Browsing by Author "Hardy, Warren N."

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    A 3-D Finite-Element Minipig Model to Assess Brain Biomechanical Responses to Blast Exposure
    Sundaramurthy, Aravind; Kote, Vivek Bhaskar; Pearson, Noah; Boiczyk, Gregory M.; McNeil, Elizabeth M.; Nelson, Allison J.; Subramaniam, Dhananjay Radhakrishnan; Rubio, Jose E.; Monson, Kenneth; Hardy, Warren N.; VandeVord, Pamela J.; Unnikrishnan, Ginu; Reifman, Jaques (Frontiers, 2021-12-17)
    Despite years of research, it is still unknown whether the interaction of explosion-induced blast waves with the head causes injury to the human brain. One way to fill this gap is to use animal models to establish “scaling laws” that project observed brain injuries in animals to humans. This requires laboratory experiments and high-fidelity mathematical models of the animal head to establish correlates between experimentally observed blast-induced brain injuries and model-predicted biomechanical responses. To this end, we performed laboratory experiments on Göttingen minipigs to develop and validate a three-dimensional (3-D) high-fidelity finite-element (FE) model of the minipig head. First, we performed laboratory experiments on Göttingen minipigs to obtain the geometry of the cerebral vasculature network and to characterize brain-tissue and vasculature material properties in response to high strain rates typical of blast exposures. Next, we used the detailed cerebral vasculature information and species-specific brain tissue and vasculature material properties to develop the 3-D high-fidelity FE model of the minipig head. Then, to validate the model predictions, we performed laboratory shock-tube experiments, where we exposed Göttingen minipigs to a blast overpressure of 210 kPa in a laboratory shock tube and compared brain pressures at two locations. We observed a good agreement between the model-predicted pressures and the experimental measurements, with differences in maximum pressure of less than 6%. Finally, to evaluate the influence of the cerebral vascular network on the biomechanical predictions, we performed simulations where we compared results of FE models with and without the vasculature. As expected, incorporation of the vasculature decreased brain strain but did not affect the predictions of brain pressure. However, we observed that inclusion of the cerebral vasculature in the model changed the strain distribution by as much as 100% in regions near the interface between the vasculature and the brain tissue, suggesting that the vasculature does not merely decrease the strain but causes drastic redistributions. This work will help establish correlates between observed brain injuries and predicted biomechanical responses in minipigs and facilitate the creation of scaling laws to infer potential injuries in the human brain due to exposure to blast waves.
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    Assessment of Crash Energy - Based Side Impact Reconstruction Accuracy
    Johnson, Nicholas S. (Virginia Tech, 2011-05-03)
    One of the most important data elements recorded in the National Automotive Sampling System / Crashworthiness Data System (NASS/CDS) is the vehicle change in velocity, or ?V. ?V is the vector change in velocity experienced by a vehicle during a collision, and is widely used as a measure of collision severity in crash safety research. The ?V information in NASS/CDS is used by the U.S. National Highway Traffic Safety Administration (NHTSA) to determine research needs, regulatory priorities, design crash test procedures (e.g., test speed), and to determine countermeasure effectiveness. The WinSMASH crash reconstruction code is used to compute the ?V estimates in the NASS/CDS. However, the reconstruction accuracy of the current WinSMASH version has not previously been examined for side impacts. Given the importance of side impact crash modes and the widespread use of NASS/CDS data, an assessment of the program's reconstruction accuracy is warranted. The goal of this thesis is to quantify the accuracy of WinSMASH ?V estimations for side impact crashes, and to suggest possible means of improving side impact reconstruction accuracy. Crash tests provide a wealth of controlled crash response data against which to evaluate WinSMASH. Knowing the accuracy of WinSMASH in reconstructing crash tests, we can infer WinSMASH accuracy in reconstructing real-world side crashes. In this study, WinSMASH was compared to 70 NHTSA Moving Deformable Barrier (MDB) - to - vehicle side crash tests. Tested vehicles were primarily cars (as opposed to Light Trucks and Vans, or LTVs) from model years 1997 - 2001. For each test, the actual ?V was determined from test instrumentation and this ?V was compared to the WinSMASH-reconstructed ?V of the same test. WinSMASH was found to systemically