The purpose of this study was to evaluate the thoracic responses of the 50th-percenitle male Hybrid III, THOR, and post mortem human surrogates (PMHS) in the rear seat during frontal sled tests using conventional and advanced restraints in multiple vehicle environments. Twenty-one sled tests were conducted using the Hybrid III and THOR in seven vehicle bucks, and 12 PMHS sled tests were performed using four vehicle bucks. Trends in chest deflections between vehicles and restraint conditions were compared between surrogates. The Hybrid III and THOR thoracic injury risk predictions were compared to the thoracic skeletal damage observed during the PMHS tests. The Hybrid III chest deflections were statistically significantly greater for vehicles equipped with conventional restraints compared to those equipped with advanced restraints. The THOR chest deflections generally followed this trend, but the differences between restraint types were not statistically significant. Hence, the THOR thoracic response and injury predictions might be less sensitive to the presence of advanced restraints. The PMHS sustained lower chest deflections and less damage, on average for the vehicles equipped with advanced restraints. However, this outcome was confounded by PMHS variability, the effect of submarining on thoracic response, and other design differences between vehicles, leading to no statistically significant difference in chest deflection between vehicles with and without advanced restraints. All PMHS sustained at least nine rib fractures regardless of restraint condition, so it was difficult to assess the accuracy of the THOR and Hybrid III injury risk predictions. However, both ATDs accurately predicted a high injury risk for the vehicle that resulted in the most severe PMHS damage. These results support previous studies that suggest the implementation of advanced restraints may reduce injury risk in the rear seat. However, the results also suggest that other vehicle characteristics, apart from restraint type, influence thoracic injury outcomes in the rear seat.

Objective The first objective was to evaluate the effect of using less censored (i.e., exact and interval-censored) data on thoracic injury risk curves and the resulting injury probabilities. The second objective was to generate new injury risk curves to predict Abbreviated Injury Scale (AIS) 3+ rib fractures based on chest deflection. Methods Two data sets consisting of postmortem human surrogate (PMHS) tests with multipoint chest deflection measurements were compiled: A less censored data set consisting of exact and interval-censored data and a doubly censored data set consisting of left- and right-censored data. Chest deflection data from both data sets were processed in a consistent manner to calculate the maximum deflections at different locations across the chest. Survival analysis methods were used to generate nonparametric and parametric injury risk curves for serious skeletal injury. The total sample sizes and proportions of less censored data used to generate the risk curves were varied for each curve to evaluate the effects of sample size and less censored data on risk curve shape and predicted injury thresholds. Results Increasing the proportion of less censored data resulted in steeper injury risk curves and a higher predicted risk for a given amount of deflection. Differences in injury risk were more pronounced in the upper half of the injury risk curves. Introducing less censored data also produced narrower confidence intervals. At a total sample size of 79, increasing the percentage of less censored data from 0 to 30 had minimal effect on the shape of the risk curve. Conclusions Doubly censored chest deflection data have historically been used to generate thoracic injury risk curves for frontal motor vehicle crash events. This study found that incorporating less censored data into thoracic injury risk curves meaningfully affected the shape of the injury risk curves and their resulting injury risk predictions. All of the injury risk curves generated in the study predicted a lower threshold for serious rib fracture injury compared to previously developed injury risks curves that are currently in use in the field. Based on the results of this study, adding less censored data to injury risk curves should be strongly considered to improve thoracic injury risk curve prediction and confidence, especially for smaller sample sizes.

There is evidence to suggest that males and females respond differently in motor vehicle collisions, making it important to study how both sexes respond to vehicle safety systems. The THOR 5th-percentile female (THOR-05F) anthropomorphic test device (ATD) was developed to represent a small female occupant better than the Hybrid III 5th-percentile female (HIII-05F) ATD. However, there are few studies in which they have been directly compared. Therefore, the objective of this study was to compare the responses of the two ATDs in matched frontal sled tests simulating a realistic driver seat environment. A 7th-generation Toyota Camry driver seat test buck was used with Camry parts (i.e., 3-point belt, modified seat, steering wheel, airbag, and column). The belt was equipped with a 4-kN load limiter and pretensioner. Rigid foam (65 psi) was used to represent the knee bolster. Thirteen tests were conducted using speeds of 30 and 56 kph. Chest bands were used to measure external chest deflection. Greater neck compression loads, flexion moments, and extension moments were measured in the HIII-05F tests due to different airbag interactions compared to the THOR-05F. Upper neck compression in the HIII-05F was greater for the 30 kph tests than the 56 kph, reinforcing a need to research crashworthiness at lower speeds. Chest deflections were greater in the THOR-05F tests, which was likely due to the more compliant rib cage. External chest deflections indicated that belt routing and breast tissue influenced the location and magnitude of maximum chest deflections. External deflections also indicated that the HIII-05F rib cage might be more coupled bilaterally than the THOR-05F. Femur loads were slightly greater in the THOR-05F, although knee bolster loads were greater for the 56 kph HIII-05F tests. Future work will include conducting matched small female PMHS sled tests.

