VTechWorks Repository :: Browsing by Author "Untaroiu, Costin D."

Browsing by Author "Untaroiu, Costin D."

Now showing 1 - 20 of 24

Compacted Snow Testing Methodology and Instrumentation
Shenvi, Mohit Nitin (Virginia Tech, 2024-03-05)
Snow is a complex material that is difficult to characterize especially due to its high compressibility and temperature-sensitive nonlinear viscoelasticity. Snow mechanics has been intensively investigated by avalanche and army researchers for decades. However, fewer research studies have been published for compacted snow, commonly defined as snow with a density in the range of 370-560 kg/m3. From a mobility perspective, the tires are the primary point of force and motion generation and their interaction with the terrain causes an increased reliance on the skill of the driver for safer mobility. Thus, standards like ASTM F1805 are implemented for the evaluation of winter tires which can be used in harsh conditions like ice and snow. This work focuses on evaluating the prior efforts performed for the measurement of snow properties. In addition, analysis using regression models and principal component analysis is performed to understand the extent to which specific measurements related to snow affect the traction of the tire. It was found that the compressive and shear properties of snow contribute more than 90% to the variation in the traction coefficient of a tire when evaluated on a compacted snow domain per ASTM F1805. Identification of this phenomenon allowed the enhancement of an existing device that can be used for measuring the compaction and shear properties of snow. The device hence conceptualized was manufactured in-house and tested at the Smithers Winter Test Center to benchmark against existing devices available commercially. Further, a more analytical method for evaluating the resistive pressure for the penetration of the device was formulated. Based on this, a possible framework for the determination of the bevameter parameters using measurements of the new device has been proposed which needs to be validated experimentally and computationally.
Correlating tire traction performance on snow with measured parameters of ASTM F1805 using regression analysis
Shenvi, Mohit Nitin; Sandu, Corina; Untaroiu, Costin D.; Pierce, Eric (Elsevier, 2023-09)
Winter tires sold in North America are often tested using the ASTM F1805 testing process to determine if they can be labeled with the ‘mountain snowflake’ symbol which indicates better performance for snow usage. The standard dictates the requirements for testing and necessary track preparation methodologies. In addition, the requirements of the standard dictate the range of three major conditions for tests to be carried out, namely the CTI penetration measurement, the snow temperature, and the ambient temperature. However, these parameters cannot be directly used in the simulation stage of snow modeling for better evaluation of prototypes. It is well-known that snow properties depend on a wide variety of parameters, making the creation of an accurate and robust snow material model, and, consequently, applying a simulation-based approach for tire design, difficult. This work focuses on the analysis of a dataset of five winter seasons of a 14-in. Standard Reference Test Tire on snow used to benchmark the performance of a potential winter tire. The blinded data measured at Smithers Winter Test Center were used in the analysis to train regression models for predicting the traction coefficient and evaluating the extent to which the measured parameters affect the variation in the traction coefficient. This study utilized twenty-six different modeling approaches and implementation of principal component analysis. The findings of this study highlight the relative importance of the compression and shear characteristics of the snow on the traction of the tire. It was found that regression methods based on Gaussian processes were better at predicting the traction coefficient. The study also highlights the importance of utilizing a single physical tire as the reference tire for benchmarking according to the ASTM F1805.
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.
Development and Validation of a Finite Element Dummy Lower Limb Model for Under-body blast Applications
Baker, Wade Andrew (Virginia Tech, 2017-07-18)
An under-body blast (UBB) refers to the use of a roadside explosive device to target a vehicle and its occupants. During Operation Iraqi Freedom, improvised explosive devices (IEDs) accounted for an estimated 63% of US fatalities. Furthermore, advancements in protective equipment, combat triage, and treatment have caused an increase in IED casualties surviving with debilitating injuries. Military vehicles have been common targets of IED attacks because of the potential to inflict multiple casualties. Anthropomorphic test devices (ATDs) are mechanical human surrogates designed to transfer loads and display kinematics similar to a human subject. ATDs have been used successfully by the automotive industry for decades to quantify human injury during an impact and assess safety measures. Currently the Hybrid III ATD is used in live-fire military vehicle assessments. However, the Hybrid III was designed for frontal impacts and demonstrated poor biofidelity in vertical loading experiments. To assess military vehicle safety and make informed improvements to vehicle design, a novel Anthropomorphic Test Device (ATD) was developed and optimized for vertical loading. ATDs, commonly referred to as crash dummies, are designed to estimate the risk of injuries to a human during an impact. The main objective of this study was to develop and validate a Finite Element (FE) model of the ATD lower limb.
