The purpose of this study was to develop material properties of human rib cortical bone using dynamic tension coupon testing. This study presents 117 human rib cortical bone coupon tests from six cadavers, three male and three female, ranging in age from 18 to 67 years old. The rib sections were taken from the anterior, lateral, and posterior regions on ribs 1 through 12 of each cadaver's rib cage. The cortical bone was isolated from each rib section with a low speed diamond saw, and milled into dog bone shaped tension coupons using a small computer numerical control machine. A high-rate servo-hydraulic Material Testing System equipped with a custom slack adaptor, to provide constant strain rates, was used to apply tension loads to failure at an average rate of 0.5 strains/sec. The elastic modulus, yield stress, yield strain, ultimate stress, ultimate strain, and strain energy density were determined from the resulting stress versus strain curves. The overall average of all cadaver data gives an elastic modulus of 13.9 GPa, a yield stress of 93.9 MPa, a yield strain of 0.883 %, an ultimate stress of 124.2 MPa, an ultimate strain of 2.7 %, and a strain energy density of 250.1 MPa-strain. For all cadavers, the plastic region of the stress versus strain curves was substantial and contributed approximately 60 strain % to the overall response and over 80 strain % in the tests with the 18 year old cadaver. The rib cortical bone becomes more brittle with increasing age, shown by an increase in the modulus (p < 0.01) and a decrease in peak strain (p < 0.01). In contrast to previous three-bending tests on whole rib and rib cortical bone coupons, there were no significant differences in material properties with respect to rib region or rib level. When these results are considered in conjunction with the previous three-point bending tests, there is regional variation in the structural response of the human rib cage, but this variation appears to be primarily a result of changes in the local geometry of each rib while the material properties remain nearly constant within an individual. / Master of Science

The objective of this study was to evaluate the effects of sex, loading rate, and age on the compressive and tensile material properties of human costal cartilage over a wide range of subject ages and sexes. Cylindrical compression samples and dog-bone shaped tension samples were tested to failure on a material testing system using target strain rates of 0.005 strain/s and 0.5 strain/s. Compression data were obtained from forty (n = 40) subjects (M = 26, F = 14) ranging in age from 11 – 69 years (Avg. = 39.1 ± 18.2 yrs.), and matched loading rate data were obtained for thirty-four (n = 34) samples. Tension data were obtained from forty-one (n = 41) subjects (M = 30, F = 11) ranging in age from 10 – 59 years (Avg. = 32.9 ± 14.9 yrs.), and matched loading rate data were obtained for seventeen (n = 17) samples. For both compression and tension, load and sample deflection data were collected and used to calculate stress and strain. For the compression data, the toe region was fit using a second-order polynomial, and the toe transition stress, toe transition strain, second-order polynomial coefficient A, and second-order polynomial coefficient B were calculated. In addition, the elastic modulus, ultimate stress, ultimate strain, and strain energy density (SED) were also calculated for each test. For the tension data, only the elastic modulus, ultimate stress, ultimate strain, and SED were calculated for each test. There were no effects of sex on the material properties for either method of loading or strain rate. Therefore, male and female data were combined for the age and loading rate analyses. For compression, toe transition stress, toe transition strain, A, elastic modulus, ultimate stress, and SED were all found to be significantly higher at 0.5 strain/s compared to 0.005 strain/s. For tension, no material properties were found to differ with respect to loading rate. Regarding the effects of age, toe transition stress, toe transition strain, A, B, ultimate stress, ultimate strain and SED were found to significantly decrease with advancing age for the 0.005 strain/s compression data. At 0.5 strain/s, toe transition stress, toe transition strain, elastic modulus, ultimate stress, ultimate strain, and SED all significantly decreased with advancing age. For tension, ultimate stress, ultimate strain, and SED were found to significantly decrease with advancing age at 0.005 strain/s and 0.5 strain/s. Comparing the two loading modes, the ultimate stress, elastic modulus, and SED were significantly higher in compression than in tension. For the compression samples, sample density and percent calcification were also obtained for each sample using physical measurements and micro-CT scans, respectively. However, since there were only a few samples with large calcifications, no meaningful trends were found. This is the first study of its kind to analyze the effects of sex, loading rate, and age on both the compressive and tensile material properties on human costal cartilage from such a wide range of subject ages. The results from this study can be used to develop more accurate finite element models of the human body, which will allow researchers to better evaluate human occupant response and injury risk in motor vehicle collisions for both young and old individuals. / Master of Science / Serious thorax injuries are often observed in motor vehicle collisions. Although a considerable amount of research has investigated the material and structural properties of rib cortical bone and whole rib sections, only a limited number of studies have focused on characterizing the material properties of costal cartilage, which comprises a substantial portion of the anterior region of the thorax. The studies that do exist include small subject pools and/or are limited to sub-failure indentation tests. Indentation tests are limited to low deflections and focal loading and are unable to obtain the failure material properties of costal cartilage. Therefore, the purpose of this study was to quantify the compressive and tensile material properties of human costal cartilage at two loading rates for a wide range of subject demographics. These properties were then evaluated with respect to sex, loading rate, and age. Cylindrical compression samples and dog-bone shaped tension samples were tested to failure on a material testing system at target strain rates of 0.005 strain/s and 0.5 strain/s. Compression data were obtained from forty (n = 40) subjects ranging in age from 11 – 69 years, and tension data were obtained from twenty-eight (n = 28) subjects ranging in age from 10 – 59 years. For both compression and tension, load and sample deflection data were collected and used to calculate stress and strain. For the compression data, the magnitude and shape of the initial loading region (i.e., the toe region), elastic modulus, ultimate stress, ultimate strain, and strain energy density (SED) were quantified for each test. For the tension data, the elastic modulus, ultimate stress, ultimate strain, and SED were calculated for each test. There were no significant effects of sex on the material properties for either method of loading or strain rate. Therefore, male and female data were combined for the age and loading rate analyses. For compression, the toe region transition point (i.e., stress and strain), toe region shape coefficient A, elastic modulus, ultimate stress, and SED were all found to be significantly higher at 0.5 strain/s compared to 0.005 strain/s. For tension, no material properties were found to differ with respect to loading rate. Regarding the effects of age, toe region transition point (i.e., stress and strain), toe region shape coefficients A and B, ultimate stress, ultimate strain, and SED were found to significantly decrease with advancing age for the 0.005 strain/s compression data. For the 0.5 strain/s compression data, toe transition stress, toe transition strain, elastic modulus, ultimate stress, ultimate strain, and SED all significantly decreased with age. For tension, ultimate stress, ultimate strain, and SED were found to significantly decrease with advancing age at 0.005 strain/s and 0.5 strain/s. The ultimate stress, elastic modulus, and SED were higher in compression than in tension. Overall, this is the first study to evaluate the effects of sex, loading rate and age on the compressive and tensile material properties of human costal cartilage from a wide range of ages. These data can be used to assess differences in the response and tolerance of the human rib cage for occupants of various age in motor vehicle collisions.