Frontal-crash sled tests were conducted to assess submarining protection and abdominal injury risk for midsized male occupants in the rear seat of modern vehicles. Twelve sled tests were conducted in four rear-seat vehicle-bucks with twelve post-mortem human surrogates (PMHS). Select kinematic responses and submarining incidence were compared to previously observed performance of the Hybrid III 50th-percentile male and THOR-50M ATDs (Anthropomorphic Test Devices) in matched sled tests conducted as part of a previous study. Abdominal pressure was measured in the PMHS near each ASIS (Anterior Superior Iliac Spine), in the inferior vena cava, and in the abdominal aorta. Damage to the abdomen, pelvis, and lumbar spine of the PMHS was also identified. In total, five PMHS underwent submarining. Four PMHS, none of which submarined, sustained pelvis fractures and represented the heaviest of the PMHS tested. Submarining of the PMHS occurred in two out of four vehicles. In the matched tests, the Hybrid III never underwent submarining while the THOR-50M submarined in three out of four vehicles. Submarining occurred in vehicles having both conventional and advanced (pretensioner and load limiter) restraints. The dominant factors associated with submarining were related to seat pan geometry. While the THOR-50M was not always an accurate tool for predicting submarining in the PMHS, the Hybrid III could not predict submarining at all. The results of this study identify substantive gaps in frontal-crash occupant protection in the rear seat for midsized males and elucidates the need for additional research for rear-seat occupant protection for all occupants.

The objective of this study was to compare head, neck, and chest injury risks between front and rear-seated Hybrid III 50th-percentile male anthropomorphic test devices (ATDs) during matched frontal impacts. Seven vehicles were converted to rear seat test bucks (two sedans, three mid-size SUVs, one subcompact SUV, and one minivan) and then used to perform sled testing with vehicle-specific frontal NCAP acceleration pulses and a rear seated (i.e., second row) Hybrid III 50th male ATD. Matched front seat Hybrid III 50th male ATD data were obtained from the NHTSA Vehicle Crash Test Database for each vehicle. HIC15, Nij, maximum chest acceleration, and maximum chest deflection were compared between the front and rear seat tests, as well as between vehicles with conventional and advanced three-point belt restraint systems in the rear seat. Additionally, a modified version of the NCAP frontal star rating was calculated for the front and rear seat tests. All injury metrics, except for chest acceleration, were higher in the rear seat compared to the front. In addition, injury thresholds were exceeded or nearly exceeded in the rear seat for Nij in three vehicles, chest acceleration in one vehicle, and chest deflection in three vehicles, while no thresholds were exceeded in the front seat. When comparing advanced and conventional restraints in the rear seat, all injury metrics were higher in the vehicles with conventional restraints. All vehicles with conventional restraints in the rear had a star rating of 1, while those with advanced restraints in the rear ranged from 2 to 3. Conversely, all vehicles had 5 stars for the front seat, except one that had 4 stars. Overall, these data highlight the disparity between front and rear seat occupant protection and the benefits of advanced rear seat safety restraints, and the need for future testing.