Development and Validation of Human Body Finite Element Models for Pedestrian Protection
Pak, Wansoo (Virginia Tech, 2019-10-21)
The pedestrian is one of the most vulnerable road users. According to the World Health Organization (WHO), traffic accidents cause about 1.34 million fatalities annually across the world. This is the eighth leading cause of death across all age groups. Among these fatalities, pedestrians represent 23% (world), 27% (Europe), 40% (Africa), 34% (Eastern Mediterranean), and 22% (Americas) of total traffic deaths. In the United States, approximately 6,227 pedestrians were killed in road crashes in 2018, the highest number in nearly three decades. To protect pedestrians during Car-to-Pedestrian Collisions (CPC), subsystem impact tests, using impactors corresponding to the pedestrian's head and upper/lower leg were included in regulations. However, these simple impact tests cannot capture the complex vehicle-pedestrian interaction, nor the pedestrian injury mechanisms, which are crucial to understanding pedestrian kinetics/kinematics responses in CPC accidents. Numerous variables influence injury variation during vehicle-pedestrian interactions, but current test procedures only require testing in the limited scenarios that mostly focus on the anthropometry of the 50th percentile male subject. This test procedure cannot be applied to real-world accidents nor the entire pedestrian population due to the incredibly specific nature of the testing. To better understand the injury mechanisms of pedestrians and improve the test protocols, more pre-impact variables should be considered in order to protect pedestrians in various accident scenarios. In this study, simplified finite element (FE) models corresponding to 5th percentile female (F05), 50th percentile male (M50), and 95th percentile male (M95) pedestrians were developed and validated in order to investigate the kinetics and kinematics of pedestrians in a cost-effective study. The model geometries were reconstructed from medical images and exterior scanned data corresponding to a small female, mid-sized male, and tall male volunteers, respectively. These models were validated based on post mortem human surrogate (PMHS) test data under various loading including valgus bending at knee joint, lateral/anterior-lateral impact at shoulder, pelvis, thorax, and abdomen, and lateral impact during CPC. Overall, the kinetic/kinematic responses predicted by the pedestrian FE models showed good agreement against the corresponding PMHS test data. To predict injuries from the tissue level up to the full-body, detailed pedestrian models, including sophisticated musculoskeletal system and internal organs, were developed and validated as well. Similar validations were performed on the detailed pedestrian models and showed high-biofidelic responses against the PMHS test data. After model development and validation, the effect of pre-impact variables, such as anthropometry, pedestrian posture, and vehicle type in CPC impacts were investigated in different impact scenarios. The M50-PS model's posture was modified to replicate pedestrian gait posture. Five models were developed to demonstrate pedestrian posture in 0, 20, 40, 60, and 80 % of the gait cycle. In a sensitivity study, the 50th percentile male pedestrian simplified (M50-PS) model in gait predicted various kinematic responses as well as the injury outcomes in CPC impact with different vehicle type. The pedestrian FE models developed in this work have the capability to reproduce the kinetic/kinematic responses of pedestrians and to predict injury outcomes in various CPC impact scenarios. Therefore, this work could be used to improve the design of new vehicles and current pedestrian test procedures, which eventually may reduce pedestrian fatalities in traffic accidents.
