The influence of impact speed on chest injury outcome in whole body frontal sled impacts

While the seatbelt restraint has significantly improved occupant safety, the protection efficiency still needs further enhance to reduce the consequence of the crash. Influence of seatbelt restraint loading on chest injury under 40 km/h has been tested and documented. However, a comprehensive profiling of the efficiency of restraint systems with various impact speeds has not yet been sufficiently reported. The purpose of this study is to analyse the effect of the seatbelt load-ings on chest injuries at different impact speeds utilizing a high bio-fidelity human body Finite Element (FE) model. Based on the whole-body frontal sled test configuration, the current simulation is setup using a substitute of Post-Mortem Human Subjects (PMHS). Chest injury outcomes from simulations are analysed in terms of design variables, such as seatbelt position parameters and collision speed in a full factorial experimental design. These outcomes are specifically referred to strain-based injury probabilities and four-point chest deflections caused by the change of the parameters. The results indicate that impact speed does influence chest injury outcome. The ribcage injury risk for more than 3 fractured ribs will increase from around 40 to nearly 100% when the impact speed change from 20 to 40 km/h if the seatbelt positioned at the middle-sternum of this study. Great injuries to the chest are mainly caused by the change of inertia, which indicates that chest injuries are greatly affected by the impact speed. Furthermore, the rib fracture risk and chest deflection are nonlin-early correlated with the change of the seatbelt position parameters. The study approach can serve as a reference for seatbelt virtual design. Meanwhile, it also provides basis for the research of chest injury mechanism

A Study on Influence of Minivan Front-End Design and Impact Velocity on Pedestrian Thorax Kinematics and Injury Risk

Thoracic injuries occur frequently in minivan-to-pedestrian impact accidents and can cause substantial fatalities. The present research work investigates the human thoracic responses and injury risks in minivan-to-pedestrian impacts, when changing the minivan front-end design and the impact velocity, by using computational biomechanics model. We employed three typical types of minivan model of different front-end designs that are quite popular in Chinese market and considered four impact velocities (20, 30, 40, and 50 km/h). The contact time of car to thorax region (CTCTR), thorax impact velocity, chest deformation, and thoracic injury risks were extracted for the investigation. The results indicate that the predicted pedestrian kinematics, injury responses, and thoracic injury risks are strongly affected by the variation of the minivan front-end design and impact velocity. The pedestrian thoracic injury risks increase with the increasing vehicle impact velocity. It is also revealed that the application of the extra front bumper is beneficial for reducing the thoracic injury risk, and a relatively flatter minivan front-end design gives rise to a higher thoracic injury risk. This study is expected to be served as theoretical references for pedestrian protection design of minivans

An Approach to Improve Vehicle-Front Design for Pedestrian Protection Using Mathematical Models

In this study a validated human-body mathematical model was used as a pedestrian substitute in computer simulations of car-pedestrian impacts to investigate the influences of car front structures on pedestrian response to the impacts. The injury related parameters were calculated with this model, and used to evaluate the risk of pedestrian injuries in vehicle impacts. The influence of car-front parts to responses of a pedestrian was investigated with varying car-front parameters. Furthermore, a strategy in new vehicle-front design for pedestrian protection was presented in this paper, and the possible improvement was described and discussed

An Approach to Improve Vehicle-Front Design for Pedestrian Protection Using Mathematical Models

In this study a validated human-body mathematical model was used as a pedestrian substitute in computer simulations of car-pedestrian impacts to investigate the influences of car front structures on pedestrian response to the impacts. The injury related parameters were calculated with this model, and used to evaluate the risk of pedestrian injuries in vehicle impacts. The influence of car-front parts to responses of a pedestrian was investigated with varying car-front parameters. Furthermore, a strategy in new vehicle-front design for pedestrian protection was presented in this paper, and the possible improvement was described and discussed

Mathematical Simulation of Knee Responses Associated with Leg Fracture in Car-Pedestrian Accidents