Previous volunteer studies focused on low-speed frontal events have demonstrated that muscle activation (specifically pre-impact bracing) can significantly affect occupant response. However, these tests do not always include a sufficient number of small female volunteers to compare their unique responses to the typically studied midsize male population. The purposes of this study were to quantify the occupant kinetics and muscle responses of relaxed and braced small female and midsize male volunteers during low-speed frontal sled tests and to compare between muscle states and demographic groups. Small female and midsize male volunteers experienced multiple low-speed frontal sled tests consisting of two pulse severities (1 g and 2.5 g) and two muscle states (relaxed and braced) per pulse severity. The muscle activity of 30 muscles (15 bilaterally) and reaction forces at the volunteer-test buck interfaces and seat belt were measured before and during each sled test. Compared to the relaxed muscle state, bracing generally increased pre-test muscle activity and pre-test forces, delayed muscle activation (relative to the pre-test value) in response to the sled pulse, and increased peak forces during the sled tests. However, relaxed volunteers exhibited greater changes in muscle activity and reaction forces relative to the pre-test value. Males exhibited higher peak forces across all reaction surfaces during the sled tests compared to females, but peak muscle activity varied as to whether males or females exhibited higher activation. The upper extremity muscles activated the most during pre-test bracing, while the upper extremity, trunk, and neck muscles activated the most during the sled tests.

The material and morphometric properties of trabecular bone have been studied extensively in bones bearing significant weight, such as the appendicular long bones and spine. Less attention has been devoted to the ribs, where quantification of material properties is vital to understanding thoracic injury. The objective of this study was to quantify the compressive material properties of human rib trabecular bone and assess the effects of loading rate, age, and morphology on the material properties. Material properties were quantified via uniaxial compression tests performed on trabecular bone samples at two loading rates: 0.005 s 1 and 0.5 s 1. Morphometric parameters of each sample were quantified before testing using micro-computed tomography. Rib trabecular bone material properties were lower on average compared to trabecular bone from other anatomical locations. Morphometric parameters indicated an anisotropic structure with low connectivity and a sparser density of trabeculae in the rib compared to other locations. No significant differences in material properties were observed between the tested loading rates. Material properties were only significantly correlated with age at the 0.005 s 1 loading rate, and no morphometric parameter was significantly correlated with age. Trabecular separation and thickness were most strongly correlated with the material properties, indicating the sparser trabecular matrix likely contributed to the lower material property values compared to other sites. The novel trabecular bone material properties reported in this study can be used to improve the thoracic response and injury prediction of computational models.

Objective The objectives of this study were to evaluate computationally efficient small female (54.1 kg, 149.9 cm) and midsize male (78.4 kg, 174.9 cm) models with active muscles using volunteer sled test data in a frontal-oblique loading direction and check their response in crash mitigating maneuvers using field test data. Methods The Global Human Body Models Consortium small female (F05-OS+Active) and midsize male (M50-OS+Active) simplified occupant models with active musculature were used in this study. The data from a total of 48 previously published sled test experiments were used to simulate a total of 16 simulations. The experimental study recorded occupant responses of six small female and six midsize male volunteers (n = 12 total) in two muscle conditions (relaxed and braced) at two acceleration pulses representing pre-crash braking (1.0 g) and a low-speed impact (2.5 g). Each model's kinematics and reaction forces were compared with experimental data. Along with sled test simulations, both of these models were simulated in abrupt braking, lane change, and turn and brake events using literature data. A total of 36 field test simulations were carried out. A CORA analysis was carried out using reaction load and displacement time-history data for sled test simulations and head CG displacement time-history was used for field test simulations. Results The occupant peak forward and lateral excursion results of both active models reasonably matched the volunteer data in the low-speed sled test simulations for both pulse severities. The differences between the active and control models were statistically significant (p-value < 0.05) based on the results of Wilcoxon signed-rank tests using peak forward and lateral excursion data. The average CORA scores calculated for the sled test (sled test: M50-OS+Active= 0.543, male control= 0.471, F05-OS+Active= 0.621, female control= 0.505) and field test (M50-OS+Active= 0.836, male control= 0.466, F05-OS+Active= 0.832, female control= 0.787) simulations were higher for active models than control. Conclusions The responses of the F05-OS+Active and M50-OS+Active models were better than control models based on overall CORA scores calculated using both sled and field tests. The results highlight their ability to predict occupant kinematics in crash-mitigating maneuvers and low-speed impacts in the frontal, lateral and frontal-oblique directions.