Development, Calibration, and Validation of a Finite Element Model of the THOR Crash Test Dummy for Aerospace and Spaceflight Crash Safety Analysis
Putnam, Jacob Breece (Virginia Tech, 2014-09-17)
Anthropometric test devices (ATDs), commonly referred to as crash test dummies, are tools used to conduct aerospace and spaceflight safety evaluations. Finite element (FE) analysis provides an effective complement to these evaluations. In this work a FE model of the Test Device for Human Occupant Restraint (THOR) dummy was developed, calibrated, and validated for use in aerospace and spaceflight impact analysis. A previously developed THOR FE model was first evaluated under spinal loading. The FE model was then updated to reflect recent updates made to the THOR dummy. A novel calibration methodology was developed to improve both kinematic and kinetic responses of the updated model in various THOR dummy certification tests. The updated THOR FE model was then calibrated and validated under spaceflight loading conditions and used to asses THOR dummy biofidelity. Results demonstrate that the FE model performs well under spinal loading and predicts injury criteria values close to those recorded in testing. Material parameter optimization of the updated model was shown to greatly improve its response. The validated THOR-FE model indicated good dummy biofidelity relative to human volunteer data under spinal loading, but limited biofidelity under frontal loading. The calibration methodology developed in this work is proven as an effective tool for improving dummy model response. Results shown by the dummy model developed in this study recommends its use in future aerospace and spaceflight impact simulations. In addition the biofidelity analysis suggests future improvements to the THOR dummy for spaceflight and aerospace analysis.
Experimental Characterization and Modeling of Tire-Ice Interface
Mousavi, Hoda (Virginia Tech, 2021-03-18)
Tire parameters play a very important role in tire performance. Depending on the driving conditions for which a given tire is designed, its parameters must be chosen appropriately (e.g., the radius of the tire, the width of the tire, material properties of different sections). Among tire characteristics, the material properties of the rubber compounds have a vital role in tire behavior. Previous studies show that the material properties of the rubber are highly dependent on temperature. Thus, a comprehensive study on the effect of the material properties of the rubber on tire performance for different temperatures as well as different road conditions is required. In this study, a theoretical model has been developed for tire-ice interaction. The temperature changes obtained from the model are used to calculate the height of the water film created by the heat generated due to the friction force. Next, the viscous friction coefficient at the contact patch is obtained. By using the thermal balance equation at the contact patch, dry friction is obtained. Knowing the friction coefficients for the dry and wet regions, the equivalent friction coefficient is calculated. The model has been validated using experimental results for three similar tires with different rubber compounds properties. For the experimental part of this study, four tires have been selected for testing. Three of them have identical tire geometry and structure but different rubber tread compounds. Several tests were conducted for the chosen tires in three modes: free-rolling, braking, and traction. The tests were performed for two different normal loads (4 kN and 5.6 kN), two different inflation pressures (21 psi (144.8 kPa) and 28 psi (193 kPa)), and three tire temperatures levels (-10°C, -5°C, and -1 °C). The Terramechanics Rig at TMVS at Virginia Tech has been used for conducting the tests. The results from this study show the sensitivity of the magnitude of the tractive force with respect to parameters such as tire temperature, normal load, etc. The results also indicate that the tire with the lowest value of the Young modulus has the highest traction among all four tires used in this study. The model developed can be used to predict the temperature changes at the contact patch, the tire friction force, the areas of wet and dry regions, the height of the water film for different ice temperatures, different normal loads, etc. The results from this study coincide with the obtained results from the experiments. According to the data available, tire B with the smallest value of Young modulus and the smallest value of the specific heat parameter was shown to have the highest friction coefficient in both simulation and experiment. After validating the results using experimentally collected data, the model was used to perform a sensitivity analysis on the tire performance with respect to six material properties of the tread rubber: thermal conductivity, rubber density, Young's modulus, specific heat, roughness parameter of the rubber, and radii of spherical asperities of the rubber. The results from this study show the sensitivity of the magnitude of the friction coefficient to the rubber material properties. The friction coefficient has a direct relationship with the density of the rubber and has an inverse relationship with Young's modulus, specific heat, and roughness parameter.