over-predict struck vehicle resultant ?V by 12% at time of vehicle separation, and by 22% at time of maximum crush. A similar pattern was observed for the MDB ?V; WinSMASH over-predicted resultant MDB ?V by 6.6% at separation, and by 23% at maximum crush. Error in user-estimated reconstruction parameters, namely Principal Direction Of Force (PDOF) error and damage offset, was controlled for in this analysis. Analysis of the results indicates that this over-prediction of ?V is caused by over-estimation of the energy absorbed by struck vehicle damage. In turn, this ultimately stems from the vehicle stiffness parameters used by WinSMASH for this purpose. When WinSMASH was forced to use the correct amount of absorbed energy to reconstruct the crash tests, systemic over-prediction of ?V disappeared. WinSMASH accuracy when reconstructing side crash tests may be improved in two ways. First, providing WinSMASH with side stiffness parameters that are correlated to the correct amount of absorbed energy will correct the systemic over-prediction of absorbed energy when reconstructing NHTSA side crash tests. Second, providing some treatment of restitution in the reconstruction process will correct the under-prediction of ?V due to WinSMASH's assumption of zero restitution. At present, this under-prediction partially masks the over-prediction of ?V caused by over-prediction of absorbed energy. If the over-prediction of absorbed energy is corrected, proper treatment of restitution will correct much of the remaining error observed in WinSMASH reconstructions of NHTSA side crash tests.
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    Biomechanical Investigation of Head Kinematics and Skull Stiffness
    Seimetz, Christina N. (Virginia Tech, 2011-05-31)
    This thesis presents two studies related to head injury. The study presented in Chapter 1 reviewed findings of cranial movement in animal and human specimens and evaluate the validity of cranial movement due to manual manipulation in humans through engineering analysis. The study had two parts. In Part I, the literature was reviewed to determine the cranial motion in animals and humans. Engineering analysis was done in Part II to determine the amount of force necessary to cause cranial motion in the studies from Part I using skull stiffness values from published studies. Chapter 2 explored data collection methodologies used in frontal sled tests. Several data collection methodologies exist for collecting kinematic data, such as Vicon motion analysis, video analysis, and sensors. Head trajectories from motion data and accelerometer data were plotted up to maximum forward excursion of the head for eight frontal sled tests, four conducted at Virginia Tech and four at the University of Virginia. In addition, the percent difference between maximum forward excursion values from sensor and motion data were calculated. Finally, Chapter 3 discusses the literary contributions of each study and to which journals they will be submitted.
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    Biomechanical Response of the Human Eye to Dynamic Loading
    Bisplinghoff, Jill Aliza (Virginia Tech, 2009-04-10)
    Blindness due to ocular trauma is a significant problem in the United States considering that each year approximately 500,000 years of eyesight are lost. The most likely sources of eye injuries include sports related impacts, automobile accidents, consumer products, and military combat. Out of the 1.9 million total eye injuries in the country, more than 600,000 sports injuries occur each year and 40,000 of them require emergency care. In 2007, approximately 66,000 people suffered from vehicle related eye injuries in the United States. Of the vehicle occupants sustaining an eye injury during a crash, as many as 15% to 25% sustained severe eye injuries and it was shown that within these severe eye injuries as many as 45% resulted in globe rupture. The purpose of this thesis is to characterize the biomechanical response of the human eye to dynamic loading. A number of test series were conducted with different loading conditions to gather data. A drop tower pressurization system was used to dynamically increase intraocular pressure until rupture. Results for rupture pressure, stress and strain were reported. Water streams that varied in diameter and velocity were developed using a customized pressure system to impact eyes. Intraocular pressure, normalized energy and eye injury risk were reported. A Facial and Ocular Countermeasure Safety (FOCUS) headform was used to measure the force applied to a synthetic eye during each hit from projectile shooting toys. The risk of eye injury for each impact was reported. These data provide new and significant research to the field of eye injury biomechanics to further the understanding of eye injury thresholds.
