European Enhanced Vehicle-Safety Committee Research Articles

A damage model for the simulation of crack initiation and propagation in automotive windshield laminated glass structures

Accident reconstructions and numerical simulations are used to evaluate and improve protective systems. Virtual testing and numerical methods can assist in the improvement safety of vulnerable road users. This work presents the tremendous potential of using computer-aided engineering by describing the development of a windshield numerical model and its damage and fracture validation. The motivation behind this study is the possibility of using such a model in the reconstruction of road accidents involving vulnerable road users. The main goal is the development and validation of a finite element model of an automobile windshield in order to use it in further studies regarding the reconstruction of road traffic accidents. In order to validate it according to experimental studies available in the literature, the 4.8 kg standard adult headform from the European Enhanced Vehicle Safety Committee is also developed and validated. A total of eight impacts at six different locations and carried at two different impact velocities (6 m/s and 11.1 m/s) were simulated. The validation of the windshield model, and consequently the damage model employed to simulate glass cracking initiation and propagation, were accomplished by comparing the acceleration at the headform’s centre of gravity and the windshield’s fracture pattern against experimental data.

DEVELOPMENT AND VALIDATION OF EEVC WG17 LOWER LEGFORM FE MODEL FOR PEDESTRIAN SAFETY

Vehicle-pedestrian collisions had claimed the lives of many in the world roads yearly. Among the types of injury that may occur in a vehicle-pedestrian collision, lower extremity injur ies have the highest account. These alarming statis tic has encouraged joining effort from researchers, car manufacturers and the governm ent to find solutions in reducing the risk of vulne rable road users. The car bumper structure design plays a crucial role in cus hioning the impact on the pedestrian leg during a cThe European Enhanced Vehicle-Safety Committee (EEVC) has develo ped test methods to evaluate severity of the lower leg injury, upper leg injury and head impact injury in a vehicle-pedestrian simu lated collision. Since lower extremity injury are m ost common, undivided attention should be paid on the lower legform to bumper test. The maximum bending angle, maximum shearing displa cement and maximum tibia acceleration are among the three injury crite rion determined for lower legform to bumper test. B efore the lower legform to bumper test can be perform the lower legform has to be certified statically and dynamically. The advancement of computerization had supported th e usage of Finite Element Method(FEM) in simulating real life scenarios for analysis. Irregular geometries are now discretized and solved numerically. Finite Element Analysis(FEA ) has proven to reduce time and cost significantly therefore the author took ad vantaged of this tool and simulated a lower legform to bumper collision. This paper presents in detail the static and dynamic certifica tion of the Finite Element (FE) legform model using the HyperWorks software. The static results for both bending and shearing has to be within the EEVC/WG17 limits and the internal en ergy at 15o shall be 100±7J. The maximum bending angle shall not be less than 6. 2o and not more than 8.2o, the maximum shearing dis placement shall not be less than 3.5mm and not more than 6mm, and the maximum u pper tibia acceleration shall not be less than 120g and not more than 250g in the dynamic certification test.

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.

Design of a bumper system for pedestrian lower-leg protection using the Taguchi method

The main aim of this study is to design a bumper system which is capable of lessening the possibility of pedestrian lower-extremity injuries in car–pedestrian collisions. The current pedestrian safety regulation recognized by most countries worldwide is to apply a lower-legform impactor to assess the lower-extremity injuries during impact. Therefore, a numerical pedestrian lower-legform impactor is developed based on the finite element method to evaluate the bumper safety in the study. Five design parameters for the bumper system, according to the stiffness and geometry of the energy absorber and the bumper beam, are selected to demonstrate this design strategy. The sensitivities of these design parameters are analysed by means of the Taguchi method to reduce the leg injuries of a pedestrian based on impact tests defined by the European Enhanced Vehicle-Safety Committee (EEVC). Consequently, the optimal combination is attained, and the result satisfies the EEVC criteria on the protection of a pedestrian from leg injury.

