Headform Impact Research Articles

Validation of restoration time for pedestrian headform impactor skin

New technical standards for pedestrian head and leg protection in which the headform and legform impact test is conducted against vehicle bonnet and bumper were introduced in Japan as of April 2013. In the headform impact test, an impactor simulating the pedestrian head is used. To simulate the impact response when the human head is dropped, the headform impactor is fitted with a synthetic resin skin made of polyvinyl chloride. Since the skin is non-metallic, it may become deformed and affect the injury reference value in the case where consecutive tests are conducted. It is considered that the skin is restored after a certain period of time after collision. However, up until the present, the exact time required for the restoration had been unclear. Currently, headform impact tests against vehicle bonnet are conducted at a 2-h interval without any scientific background. Therefore, the purpose of this study is to validate the 2-h time interval required for the skin to be restored after collision. By conducting headform impact tests against vehicle bonnet and drop certification tests regulated by the technical standard at different time intervals, we investigated the restoring time for pedestrian headform impactor skin for consecutive impacts.

A numerical model on PVB laminated windshield subjected to headform low-speed impact

Polyvinyl butyral (PVB) laminated windshield is one of the most important components in automotive to protect vulnerable road users. First, a windshield finite element (FE) model is set up using a piece of interlayer (PVB) sandwiched by two glass layers. Four parameters which have an critical impact on the simulation results, i.e. glass Young's modulus, glass plastic failure strain, PVB stress-strain curve and boundary condition, are suggested to measure the influence on the windshield model. Each windshield model is impacted by a standard headform impactor at the speed of 8m/s based on the LS-DYNA platform and the results are compared with the dynamic experiments of PVB laminated windshield under headform impact to find the most accurate FE model. Furthermore, the most accurate FE windshield model is compacted by the standard headform impactor on various impact velocities (6.6m/s-11.2m/s), angles (60°–90°) compared with the parametric dynamic experiments of PVB laminated windshield to verify the windshield finite element model. This paper provides a useful finite element model of windshield for further systematically numerical studies based on the finite element method to explore the ability of the energy absorption and safety design of PVB laminated windshield.

Features of Fatal Pedestrian Injuries in Vehicle-to-Pedestrian Accidents in Japan

The number of traffic deaths in Japan was 4,612 in 2011. Looking at the road accident fatalities, it revealed that pedestrians accounted for the highest number in 2011 (1,686, 36.6%). To develop safety countermeasures to decrease the severity of injuries and to reduce the number of deaths in traffic accidents, the detailed characteristics of pedestrian injury in vehicle-to-pedestrian crashes are necessary. The purpose of this study is to understand the scenarios of vehicle accidents in which pedestrians suffer fatal injuries. In the present study, we investigated the characteristics of pedestrian injuries in fatal crashes from accident analyses and compared them to head injury severity levels in impact tests against a road pavement and vehicle contact surfaces. In the accident analyses, we investigated the main body regions injured, that is, the most serious extent of injuries over the whole body of pedestrians by using macro vehicle-pedestrian accident data from database of the Institute for Traffic Accident Research and Data Analysis (ITARDA) of Japan. In comparing the differences in injury frequencies for various body regions between 1999 and 2009, it is noted that the frequencies of pedestrian fatalities due to head injuries were significantly reduced. The result indicated that even though head injuries were the most frequent cause of pedestrian fatalities in traffic accidents, the introduction of pedestrian head protection regulation in Japan in 2005 could be considered effective in reducing fatal head injuries. On the other hand, the frequencies of pedestrian fatalities due to hip injuries increased significantly in sedans, light passenger cars, and light cargo vans. Using the macro accident data in 2009, we investigated the frequency of pedestrian fatalities by gender, age group, vehicle travel speed, and fatal head injuries due to vehicle impacts or road pavement impacts. The results also indicated that the frequencies of female pedestrian fatalities due to hip injuries were significantly higher than those of males. Additionally, the results showed that the frequency of pedestrian fatalities due to hip injuries for the age group of over 65 years was significantly higher than that of the industrial age group (aged 13-59). Focusing on the frequency of pedestrian fatalities due to hip injuries in all age groups, vehicle travel speed appeared likely not to be an extremely important factor in increasing fatal hip injuries. In examining the differences in the frequency of fatal head injuries due to contacts with vehicles or road pavements, it is noted that injury frequency in crashes involving vehicles travelling at high speeds were significantly higher than those at lower speeds for pedestrians over 60 years of age. Focusing on head injury severity levels in impact tests against a road and vehicle surfaces using an adult pedestrian headform impactor, the impacts against a road pavement (HIC 6525) was considered to be more severe than those against vehicle front components with high stiffness (HIC from 2600 to 4032). Language: en