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    Biomechanical Responses of Human Surrogates under Various Frontal Loading Conditions with an Emphasis on Thoracic Response and Injury Tolerance
    Albert, Devon Lee (Virginia Tech, 2018-06-04)
    Frontal motor vehicle collisions (MVCs) resulted in 10,813 fatalities and 937,000 injuries in 2014, which is more than any other type of MVC. In order to mitigate the injuries and fatalities resulting from MVCs, new safety restraint technologies and more biofidelic anthropomorphic test devices (ATDs) have been developed. However, the biofidelity of these new ATDs must be evaluated, and the mechanisms of injury must be understood in order to accurately predict injury. Evaluating the biomechanical response, injury mechanisms, and injury threshold of the thorax are particularly important because the thorax is one of the most frequently injured body regions in MVCs. Furthermore, sustaining a severe thoracic injury in an MVC significantly increases mortality risk. The overall objective of this dissertation was to evaluate the biomechanical responses of human surrogates under various frontal loading conditions. This objective was divided into three sub-objectives: 1) to evaluate the biofidelity of the current frontal impact ATDs, 2) to evaluate the effect of different safety restraints on occupant responses, and 3) to evaluate rib material properties with respect to sex, age, structural response, and loading history. In order to meet sub-objectives 1 and 2, full-scale frontal sled tests were performed on three different human surrogates: the 50th percentile male Hybrid III (HIII) ATD, the 50th percentile male Test Device for Human Occupant Restraint (THOR-M) ATD, and approximately 50th percentile male post-mortem human surrogates (PMHS). All surrogates were tested under three safety restraint conditions: knee bolster (KB), KB and steering wheel airbag (KB/SWAB), and knee bolster airbag and SWAB (KBAB/SWAB). The kinematic, lower extremity, abdominal, thoracic, and neck responses were then compared between surrogates and restraint conditions. In order to assess biofidelity, the ATD responses were compared to the PMHS responses. For both the kinematic and thoracic responses, the HIII and THOR-M had comparable biofideltiy. However, the HIII responses were slightly more biofidelic. The ATDs experienced similar lower extremity kinetics, but very different kinetics at the upper and lower neck due to differences in design. Evaluation of the different restraint conditions showed that the SWAB and KBAB both affected injury risk. The SWAB decreased head injury risk for all surrogates, and increased or decreased thoracic injury risk, depending on the surrogate. The KBAB decreased the risk of femur injury, but increased or decreased tibia injury risk depending on the surrogate and injury metric used to predict risk. In order to meet sub-objective 3, the tensile material properties of human rib cortical bone and the structural properties of whole ribs were quantified at strain rates similar to those observed in frontal impacts. The rib cortical bone underwent coupon tension testing, while the whole ribs underwent bending tests intended to simulate loading from a frontal impact. The rib material properties accounted for less than 50% of the variation observed in the whole rib structural properties, indicating that other factors, such as rib geometry, were also influencing the structural response of whole ribs. Age was significantly negatively correlated with the modulus, yield stress, failure strain, failure stress, plastic strain energy density, and total strain energy density. However, sex did not significantly influence any of the material properties. Cortical bone material properties were quantified from the ribs that underwent the whole rib bending tests and subject-matched, untested (control) ribs in order to evaluate the effect of loading history on material properties. Yield stress and yield strain were the only material properties that were significantly different between the previously tested and control ribs. The results of this dissertation can guide ATD and safety restrain design. Additionally, this dissertation provides human surrogate response data and rib material property data for the validation of finite element models, which can then be used to evaluate injury mitigation strategies for MVCs.
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    The Biomechanics of Thoracic Skeletal Response
    Kemper, Andrew R. (Virginia Tech, 2010-03-30)
    The National Highway Traffic Safety Administration (NHTSA) reported that in 2008 there were a total of 37,261 automotive related fatalities, 26,689 of which were vehicle occupants. It has been reported that in automotive collisions chest injuries rank second only to head injuries in overall number of fatalities and serious injuries. In frontal collisions, chest injuries constitute 37.6% of all AIS 3+ injuries, 46.3% of all AIS 4+ injuries, and 43.3% of all AIS 5+ injuries. In side impact collisions, it has been reported that thoracic injuries are the most common type of serious injury (AIS≥3) to vehicle occupants in both near side and far side crashes which do not involve a rollover. In addition, rib fractures are the most frequent type of thoracic injury observed in both frontal and side impact automotive collisions. Anthropomorphic test devices (ATDs), i.e. crash test dummies, and finite element models (FEMs) have proved to be integral tools in the assessment and mitigation of thoracic injury risk. However, the validation of both of these tools is contingent on the availability of relevant biomechanical data. In order to develop and validate FEMs and ATDs with improved thoracic injury risk assessment capabilities, it is necessary to generate biomechanical data currently not presented in the literature. Therefore, the purpose of this dissertation is to present novel material, structural, and global thoracic skeletal response data as well as quantify thoracic injury timing in both frontal belt loading and side impact tests using cadaveric specimens.
