Design of a Conceptual Bumper Energy Absorber Coupling Pedestrian Safety and Low-Speed Impact Requirements

The car front bumper system needs to meet the requirements of both pedestrian safety and low-speed impact which are somewhat contradicting. This study aims to design a new kind of modular self-adaptive energy absorber of the front bumper system which can balance the two performances. The X-shaped energy-absorbing structure was proposed which can enhance the energy absorption capacity during impact by changing its deformation mode based on the amount of external collision energy. Then, finite element simulations with a realistic vehicle bumper system are performed to demonstrate its crashworthiness in comparison with the traditional foam energy absorber, which presents a significant improvement of the two performances. Furthermore, the structural parameters of the X-shaped energy-absorbing structure including thickness (tu), side arc radius (R), and clamping boost beam thickness (tb) are analyzed using a full factorial method, and a multiobjective optimization is implemented regarding evaluation indexes of both pedestrian safety and low-speed impact. The optimal parameters are then verified, and the feasibility of the optimal results is confirmed. In conclusion, the new X-shaped energy absorber can meet both pedestrian safety and low-speed impact requirements well by altering the main deformation modes according to different impact energy levels

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

Investigation on risk prediction of pedestrian head injury by real-world accidents

Head injury is the most common and fatal injury in car-pedestrian accidents. Due to the lack of human test data, real-world accident data is useful for the research on the mechanism and tolerance of head injuries. The objective of the present work is to investigate pedestrian head-brain injuries through real car-pedestrian accidents and evaluate the existed injury criteria. Seven car-to-pedestrian accidents in China were selected from the IVAC (Investigation of Vehicle Accident in Changsha) database. Accident reconstructions using multi-body models were conducted to determine the kinematic parameters associated with the injury and were used to measure head injury criteria. Kinematic parameters were input into a finite element model to run simulations on the head-brain and car interface to determine levels of brain tissue stress, strain, and brain tissue injury criteria. A binary logistic regression model was used to determine the probability of head injury risk associated with AIS3+ injuries (Abbreviated Injury Scale). The results showed that head injury criteria using kinematic parameters can effectively predict injury risk of a pedestrians’ head skull. Regarding brain injuries, physical parameters like coup/countercoup pressure are more effective predictors. The results of this study can be used as the background knowledge for pedestrian friendly car design

Towards lower limbs new injury criteria for pedestrian safety based on realistic impact conditions

La sécurité du piéton est un problème de santé publique, qui doit être traité tant par les acteurs de la recherche que par l'industrie automobile pour apporter des solutions technologiques innovantes. Dans les accidents impliquant des piétons, le premier contact est généralement localisé sur les membres inférieurs exhibant de fréquentes et nombreuses lésions pouvant être très sévères. Compte tenu des caractéristiques biomécaniques du membre inférieur, comment améliorer les critères de blessures existants pour contribuer au développement d'une voiture moins agressive pour les piétons ? La présente étude vise donc à promouvoir des améliorations significatives de critères de blessure des membres inférieurs pour la sécurité des piétons combinant des essais expérimentaux et des simulations numériques. Un modèle par éléments finis des membres inférieurs (modèle LLMS) a été utilisé et amélioré pour étudier les réponses mécaniques des membres inférieurs dans des conditions de chargement realists. Une attention particulière a été accordée sur la capacité du modèle à prédire séparément les blessures des os longs et celles de l'articulation du genou pour développer deux critères de blessures distincts. Pour le tibia, la nature de sa structure et les conditions de chargement qui lui sont appliquées nous ont conduit à proposer une courbe quadratique de moment en flexion qui tient compte de différents points d'impact. Pour le genou, le critère de blessure a été établi à partir d'une fonction combinant cisaillement latéral et flexion latérale. Ce critère permet de hiérarchiser la nature et la sévérité des lésions en fonction du mécanisme de blessure prépondérant.Pedestrian safety is a worldwide concern, which needs to be investigated by both vehicle manufacturers and researchers to approach innovative solutions. In car-Pedestrian accidents, lower limbs have been demonstrated to be the most frequently injured body region of the pedestrian. Given the biomechanical features of lower limbs, how the existing injury criteria could be improved to aid the development of a pedestrian friendly car? The current study aims to promote significant improvements in the injury criteria of lower limbs for pedestrian safety combining experimental tests and numerical simulations. A finite element lower limb model (LLMS model) was used and improved to investigate the mechanical responses of lower limbs in the loading conditions reflecting the car-Pedestrian impact. A particular attention was paid on the model ability of predicting separately the injuries of long bones and knee joints to develop the corresponding injury criteria. With regard to the tibia structure and its loading condition in pedestrian accidents, we proposed a quadratic curve of bending moments to tibia locations as its injury tolerance. Given dominant injury mechanisms of the ligaments, the knee injury criterion was established as a function of combined joint kinematics including lateral bending and lateral shearing. Moreover, these criteria are relevant with the previous and current experimental test results. Finally, the efficiency of the proposed criteria was evaluated by a parametric study of the realistic car-Pedestrian impact conditions

Investigation of the injury threshold of knee ligaments by the parametric study of car–pedestrian impact conditions

