Browsing by Author "Meng, Yunzhu"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Development and Validation of a Child Finite Element Model for Use in Pedestrian Accident Simulations
    Meng, Yunzhu (Virginia Tech, 2017-06-09)
    Car collisions are the third leading cause of unintentional death and injury among children aged 5 to 14. The pedestrian lower-extremity represents the most frequently injured body region in car-to-pedestrian accidents. Several sub-system tests (head, upper and lower legs) were developed for pedestrian protection in Asia and Europe. However, with exception of a child headform impact test, all other subsystem tests are designed for prediction of adult pedestrian injuries. Due to differences in impact location and material properties, existing subsystem tests and dummies designed for adult pedestrian cannot be used for child pedestrian protection by simple scaling. Thus, the development of a computational child pedestrian model could be a better alternative that characterizes the whole-body response of vehicle-pedestrian interactions and assesses the pedestrian injuries. Although several computational models for child pedestrian were developed in MADYMO/LS-DYNA, each has limitations. Children differ structurally from adults in several ways, which are critical to addressing before studying pediatric pedestrian protection. To aid in the development of accurate pediatric models, child pedestrian lower-extremity data presented in literature were first summarized. This review includes common pedestrian injuries, anatomy, anthropometry, structural and mechanical properties. A Finite Element (FE) model corresponding to a six-year-old child pedestrian (GHBMC 6YO-PS) was developed in LS-DYNA. The model was obtained by linear scaling an existing adult model corresponding to 5th percentile female anthropometry to an average six-year-old child's overall anthropometry taken from literature, and then by morphing to the final target geometry. Initially, the material properties of an adult model were assigned to the child model, and then were updated based on pediatric data during the model validation. Since the lower extremity injuries are the most common injuries in pedestrian accidents, the model validation focus on the pelvis and lower extremity regions. Three-point bending test simulations were performed on the femur and tibia and the results were compared to Post-Mortem Human Subject (PMHS) data. The knee model was also simulated under valgus bending, the primary injury mechanism of the knee under lateral loading. Then, the whole pedestrian model was simulated in lateral impact simulation and its response was compared to PMHS data. Finally, the stability of the child model was tested in a series of pediatric Car-to-Pedestrian Collision (CPC) with pre-impact velocities ranging from 20 km/h up to 60 km/h. Overall, the lower extremity and pelvis models showed biofidelity against PMHS data in component simulations. The stiffness and fracture FE responses showed a good match to PMHS data reported in the literature. The knee model predicted common ligament injuries observed in PMHS tests and a lower bending stiffness than adult data. The pelvis impact force predicted by the child model showed a similar trend with PMHS test data as well. The whole pedestrian model was stable during CPC simulations. In addition, the most common injuries observed in pedestrian accidents including fractures of lower limb bones and ruptures of knee ligaments were predicted by the model. The child model was accepted to be used according to Euro-NCAP protocol, so it will be used by safety researchers in the design of front ends of new vehicles in order to increase pedestrian protection of children.
  • Thumbnail Image
    Implications of Truck Platoons for Roadside Hardware and Vehicle Safety
    Dobrovolny, Chiara Silvestri; Untaroiu, Costin D.; Sharma, Roshan; Jin, Hanxiang; Meng, Yunzhu (SAFE-D: Safety Through Disruption National University Transportation Center, 2019-10)
    Platooning is an extension of cooperative adaptive cruise control and forward collision avoidance technology, which provides automated lateral and longitudinal vehicle control to maintain short following distances and tight formation. The capacity and adequacy of existing roadside safety hardware deployed at strategic locations may not be sufficient to resist potential impact from an errant fleet of multiple trucks platooning at high speed. It is unknown how these impacting trucks might interact with roadside safety barriers after leaving their platoon and what the occupant risks associated with such impacts may be. This research identifies and prioritizes the critical Manual for Assessing Safety Hardware TL5 roadside safety devices for truck platooning impact assessment in order to understand the associated roadside and occupant risks and hazards. Finite element models of the trucks and roadside safety devices are examined using multiple computer simulations for various scenarios. Occupants injury risks during truck collision simulations are assessed using dummy and human finite element models. The results and implications can provide a better understanding of whether any roadside safety device improvements and/or platooning constraint modifications will be necessary before implementing truck platooning.
  • Thumbnail Image
    Investigation of W-Beam Energy-Absorbing Guardrail End Terminal Safety Performance Using Finite Element Modeling
    Meng, Yunzhu (Virginia Tech, 2022-08-23)
    Guardrails were designed to deter vehicle access to off-road areas and consequently prevent hitting rigid fixed object alongside the road (e.g., trees, utility poles, traffic barriers, etc.). However, guardrails cause 10% of deaths of vehicle-to-fixed object crashes which has attracted attention in the highway safety community on the vehicle-based injury criteria used in guardrail regulations. The objectives of this study were 1) to develop and validate a Finite Element (FE) model of the ET-Plus, a commonly used energy-absorbing guardrail end terminal; 2) to examine the conditions of in-service end terminals, and to evaluate the performance of the damaged relative to undamaged end terminals in simulated impacts; 3) to investigate both full-body and body region driver injury probabilities during car-to-end terminal crashes using dummy and human body FE models; to analyze the relationship between the vehicle-based crash severity metrics used currently in regulations and the injury probabilities assessed using biomechanics injury criteria; and 4) to quantify the influence of pre-impact conditions on injury probabilities. In this dissertation, an ET-Plus FE model was developed based on publicly available data on ET-Plus dimensions and material properties. The model was validated against the NCHRP-350 crash tests. The developed ET-Plus model was used to develop to five damaged ET-Plus whose damage patterns were identified based on an investigation of in-service end terminals mounted along U.S. roads. It was observed that damaged end terminals usually increase collision severity compared to undamaged end terminals. Meanwhile, a total of 40 FE impact simulations between a car with a dummy/human body model in the driver seat and an end terminal model were performed in various configurations. The vehicle-based severity metrics were observed to be correlated to full-body and certain body-region injury risks while no head injury risk could be predicted. The results pointed out that more advanced vehicle-based metrics should be proposed and investigated to improve the predictability in terms of occupant injury risks in the crash tests. The simulation models could also supplement crash compliance tests of new hardware designs, by investigating their safety performance for a large variety of pre-impact conditions, observed in traffic accidents, but not included the compliance tests.
  • Thumbnail Image
    A Review of Pediatric Lower Extremity Data for Pedestrian Numerical Modeling: Injury Epidemiology, Anatomy, Anthropometry, Structural, and Mechanical Properties
    Meng, Yunzhu; Untaroiu, Costin D. (Hindawi, 2018-09-04)
    Pedestrian injuries are the fourth leading cause of unintentional injury-related death among children aged 1 to 19. The lower extremity represents the most frequently injured body region in car-to-pedestrian accidents. The goal of this study was to perform a systematic review of the data related to pedestrian lower extremity injuries, anatomy, anthropometry, structural, and mechanical properties, which can be used in the development of new pediatric computational models. The study began with a review of epidemiologic data related to pediatric pedestrian accidents. Anatomy of the child lower extremity and age-related anthropometry data were presented as well. Then, both the mechanical and structural properties of the lower extremity main components (e.g., bones, cartilages, knee ligaments, muscles, tendons, and growth plates) available in literature were summarized. The study concluded with a brief description of current child pedestrian models, which included a discussion about their limitations. We believe that data included in this review study can help in improving the biofidelity of current child models and support the development and validation of new child models used by safety researchers for protection of pediatric population.