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    Characteristics of Thoracic Organ Injuries in Frontal Crashes
    Thor, Craig Phillip (Virginia Tech, 2008-12-10)
    The introduction of airbags has not significantly reduced serious thoracic injury for belted occupants in frontal crashes. This thesis has investigated the effectiveness of airbags and the characteristics of residual thoracic organ injury incurred by belted occupants in vehicles equipped with airbags. This study was based on the injury outcome of over 28,000 belted front seat occupants involved in frontal collisions. Data for this analysis was extracted from National Automotive Sampling System / Crashworthiness Data System (NASS/CDS) case years 1993-2007. The use of odds ratios for comparing the effect of airbags on the occurrence of injury has shown that airbags do not significantly increase protection against head and chest injuries. Overall, the lower extremity and the upper extremity were shown to be adversely affected by airbags. The face was the only body region that was shown to benefit from the combination of seat belts and airbags as compared to seat belts alone. An investigation into the characteristics and distributions associated with thoracic organ injuries showed the heart and great vessels are the only thoracic organs that showed a significant reduction in the rate of injury with the inclusion of airbags. In vehicles with airbags, the thoracic organs are injured more frequently than the ribs. When occupants sustain thoracic organ injury, the delta-V of the crash for vehicles with and without airbags is not significantly different. The odds of serious injury to the lungs and spleen are higher for occupants in vehicles with airbags as compared to those in vehicles without airbags. Rib fracture was found to be a poor predictor of moderate to fatal thoracic organ injury. Only 31-61% of thoracic organ injuries occur with an associated rib fracture.
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    Characterizing the Biomechanical Response of Liver
    Santago II, Anthony Charles (Virginia Tech, 2010-04-27)
    Motor vehicle collisions can result in life threatening liver injuries. Dummies are utilized to study injury in motor vehicle collisions; however, no crash test dummies are currently equipped to represent individual solid organs. This has increased the use of finite element models to help reduce these injuries; however, accurate material models need to be established to have accurate injury assessment using these models. This thesis presents a total of 4 studies that explore the biomechanical response of liver. The research on bovine liver is geared to understanding whether or not liver tissue can be frozen prior to testing and what environmental temperature the liver should be tested at. The first study utilized two bovine livers that were each divided in half and one half was tested at 75°F while the other half was tested at 98°F. A total of 24 tensile failure tests were performed on the parenchyma. It was determined that there were no statically significant differences between failure stresses and strains between the testing temperatures. To test the effects of freezing, tensile tests were performed on the parenchyma of a single bovine liver that was divided in half. One half was frozen and then thawed prior to tensile testing while the other was tested fresh. It was determined that freezing reduces average failure strain by 50%. The research on human liver was geared toward understanding the rate dependence during uniaxial tension tests and unconfined compression tests. Samples were constructed of only the parenchyma. A total of 7 livers were used to create the 51 tensile specimens and a total of 6 livers were used to obtain the 36 unconfined compression specimens. For the uniaxial tensile tests, average failure stresses ranged from 40.21 to 61.02 kPa while average failure strain ranged from 24% to 34%. For the unconfined compression tests, average failure stresses ranged from -165 to -203 kPa while average failure strain ranged from -46% to -61%. It is expected that the results presented in this thesis will: 1) Help establish correct transportation and procurement methodology for soft tissue mechanical testing. 2) Provide tension and compression material response of the human liver at multiple strain rates for use as material properties and injury tolerance values to validate finite element models.
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    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.
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    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.
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    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.
