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Influence of Body and Head Angular Velocity on Brain Injury Prediction in Pedestrian Accidents
KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.ORCID iD: 0000-0001-7908-6270
KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
Autoliv Research.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Pedestrian protection has historically not been prioritized in the vehicle safety development, but represents a large portion of the severe and deadly injuries in vehicle accidents. One of the most common severely injured body parts is the head and the focus of many researchers and safety system developers. The Finite Element (FE) method is an increasingly popular approach to better understand the injury biomechanics, but due to the large system needed to be solved in pedestrian simulations a common approach is to reduce the problem to a head only impact. In EuroNCAP rating an isolated head form is impacted towards different regions of the vehicle with only linear velocity components. The aim of this study is to determine the effect of removing the neck and body, as well as rotational velocity components on the brain injury prediction. A pedestrian full body human FE model was impacted against a generalized buck model to simulate pedestrian accidents involving windscreen impacts, at three velocities (30, 40 and 50 or 45 km/h), two pedestrian velocities (0 and 5 km/h) and two standard walking gaits. The head position was extracted from the pedestrian full body simulations at 1 ms before head impact. The isolated head was impacted with the vehicle model using either all velocity components from the full body simulations, or only the linear components. The results show that the body and neck can affect the brain injury prediction in windscreen impacts, reducing the strains by up to 49%. It was also shown that removing the rotational impact velocities, in general, further increased the strain, with up to 138%. However, several cases showed a reduction in brain strains for the head only simulations by up to 40%, and in other cases only very small difference down to 1% were seen, indicating a high sensitivity to impact conditions and highlighting the difficulty in generalizing the effect. It is however generally seen that the body is limiting the severity in impacts close to the windscreen center, and amplifying the severity of those close to the lower frame. It could also be seen that removing the angular velocity, in most cases, further increased the difference between the full body and head only simulations.

Keyword [en]
Pedestrian Accident, Finite Element, Brain injury, Head only, Full body, Windscreen
National Category
Other Medical Engineering
Research subject
Applied Medical Technology
Identifiers
URN: urn:nbn:se:kth:diva-215645OAI: oai:DiVA.org:kth-215645DiVA: diva2:1148614
Projects
Human Body Model with Active Muscles and Detailed Head for Pedestrian Protection - Prediction of Neck and Head Injuries
Funder
VINNOVA
Note

QC 20171012

Available from: 2017-10-11 Created: 2017-10-11 Last updated: 2017-10-12Bibliographically approved
In thesis
1. Understanding Boundary Conditions for Brain Injury Prediction: Finite Element Analysis of Vulnerable Road Users
Open this publication in new window or tab >>Understanding Boundary Conditions for Brain Injury Prediction: Finite Element Analysis of Vulnerable Road Users
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Vulnerable road users (VRUs) are overrepresented in the statistics on severe and deadly injuries in traffic accidents, most commonly involving the head. The finite element (FE) method presents the possibility to model complex interactions between the human body and vehicles in order to better understand the injury mechanisms. While the rapid development of computer capacity has allowed for increasingly detailed FE-models, there is always a benefit of reducing the studied problem. Due to its material properties, the brain is more sensitive to rotational motion than to purely linear, resulting in complex injury causation. When studying brain injuries caused by a direct impact to the head, simulations using an isolated head model significantly increases efficiency compared to using a complete human body model. Also evaluation of head protective systems uses isolated mechanical head representations. It is not, however, established the extent to which the boundary conditions of the head determine the outcome of brain injuries.

FE models of both the entire human body and the isolated head were used in this thesis to study the effect of the body, as well as active neck muscle tension, on brain injury outcome in VRU accidents. A pediatric neck model was also developed to enable the study of age-specific effects. A vehicle windscreen model was developed to evaluate the necessity of capturing the failure deformation during pedestrian head impacts.

It was shown that the influence of the neck and body on brain injury prediction is greater in longer duration impacts, such as pedestrian head-to-windscreen impacts with an average difference of 21%. In accidents with shorter duration impacts, such as head-to-ground bicycle accidents, the average influence was between 3-12%. The influence did not consistently increase or limit the severity, and was dependent on the degree of rotation induced by the impact, as well as the mode of deformation induced in the neck. It was also shown that the predicted brain injury severity is dependent on capturing the large deformations of fractured windscreen, with the greatest effect near the windscreen frame. The pediatric neck model showed a large effect of age-dependent anatomical changes on inertial head loading, making it a promising tool to study the age-dependent effects in VRU accidents.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. 83 p.
Series
TRITA-STH : report, ISSN 1653-3836 ; 2017:11
Keyword
Brain injuries; Vulnerable Road Users; windscreen impacts; Finite Element Analysis; pedestrian accidents; cycling accidents; pediatric neck
National Category
Other Medical Engineering
Research subject
Applied Medical Technology
Identifiers
urn:nbn:se:kth:diva-215643 (URN)978-91-7729-568-6 (ISBN)
Public defence
2017-11-06, T2, Hälsovägen 11C, Huddinge, 10:00 (English)
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Supervisors
Note

QC 20171013

Available from: 2017-10-13 Created: 2017-10-12 Last updated: 2017-10-16Bibliographically approved

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