Objective The purpose of this study was to provide a whole-body biofidelity assessment of the Hybrid III (HIII) and THOR 50th percentile male anthropomorphic test devices (ATDs) during frontal sled tests, incorporating data from kinematics, chest deflection, and test buck reaction load cells. Additionally, the accuracy of the injury risk prediction capabilities for each ATD was evaluated against injuries observed in matched postmortem human surrogate (PMHS) tests. Methods Sled tests, designed to simulate a United States New Car Assessment Program (US-NCAP) frontal test, were conducted using the HIII, THOR, and 8 approximately 50th percentile male PMHS under 3 restraint conditions. The test buck was instrumented with load cells on the steering column, knee bolster supports, and foot supports. ATD and PMHS reaction force-time histories were quantitatively compared using the ISO/TS-18571 objective rating metric. Previously published biofidelity analyses of kinematic and chest deflection data from the same tests were combined with the reaction force analyses to perform an overall assessment of the comparative biofidelity of each ATD. Injury risk predictions from existing HIII and proposed THOR injury risk curves for the US-NCAP were compared to observed injuries. Results For the reaction forces, the HIII and THOR had similar levels of biofidelity on average, except for 2 locations. The HIII produced more biofidelic knee bolster support forces, and the THOR lap belt forces were more biofidelic. The comparative biofidelity of the ATDs also varied by body region. The THOR head response was more biofidelic, whereas the HIII thorax and lower extremity responses had higher biofidelity. When all body regions were pooled, the HIII was more biofidelic, but differences between ATDs were generally small. Both ATDs were able to predict the observed injuries, except for the HIII chest, HIII neck, and THOR neck, all of which underpredicted PMHS injury outcomes. Conclusions This study revealed that biofidelity assessed through response time histories and accuracy of injury risk predictions do not always align. Specifically, the HIII had marginally better time history biofidelity, whereas the THOR had better injury prediction. However, not all THOR responses could be fully assessed, so more work is needed to assess the THOR in complex loading environments.

OBJECTIVE:The objective of this study was to implement active muscles in a computationally efficient small female finite element model (54.1 kg, 149.9 cm) suitable for predicting occupant response during precrash braking and low-speed frontal sled tests. We further calibrate and compare its results against an average male model (78.4 kg, 174.9 cm) using the same developmental approach. METHODS:The active female model (F05-OS + Active) was developed by adding active skeletal muscle elements (n = 232) to the Global Human Body Models Consortium (GHBMC) 5th percentile female simplified occupant model (F05-OS v2.3). The muscle properties and physiological cross-sectional area (PCSA) for each muscle were taken from the M50-OS + Active v2.3 model but PCSAs were mass scaled to a 5th percentile female. A total of 8 simulations were conducted; 2 acceleration pulses (1.0 g and 2.5 g), 2 models (F05-OS + Active and M50-OS + Active), and 2 muscle states (activation and control; e.g., no activation). Each model's kinematics and reaction forces were compared with experimental data. Occupant responses of 6 5th percentile female and 6 50th percentile male volunteers (n = 12 total) were used. The data depict occupant response in precrash braking and low-speed frontal sled tests in a rigid test buck. All procedures were reviewed and approved by the Virginia Tech institutional review board. Each volunteer was in a relaxed state before the applied acceleration. RESULTS:The occupant peak forward excursion results of both active models reasonably match the volunteer data for both pulse severities. The differences between active and control models were found to be significant by Wilcoxon signed-rank test (p < .05). The reaction loads of the active and control models lie within the experimental corridors. CONCLUSIONS:To the authors' knowledge, this study is the first to concurrently calibrate and compare equivalently developed computational models of females and males in precrash and low-speed impacts. The modeling approach is capable of capturing the varied kinematics observed in the relaxed condition, which may be an important factor in studies focused on the effects of low-g vehicle dynamics on the occupant position. Finally, the computationally efficient modeling approach is imperative given the long duration (>500 ms) of the events simulated.