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    Development of a Deflection Measurement System for the Hybrid III Six-Year Old Biofidelic Abdomen
    Gregory, Thomas S. (Virginia Tech, 2012-12-17)
    Despite advancements in automotive safety, motor vehicle collisions remain the leading cause of unintentional death for children ages 5 to 14. Enhancement of child occupant protection depends on the ability to accurately assess the effectiveness of restraint systems. Booster seat design and proper belt fit require evaluation using child anthropomorphic test devices, yet biofidelity of the abdomen and pelvis of the current anthropomorphic test device, the Hybrid III 6-year-old, needs improvement. Further, measurement of abdominal deflection is needed for quantification of the degree of submarining and associated potential injury risk. A biofidelic abdomen for the Hybrid III 6-year-old dummy is being developed by the Ford Motor Company. A practical measurement system for the biofidelic abdominal insert has been developed and demonstrated for three dimensional determination of abdominal deflection. Quantification of insert deflection is achieved via differential signal measurement using electrodes mounted within a conductive medium. Signal amplitude is proportional to the distance between the electrodes. A microcontroller is used to calculate distances between ventral electrodes and a dorsal electrode in three dimensions. This system has been calibrated statically, as well as evaluated dynamically. Its performance has also been demonstrated in a series of sled tests. Deflection measurements from the instrumented abdominal insert showed clear differences between two booster seat designs, yielding an average peak anterior to posterior displacement of the abdomen of 1.0 ± 3.4 mm and 31.2 ± 7.2 mm for the seats, respectively. Implementation of a 6-year-old abdominal insert with the ability to evaluate submarining potential will likely advance the effectiveness of booster seat design and restraint performance, and help mitigate child occupant injury severity in automobile collisions.
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    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.
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    Effect of Belt Usage Reporting Errors on Injury Risk Estimates
    Swanseen, Kimberly Dawn (Virginia Tech, 2009-12-09)
    This thesis presents the results of a research effort investigating the effect of belt usage reporting errors of National Automotive Sampling System-Crash Data System (NASS-CDS) investigators on injury risk estimates. Current estimates of injury risk are developed under the assumption that NASS-CDS investigators are always accurate at determining seat belt usage. The primary purpose of this research is to determine the accuracy of NASS-CDS investigators using event data recorders (EDRs) as the baseline for accuracy, and then recalculating injury risk estimates based on our findings. The analysis of a 107 EDR dataset, from vehicle tests conducted by the National Highway Traffic Safety Administration (NHTSA) and the Insurance Institute for Highway Safety (IIHS), was conducted to determine the accuracy of Chrysler, Ford, GM and Toyota EDRs. This accuracy was examined by both EDR module type and vehicle make. EDR accuracy was determined for crash delta-V, seat belt buckle status, pre-impact speed, airbag deployment status and front seat position. From this analysis we were able to conclude that EDRs were accurate, within 4.5%, when comparing maximum delta-V of EDRs that recorded the entire crash pulse length. We also determined that EDRs were 100% accurate when reporting driver seat belt status for EDRs that completely recorded the event and recorded a status for the driver's seat belt. All GM, Ford and Chrysler EDRs in our database reported a pre-impact velocity less than 6 mph different than the NHTSA and IIHS reported pre-impact velocities. We also found that all but 2 (101 out of 103) of the GM, Ford, and Toyota EDRs correctly reported airbag deployment status. Lastly we were able to conclude that seat position status was useful in determining when a smaller sized occupant was the driver or right front occupant. EDRs reported seat position of 5% Hybrid III females as "forward" in every case that seat position was recorded for this smaller occupant size. Based on the analysis of seat belt status accuracy, a comparison of NASS-CDS investigator driver seat belt status and EDR driver seat belt status was conducted to determine the accuracy of the NASS-CDS investigators. This same comparison was conducted on reports of driver seat belt status provided by police. We found that NASS-CDS investigators had an overall error of 9.5% when determining driver seat belt status. When the EDR stated that the driver was unbuckled, investigators incorrectly coded buckled in of 29.5% of the cases. When the EDR stated that the driver was buckled, NASS-CDS error was only 1.2%. Police officers were less accurate than NASS-CDS investigators, with an overall error of 21.7%. When the EDR stated that the driver was buckled, police had an error of 2.4%. When the EDR stated that the driver's belt was unbuckled, police had an error of around 69%. In 2008, NASS-CDS investigators reported that drivers had an overall belt usage rate during accidents of 82%. After correcting for the errors we discovered, we estimate that the driver belt buckle status during a crash is around 72.6%. Injury risk estimates and odd ratio point estimates were then calculated for NASS-CDS investigator and EDR buckled versus unbuckled cases. The cases included only frontal collisions in which there was no rollover event or fire. Injury was defined as AIS 2+. The risk ratios and point estimates were then compared between investigators and EDRs. We found that injury risk for unbelted drivers may be over estimated by NASS-CDS investigators. The unbuckled to buckled risk ratio for EDRs was 8%-12% lower than the risk ratio calculated for NASS-CDS investigators.