Finite element modeling of crash test behavior for windshield laminated glass

The objective of the present study is to investigate the mechanical behavior of windshield laminated glass in the case of a pedestrian's head impact. Windshield FE models were set up using different combinations for the modeling of glass and PVB, with various connection types and two mesh sizes (5 mm and 10 mm). Each windshield model was impacted with a standard adult headform impactor in an LS-DYNA simulation environment, and the results were compared with the experimental data reported in the literature. The results indicated that the behavior of the windshield model with a double-layered shell of glass and PVB and a tied element connection support test results from previous studies. Furthermore, the influence of glass fracture stress on the same windshield model was investigated, and the cracked area and the peak value of the headform's linear acceleration were determined by the critical fracture stress. It was observed that a 50-MPa fracture stress in the glass best predicted the observed headform's linear acceleration level and the cracks of the windshield at the time of impact.

Design of car hood of sandwich structures for pedestrian safety

Vehicle safety factors should simultaneously consider occupant and pedestrian safety, given that pedestrians are the third largest category of traffic fatalities. Most pedestrian deaths occur due to traumatic brain injury, resulting from the hard impact of the human head against the vehicle’s stiff hood or windshield. Therefore, how to design a pedestrian-friendly vehicle and propose a new hood structure is a matter of urgency for minimising pedestrian head injuries. In this study, three kinds of sandwich hood structures are proposed for reducing pedestrian head injuries, including carbon fibre-reinforced polycarbonate, carbon fibre-reinforced foam and aluminium-reinforced polycarbonate. In assessing the friendliness of vehicle hoods, this study adopts the EEVC/WG17 regulations on headforms for hood tests. The finite element method is used to simulate the impact between the vehicle’s hood and the headform impactor. The software used in simulation is LS-DYNA. The results predicted by the headform–hood tests show that the hood structure with aluminium-reinforced polycarbonate material provides enough absorption capability to protect pedestrians from the impacts of accidents. It is also stiff enough to keep pedestrians’ heads away from the inner parts of the engine cavity. The analysis models and sandwich materials proposed herein contribute to efforts to design vehicle hood structures and pave the way for developing pedestrian protection technologies.

Experimental Research on Energy Absorption Characteristic of PVB Laminated Windshield Subjected to Headform Low-speed Impact

Parametric dynamic experiments on various impact velocities(6.6-11.2 m/s), angles(60°-90°), directions are performed to obtain the energy characteristics of windshield under headform impact. Dynamic response of headform is systematically analyzed via the acceleration-time curve obtained by acceleration sensor. High-speed camera is employed to capture and analyze the crack propagation process. Macro damage morphology of windshield is discussed, and compared with it in real accident. With the definition of maximum contact force, maximum plastic hollow, head injury criteria, loss of headform kinetic energy and kinetic absorption ratio, the energy absorption characteristics of windshield under above mentioned parametric experiments are investigated. Experiment results may provide fundamental data and theoretical base for future research.

Assessing the benefit of the brake assist system for pedestrian injury mitigation through real-world accident investigations

The compulsory fitting of the brake assist system (BAS) for new vehicles in the European Union has been recently established by Regulation (EC) 78/2009 to enhance the protection of pedestrians. This paper describes the main findings of a coordinated study performed by four Spanish Safety Research Centres aimed at assessing the potential influence of the BAS in vehicle–pedestrian collisions through the reconstruction of real-world accidents that occurred in three different cities of Spain. A total of 139 vehicle–pedestrian collisions were investigated in-depth following a common methodology, including on-the-spot data collection, analysis and reconstruction to estimate the collision speed and the pedestrian kinematics. A specific procedure was defined to emulate, through computer simulations, the performance of the BAS acting together with the antilock braking system (ABS). The benefit was assessed in terms of both collision speed and Injury Severity Probability (ISP) by comparing the reduction of their values from the real conditions to the virtual BAS+ABS simulations. The pedestrian ISP was estimated, depending on the collision speed and the head impact point, using a specific application that calculated its value based on the results of headform impact laboratory tests. The ISP values obtained in both conditions were compared. The findings show that while implementing the BAS+ABS would not have prevented the collision in most of the cases, it would have reduced their consequences in terms of the estimated ISP. It was also found that in few cases, a small reduction in the collision speed would increase the head injury severity.