Assessment of the pedestrian friendliness of a vechicle using subsystem impact tests

Annually, thousands of unprotected pedestrians are killed or suffer serious injuries in accidents with moving vehicles. Numerous automobile organizations have performed research on pedestrian safety. The European Enhanced Vehicle- Safety Committee (EEVC), Working Group 17 (WG17) proposed three component subsystem tests to evaluate the friendliness of a vehicle to pedestrians: the legform to hood test, the upper legform to bonnet leading edge test and the headform to bonnet top test. In assessing the pedestrian friendliness of a vehicle, the present study adopted the WG17 regulations of the three component subsystem tests. We herein describe in detail a finite element subsystem model built to analyze the pedestrian friendliness of a vehicle using LS-DYNA. The first objective of this study was to simulate these three component subsystem impact tests and evaluate car front aggressiveness. The second objective was to analyze the frontal structures of a vehicle and, based on the simulation results, identify dangerous areas and provide suggestions for vehicle front design that may decrease pedestrian injuries. The analysis of these models and the results obtained may be used to help evaluate the pedestrian friendliness of a vehicle and guide the future development of pedestrian-friendly vehicle technologies.

Lower extremity injuries in vehicle-pedestrian collisions using a legform impactor model

Though the bumper of a vehicle plays a major role in protecting the vehicle body against damage in low speed impacts, many bumpers, particularly in large vehicles, are too stiff for pedestrian protection. In designing a bumper for an automobile, pedestrian protection is as important as bumper energy absorption in low speed collisions. To prevent lower extremity injuries in car-pedestrian collisions, it is important to determine the loadings that car front structures impart on the lower extremities and the mechanisms by which injury is caused by these loadings. The present work was focused on gaining more insight into the injury mechanisms leading to both ligament damage and bone fracture during bumper-pedestrian collisions. The European Enhanced Vehicle-safety Committee (EEVC) legform impactor model was introduced and validated against EEVC/WG17 criteria. The collision mechanism between a bumper and this legform impactor was investigated numerically using LS-DYNA software. To identify the effect of the bumper beam material on leg injuries, four analyses were performed on bumpers that had the same assembly but were made from different materials.

Challenge and approach to real-world pedestrian protection – investigated by Polar-II pedestrian dummy

The head impact in the windscreen area is currently the focus of the research regarding pedestrian protection by the Institute of Automotive Engineering (IKA) of RWTH Aachen University. Head injuries are the most relevant cause for severe and fatal injuries. Only consumer testing and – within a limited area – phase I of the European Directive on pedestrian protection considers the testing in this area, where in most cases involving an average sedan-shaped vehicle the head of the 50th percentile male will contact. For representation of the typical sedan-shaped vehicle, Opel Signum was chosen as the model. In the first test series the experimental vehicle has been tested using the European Enhanced Vehicle Safety Committee Working Group 17 (EEVC WG 17) adult-head impactor. For the triggering and timing of the head impactor in the airbag test, the previously determined head-impact time from numerical simulations has been used. In the second test series, Polar-II pedestrian dummy tests have been performed. In parallel to these test series an airbag developed by TAKATA has been tested. The airbag is able to lift the rear end of the hood and in addition cover the windscreen surrounding. The development of the necessary hinge modifications, to get an additional degree of freedom, and adjustments of the airbag mounting area were carried out by the IKA. The results of these tests should lead to an evaluation of and methods to test future protection systems for the head impact of pedestrians in the windscreen area.

