Jikuang Yang

Computer Simulation of Impact Response of the Human Knee Joint in Car-pedestrian Accidents

A 3D pedestrian knee joint model was deve-loped as a first step in a new description of the whole pedestrian body for computer simulations. The model was made to achieve better correlation with the results from previous tests with biological material. The model of the knee joint includes the articular surfaces, ligaments and capsule repre-sented by the ellipsoid and plane elements as well as the spring-damping elements, respectively. The mechanical properties of the knee joint were based on available biomechanical data. To verify the new developed model with results from tests with biological material previously performed at the Department of Injury Prevention, Chalmers University of Technology, the computer simulations were carried out with the model of the knee joint using the MADYMO 3D program. To simulate different test conditions, which correspond to previous tests with biomechanical system, the following parameters were varied in our simulations: bumper height and bumper compliance. Four com-puter simulations were performed and compared with four test series with biological material with five tests in each series. The impact force, the condyle interface forces, the ligament forces and the ligament relative elongations were calculated and verified with the results of the tests with biological material. The output parameters calculated from the knee joint model correspond in general to what was observed in the studies with biological material. Complementary two computer simulations were performed to study the influence of the upper body mass to the distribution of the forces in the simulated knee structures. These simulations appear that body mass has an influence on the impact and condyle forces, the ligament strain and on the trajectory of the lower extremities.

A Human-Body 3D Mathematical Model for Simulation of Car-Pedestrian Impacts

A 3D mathematical model of the human body was developed to simulate responses of pedestrians in car impacts. The model consists of fifteen body segments connected by fourteen joints, including two human-like knee joints and two breakable-leg segments. The anthro pometrical data for the model were generated by the GEBOD program, and characteristics of the body segments and the joints were defined based on available biomechanical data. The validity of the model was evaluated against full-scale impact tests with pedestrian substitutes and an experimental car in terms of the kinematics of the pedestrian substitute, bumper impact forces, accelerations of the body segments, and failure description from anatomical investigations of the pedestrian substitutes. The sensitivity of the model to input variables was studied at impact speeds of 15 and 40 km/h with the following car-front parameters: bumper height, bumper stiffness, bumper lead distance, height of hood edge, and hood-edge stiffness. The validated model demonstrated its capability in simulations of car-pedestrian impacts for the assessment of responses of pedestrians, prediction of risks of pedestrian injuries and for the development of safety countermeasures.

A Study of Influences of Vehicle Speed and Front Structure on Pedestrian Impact Responses Using Mathematical Models

A validated pedestrian multibody model was used to investigate the influences of impact speed and vehicle front structure on the pedestrian dynamic responses in vehicle collisions. To predict the injury risks of pedestrians at different impact speeds, the injury-related parameters concerning head, chest and lower extremity areas were calculated from mathematical simulations. Four vehicle types including large and compact passenger cars, minivans and light trucks were simulated according to their frequency of involvement in real world accidents. The influences of various vehicle front shape and compliance parameters were analyzed. Based on the results from the parametric study, the possible benefits from speed control in urban area were assessed, and a feasible speed limit was proposed to reduce the risks of pedestrian injuries. Moreover, the possible countermeasures on basis of vehicle front design to mitigate the injury severity of the pedestrians were discussed.

Head Injuries in Child Pedestrian Accidents—In-Depth Case Analysis and Reconstructions

Objective. The aim of this study was to investigate head injuries, injury risks, and corresponding tolerance levels of children in car-to–child pedestrian collisions. Methods. An in-depth accident analysis was carried out based on 23 accident cases involving child pedestrians. These cases were collected with detailed information about pedestrians, cars, and road environments. All 23 accidents were reconstructed using the MADYMO program with mathematical models of passenger cars and child pedestrians developed at Chalmers University of Technology. The contact properties of the car models were derived from the European New Car Assessment Program (EuroNCAP) subsystem tests. Results. The accident analysis demonstrated that the head was the most frequently and severely injured body part of child pedestrians. Most accidents occurred at impact speeds lower than 40 km/h and 98% of the child pedestrians were impacted from the lateral direction. The initial postures of children at the moment of impact were identified. Nearly half (47%) of the children were running, which was remarkable compared with the situation of adult pedestrians. From accident reconstructions it was found that head impact conditions and injury severities were dependent on the shape and stiffness of the car front, impact velocity, and stature of the child pedestrian. Head injury criteria and corresponding tolerance levels were analyzed and discussed by correlating the calculated injury parameters with the injury outcomes in the accidents. Conclusions. Reducing head injuries should be set as a priority in the protection of child pedestrians. HIC is an important injury criterion for predicting the risks of head injuries in child pedestrian accidents. The tolerance level of head injuries can have a considerable variation due to individual differences of the child pedestrians. By setting a suitable speed limit and improving the design of car front, the head injury severities of child pedestrians can be reduced.