Pedestrian safety is a serious global problem that needs to be addressed by drivers, vehicle manufacturers and researchers. Since the first European Committee directive for pedestrian safety was published, vehicle suppliers have implemented pedestrian protection requirements to automobile structures at the design level. As to the development of current automobile front-end structures, a question arises about pedestrian safety: are there existing injury criteria for the new generation of cars? Most previous injury thresholds for knee ligaments were principally based on isolated sub-segment tests with contrived loading conditions, and rarely took the entire front-end shape of the car model into account to simulate realistic pedestrian loading conditions. Hence, the current study aims to investigate injury thresholds of primary knee ligament injuries in car–pedestrian impact environments as well as to evaluate the previous criteria proposed by isolated sub-segment tests. The entire front-end shape of a car model was employed. A parametric study of various pedestrian loading conditions was implemented by finite element simulations regarding three influencing factors: impact heights, locations of impact and impact velocities. Finally, the injury thresholds associated with primary knee ligament injuries of pedestrians were defined with the dominant injury mechanisms: combined lateral bending and shearing effects. These thresholds are also well correlated with the previous criteria defined by isolated lower limb tests

Coupling Lateral Bending and Shearing Mechanisms to Define Knee Injury Criteria for Pedestrian Safety

In car–pedestrian accidents, lateral bending and shearing kinematics have been identified as principal injury mechanisms causing permanent disabilities and impairments to the knee joint. Regarding the combined lateral bending and shearing contributions of knee joint kinematics, developing a coupled knee injury criterion is necessary for improving vehicle countermeasures to mitigate pedestrian knee injuries. The advantages of both experimental tests and finite element (FE) simulations were combined to determine the reliable injury tolerances of the knee joint. First, 7 isolated lower limb tests from postmortem human subjects (PMHS) were reported, with dynamic loading at a velocity of 20 km/h.With the intention of replicating relevant injury mechanisms of vehicle–pedestrian impacts, the experimental tests were categorized into 3 groups by the impact locations on the tibia: the distal end to prioritize pure bending, the middle diaphysis to have combined bending and shearing effects, and the proximal end to acquire pure shearing. Then, the corresponding FE model was employed to provide an additional way to determine exact injury occurrences and develop a robust knee injury criterion by the variation in both the lateral bending and shearing contributions through a sensitivity analysis of impact locations. Considering the experimental test results and the subsequent sensitivity analysis of FE simulations, both the tolerances and patterns of knee joint injuries were determined to be influenced by impact locations due to various combined contributions of lateral bending and shearing. Both medial collateral ligament and cruciate ligament failures were noted as the onsets of knee injuries, namely, initial injuries. Finally, a new injury criterion categorized by initial injury patterns of knee joint was proposed by coupling lateral bending and shearing levels. The developed injury criterion correlated the combined joint kinematics to initial knee injuries based on subsegment tests andFEsimulations conductedwith a biofidelic lower limbmodel. This provides a valuableway of predicting the risk of knee injury associated with vehicle–pedestrian crashes and thereby represents a further step to promote the design of vehicle countermeasures for pedestrian safety

Experimental and numerical study of hat shaped CFRP structures under quasi-static axial crushing

Carbon fiber reinforced polymers (CFRP) has been increasingly applied in automobile industry for vehicle body lightweight and safety performance improvement. However, design of CFRP components especially for crushing structures is still highly ambiguous. The present study aims to study the deformation behaviour and energy absorption of the hat shaped CFRP structures and optimize the section shape. Two types of hat shaped CFRP structures with various thicknesses and ply orientation were tested under axial quasi-static crushing. The results show that the Type II hat shaped structure presents a stable progressive crushing mode and better energy absorbing ability as compared with the Type I hat shaped structure. Then, a finite element model was developed using the multi-layer shell element method, and was validated by the axial crushing test results. Finally, the section shape of the Type II CFRP structure was optimized through the surrogate model of radial basis function and global response surface method, and the influences of the section shape on crushing behaviours and energy absorbing abilities were analysed

Meso/macro scale response of the comingled glass polypropylene 2-2 twill woven fabric under shear pre-tension coupling

International audienc

Injury Thresholds of Knee Ligaments Under Lateral–Medial Shear Loading: An Experimental Study

Knee ligament injuries frequently cause devastating impairment to the injured. In car–pedestrian impact accidents, lateral–medial shear displacement is one of principal mechanisms of knee ligament injuries. The current study aims to investigate injury thresholds of knee ligaments under lateral–medial shear loading to improve pedestrian safety. Methods: Ten isolated human knee joints without surrounding muscles were tested under dynamic lateral–medial shear loading in 2 groups: 3 left knee joints were tested in the shearing of medial tibial translation, and other knee joints were tested in lateral tibial translation. Based on combined analysis of experimental videos and force curves, the primary failure time of knee ligaments and the corresponding shear displacement were determined. Results: Under lateral tibial translation and medial tibial translation, both primary injury types of knee ligaments and force curves showed essential differences. It appears that the majority of primary failure modes were anterior cruciate ligament (ACL) injury when the tibia was displaced medially and posterior cruciate ligament (PCL) injury when the tibia was displaced laterally. Overall experimental results indicated that the injury threshold of the knee joint under lateral–medial shear loading varied from 11.4 to 17.6 mm, with an average level approximately 14.3 mm. Conclusion: Based on the bone–ligament–bone complex experiment of the knee, we present injury occurrences of the knee joints in lateral and medial shear loading. The testing data provide a basis for improving knee injury criteria that regulate passenger cars to reduce their aggressiveness to pedestrians. Supplemental materials are available for this article. Go to the publisher’s online edition of Traffic Injury Prevention to view the supplemental file