Exploring the Link Between E-scooter Crash Mechanism and Injury Outcome Using Finite Element Analysis
Chontos, Rafael Cameron (Virginia Tech, 2023-07-06)
The recent emergence of electric scooter (e-scooter) ride share companies has greatly increased the use of e-scooters in cities around the world. In this thesis, firstly, e-scooter injuries reported in the current literature as well as an overview of current e-scooter company policies, state laws, and local laws are reviewed. The most injured regions of the body were the head and extremities. These injuries are generally minor to moderate in severity and commonly include fractures and lacerations. A primary cause of e-scooter accidents is front wheel collisions with a vertical surface such as a curb or object, generically referred to as a "stopper." Therefore, various e-scooter-stopper crashes were simulated numerically across different impact speeds, approach angles, and stopper heights to characterize their influence on rider injury risk during falls. A finite element (FE) model of a standing Hybrid III anthropomorphic test device was used as the rider model after being calibrated against certification test data. The angle of approach was found to have the greatest effect on injury risk to the rider, and it was shown to be positively correlated with injury risk. Smaller approach angles were shown to cause the rider to land on their side, while larger approach angles caused the rider to land on their head and chest. Additionally, arm bracing was shown to reduce the risk of serious injury in two thirds of the impact scenarios. The majority of e-scooter rider fatalities (about 80%) are recorded in collisions between a car and an e-scooter. Therefore, crashes between an e-scooter and a sedan (FCR) and a sports utility vehicle (SUV) were simulated using finite element models. The vehicles impacted the e-scooter at a speed of 30 km/hr in a perpendicular collision and at 15 degrees towards the vehicle, to simulate a rider being struck by a turning vehicle. The risks of serious injury to the rider were low for the head, brain, and neck, but femur/tibia fractures were observed in all simulations. The primary cause of head and brain injuries was found to be the head-ground impact if such an impact occurred.
A finite element of an electric scooter model for simulating traffic accidents
Chontos, Rafael; Grindle, Daniel M.; Untaroiu, Alexandrina; Untaroiu, Costin D. (2021-10-07)
Full Field Reconstruction Enhanced With Operational Modal Analysis and Compressed Sensing for General Dynamic Loading
Fu, Gen (Virginia Tech, 2021-06-09)
In most applications, the structure components have to be tested under different loading conditions before being placed in operation. A reliable and low cost measuring technique is desirable. However, most currently employed measuring approaches can only provide the structural response at several discrete locations. The accuracy of the measurements varies with the location and orientation of the sensors. Practically, it is not possible to place sensors at all the critical locations for different excitations. Therefore, an approach that derives the full field response using a limited set of measured data is desirable. In contrast to experimental full field measurement techniques, the expansion approach involves analytically expanding the limited measurements to all the degrees of freedom of the structure. Among all the analytical methods, the modal expansion method is computationally efficient and thus more suitable for real time expansion of measured data. In this method, the full-field response is approximated by the linear combination of mode shapes. In previous studies, the modal expansion method is limited by errors from mode aliasing, inaccuracy of the calculated mode shapes and the noise in measurements. In order to overcome these limitations, the modal expansion method is enhanced by mode selection and error compensation in this study. First, the key parameters used in modal expansion method were analyzed using a cantilever beam model and a method for optimal placement of sensors was developed. A mode selection method and error compensation method based on operation modal analysis and adaptive compressed sensing techniques were then developed to reduce the effects of mode aliasing, mode shape inaccuracy and measurement noise. The developed approach was further tested virtually using a numerical model of rotor 67. The numerical model was created using a two-way coupled fluid structure interaction technique. By developing these methods, the enhanced modal expansion approach can provide full field response for structures under different load conditions. Compared to the traditional modal expansion method, it can expand the data with high noise and under general dynamic loading.
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.
Improving E-Scooter Safety: Deployment Policy Recommendations, Design Optimization, and Training Development
Novotny, Adam James (Virginia Tech, 2023-01-19)
The Influence of the Specimen Shape and Loading Conditions on the Parameter Identification of a Viscoelastic Brain Model
Untaroiu, Costin D. (Hindawi Publishing Corporation, 2013)
The mechanical properties of brain under various loadings have been reported in the literature over the past 50 years. Step-and-hold tests have often been employed to characterize viscoelastic and nonlinear behavior of brain under high-rate shear deformation; however, the identification of brain material parameters is typically performed by neglecting the initial strain ramp and/or by assuming a uniform strain distribution in the brain samples. Using finite element (FE) simulations of shear tests, this study shows that these simplifications have a significant effect on the identified material properties in the case of cylindrical human brain specimens. Material models optimized using only the stress relaxation curve under predict the shear force during the strain ramp, mainly due to lower values of their instantaneous shear moduli. Similarly, material models optimized using an analytical approach, which assumes a uniform strain distribution, under predict peak shear forces in FE simulations. Reducing the specimen height showed to improve the model prediction, but no improvements were observed for cubic samples with heights similar to cylindrical samples. Models optimized using FE simulations show the closest response to the test data, so a FE-based optimization approach is recommended in future parameter identification studies of brain.