Development of Child Pedestrian Mathematical Models and Evaluation with Accident Reconstruction

Four mathematical models were developed to represent 3-, 6-, 9-, and 15-year-old child pedestrians. In the absence of biomechanical data of children, resistive properties of various joints and body segments were scaled down from that of a validated adult model. Differences in anatomical structure and age-dependent properties of biological tissues were taken into consideration. In this study, the primary effort was emphasized on the scaling of lateral bending properties of the vertebrae column and knee joint, as well as the contact stiffness of the lower extremity. The scaling factors of contact stiffness for other body regions, such as head and thorax, were adopted from the literature. To evaluate the performance of the child pedestrian models, two real-world accidents were reconstructed by using the accident data from in-depth investigation. The impact responses of child models agreed reasonably well with the actual injury outcomes in accidents.

Finite element analysis of kinematic behaviour and injuries to pedestrians in vehicle collisions

In vehicle-to-pedestrian collisions, the characteristics of a vehicles frontal shape and structural stiffness have a significant influence on the kinematics and injury risk of the pedestrians body regions. In the present study, the kinematic behaviour and injury risk of the pedestrians were investigated in collisions against vehicles with different frontal shapes. The THUMS (Total HUman Model for Safety) pedestrian finite element (FE) model was used and impacted by three different types of vehicle FE models (passenger car, one-box vehicle and sport-utility vehicle [SUV]) representing the different frontal shapes at 40 km/h. In the simulation with the passenger car-to-pedestrian impact, the pedestrian wrapped around the hood, and the resulting bending moment of the lower extremity and head injury criterion (HIC) value were high. In the simulation with the one-box vehicle-to-pedestrian impact, the pedestrians upper torso was directly hit by the front end of the vehicle. The pelvis and chest had contact with the stiff vehicle frontal panel, resulting in a high stress being observed on the rib cage. In the simulation with the SUV-to-pedestrian impact, the force of the pelvis was high due to the contact with the vehicle hoods leading edge. The results indicated that the frontal shape of the vehicle has a large effect on the pedestrian kinematic behaviour, including the impact velocity of the pelvis, chest, and head against the vehicle. Moreover, the stiffness of the vehicle structure can affect the deformation mode of the human body segments, such as the lower extremities and the rib cage. The injury predictions for each body region from the FE analyses agreed with observations from pedestrian accidents involving a car, one-box vehicle and SUV, respectively.

Reconstruction of Head-to-Hood Impact in an Automobile-to-Child-Pedestrian Collision

Abstract Head injuries are among the most common injuries sustained in automobile-to-childpedestrian collisions (ACPCs), and are the leading cause of death. The aim of this article is to systematically investigate child impact dynamics, head injury biomechanics and associated tolerance levels. For this purpose, two numerical methods, a multibody system (MBS) method with MBS pedestrian and car models and a facet element method with facet pedestrian and car models, were used to reconstruct an actual ACPC. Reconstruction results revealed good agreement between the kinematics generated by the child pedestrian models and the corresponding values from the actual accident in terms of wrap-around distance and throw distance. Both methods generated similar estimates of head-impact conditions, like impact velocity, impact angle and impact timing. The calculated head injury parameters of these two pedestrian models also exhibited good correlation with the head injuries sustained in the actual accident.