Development and validation of FE models of impactor for pedestrian testing

Car-pedestrian accidents account for a considerable number of automobile accidents in industrialized countries. Safeguarding of pedestrians is taking on an increasingly important role in car design. Working Group 17 (WG17) of the European Enhanced Vehicle-safety Committee (EEVC) proposed four impactor models for assessing pedestrian friendliness of a vehicle. In this study, finite element models of adult headform, child headform, upper legform, and legform impactor of pedestrians were created by using LS-DYNA finite element code. The impactor structures follow the descriptions in the reports of WG17 specifications. Simulated certification tests were performed. Some materials were selected from different trademarks of the same kind of materials. The knee of the legform impactor was designed. The parameters of the springs and dampers were adjusted to satisfy the requirements. Results of simulated certification tests for the four impactors are within WG17 limit ranges. These finite element impactor models obtained herein can help evaluate the pedestrian friendliness of vehicle and guide the future development of pedestrian safety technologies.

Car-car crash compatibility: development of crash test procedures in the VC-Compat project

A major component of the EU Fifth Framework Programme sponsored project “Improvement of Vehicle Crash Compatibility Through the Development of CrashTest Procedures” (VC-Compat) focused on car-to-car frontal crash compatibility. The work program was composed of four main activities, a structural survey, cost-benefit analyses, crash testing, and supporting modeling work. All these activities focused on the development of two candidate test procedures, namely the full-width deformable barrier (FWDB) and progressive deformable barrier (PDB), which are capable of assessing a car's structural interaction potential. These tests have different approaches; the FWDB assessment is based on load cell wall force measurements, whereas the PDB assessment is based on deformation measurements. This work supports the activities of the European Enhanced Vehicle Safety Committee working group on frontal impact and compatibility, which has the task to propose draft test procedures to assess a vehicle's crash compatibility in 2007.

The effect of leg fracture level and vehicle front-end geometry on pedestrian knee injury and response

In this study a MADYMO (mathematical dynamic modelling) model has been used to identify the influence of leg fracture on the injuries sustained by the pedestrian during front end impact with a vehicle. A factorial study of a MADYMO pedestrian and vehicle model are used to investigate the effect of different leg fracture tolerances, geometry, and vehicle compliance on the criteria measured in the European Enhanced Vehicle-safety Committee (EEVC) pedestrian safety tests. These criteria include knee bending, knee shear response, and lower leg bone (tibia) acceleration. The main study examines the spread of typical values of lower limb tolerance based on reported literature and contrasts the response of weaker, low-strength bones, normal tolerance, and limbs which do not fracture. Results show that knee bending angles and therefore ligament strains are significantly increased when fracture does not occur, and are decreased in bones exhibiting a low-strength response. Bone fracture tolerance is shown to be a significant parameter influencing knee bending. The parameters are compared to show that knee shear is significantly influenced by vehicle bumper compliance and that both criteria are heavily influenced by bumper height. Vehicles with more aggressive geometry, higher bumpers, and larger bumper lead were considered for comparative purposes.

Proposal of injury risk curves for evaluating pedestrian femur/pelvis injury risk using EEVC upper legform impactor based on accident reconstruction

New injury risk curves for the evaluation of pedestrian femur and pelvic injury risk by means of the upper legform impactor of the European Enhanced Vehicle-Safety Committee (EEVC) developed by the Transport Research Laboratory are proposed in this study. Lower extremity responses related to the risk of pedestrian femur and pelvic fractures caused by the bonnet leading edge and wing contact in a real-world pedestrian accident, such as impact force and bending moment, were reconstructed in the present study using the EEVC upper legform impactor. The femur and pelvic injury risk curves were developed from application of the model of Weibull cumulative frequency to measured impact force and bending moment. The newly developed injury risk curves indicated that an impact force of 6.3 kN and a bending moment of 417 Nm measured by the EEVC upper legform impactor correspond to a 0.2 probability of femur and pelvic fractures. The injury risk curves also showed that an impact force of 7.5 kN and a bending moment of 510 Nm measured by the EEVC upper legform impactor correspond to a 0.5 probability of injuries.

