Jesse S. Ruan

Investigation of the critical geometric characteristics of living human skulls utilising medical image analysis techniques

A non-invasive method has been developed to study and analyse the critical geometric characteristics of living human skulls based on CT scan images. The CT scan images were obtained from patients who were admitted to the hospital and needed a head CT scan diagnosis. The A-P length and breadth of the whole skull, the thickness of the frontal, parietal and occipital bones of 3000 living skulls were analysed in this study. The results have shown that the average thicknesses of the frontal, parietal and occipital bones were (in mm) 6.58, 5.37 and 7.56, respectively, for the male; and 7.48, 5.58 and 8.17, respectively, for the female. The A-P length and breadth of the skull were 175.81 and 145.35, respectively, for the male and 170.61 and 140.11, respectively, for the female. The thickness and the breadth of the human skull are not normally distributed; and in general, females have thicker skulls than males; but males have wider breadth and longer A-P length than females.

Limitation of scaling methods in child head finite element modelling

During growth, a childs head undergoes different modifications in morphology and structure. This paper presents an anthropometric study in terms of dimension compared to the scaling method developed by Mertz which consists of reducing the adult head model with a scaling coefficient to obtain a child head. A detailed sizes and shape analysis of brain contour in sagittal and frontal plans is then proposed, for child head versus a scaled adult head. The superimposition of those contours allowed pointing to main differences. Numerical simulations performed with the detailed three year old child head model developed in this present study, and a scaled adult head finite element model, showed that reducing an adult finite element model to obtain a child head by scaling method does not seem to be realistic. Then, the creation of specific finite element models of child head seems necessary to understand paediatric injuries.

Head Injury Potential Assessment in Frontal Impacts by Mathematical Modeling

The potential of head injury in frontal barrier impact tests was investigated by a mathematical model. This model consisted of: a finite element human head model, a four segments rigid dynamic neck model, a rigid body occupant model, and a lumped-mass vehicle structure model. The finite element human head model represents anatomically an average adult head. The rigid body occupant model simulates an average adult male. The structure model simulates the interior space and the dynamic characteristics of a vehicle. The neck model integrates the finite element human head to the occupant body to give a more realistic kinematic head motion in a barrier crash test. Model responses were compared with experimental cadaveric data and vehicle crash data for the purpose of model validation to ensure model accuracy. Model results show a good agreement with those of the tests. The model was used to assess head injury severity, when the occupant was restrained by an airbag only (31 mph barrier test) and by an airbag and a 3-point belt (35 mph barrier test). Head acceleration, stress and strain in the brain were investigated as injury parameter indicators. The model advances the study of brain motions and accompanying stresses during large linear and angular displacements encountered in vehicle frontal collisions. (A) For the covering abstract of the conference see IRRD 879189.

The influence of human head tissue properties on intracranial pressure response during direct head impact

The influence of human head tissue properties on intracranial pressure response during direct head impact was studied using finite element analysis and Design-of-Experiment (DOE) techniques. A three-factor, three-level factorial experiment design was applied to the skull, cerebrospinal fluid and brain of a finite element human head model to characterise the effects of these tissues on intracranial pressure response of the human head. This study has demonstrated that a DOE approach can provide more modelling information than the approach using one factor at a time. It has also shown that the incompressibility of the brain contributes much more to the variability of coup and contrecoup pressures than other cranial contents (73% and 53%, respectively).

Development of a Six-Year Old Digital Human Body Model for Vehicle Safety Analysis

Biomechanical differences between children and adults are anatomically obvious and physiologically evident. Nevertheless, scaling laws have been used between child and adult mechanical properties in biomechanical injury studies. These laws may or may not be valid depending on the aging properties of the tissue being studied. Detailed adult human body finite element models have been developed in recent years, but not for children. Therefore, the objective of this study is to develop an industry-first, full-body digital human finite element (FE) model of a six-year old child aimed at helping improve vehicle safety for children and also validating the scaling laws between child and adult mechanical properties.The child digital model was developed based on CT scan images from a living six-year old child++. Model geometry was extracted from the CT scans through image analysis. Finite element (FE) mesh for different parts of the body was created from the geometric data obtained in the CT scan image analysis process. While the CT scans were taken with the subject supine, the model in this study is in a standing position, representing a pedestrian posture. Biomechanical properties of each component in the model were obtained from the literature. The model includes a detailed anatomical representation of human organs for a six-year old child, from head to toe. Predicted model responses are compared with test data found in the literature. Forces, displacements for the neck, chest, and abdomen; pressures for the brain are output for injury reference analysis. The analysis of the FE model was performed by using LS-DYNA software. Although the geometric accuracy of the six-year child FE model has been ensured by extracting data from living CT scan images, the mechanical property data used in the model and the impact response used for model comparison can only be considered tentative; since these data are sparse in literature.