Effects of pedestrian gait, vehicle-front geometry and impact velocity on kinematics of adult and child pedestrian head

The objective of the study is to investigate the effects of pedestrian gait, vehicle-front geometry and impact velocity on the dynamic responses of the head. The multi-body dynamic (MBD) models were used to simulate the head responses in vehicle to pedestrian collisions with different vehicle types in terms of head-impact point measured with Wrap Around Distance (WAD), head relative velocity and impact angle. Furthermore, the distribution of the head contact point on the vehicle fronts is analysed for a comparison of the contact point with the testing areas in the EEVC headform impactor test procedures. A simulation matrix is established using five vehicle types, two mathematical models of the pedestrians represented a 50th male adult and a 6-year-old child as well as seven pedestrian gaits based on typical postures in pedestrian accidents. In order to simulate a large range of impact conditions, four vehicle velocities (30 km/h, 40 km/h, 50 km/h and 60 km/h) are considered for each pedestrian position and vehicle type. The results indicated that the pedestrian gait and vehicle-impact velocity strongly influence head-impact condition. It is obvious that due to different vehicle-front geometry, the head-impact velocity, impact angle and head-impact point could be varied as well. This study provides suggestions for different head-impact conditions of subsystem test to the front part of different passenger vehicles.

The effect of impact speed on the HIC obtained in pedestrian headform tests

Pedestrian headform impact tests are generally carried out at a fixed impact speed, which varies depending on the test protocol in use. Thus, it may be desirable to extrapolate a single test result to higher and lower test speeds. This paper investigates the influence of impact speed on the Head Injury Criterion (HIC) and the peak dynamic displacement. The relationship between impact speed and these test measurements is first considered analytically using a linear spring model, and then empirically using the results of 29 headform tests on seven different locations. The results indicate that power functions can be used to predict the effect of impact speed, with exponents of approximately 2.5 for HIC and 0.8 for peak displacement. These relationships might be used for assessing head impact performance over a wider range of speeds than are presently tested.

Headform Impact Tests to Assess Energy Management of Seat Back Contact Points Associated with Head Injury for Pediatric Occupants

Head injuries are the most common injuries sustained by children in motor vehicle crashes regardless of age, restraint and crash direction. Previous research identified the front seat back as relevant contact point associated with head injuries sustained by restrained rear seated child occupants. The objective of this study was to conduct a test series of headform impacts to seat backs to evaluate the energy management characteristics of relevant contact points for pediatric head injury. A total of eight seats were tested: two each of 2007 Ford Focus, Toyota Corolla, 2006 Volvo S40, and 2008 Volkswagen Golf. Five to six contact points were chosen for each unique seat model guided by contact locations determined from real world crashes. Each vehicle seat was rigidly mounted in the center track position with the seatback angle adjusted to 70 degrees above the horizontal. A 3.5 kg child pedestrian headform was fired at a velocity of 24 km/h (6.67 m/s) in accordance to FMVSS 201 at 22 degrees above the horizontal starting from 10 cm from the center of the target. Resultant acceleration and HIC (15 ms and 36 ms) were calculated for each impact. Within the class of small family vehicles, there was substantial variation in underlying seat structure across the locations of head impact identified in the case series resulting in a wide range of maximum resultant head acceleration - 27-165 g. Several impact locations, particularly those around the edge of seat back resulted in head acceleration greater than 80g used in regulatory tests. These data highlight the need to re-examine the current FMVSS 201, Occupant Protection in Interior Impact, to account for the typical impact locations of child occupants in crashes. In addition, further study is needed to understand the tolerance of the pediatric skull and brain to these types of impacts. Language: en

성인 머리모형 임팩터의 FE 모델 개발

Head injury is one of the most common cause of deaths in car-to-pedestrian collisions. To reduce the severity of such injuries, many international safety committees have performed headform impact test for pedestrian protection. In this paper, an adult headform impactor model is developed based on the finite element (FE) method and validated through the numerical simulation. The skin material of headform impactor is known as polyvinyl chloride skin (PVC) and its material was assumed as viscoelastic. The viscoelastic parameters of headform skin are identified by a series of trial and error methods. The new developed FE adult headform impactor is verified by the drop test and FE JARI adult headform impactor provided by Madymo program.

