a resin composite cover, which considers the effect of the shape and the material properties of the microscopic reinforcements in a resin-composite. The mean material properties of the material are calculated with the homogenization method and the acoustic structural coupling analysis is made with the obtained material constants. The calculated results show that the sound insulation levels are affected seriously by the shape or rate of the reinforcements in the material, which suggests that the present method can be a good numerical method to determine the reinforcements in a resin to improve the sound insulation ability.