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.
Probabilistic Analysis of the Material and Shape Properties for Human Liver
Lu, Yuan-Chiao (Virginia Tech, 2014-08-19)
Realistic assessments of liver injury risk for the entire occupant population require incorporating inter-subject variations into numerical human models. The main objective of this study was to quantify the variations in shape and material properties of the human liver. Statistical shape analysis was applied to analyze the geometrical variation using a surface set of 15 adult human livers recorded in an occupant posture. Principal component analysis was then utilized to obtain the modes of variation, the mean model, and a set of 95% statistical boundary shape models. Specimen-specific finite element (FE) models were employed to quantify material and failure properties of human liver parenchyma. The mean material model parameters were then determined, and a stochastic optimization approach was utilized to determine the standard deviations of the material model parameters. The distributions of the material parameters were used to develop probabilistic FE models of the liver implemented in THUMS human FE model to simulate oblique impact tests under three impact speeds. In addition, the influence of organ preservation on the biomechanical responses of animal livers was investigated using indentation and tensile tests. Results showed that the first five modes of the human liver shape models accounted for more than 70% of the overall anatomical variations. The Ogden material model with two parameters showed a good fit to experimental tensile data before failure. Significant changes of the biomechanical responses of liver parenchyma were found after cooling or freezing storage. The force-deflection responses of THUMS model with probabilistic liver material models were within the test corridors obtained from cadaveric tests. Significant differences were observed in the maximum and minimum principal Green-Lagrangian strain values recorded in the THUMS liver model with the default and updated average material properties. The results from this study could help in the development of more biofidelic human models, which may provide a better understanding of injury mechanisms of the liver during automobile collisions.
Protection of Rear Seat Occupants Using Finite Element Analysis
Yates, Keegan M. (Virginia Tech, 2020-12-10)
The majority of car crash deaths occur in the front seats because the majority of occupants sit in the front seats. Traditionally, the rear seats were safer than the front seats because a front seated occupant would be closer to rigid structures such as the steering wheel, and they would be closer to the location of the impact. Therefore, government crash test regulations as well as academic and industry testing up to this point have principally focused on the front seats. Since the beginning of efforts to make cars safer, innovations were applied to the front seats first. Only some of these safety innovations have transitioned into the rear seats. Over the years, the front seats have gotten much safer due to advanced seatbelts with pretentioners and load limiters, airbags surrounding the driver, and structural changes to the vehicle frame to prevent intrusion into the occupant compartment. At the same time, occupant safety in the rear seats has also improved, however at only a fraction of the improvement of the front seats. With modern vehicles, the front seats have actually become safer than the rear seats for certain occupants and specific crash types (e.g., adult occupants in frontal crash). The lagging performance of the rear seats represents a problem because thousands of rear-seated occupants are injured or killed each year. With the rise in autonomous driving systems, the amount of occupants sitting in the rear seats, and therefore sustaining injury, could increase dramatically. In this dissertation, rear seats of a range of current vehicles were reconstructed to examine injury risk with the finite element models of two anthropomorphic test devices. These models showed a wide range of injury risks in the reconstructed seats. They were also able to show results similar to sled impact tests with the same vehicles. Knowledge gained from these reconstructions was then used to perform parametric studies on key variables that influence injury risk in the rear seats. From the parametric studies, it was found that the seat back angle, the width of the seatbelt anchors, and the presence of a seatbelt pretensioner had the largest influences on the injury risk. One of the injury mechanisms prevalent in the rear seats is submarining. Submarining likelihood and injury probability is difficult to predict with anthropomorphic test devices; however, human body models can help to improve injury prediction in these cases. To improve the injury prediction capability of human body models, several additions to the models are necessary. This dissertation outlines the investigation of spleen and kidney shapes through statistical shape analysis. This type of analysis allows more customizable human body models which could better capture the injury probability to these organs for a wider range of the population. Finally, subject-specific models of ribs were created to investigate factors affecting the predictive capability of finite element models. The findings and methodology from this body of work have the ability to add critical contributions to the understanding of injury risk and injury mechanisms in the rear seats.