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    The Effect of Lane Departure Warning Systems on Cross-Centerline Crashes
    Holmes, David Alexander (Virginia Tech, 2018-05-16)
    Cross-centerline crashes occur rarely in the United States but are especially severe. This type of crash is characterized by one vehicle departing over a centerline and encountering a vehicle traveling in the opposite direction. In recent years, automakers have started developing and implementing lane departure warning (LDW) on newer vehicles. This system provides the potential to reduce or significantly impact the frequency of cross-centerline crashes. The objective of this thesis was to estimate the potential crash and injury benefits of a LDW system if installed on every vehicle in the US fleet. This research includes the following 1) a characterization of cross-centerline crashes in the United States today with current and future prevention methods, 2) a reconstruction methodology used for all crashes including rollovers and heavy vehicles, and 3) a simulation model and approach method used to estimate potential benefits of LDW systems on cross-centerline crashes. Cross over to left crashes account for only 4% of non-junction non-interchange crashes but account for 44% of serious injury crashes of the same type. As part of this research, 42 cross-centerline crashes were reconstructed and simulated as if they had a LDW system installed. Accounting for driver capability to react to a LDW alert, crash reduction benefits ranged from 22 – 30%.Using injury risk curves, the probability of experiencing a MAIS2+ injury in a cross-centerline crash was reduced by 29% when using a LDW system.
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    Effect of Postmortem Time and Preservation Fluid on the Tensile Material Properties of Bovine Liver Parenchyma
    Dunford, Kristin Marie (Virginia Tech, 2017-12-21)
    The liver is one of the most frequently injured abdominal organs in motor vehicle collisions. Although previous studies have quantified the tensile failure properties of human liver parenchyma at 48hrs postmortem, it is currently unknown how the material properties change between time of death and 48hrs postmortem. Therefore, the purpose of this study was to quantify the effects of postmortem degradation on the tensile material properties of bovine liver parenchyma when stored in DMEM or saline. Fourteen fresh bovine livers were obtained from a local slaughter house and stored in either DMEM or saline as large blocks, small blocks, or slices of tissue. Multiple parenchyma dog-bone samples from each liver were tested once to failure at three time points: ~6hrs, ~24hrs, and ~48hrs postmortem. The data were then analyzed to determine if there were significant changes in the material properties with respect to postmortem time. The results showed that the failure strain decreased significantly between 6hrs and 48hrs after death when stored as large blocks in saline. Conversely, neither the failure stress nor failure strain changed significantly with respect to postmortem time when stored as large blocks in DMEM. The modulus did not significantly change for tissue stored as large blocks in either fluid. Preliminary results indicated that reducing the tissue storage size had a negative effect on the material properties and cellular architecture. Overall, this study illustrated that the effects of postmortem liver degradation varied with respect to the preservation fluid, storage time, and storage block size.
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    Effectiveness of Intersection Advanced Driver Assistance Systems in Preventing Crashes and Injuries in Left Turn Across Path / Opposite Direction Crashes in the United States
    Bareiss, Max (Virginia Tech, 2019)
    Intersection crashes represent one-fifth of all police reported traffic crashes and one-sixth of all fatal crashes in the United States each year. Active safety systems have the potential to reduce crashes and injuries across all crash modes by partially or fully controlling the vehicle in the event that a crash is imminent. The objective of this thesis was to evaluate crash and injury reduction in a future United States fleet equipped with intersection advanced driver assistance systems (I-ADAS). In order to evaluate this, injury risk modeling was performed. The dataset used to evaluate injury risk was the National Automotive Sampling System / Crashworthiness Data System (NASS/CDS). An injured occupant was defined as vehicle occupant who experienced an injury of maximum Abbreviated Injury Scale (AIS) of 2 or greater, or who were fatally injured. This was referred to as MAIS2+F injury. Cases were selected in which front-row occupants of late-model vehicles were exposed to a frontal, near-, or far-side crash. Logistic regression was used to develop an injury model with occupant, vehicle, and crash parameters as predictor variables. For the frontal and near-side impact models, New Car Assessment Program (NCAP) test results were used as a predictor variable. This work quantitatively described the injury risk for a wide variety of crash modes, informing effectiveness estimates. This work reconstructed 501 vehicle-to-vehicle left turn across path / opposite direction (LTAP/OD) crashes in the United States which had been originally investigated in NMVCCS. The performance of thirty different I-ADAS system variations was evaluated for each crash. These variations were the combinations of five Time to Collision (TTC) activation thresholds, three latency times, and two different intervention types (automated braking and driver warning). In