Further Validation of the Head in the Ford Human Body FE Model

The head in the Ford human body model (FHBM) was previously validated against impact test data involving post mortem human subjects (PMHS). The objective of the current study was to further validate the head model against more PMHS tests. The data included the following published tests: rigid bar impact to the forehead, zygoma, and maxilla (2.5–4.2 m/s), lateral pendulum impact (5.7 m/s), and front pendulum impact to the frontal bone, nasal bone, and maxilla (2.2 m/s). The responses from the model were compared to available published cadaveric response corridors and to various cadaveric responses. When compared to the cadaveric response corridors, the responses from the model were within those corridors. In addition, the model responses demonstrated acceptable fidelity with respect to the test data. The head injury criterion (HIC15 ), strain, and stress values from the model were also reported.Copyright

Development and Validation of a 50th Percentile Male Pedestrian FE Model

The objective of this study was to develop and validate a finite element (FE) human model that represents a 50th percentile adult pedestrian male. The geometry of the previously developed and well validated Ford Human Body (FHB) model was modified to change the posture from driving to standing. The femur, tibia, and fibula were validated against published test data of human bone specimens in different dynamic loading scenarios. The leg model was validated against dynamic, three-point bending test data of human legs from Post Mortem Human Subjects (PMHS). The kinematics and dynamics of the full pedestrian model was validated against PMHS car-pedestrian impact test data under different levels of severity. The model responses were compared with the corresponding published generalized response corridors. In all the component level and full body model simulations the responses from the model correlated well with both the generalized response corridors and the responses from the individual cadavers.© 2010 ASME

Chest Deflection vs. Chest Acceleration as Injury Indicator in Front Impact Simulations Using Full Human Body Finite Element Model

The Ford Motor Company Human Body Finite Element Model (FHBM) was validated against rib dynamic tension and 3-point bending tests. The stress-strain and moment-strain data from the tension and bending simulations respectively were compared with human rib specimen test data. The model used represented a 50th percentile adult male. It was used to compare chest deflection and chest acceleration as thoracic injury indicator in blunt impact and belted occupants in front sled impact simulations. A 150 mm diameter of 23.4 kg impactor was used in the blunt impact simulations with impact speeds of 2, 4, and 8 m/s. In the Front sled impact simulations, single-step acceleration pulses with peaks of 10, 20, and 30 g were used. The occupants were restrained by 3-point belt system, however neither pretensioner nor shoulder belt force limiter were used. The external force, head acceleration, chest deflection, chest acceleration, and the maximum values of Von Mises stress and plastic strain were the model outputs. The results showed that the external contact force, head acceleration, chest deflection, and chest acceleration in the blunt impact simulations varied between 1.5–7 kN, 5–28 g, 18–80 mm, and 8–40 g respectively. The same responses varied between 7–24 kN, 13–40 g, 15–50 mm, and 16–46 g respectively in the front sled impact simulations. The maximum Von Mises stress and plastic strain were 50–127 MPa, and 0.04–2% respectively in the blunt impact simulations and 72–134 MPa, and 0.13–3% respectively in the sled impact simulations.Copyright

Further Validation of the Ford Human Body FE Model and Use of the Model to Investigate the Effects of Shoulder Belt Force Limiting of 3-Point and 4-Point Restraints in Frontal Impact

Ford Motor Company human body FE model was validated against 3-point & 4-point belted PMHS tests in frontal impact and PMHS knee impact. The chest deflection, chest acceleration, and belt force in frontal impact simulations were compared with the PMHS test data, while the impact force, femur acceleration, pelvis acceleration, and sacrum acceleration of the knee impact simulations were compared with the respective corridors from PMHS tests. The model used represents a 50th percentile adult male. It was used to study the effects of shoulder belt force limit on 3-point and 4-point restrained occupants in frontal impacts without airbags. A 25 g pulse and a shoulder belt load limit of 1, 2, 3, 4, 6, and 8 kN were used for the 3-point and 4-point restraint systems with a rigid steering wheel, front header, and windshield of a stiffer larger vehicle structure. The results showed that the head acceleration and the chest deflection of the 4-point belt system are less than the respective cases of the 3-point system while the chest acceleration levels were about the same in 3-point and 4-point belt. The mid-shaft femur forces were always higher in the 4-point belt than those of the 3-point belt.Copyright

Evaluation of safety of helmets using a featureless Hybrid III headform

This paper proposes a new procedure for designing helmets for head impact protection to road users such as two-wheeler riders and pedestrians. The new procedure suggests that a helmet be mounted on a featureless Hybrid III headform that is used for assessing upper interior head impact safety specified in the vehicle safety standard FMVSS 201 in the USA. To ascertain a helmets effectiveness as a countermeasure for minimising the risk of severe head injury, an impact velocity of 6 m/s (13.5 mph) was used for the helmet-headform system striking a rigid target. The resultant head impact response is measured by Head Injury Criterion (HIC). The threshold HIC(d) limit of 1000 is applied for adjudging the efficacy of helmets. The proposed procedure is demonstrated with the help of a validated LS-DYNA model of a featureless Hybrid III headform and a helmet. The helmet model consists of an outer General Electric (GE) plastic-based shell to the inner surface of which is bonded a protective energy-absorbing foam padding of a given thickness. Based on simulation results of impact on a rigid surface, it appears that foam padding of suitable strength and a minimum thickness of 35–40 mm along with a shell thickness of 3–4 mm is necessary for obtaining an acceptable value of HIC(d), and therefore, an acceptable helmet safety design.