Protection of Standing and Seated Pedestrians Using Finite Element Analysis
Grindle, Daniel Mark (Virginia Tech, 2023-06-06)
In the United States pedestrian fatalities in vehicle impacts have increased over the last 40 years and pedestrians who use wheelchairs (seated pedestrians) have higher mortality rates than standing pedestrians in vehicle impacts. Standing pedestrian protection has generated increased attention and regulatory action but seated pedestrian protection has not been investigated or regulated. To investigate standing pedestrian safety researchers use finite element models of the human body and simulate vehicle impacts. Finite element models can be useful but they are limited by their biofidelity, and often simplify the complex anatomy of the human body for the sake of computational expense. If modeling results are to be taken seriously to investigate standing and seated pedestrian protection, then further model development and validation is necessary. In this dissertation a finite element model of a male 50th percentile standing pedestrian was enhanced and validated for use in vehicle impact simulations. The standing pedestrian model lower body was further enhanced and validated to study the importance of stabilizing components of the knee. These updates to the standing pedestrian knee joint were imported into an occupant model and further validated in occupant loading scenarios. The updated standing pedestrian was used to explore the effect of modeling component failure on vehicle impact. Simplified and detailed occupant models were used to model seated pedestrians in vehicle impacts to explore seated pedestrian injury risks. The seated pedestrian head and brain typically reported the highest risks of injury, usually because of head-ground contact. A lap belt, airbag vest, and bicycle helmet were tested on the seated pedestrians. The lap belt and airbag vest typically increased injury risks and the bicycle helmet reduced injury risks. The work presented in this dissertation may inform future modelers, vehicle designers, and safety equipment developers on standing and seated pedestrian safety.
Quantifying the Response of Relative Brain/Skull Motion to Rotational Input in the PMHS Head
Guettler, Allison Jean (Virginia Tech, 2018-02-27)
Post-mortem human surrogate (PMHS) head specimens were subjected to two different angular speed pulses. Each pulse was approximately a half-sine with either a peak angular speed of either 40 or 20 rad/s and duration of either 30 or 60 milliseconds. High-speed biplane x-ray was used to record the motion of the brain and skull via radio-opaque markers implanted at specified locations in the brain, and lead markers on the skull. Specimens were perfused to physiologic conditions throughout preparation and testing to maintain the integrity of the brain tissue and ensure coupling of the brain and skull. Intracranial pressure was measured anteriorly and posteriorly. The test event was controlled by a cam-follower-flywheel mechanism, which facilitated control of pulse parameters and provided a form of "infinite energy" so that the device and therefore the test input would not be influenced by the characteristics of the object under test. This approach kept the independent and dependent variables separated. The brain targets were also deployed in a prescribed manner with two methodologies that were scalable to different specimens. The repeatable input and target deployment schemes helped reduce experimental variation (between tests and subjects) to produce consistent response data. Displacement of the brain was calculated with respect to a body-fixed basis on the skull. The relative motion of the brain with respect to the skull was shown to be dependent on the location of the target in the brain. The major deformation axis of each target followed the contour of the skull or bony landmark to which it was closest. Intracranial pressure was relatively low because the changes were due to inertial effects in the absence of impact. Tests with lower speeds and longer durations produced less deformation, lower intracranial pressures, and longer pressure durations than the tests that were high-speed, short-duration. The response of the brain to rotation of the head was quantified at two test levels and on two PMHS specimens.
Review of compressed snow mechanics: Testing methods
Shenvi, Mohit Nitin; Sandu, Corina; Untaroiu, Costin D. (Elsevier, 2022-04)
Snow is a complex material that is difficult to characterize especially due to its high compressibility and temperature-sensitive nonlinear viscoelasticity. Snow mechanics has been intensively investigated by avalanche and army researchers for decades. However, fewer research studies were published for the compacted snow, defined as snow with a density in a range of 370–560 kg/m3. This review focuses on the various testing methods that are used especially to characterize the behavior of compacted snow under compressive and shear loading. The working principles, inherent assumptions, and advantages/disadvantages of the devices are summarized. In addition, some of the important material properties of snow like density, elastic modulus, etc., and their measurement is highlighted. Lastly, a correlation of the testing methods to commonly used approaches in modeling snow is presented. Overall, we believe that this study can help to better understand the existing test data related to compacted snow and guide future testing in this field.
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.

Browsing by Author "Untaroiu, Costin D."

Results Per Page

Sort Options