A method of estimating linear and angular accelerations in head impacts to pedestrians

Parameter sensitivity analysis of pedestrian head dynamic response and injuries based on coupling simulations

There are a very limited number of reports studying on the dynamic response and injuries of pedestrian head in the scenarios with head hitting windshield. This study aims to investigate the significant factors that affect the dynamic response and injuries of pedestrian head through finite element-multi-body coupling simulations. Two finite element vehicle models and two multi-body pedestrian human models were used to build the coupling simulations. Orthogonal experimental design and analysis of variance were used for parameter combination and data analysis. This study demonstrated that the dynamic response of pedestrian head and HIC15 were strongly associated with collision speed and pedestrian orientation. Vehicle type had a significant influence on the dynamic response of pedestrian head and HIC15, while there was no significant relationship between the dynamic response of pedestrian head and HIC15 and the size of pedestrian human models. Collision speed, pedestrian orientation, and vehicle type should be prioritized over the other collision parameters in the study of head injury mechanism and reconstruction of vehicle-pedestrian collisions in the scenarios with head hitting windshield.

Real-world car-to-pedestrian-crash data from an urban centre

BACKGROUND

Pedestrians are at a high risk for crash and injury. This study aims at comparing data from real world crashes with data gathered from experimental settings.

METHODS

IMPAIR (In-Depth Medical Pedestrian Accident Investigation and Reconstruction) was a prospective, observational study performed in a metropolitan area. Data was collected on-scene, from clinical records, and interviews. Data comprise crash data, details on injury pattern and injury severity.

RESULTS

Thirty-seven pedestrians (of which 19 males) with a mean 37.1 years of age were included in the study. The mean collision speed was 49.5 km/h (SD 13.7, range, 28 - 93). The mean ISS (31.0, SD 25.4) and the 24% fatality rate indicate a substantial trauma load. The most common AIS 4+ injuries were to the head (23 subjects), followed by chest (8), pelvis (4), and abdomen (2). An association of impact side and injury side (right/left) was found for abdominal, chest, pelvic, and upper limb injuries. Primary head impacts were documented on the windscreen (19 subjects), hood (10), A-pillar (2), and edge of the car roof (2). With bivariate analysis, a significant increase of MAIS 4+ head injury risk was found for collision speeds of >40 km/h (OR 9.00, 95% CI 1.96-41.36).

CONCLUSION

The real-world data from this study is in agreement with previous findings from biomechanical models and other simulations. This data suggest that there may be reason to include further pedestrian regulations in EuroNCAP.

Non-collision injuries in urban buses--strategies for prevention

Public transport is a potentially important part of independent living for older people, but they are over-represented in non-collision bus injuries. This paper reports on a computational modelling approach to addressing this problem: the Madymo human model validated for simulating passive, seated vehicle occupants was adapted to simulate a standing passenger in an accelerating bus. The force/deformation characteristics of the bus were measured and the human model was expanded to include a validated active hand grip. Real world urban bus acceleration profiles were measured and used as inputs for the simulations. Balance loss could not be predicted, but injuries from contact with the vehicle floor following a fall were evaluated. Results show that peak bus accelerations measured (+/-0.32g) exceed reported acceleration thresholds for balance loss for a standing passenger using a handgrip (0.15g). The maximum predicted probability of knee and head injuries arising from impact with bus seats, handrails and walls were 53% and 35%, respectively. The stairwell and horizontal seatback handles were particularly hazardous and the latter should be replaced with vertical handrails. Driver training should be expanded to include video training based on multibody simulations to highlight the risks for standing passengers induced by harsh braking and acceleration.

Three-dimensional finite element analysis of subdural hematoma

BACKGROUND

Head motion, an important factor in acute subdural hematoma (ASDH), can be broken down into translational and rotational elements. We used three-dimensional finite element analysis to examine the thresholds of angular and tangential acceleration required to tear bridging veins in humans during head impact.

METHODS

The lengths of midsagittal and parasagittal bridging veins were calculated first. To assess the effect of translational and rotational acceleration, the strain of each vein was then computed under three different motions. The threshold of ASDH was expressed in terms of tangential and rotational acceleration.

RESULTS

Deformation-angle histories of the midsagittal and parasagittal bridging veins showed that veins that drain forward into the superior sinus at a 130-degree angle incurred the greatest stretch strain during occipital impact. In the midsagittal plane, pure rotation induced greater stretch strain on these veins (14.4%) than pure translation (2.5%) or combined translation and rotation motion (10.4%). A tangential acceleration of 3,912.9 G or an angular acceleration of 71.2 krad/s2 seemed to approximate the threshold for ASDH in the human midsagittal plane, whereas 5,010.9 G and 97.4 krad/s2 approximated the threshold in the parasagittal plane.

CONCLUSION

Impact direction and orientation of bridging veins are both important factors in ASDH. Threshold criteria for ASDH can be expressed in terms of tangential and rotational acceleration.

Field and analytic observations of impact brain injury in fatally injured pedestrians

To develop more effective head protection against impact injury, maximum levels of mechanical impact or injury tolerance criteria, or both, should be specified for particular levels of injury and for particular structures of the brain. By using a development of an existing very simplified model of the head-vehicle impact for pedestrians we were able to make estimates of the peak angular acceleration and change in angular velocity of head impacts for fatally injured pedestrians. This model also enabled us to examine the relationship between the parameters of the impact, and the critical strain curves for brain injury proposed by Margulies and Thibault (1992). It was found that the offset of the impact from the center of mass of the head was a major influence, and, in addition, in impacts with a combined head/vehicle stiffness above 130 kN/m, the head impact velocity and change in head angular velocity were important, whereas for impacts with lower stiffness, the stiffness of the impact structure and hence, peak angular acceleration, were the major influences. Transformed into the frequency domain, the 130 kN/m region corresponds roughly to a harmonic of the natural frequency of the brain and skull, and the change in behavior may be related to decoupling of the skull and brain at impact. In 12 cases of lateral head impact, all but one case with visible injury in the corpus callosum were found to lie close to or above the 10% critical strain curve. Despite the very wide error limits around each data point, there is sufficient consistency between the field observations of brain injury and the analytic findings to suggest that the 10% critical strain curve represents a threshold for brain injury, expressed in terms of peak angular acceleration and change in angular velocity.