The objective of this study was to evaluate the thoracic response and injury metrics of the Hybrid III (HIII-50M) and Test device for Human Occupant Restraint (THOR-50M) 50th-percentile male Anthropomorphic Test Devices (ATDs) during frontal, rear-seated sled tests using modern vehicles with various rear seat characteristics. Test bucks were fabricated from seven vehicles (two sedans, three midsize sport utility vehicles [SUVs], one SUV, and one minivan) that represented varying levels of rear seat designs and safety technologies, e.g., three vehicles had advanced restraints with pretensioners (PT) and load limiters (LL). Twenty-four frontal sled tests were conducted using three sled pulses derived from the vehicle-specific New Car Assessment Program (NCAP) crash pulses (NCAP85 Delta V = 56 kph, Scaled Delta V = 32 kph, and Generic Delta V = 32 kph). The HIII-50M and THOR-50M ATDs were positioned in the right and left rear seats, respectively. Maximum chest acceleration (3 ms clip), maximum chest deflection, and deflection-based thoracic injury risk were quantified for both ATDs. For the HIII-50M, the maximum chest acceleration was below the injury threshold (60 g) for all Scaled and Generic tests, but above the threshold during one NCAP85 test with conven-tional restraints. The THOR-50M maximum chest acceleration was below the injury threshold for all tests. The HIII-50M Abbreviated Injury Scale (AIS)3+ maximum sternum deflection injury risk threshold was exceeded or nearly exceeded during the NCAP85 tests for three vehicles, none of which had advanced restraints. The THOR-50M AIS3+ maximum chest deflection injury risk threshold was exceeded during the NCAP85 test for one vehicle, which had PT and LL. Although this study indicates that there may be room for improvement with regard to rear-seat occupant protection, it is currently unknown whether or not either ATD provides a realistic kinematic response or injury risk prediction in the rear seat. Future matched postmortem human subjects (PMHS) testing will facilitate the assessment of the biofidelity and injury risk prediction capabilities of these ATDs in the rear seat.

While historically the rear seat has been considered safer than the front seat, recent studies have suggested that adult occupants have a higher relative risk of injury and death in the rear seat compared to the front seat. Advancements in safety technologies in the front seat have outpaced those in the rear seat, where they vary greatly between vehicle makes and models. Of particular concern is occupant submarining, for which the lap belt slips off of the pelvis and directly loads the abdomen. In this study, frontal crash sled tests with seven vehicle bucks were conducted to assess submarining protection for two rear-seated 50th-percentile male anthropomorphic test devices (ATDs), the Hybrid III-50M and THOR-50M. Tests involved either a Delta V of 56 kph or 32 kph. Submarining incidence and severity for the Hybrid III and THOR were assessed using post-test photographs, high-speed videos, and seat belt loads. Abdominal pressure (using the ABdominal Injury and SUbmarining Prediction [ABISUP] prototype abdomen) and anterior superior iliac spine (ASIS) forces and moments were also used in the submarining assessment for the THOR. Twenty-four tests were conducted including three repeated tests. The Hybrid III did not submarine in any test, but the THOR submarined in 16 of 24 tests (in 5 of 7 vehicles). Submarining occurred in 3 out of 4 vehicles having conventional restraints and 2 out of 3 vehicles having advanced restraints. The results indicate that the Hybrid III-50M and THOR-50M have different submarining responses. Additionally, advanced restraints alone will not mitigate submarining, but other factors in seat, restraint, and vehicle design also contribute to submarining protection in the rear seat.

Rib fractures are common thoracic injuries in motor vehicle crashes. Several human finite element (FE) human models have been created to numerically assess thoracic injury risks. However, the accurate prediction of rib biomechanical response has shown to be challenging due to human variation and modeling approaches. The main objective of this study was to better understand the role of modeling approaches on the biomechanical response of human ribs in anterior-posterior bending. Since the development of subject specific rib models is a time-consuming process, the second objective of this study was to develop an accurate morphing approach to quickly generate high quality subject specific rib meshes. The exterior geometries and cortical-trabecular boundaries of five human 6th-level ribs were extracted from CT-images. One rib mesh was developed in a parametric fashion and the other four ribs were developed with an in-house morphing algorithm. The morphing algorithm automatically defined landmarks on both the periosteal and endosteal boundaries of the cortical layer, which were used to morph the template nodes to target geometries. Three different cortical bone material models were defined based on the stress-strain data obtained from subject-specific tensile coupon tests for each rib. Full rib anterior-posterior bending tests were simulated based on data recorded in testing. The results showed similar trends to test data with some sensitivity relative to the material modeling approach. Additionally, the FE models were substantially more resistant to failure, highlighting the need for better techniques to model rib fracture. Overall, the results of this work can be used to improve the biofidelity of human rib finite element models.