COMPUTER SIMULATION OF SHEARING AND BENDING RESPONSE OF THE KNEE JOINT TO A LATERAL IMPACT

A three-dimensional multibody system model of the lower extremity was used to simulate two series of previously performed experiments with lower extremity specimens at lateral impact speeds of 15 and 20 km/h. In the simulation of lateral shearing response of the knee joint, the predicted peak shearing displacement was 8-9 mm during the first 10 ms of the impact. This displacement is the main effect of the intra-articular failure of the knee joint to the lateral shearing force. In simulations of response of the knee joint to lateral bending load, the predicted lateral bending angle was about 8-13 degrees at 20 ms after impact, the corresponding strain of the medial collateral ligament (MCL) was 12-15%. The results confirmed that bending failure of the knee is dominated by the knee lateral rotation during the period of 15-50 ms after impact. The outcomes from the simulations are analysed and discussed in terms of the injury mechanisms of the knee joint. The mathematical modelling of the response of the knee joint to transient shearing and bending loads gives a better understanding of the injury mechanism of this body region in car-pedestrian accidents, and it is able to predict the risk of knee injuries corresponding to these two mechanisms. For the covering abstract of the conference see IRRD 882980.

A study of bicyclist kinematics and injuries based on reconstruction of passenger car-bicycle accident in China.

Like pedestrians, bicyclists are vulnerable road users, representing a population with a high risk of fatal and severe injuries in traffic accidents as they are unprotected during vehicle collisions. The objective of this study is to investigate the kinematics response of bicyclists and the correlation of the injury severity with vehicle impact speed. Twenty-four car-bicyclist cases with detailed information were selected for accident reconstruction using mathematical models, which was implemented in the MADYMO program. The dynamic response of bicyclists in the typical impact configuration and the correlation of head impact conditions were analyzed and discussed with respect to the head impact speed, time of head impact and impact angle of bicyclists to vehicle impact speed. Furthermore, the injury distribution of bicyclists and the risk of head injuries and fractures of lower limbs were investigated in terms of vehicle impact speed. The results indicate that wrap-around distance (WAD), head impact speed, time of head impact, head impact angle, and throw-out distance (TOD) of the bicyclists have a strong relationship with vehicle impact speed. The vehicle impact speed corresponding to a 50% probability of head AIS 2+ injuries, head AIS 3+ injuries, and lower limb fracture risk for bicyclists is 53.8km/h, 58.9km/h, and 41.2km/h, respectively. A higher vehicle impact speed produces a higher injury risk to bicyclist. The results could provide background knowledge for the establishment or modification of pedestrian regulations considering bicyclist protection as well as being helpful for developing safety measures and protection devices for bicyclists.

A Study of Adult Pedestrian Head Impact Conditions and Injury Risks in Passenger Car Collisions Based on Real-World Accident Data

Objective: The aim of the current study was to study the kinematics of adult pedestrians and assess head injury risks based on real-world accidents. Methods: A total of 43 passenger car versus pedestrian accidents, in which the pedestrians head impacted the windscreen, were selected from accident databases for simulation study. According to real-world accident investigation, accident reconstructions were conducted using multibody system (MBS) pedestrian and car models under MADYMO environment (Strasbourg University) to calculate head impact conditions in terms of head impact velocity, head position, and head orientation. Pedestrian head impact conditions from MADYMO simulation results were then used to set the initial conditions in a simulation of a head striking a windscreen using finite element (FE) approach. Results: The results showed strong correlations between vehicle impact velocity and head contact time, throw distance, and head impact velocity using a quadratic regression model. In the selected samples, the results indicated that Abbreviated Injury Scale (AIS) 2+ and AIS 3+ severe head injuries with probability of 50 percent were caused by head impact velocity at about 33 and 49 km/h, respectively. Further, the predicted head linear acceleration (head injury criterion, HIC) value, resultant angular velocity, and resultant angular acceleration for 50 percent probability of AIS 2+ and AIS 3+ head injury risk were 116 g, 825, 40 rad/s, 11,368 rad/s2 and 162 g, 1442, 55 rad/s, 18,775 rad/s2, respectively, and the predicted value of 50 percent probability of skull fracture was 135 g. Conclusions: The present study provides new insight into pedestrian head impact conditions in terms of velocity, angle, and impact location based on a number of real-world cases. Therefore, it may perform a critical analysis for current pedestrian head standard tests.