A new mathematical model of a pedestrian with a breakable leg and a human-like knee was developed to simulate the fracture of the leg in a car-pedestrian impact, and knee responses associated with leg fracture in such an impact to the leg. The leg model consists of two elements connected by a frangible joint. The characteristics of the frangible joint are described by a moment-rotation function; this is based on the leg fracture tolerance data from tests with leg specimens. The knee model origin was based on the anatomical structure of the knee; it represents a femoral condyle-ligament-tibial condyle complex. The pedestrian mathematical model was implemented using the MADYMO 3D program and verified against previous impact tests with biological specimens at a speed of 31 km/h. In the simulation of leg fracture, calculated ligament strain was 9% for MCL (medial collateral ligament), and 25% in the simulation without leg fracture. Contact forces between the lateral articular surfaces in the case of no leg fracture were about 85% higher than in the case of leg fracture. Results from computer simulations confirmed that the impact response and injury mechanism of the knee joint are dependent on whether or not the leg is fractured. The breakable leg model gave a higher biofidelity than did the original one-legged pedestrian model with an undeformable representation of the leg segment

Injury Biomechanics and Protective Systems in Car-to-Pedestrian Collisions

The injury biomechanics of pedestrians in vehicle impacts and research approaches are described in this paper. Of which include identification of injury patterns in car pedestrian collisions, determination of injury mechanisms and body segment tolerance levels, development of method and techniques for injury assessment and safety system evaluation. The possible protective countermeasures are summarized and further studies on pedestrian protection are proposed

Injury Biomechanics in Car-Pedestrian Collisions: Development, Validation and Application of Human-Body Mathematical Models

The aim of this study was to develop and validate human-body mathematical models which can be used to simulate the dynamic responses of pedestrians in a car impact. The main focus has been on simulations of bumper impact to the lower extremities, since lower extremity injuries most frequently occur in car-pedestrian accidents and result in long-term consequences and high social costs. Two approaches were used: (1) modeling with the multibody system (MBS); (2) modeling with the finite element method (FEM). Different models were developed, including a human-like knee joint MBS model, a breakable leg MBS model, a complete human-body MBS model, and a lower extremity skeleton FEM model. The MBS models were implemented by the MADYMO 3D program, and the FEM model by DYNA3D program. The models were validated by tests with biological subjects. The models enabled simulations of the responses of the lower extremity to a lateral bumper impact to be carried out. The injury mechanisms and the prediction of injury risk of the knee-leg complex was the focus of this study. Furthermore, simulations of full scale car-pedestrian impacts were done to predict the risk of pedestrian injuries in car accidents and to investigate influences of car-front parameters on the risk of pedestrian injuries. The human-like knee model gives insights into the injury mechanisms of the knee in a lateral impact. The knee responses were analyzed in terms of ligament strain, condyle contact force, and transverse dislocation between articular surfaces. The correlation between the outcome from simulations and injuries observed in tests with biological subjects was established. Calculated ligament strains greater than 20% were related to ligament failure in tests, and condyle contact forces greater than 6 kN were related to condyle fracture. Predicted transverse dislocations of 8-9 mm between articular surfaces in simulations confirmed the findings in the high-speed film analysis of the knee responses to lateral impacts at 15-20 km/h. The knee-injury mechanisms can be summarized as ligament tension and condyle compression due to a combination of shearing, bending, and torsional loading applied to the knee joint. The knee injuries are dominated by bending load. The breakable leg model filled a gap in modeling leg fracture and improved the sensitivity of the pedestrian model. The simulation of the knee responses associated with leg fracture in car-pedestrian impacts indicated that the impact response and injury mechanism of the knee in a lateral bumper impact with the upper part of the leg are both dependent on whether or not the leg is fractured. For a more realistic model of the lower extremity skeleton, the FEM model was used. It contributed to a better understanding of the impact responses of the knee-leg complex by means of an analysis of stress distribution within the simulated structures. The stress analysis with the FEM model indicated that the calculated tensile stress of 160 MPa in a lateral impact at 31 km/h correlates well with the ultimate tensile strength of the leg bone determined in biological tests. The complete human-body model was used to simulate car-pedestrian impacts. The effects of the car-front on pedestrian responses were evaluated in terms of the bumper height and stiffness, the bumper-lead distance, hood-edge height and stiffness. The effects of bumper and hood edge on knee-leg responses were identified. It was found that the head responses are significantly influenced by the height of the hood-edge and less influenced by the bumper. The developed models demonstrated capabilities for predicting the risk of pedestrian injuries in an impact with a vehicle. For instance, the breakable leg model can be used to predict the risk of long bone fractures. From the knee model, the forces and moments transferred through the knee, and the strain of the knee ligaments can be calculated to evaluate the knee failures. For the head, the linear acceleration, the HIC value and the angular acceleration can be calculated to predict risk of head injuries. The models are thus valuable tools to acquire better knowledge of impact biomechanics in car-pedestrian accidents and help assess the performance of vehicle front structures and develop safety countermeasures