addition, two sightline assumptions were modeled for each crash: one where the turning vehicle was visible long before the intersection, and one where the turning vehicle was only visible after entering the intersection. For resimulated crashes which were not avoided by I-ADAS, a new crash delta-v was computed for each vehicle. The probability of MAIS2+F injury to each front row occupant was computed. Depending on the system design, sightline assumption, I-ADAS variation, and fleet penetration, an I-ADAS system that automatically applies emergency braking could avoid 18%-84% of all LTAP/OD crashes. An I-ADAS system which applies emergency braking could prevent 44%-94% of front row occupants from receiving MAIS2+F injuries. I-ADAS crash and injured person reduction effectiveness was higher when both vehicles were equipped with I-ADAS. This study presented the simulated effectiveness of a hypothetical intersection active safety system on real crashes which occurred in the United States, showing strong potential for these systems to reduce crashes and injuries. However, this crash and injury reduction effectiveness made the idealized assumption of full installation in all vehicles of a future fleet. In order to evaluate I-ADAS effectiveness in the United States fleet the proportion of new vehicles with I-ADAS was modeled using Highway Loss Data Institute (HLDI) fleet penetration predictions. The number of potential LTAP/OD conflicts was modeled as increasing year over year due to a predicted increase in Vehicle Miles Traveled (VMT). Finally, the combined effect of these changes was used to predict the number of LTAP/OD crashes each year from 2019 to 2060. In 2060, we predicted 70,439 NMVCCS-type LTAP/OD crashes would occur. The predicted number of MAIS2+F injured front row occupants in 2060 was 3,836. This analysis shows that even in the long-term fleet penetration of Intersection Active Safety Systems, many injuries will continue to occur. This underscores the importance of maintaining passive safety performance in future vehicles.
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    Effects of Sex, Strain Rate, and Age on the Tensile and Compressive Material Properties of Human Rib Cortical Bone
    Katzenberger Jr, Michael J. (Virginia Tech, 2019-10-07)
    The objective of this study was to evaluate the effects of sex, loading rate, and age on the tensile and compressive material properties of human rib cortical bone over a wide range of subject demographics. Tension coupons were tested from sixty-one (n = 61) subjects (M = 32, F = 29) ranging in age from 17 to 99 years of age (Avg. = 56.4 +/- 26.2 yrs.). Compression samples were tested from thirty (n = 30) subjects (M = 19, F = 11) ranging in age from 18 to 95 years of age (Avg. = 49.0 +/- 23.9 yrs.). For each subject, one coupon/sample was tested to failure on a material testing system at a targeted strain rate of 0.005 strain/s, while a second coupon/sample was tested at 0.5 strain/s. A load cell was used to measure axial load for both the tension coupons and compression samples. An extensometer was used to measure displacement within the gage length of the tension coupons and a deflectometer was used to measure displacement of the compression samples. Tension data were obtained from fifty-eight (n = 58) coupons at 0.005 strain/s and fifty-eight (n = 58) coupons at 0.5 strain/s, with fifty-five (n = 55) matched pairs. Compression data were obtained from thirty (n = 30) compression samples at 0.005 strain/s and thirty (n = 30) samples at 0.5 strain/s. The elastic modulus, yield stress, yield strain, ultimate stress, elastic strain energy density (SED), plastic SED, and total SED were then calculated for each tensile and compression test. In addition, failure stress and failure strain were calculated for each tension test. There were no significant differences in the tensile material properties between sexes and no significant interactions between age and sex for either method of loading. In regard to the differences in tensile material properties with respect to loading rate, yield stress, yield strain, failure stress, ultimate stress, elastic SED, plastic SED, and total SED were significantly lower at 0.005 strain/s compared to 0.5 strain/s. All material properties were significantly lower at 0.005 strain/s compared to 0.5 strain/s in compression. Spearman correlation analyses showed that all tensile material properties had significant negative correlations with age at 0.005 strain/s except modulus. At 0.5 strain/s, all tensile material properties except yield strain had significant negative correlations with age. No significant correlations were observed in material properties with respect to advanced age in compression at either loading rate. Although the results revealed that the tensile material properties of human rib cortical bone varied significantly with respect to chronological age, the R2 values only ranged from 0.15 - 0.62, indicating that there may be other underlying variables that better account for the variance within a given population. Overall, this is the first study to analyze the effects of sex, loading rate, and age on tensile material properties of human rib cortical bone using a reasonably large sample size and the first study to test the compressive material properties of human rib cortical bone. The results of this study provide data that allows FEMs to better assess thoracic injury risk for all vehicle occupants. Additionally, this study provides the necessary data to more accurately model and assess differences in the material response of the rib cage for nearly all vehicle occupants of driving age.