In order to accurately represent the response of live occupants during pre-crash events and frontal crashes, computational human body models (HBMs) that incorporate active musculature must be validated with appropriate volunteer data that represents a wide range of demographic groups and potential crash conditions. The purpose of this study was to quantify and compare occupant kinematic responses for unaware (relaxed) small female and midsize male volunteers during low-speed frontal and frontal-oblique sled tests across multiple test conditions, while recognizing, assessing, and accounting for potential acclimation effects due to multiple exposures. Six 5th percentile female and six 50th percentile male volunteers were exposed to multiple low-speed frontal and frontal-oblique sled tests on two separate test days. Volunteers experienced one test orientation and two pulse severities (1 g and 2.5 g) on each test day. A Vicon motion capture system was used to quantify the three-dimensional (3D) kinematics of the volunteers. Peak forward excursions of select body locations were compared within a test day and between test days for the same test condition to determine if and how acclimation occurred. Differences between demographic groups were also compared after accounting for any observed acclimation. Acclimation was not observed within a test day but was observed between test days for some demographic groups and some test conditions. In general, head, neck, and shoulder responses were affected, but the elbow, hip, and knee responses were not. Males generally moved farther forward compared to females during the frontal tests, but both groups moved forward similarly during the frontal-oblique tests. Overall, this study provides new female and male biomechanical data that can be used to further develop and validate HBMs that incorporate active musculature in order to better understand and assess occupant response and injury risk in pre-crash events and frontal crashes.

The objectives of this study were to develop novel methods for quantifying human rib cortical bone material properties in compression and to compare the compressive material property data to existing tensile data for matched subjects. Cylindrical coupons were obtained from the rib cortical bone of 30 subjects (M = 19, F = 11) ranging from 18 to 95 years of age (Avg. = 48.5 ± 24.3). Two coupons were obtained from each subject. One coupon was tested in compression at 0.005 strain/s, while the other coupon was tested in compression at 0.5 strain/s. Load and displacement data were recorded so that the elastic modulus, yield stress, yield strain, ultimate stress, ultimate strain, elastic strain energy density (SED), plastic SED, and total SED could be calculated. All compressive material properties were significantly different between the two loading rates. An ANOVA revealed that sex alone had no significant effect on the compressive material properties. The interaction between sex and age was significant for some material properties, but this may have been a consequence of the lack of older females in the subject pool. None of the compressive material properties were significantly correlated with age, but were more correlated with sample density. This finding differed for the tensile material properties, which showed stronger correlations with age. When comparing between tension and compression, significant differences were observed for all material properties except for the total SED, once the effects of loading rate and age had been accounted for. This was the first study to quantify the material properties of human rib cortical bone in compression. The results of this study demonstrated that rib and thorax finite element models should consider the effects of loading rate, loading mode, and age when incorporating material properties published in the literature.

The CORA rating metric is frequently used in the field of injury biomechanics to compare the similarity of response time histories. However, subjectivity exists within the CORA metric in the form of user-customizable parameters that give the metric the flexibility to be used for a variety of applications. How these parameters are customized is not always reported in the literature, and it is unknown how these customizations affect the CORA scores. Therefore, the purpose of this study was to evaluate how variations in the CORA parameters affect the resulting similarity scores. A literature review was conducted to determine how the CORA parameters are commonly customized within the literature. Then, CORA scores for two datasets were calculated using the most common parameter customizations and the default parameters. Differences between the CORA scores using customized and default parameters were statistically significant for all customizations. Furthermore, most customizations produced score increases relative to the default settings. The use of standard deviation corridors and exclusion of the corridor component were found to produce the largest score differences. The observed differences demonstrated the need for researchers to exercise transparency when using customized parameters in CORA analyses.

In this study, the outstanding toughness effect and corresponding mechanism of poly(methyl methacrylate)-polybutadiene-polystyrene (MBS) on polyamide 1012 (PA1012) was studied. Both physical entanglement and chemical crosslinking which exist between MBS particle and PA1012 to improve the interface and contribute to the stress transfer were confirmed by rheology characterization. Herman's orientation function based on in situ wide angle X-ray diffraction certified MBS particles weaken the loading stress of matrix as stress concentration points by during the tensile deformation. It was found that MBS particles were conducive to crystallization to maintain the strength, and the transformation of more toughness γ-form from α-form. The syngenetic effects demonstrated substantially-high toughness as well as maintained the original strength.