A study on chest injury mechanism and the effectiveness of a headform impact test for pedestrian chest protection from vehicle collisions

This study was aimed at investigating the injury mechanism of pedestrian chests in collisions with passenger vehicles of various frontal shapes and examining the influence of the local structural stiffness on the chest injury risk by using the headform impact test at the chest contact area of the vehicle. Three simulations of vehicle to pedestrian collisions were conducted using three validated pedestrian finite element (FE) models of three pedestrian heights of 177 (AM50th), 165 and 150cm and three FE vehicles models representing a one-box vehicle, a minicar and a medium car. The validity of the vehicle models was evaluated by comparing the headform acceleration against the measured responses from headform impact tests. The chest impact kinematics and the injury mechanisms were analyzed in terms of the distribution of the von Mises stress of the ribcage and in terms of the chest deflections. The chest contact locations on the front panel and the bonnet top were identified in connection to the causation of rib fractures. The risk of rib fractures was predicted by using the von Mises stress distribution. The headform impact tests were carried out at the chest contact area on the front panel and bonnet to examine the safety performance with respect to pedestrian chest protection. In simulations of the one-box vehicle to pedestrian collisions, the chest was struck directly by the frontal structure at a high velocity and deformed substantially, since a shear force was generated by the stiff windshield frame. The acceleration of the headform was related to the rib deflections. The injury threshold of the ribcage deflection (42mm) corresponded to the headform average acceleration of 68G. In the minicar collision, the chest was struck with the bonnet top and cowl area at a low velocity, and the deformation was small due to the distributed contact force between the chest and the bonnet top. Besides, the ribcage deformation was too small for bridging a relation between the headform accelerations and rib deflections. In the medium car collision, the deformation mode of the chest was similar to that in the minicar collision. The chest collided with the bonnet top at a low velocity and deformed uniformly. The deflection of the ribs had an observable correlation with the headform accelerations measured in the headform impact tests. The frontal shape of a vehicle has a large influence on a pedestrian’s chest loadings, and the chest deformation depends on the size of the pedestrian and the stiffness of the vehicle. The one-box passenger vehicle causes a high chest injury risk. The headform impactor test can be utilized for the evaluation of the local stiffness of a vehicle’s frontal structure. The reduction of the headform acceleration is an effective measure for pedestrian chest protection for specific shapes of vehicles by efficacy in modifying the local structural stiffness.

Study of Carbon Fiber/Polycarbonate (<i>CF/PC</i>) Material Sandwich Structure for Vehicle Hood

Traffic accidents are the worldwide problem. Based on many reports in the word, the front parts of vehicle is the most likely to strike at pedestrians when the accident occurs. And the fatal injuries almost occurred to pedestrians when their head impact to the vehicle hood. So it’s necessary to reduce the pedestrian injuries as much as possible to enhance the safety characteristic, one of the most importance criteria for vehicles manufactures. In this study, the effect of sandwich structure with material of carbon fiber reinforced polycarbonate (CF/PC) will be concerned as vehicle bonnet change. The finite element model of headform impactor and Honda vehicle model was analyzed detail by LS-DYNA as simulation. The impact between headform impactor and original vehicle model or the carbon fiber reinforced polycarbonate material bonnet vehicle model was executed and the comparison result was shown. This study, the European Enhanced Vehicle-safety Committee/ Working Group 17 (EEVC/WG17) and NCAP requirements was adopted.

Comparison of steel, aluminum and composite bonnet in terms of pedestrian head impact

Material selection for automotive closures is influenced by different factors such as cost, weight and structural performance. Among closures, the automotive bonnet must fulfill the requirements of pedestrian safety which is evaluated by child and adult headform impactors. The mechanisms of injury are complex, therefore; the Head Injury Criterion (HIC) which shows a measure of the likelihood of head injury arising from an impact is developed. HIC includes the effects of head acceleration and the duration of the acceleration. In this paper a new finite element model has been developed which is capable to simulate head impact phenomenon between headform impactors and composite bonnet. Then the behavior of three identical bonnets made of steel, aluminum and composite have been investigated by the developed model. It is shown that the energy absorption of aluminum bonnet is smaller than steel and composite ones and for keeping the aluminum bonnet at the same level of stiffness, it is necessary to increase the thickness. Therefore, the aluminum bonnet needs a larger space between the bonnet and the parts in the engine compartment. It is shown that although the displacement of headform for composite bonnet is more than that of steel and aluminum ones, but the amount of HIC’s, which are measured at the collision points are much less than those measured at the same collision points for steel and aluminum bonnets. In addition the comparison of three bonnets of the different materials has been done to highlight cost, weight, and structural performance issues.