Evaluation of Pedestrian Subsystem Test Method Using Legform and Upper Legform Impactors for Assessment of High-Bumper Vehicle Aggressiveness

In accidents involving sports utility vehicles (SUVs), injuries to pedestrian leg, knee ligaments, and femur are likely to occur. Therefore, the European Enhanced Vehicle Safety Committee proposed two subsystem test methods for evaluation of SUV bumper aggressiveness. Such evaluation can be conducted by means of either a legform impactor (evaluation of risk of knee and tibia injury), or an upper legform impactor (evaluation of risk of thigh and pelvis injury) test. Each of these two test methods has its own injury criteria and injury acceptance levels. Therefore, the first objective of this research is to clarify any differences between the test results obtained when evaluating SUV bumper aggressiveness by means of these two impactors. The second objective is to determine whether or not a legform impactor can be applied to estimate the risk of femur fracture, and if an upper legform impactor can be used to estimate the risk of knee ligament injury. The present results indicate the test method using an upper legform impactor yields higher ratios of injury criteria to the relevant EEVC/WG17 injury acceptance levels than by using a legform impactor. Thus, the upper legform impactor test rates an SUV bumper as more aggressive than the legform impactor test. The present study suggests the lower leg acceleration obtained by the legform impactor can be used to adequately assess the risk of femur fracture, when evaluating the aggressiveness of an SUV bumper using proposed injury acceptance levels reported in the literature. Similarly, the impact force obtained by the upper legform impactor can be used to assess the risk of cruciate ligament injury.

Factor causing scatter in dynamic certification test results for compliance with EEVC WG17 legform impactor standard

A pedestrian legform impactor is a tool for the evaluation of car front bumper aggressiveness when simulating a pedestrian leg hit by a car. The Transport Research Laboratory (TRL) developed a legform impactor in compliance with the European Enhanced Vehicle-safety Committee (EEVC)/ WG17 specifications. The Commission of the European Communities (EC) proposed a dynamic certification test for a legform impactor, however, the test results using the TRL legform impactors manufactured to date have indicated an extremely wide scatter, especially in the maximum lower leg acceleration. Thus, the objectives of the present research are to clarify the factor possibly causing this scatter in the lower leg acceleration of the TRL legform impactor in the setup of the dynamic certification test, and to propose a way to adjust lower leg acceleration so as to comply with the corridor proposed by the EC. The repeatability and reproducibility of the legform impactor products and different impact points of the ram in the setup for the dynamic certification test were thus investigated. High repeatability and reproducibility of the legform impactor products were observed. No difference was observed in the effect of different ram points of impact against a stationary legform impactor on the maximum lower leg acceleration. On the other hand, the lower leg acceleration was found to be greatly affected by humidity in the test apparatus. Therefore, the effect of humidity on the dynamic certification test setup was also investigated. The results indicated that the maximum lower leg acceleration increased drastically with higher humidity. Next, the relation between humidity and acceleration measured by a ram impacting a piece of confor™ foam was investigated using a simplified test rig, since such foam sheathes the metal part of the legform impactor in a dynamic certification test setup. A strong relation between the humidity and acceleration was found. Thus concluded that humidity is a key factor affecting lower leg acceleration, and that adjusting it will be one of the many ways the lower leg acceleration can be made to comply with the proposed EC corridor in the dynamic certification test.

How to reduce the toll of road traffic accidents

How to reduce the toll of road traffic accidents

Pedestrian subsystem head impact results reflect the severity of pedestrian head injuries

Ten head impacts between pedestrians and cars were reconstructed to compare the head injuries sustained by pedestrians with the results of reconstruction tests using the headform impactors designated by the European Enhanced Vehicle-safety Committee (EEVC) Working Group 10 for assessing pedestrian head protection. The methodology of this study included at-scene accident investigation, computer simulation, and physical reconstruction in a laboratory of the head impacts that occurred in the accident cases that were investigated. The main finding was that the results from using the EEVC headform impactors test correlate well with the severity of any head injury, as measured by the Abbreviated Injury Scale, in actual pedestrian accidents. Head impacts that exceeded a HIC value of 1000 were positively associated with head injuries that were AIS3 or above.