The objective of this study was to evaluate the effects of sex, loading rate, and age on the tensile material properties of human rib cortical bone over a wide range of subject demographics. 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) were used in this study. Two rectangular coupons of cutaneous rib cortical bone were obtained from each subject and milled into dog-bone coupons for testing. For each subject, one coupon was tested to failure in tension on a material testing system at a targeted strain rate of 0.005 strain/s, while the other coupon was tested at 0.5 strain/s. A reaction load cell was used to measure axial load, and an extensometer was used to measure displacement within the gage length of the coupon. Data were obtained from fifty-eight (n = 58) subjects at 0.005 strain/s and fifty-eight (n = 58) subjects at 0.5 strain/s, with fifty-five (n = 55) matched pairs. The elastic modulus, yield stress, yield strain, failure stress, failure strain, ultimate stress, elastic strain energy density (SED), plastic SED, and total SED were then calculated for each test. There were no significant differences in material properties between sexes and no significant interactions between age and sex. In regard to the differences in 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. Spearman correlation analyses showed that all material properties had significant negative correlations with age at 0.005 strain/s except modulus. At 0.5 strain/s, all material properties except yield strain had significant negative correlations with age. Although the results revealed that the material properties of human rib cortical bone varied significantly with respect to chronological age, the R2 values only ranged from 0.15 to 0.62, indicating that there may be other underlying variables that better account for the variance within a given population. 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. Overall, the results of this study provide data that will allow FEMs to better model and assess differences in the material response of the rib cage for nearly all vehicle occupants of driving age.

Lower extremity injuries are prevalent in motor vehicle collisions. Therefore, it is necessary to accurately quantify lower extremity kinetics in order to evaluate strategies for mitigating these injuries. Current methods for quantifying lower extremity loads in post-mortem human subjects (PMHS) have limitations that could affect the accuracy of the measured loads. Hence, the purpose of this study is to evaluate the efficacy of using strain gauge arrays (SGAs) to quantify axial and anterior-posterior shear femur forces in PMHS during fullscale frontal sled tests. Six PMHS were instrumented with SGAs to measure bilateral axial and shear femur forces before undergoing frontal sled tests. Several calibration procedures were performed to convert the SGA outputs (mV) to forces. The resulting forces were compared to knee bolster reaction forces and femur forces from matched sled tests performed using anthropomorphic test devices. Overall, the PMHS SGAs measured reasonable axial forces during the sled tests, but more work is necessary to validate the shear forces. Given the degree of crosstalk observed during the calibration procedure, future studies should use axial, anterior-posterior shear, and medial-lateral shear SGAs together to facilitate full crosstalk compensation. Furthermore, precise post-test calibrations capable of evaluating crosstalk should be performed on long bones instrumented with SGAs.

Objective: The current state of the art human body models (HBMs) underpredict the number of fractured ribs. Also, it has not been shown that the models can predict the fracture locations. Efforts have been made to create subject specific rib models for fracture prediction, with mixed results. The aim of this study is to evaluate if subject-specific finite element (FE) rib models, based on state-of-the-art clinical CT data combined with subject-specific material data, can predict rib stiffness and fracture location in anterior-posterior rib bending. Method: High resolution clinical CT data was used to generate detailed subject-specific geometry for twelve FE models of the sixth rib. The cortical bone periosteal and endosteal surfaces were estimated based on a previously calibrated cortical bone mapping algorithm. The cortical and the trabecular bone were modeled using a hexa-block algorithm. The isotropic material model for the cortical bone in each rib model was assigned subject-specific material data based on tension coupon tests. Two different modeling strategies were used for the trabecular bone. The capability of the FE model to predict fracture location was carried out by modeling physical dynamic anterior-posterior rib bending tests. The rib model predictions were directly compared to the results from the tests. The predicted force-displacement time history, strain measurements at four locations, and rotation of the rib ends were compared to the results from the physical tests by means of CORA analysis. Rib fracture location in the FE model was estimated as the position for the element with the highest first principle strain at the time corresponding to rib fracture in the physical test. Results: Seven out of the twelve rib models predicted the fracture locations (at least for one of the trabecular modeling strategies) and had a force-displacement CORA score above 0.65. The other five rib models, had either a poor force-displacement CORA response or a poor fracture location prediction. It was observed that the stress-strain response for the coupon test for these five ribs showed significantly lower Young’s modulus, yield stress, and elongation at fracture compared to the other seven ribs. Conclusion: This study indicates that rib fracture location can be predicted for subject specific rib models based on high resolution CT, when loaded in anterior-posterior bending, as long as the rib’s cortical cortex is of sufficient thickness and has limited porosity. This study provides guidelines for further enhancements of rib modeling for fracture location prediction with HBMs.