Lower Legform Research Articles

Numerical investigation on automotive bumper structure improvements for pedestrian protection

ABSTRACTVehicle bumper design remains a key automotive engineering design challenge for ensuring pedestrian safety in car accidents. In this study, a three-dimensional finite-element lower legform is simulated and validated using static and dynamic tests according to three main criteria, namely, the upper tibia acceleration, knee shearing displacement and bending angle. Important design parameters such as material, thickness and location of different parts of the front vehicle structure were studied. The lower legform and dynamic impactor were simulated in LS-DYNA according to European commission (EC) regulation No 631/2009. Then, the legform and a Class-B car front bumper were used in collision tests at three different distances from the bumper centre point. Finally, the design was optimised in order to meet all requirements of the EC regulation related to vehicle pedestrian collision tests, and an improved bumper model which guarantees complete pedestrian protection is presented and discussed along with guidelines which can have significant applications in the design of pedestrian-friendly bumper structure components.

Design and Validation of a Structural Flexibility Pedestrian Lower Legform

Nowadays automobiles are with good performance and comfortable; however, safety gradually becomes an issue because of high incidence of traffic accidents. Except for occupants injured in traffic accidents, other vulnerable road users, like pedestrians, are also in danger. Pedestrians make up 16% of all road traffic fatalities in the EU and over 30% in Japan, their percentage can exceed 50% in developing countries. In nonfatal car-pedestrian accidents, lower extremities are the most commonly injured body parts.EEVC proposed sub-system tests to evaluate responses and injuries of pedestrians in lateral car-pedestrian accidents, in which lower legform to bumper tests are used to investigate leg injuries. Now the TRL-PLI and Flex-PLI have developed, and both have their pros and cons. In this study it is to modify existing lower legform impactor model, and the new model is still with high biofidelity, inexpensive and easy to manufacture and assemble. The new model can then be made physically and applied to relevant tests and development of pedestrian passive safety system.In order to ensure the biofidelity of new legform impactor model, it is needed to conduct certification tests. Setup and biofidelic corridor of certification tests are based on PMHS tests. This study constructs the finite element model of human-like legform impactor model and makes use of LS-DYNA to perform the same tests as PMHS to evaluate its biofidelity. Certification tests consist of component and assembly tests. Component tests include 3-point leg bending tests and 4-point knee joint bending tests, and assembly tests comprise shearing and bending tests, all above in lateral direction. After finishing all the certification tests, testing results are analyzed and compared with those of two existing legform impactors. One legform to bumper test is conducted as a case of application.

Computer Model of a Mechanical Surrogate for Pedestrian Lower Extremity on Bumper Safety Evaluation

This study proposes engineering countermeasures for lowering the possibility of pedestrian lower-extremity injuries. Pedestrian safety tests are commonly performed using anthropometric test device (ATD) subsystems. The lower legform is used to assess lower-extremity injuries during impact. In this study, a computer model of a mechanical surrogate for a pedestrian lower extremity is developed based on the finite element (FE) method. Results from the FE model indicate that the surrogate passes all certification tests proposed by the European Enhanced Vehicle-Safety Committee (EEVC), meaning that the model is biofidelic and suitable for the assessment of lower-extremity injuries due to car-pedestrian impact. In addition, a bumper system is chosen as an example to demonstrate safety evaluation by this pedestrian lower extremity surrogate. Based on the demonstration results, the safety of the bumper system is investigated.

Performance analysis of a bumper–pedestrian contact sensor system by using finite element models

A pedestrian contact sensor in the car bumper is a potential solution to trigger an active hood system. Because of the high level of temperature dependency for the bumper foam stiffness, the sensor output can be unstable at varying temperatures. A new contact sensor was, therefore, developed to provide a temperature-independent measurement for pedestrian impacts. This study analysed the performance of the bumper–pedestrian contact sensor system. First, a baseline finite element (FE) bumper model of a production car was developed and validated. On the basis of the baseline model, an improved bumper model was subsequently developed to meet the requirements of the lower leg form impact tests proposed by Working Group 17 of the European Enhanced Vehicle-safety Committee. Second, an FE human lower extremity model was developed. Using this model, the baseline and improved bumper models were further evaluated in terms of the predicted knee ligament raptures and long bone fractures. Finally, the new contact sensor was built into the improved bumper model. A performance study was then conducted to evaluate the sensor effectiveness. Consequently, a better diameter for the sensor tube was identified in terms of the temperature stability and mass sensitivity of the sensor output.