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    Feasibility of Restricted Driver Licenses for Suspended New Jersey Drivers
    Kusano, Stephanie Marie (Virginia Tech, 2012-07-23)
    In 2010, there were 6,714,288 total registered drivers in New Jersey. Approximately 4% (267,485) of these drivers had a suspended driver's license. The intent of suspending a driver's license is to keep hazardous drivers off of the roads, in hopes of having a safer driving environment for others on the road. Drivers in New Jersey can have their driver's license suspended for a number of reasons. These include dangerous driving behaviors such as reckless driving and driving under the influence of alcohol or drugs. However, there are also reasons for suspension that have little or nothing to do with driver behavior, such as failure to pay child support, failure to pay MVC insurance surcharge, or failure to appear in court. While these offenses are all due of consequence, they have little or nothing to do with driver behavior. This research program will conduct an analysis of the issues and implications of implementing a restricted-use license program for suspended New Jersey drivers, detailing key issues associated with restricted-use license programs. It was found that over two-thirds of suspended drivers in New Jersey receive driver's license suspensions for both driving and non-driving-related offenses, whereas only about four-percent of suspended drivers in New Jersey receive a driver's license suspension for driving-related reasons only. It was also found that drivers suspended for non-driving related reasons have different driver behavior than drivers suspended for driving related reasons. Surveying both New Jersey police chiefs, as well as U.S. state motor vehicle agencies, it was found that there is a generally positive perception of restricted driver's license programs. Overall, it is recommended that the New Jersey Motor Vehicle Commission implement a restricted driver's license program in New Jersey.
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    Finite Element Modeling of Occupant Injury Risk and Crash Performance of W-Beam Guardrail Barriers in Roadside Crashes
    Wang, Qian (Virginia Tech, 2009-04-09)
    This thesis presents the results of a research effort aimed at investigating the crash performance of w-beam guardrail barriers in vehicle-roadside crashes using the finite element method. The developed roadside barrier models can be used to assess the occupant injury risk, vehicle performance, and damage to guardrail barriers during a roadside accident. The finite element models of w-beam guardrail barriers may also help evaluate the crash performance of the w-beam barriers with minor damage in vehicle-barrier crashes. Thus, the results can be used to develop repair guidelines to assist highway personnel in identifying levels of minor barrier damage and deterioration. Finite element models of the weak post w-beam guardrail barriers were developed and simulated using LS-DYNA. The simulation results were validated against full scale crash tests of pickup trucks and passenger cars impacting w-beam guardrail barriers. The maximum dynamic deflection of the guardrail, exit velocity and angle of the vehicle, and occupant injury risk were calculated and compared to the tests. Kinematics of the vehicle and guardrail were assessed qualitatively as well as quantitatively. The analysis showed that simulation results were in good agreement with test data. Additionally, the models were validated against pendulum tests conducted the Federal Outdoor Impact Laboratory (FOIL). Simulation results of pendulum tests showed that the test section taken from the current full scale models performed very similarly to that in the real pendulum tests. The developed finite element models were subsequently used to examine the crash performance of weak post w-beam guardrail barriers with minor damage under vehicle impacts. Only rail/post deflection based minor damage to weak post w-beam guardrail barriers was considered in this study. Simulations were completed to obtain the damaged profiles of the guardrail systems; the damaged weak post guardrail barriers were impacted by the pickup model at mid-span for the second time. The impacting vehicle remained stable in all of these simulations. No conclusions could be drawn however whether these second impacts could have resulted in rail tearing or rupture.