Influence of the body on the response of the helmeted head during impact

The most frequent type of injury that causes death or disability in motorcycle accidents is head injury. The only item of personal protective equipment that protects a motorcyclist's head in real-world accidents is the safety helmet. The protective capability of a helmet is assessed, according to international standards, through the impact of a headform fitted with the helmet onto an anvil. The purpose of the present work was to study the influence of the presence of the body on the impact response of the helmeted head. Full-body and detached-head impacts were simulated using the finite element (FE) method. As a consequence of the presence of the body, the crushing distance of the helmet liner was drastically increased. This evidence indicated that the effect of the body should be included in impact absorption tests in order to provide conditions that are more realistic and stringent. The solution to an analytical model of the helmeted headform impact revealed that increasing the headform mass has the same influence on impact outputs, particularly the liner's crushing distance, as including the whole body in impact tests. The added mass was calculated by using a helmeted Hybrid III dummy for an impact configuration that frequently occurred in real-world accidents.

Improvement of Hood Hinge Based on Protection of Pedestrian Head

This paper established finite element models of adult head based on GB/T 24550-2009 and hood of a car. When the finite element model of the adult headform impactor was established, tests were carried out to prove that the impactor was valid. Then experiments were carried out at adult head test area of the hood. The results show that some areas of the hood are too hard where the hood hinges are installed. It is very bad for pedestrian head to hit those areas in accident. In order to protect pedestrian head efficiently, this paper proposed a new kind of hood hinge, called buffer-type hinge. Comparison tests were carried out. The buffer-type hinge is proved to be more effective to protect pedestrian head in traffic accident.

Improvement of accelerometers for pedestrian headform impactors in testing following Japanese vehicle safety regulations

Most pedestrian deaths in car–pedestrian accidents are due to head injuries. In 2005, the Japanese Ministry of Land, Infrastructure, Transport and Tourism (J–MLIT) began assessing the safety of bonnets impacting on pedestrians' heads using headform impactors with designated technical specifications. J–MLIT has used Type Approval Regulation Version 1 of headform impactors fitted with small un–damped accelerometers since 2005. Meanwhile, oil–damped accelerometers have been used by J–MLIT Type Approval Regulation Version 2 headform impactors since 2010. This paper summarises the development of pedestrian headform impactors used in headform impact tests in Japan and points to increasing safety levels.

Study on the Head Impacting Properties of Foam Composite Material Engine Hood

The head impacting properties and the lightweight effect of a kind of foam composite material engine hood are studied in this paper. The finite elements model of headform impactor impacting the engine hood is created, LS-DYNA is used to do the simulation of impacting, the dynamic response of original steel material and foam composite material are simulated. The results show that using foam composite material can reduce the injury value of pedestrian head. In the end, the lightweight effect after using the new material is analyzed.

The predicted risk of head injury from fall-related impacts on to third-generation artificial turf and grass soccer surfaces: A comparative biomechanical analysis

The risk of soccer players sustaining mild traumatic brain injury (MTBI) following head impact with a playing surface is unclear. This study investigates MTBI by performing headform impact tests from varying heights onto a range of third-generation artificial turf surfaces. Each turf was prepared as per manufacturers specifications within a laboratory, before being tested immediately following installation and then again after a bedding-in period. Each turf was tested dry and when wetted to saturation. Data from the laboratory tests were compared to an in situ third-generation surface and a professional grass surface. The surface performance threshold was set at a head impact criterion (HIC) = 400, which equates to a 10% risk of the head impact causing MTBI. All six third-generation surfaces had a >10% risk of MTBI from a fall >0.77 m; the inferior surfaces required a fall from just 0.46 m to have a 10% MTBI risk. Wetting the artificial turf did not produce a statistically significant improvement (P > 0.01). The in situ third-generation playing surface produced HIC values within the range of bedded-in experimental values. However, the natural turf pitch was the superior performer – necessitating fall heights exceeding those achievable during games to achieve HIC = 400.

An Approach to Modeling Impact Energy Absorption by Surfaces

The energy return characteristics of an impacted surface are important for human impacts such as a child falling onto a play surface or an athlete landing on a gymnastic mat. The amount of energy dissipated or returned to the impacting body will contribute to the surface's injury-minimizing or performance-enhancing potential. We describe a simple approach for selecting a rheological computer model to simulate a human-surface impact. The situation analyzed was of a head form impact onto gymnastic tumbling mats. The approach can be used to characterize other surfaces and impacts. The force-time-displacement characteristics of the mats were determined from laboratory drop tests. Various spring-damper models were evaluated for their ability to reproduce the experimental acceleration-time and force-displacement impact curves. An exponential spring and depth damper combination was found to best replicate the surface characteristics of the mats tested here, and to demonstrate their energy flow and exchange properties. Rheological modeling is less complex than finite element modeling but still accounted for the depth, velocity, and energy characteristics of the impacted surfaces. This approach will be useful for reproducing the characteristics of surfaces when the impacting body cannot be instrumented, and for predicting force and energy flow in nonrigid impacts.