Frontal motor vehicle collisions (MVCs) account for the majority of injuries and fatalities in MVCs according to the Fatality Analysis Reporting Systems (FARS). One of the most commonly injured regions of the body during MVCs is the thorax. While there are fewer adult passengers riding in the rear seat compared to the front seat, the number of adults in the rear seat may increase dramatically in the near future with the rise of ridesharing services and highly automated vehicles (HAVs). With the increase in exposure for adults riding in the rear seat, the safety of these passengers needs to be evaluated. Previous research has shown that occupant protection in the rear seat is disproportionately lower than that of the front seat in modern vehicles due to the focus on front seat occupants in both regulatory and market-driven crash tests. This has resulted in many of the occupant safety systems, e.g., pretensioners (PT), load limiters (LL), and airbags, being widely available in the front seat, but sparsely available in the rear seat. Anthropomorphic test devices (ATDs) have been developed to investigate occupant safety during frontal MVCs and can be utilized in the investigation of rear seat occupant injuries. However, the biofidelity and injury risk criteria used for these ATDs has only been validated when seated in the front seat. To validate the response and injury risk predictions of existing frontal ATDs in the rear seat it is necessary to generate new biomechanical data in the rear seat of modern vehicles. The purpose of this work is to quantify the biomechanical responses of two frontal ATDs, i.e., the Hybrid III and THOR-50M 50th percentile male ATDs, and 50th percentile male post mortem human surrogates (PMHS) seated in the rear seat of modern vehicles, which have various seat geometries and restraint types, during frontal MVCs. Emphasis is placed on comparisons between the thoracic responses of the three human surrogates e.g., thoracic deflection time histories, and thoracic injury risks, i.e., ATD injury risk prediction versus instances of PMHS injuries. A series of twenty-four frontal sled tests were first conducted with the HIII and THOR-50M ATDs seated in the rear seats of seven vehicle test bucks with varying seat geometries and two different restraint types. Three vehicles had advanced restraints while four had conventional restraints. Three different crash pulses were used derived from vehicle specific US New Car Assessment Program frontal crash data: Scaled (32kph), Generic (32kph), and NCAP85 (56kph). Thoracic injury metrics were not exceeded in the lower severity pulses for either ATD but were exceeded during some of the high severity tests. A matched comparison analysis between a front and rear seated Hybrid III 50th percentile male ATD is presented second that highlights the disparities between front and rear seat iii occupant safety of modern vehicles during frontal MVCs. The Hybrid III ATD data were used for this comparison. Thoracic injury risk was found to be higher for the rear seated HIII across all vehicles, while thoracic acceleration was lower in the rear than the front for some vehicles. PMHS thoracic responses and injury risk equations were then evaluated in four of the vehicles used for the ATD tests using the high severity sled pulse, i.e., NCAP85 (56kph). Thoracic acceleration and normalized deflection values were higher in vehicles with conventional restraints, and the location of maximum deflection was always inboard of the sternum. The resulting thoracic injuries ranged from AIS 3 to AIS 5. Additionally, there were a larger average number of rib fractures in vehicles with conventional restraints versus advanced restraints. A multi-point deflection injury risk equation predicted injury the best. However the less censored rib fracture data that were obtained suggest that all three of the injury equations evaluated could be improved. Lastly, the PMHS data were used to assess the similarities in thoracic response between the ATDs and PMHS. An objective rating metric was used for the response comparison. The HIII had a slightly better average score than the THOR-50M; however, the THOR-50M had a more biofidelic kinematic response during the tests. This analysis furthers the understanding of the effect of different occupant protection systems on thoracic injury risk in a rear seat environment and the biofidelity of frontal 50th percentile male ATDs in the rear seat. / Doctor of Philosophy / Frontal motor vehicle collisions (MVCs) account for the majority of injuries and fatalities in MVCs according to the Fatality Analysis Reporting Systems (FARS), a nationwide census of fatal injuries suffered during crashes. One of the most commonly injured regions of the body during MVCs is the thorax i.e. the chest. While there are fewer adult passengers riding in the rear seat compared to the front seat, the number of adults in the rear seat may increase dramatically in the near future with the rise of ridesharing services and in the future, the rise of highly automated vehicles (HAVs commonly called "driverless cars"). The safety of adult rear seat passengers needs to be evaluated due to the potential increase in occupancy rates. Previous research has shown that occupant protection in the rear seat is disproportionately lower than that of the front seat in modern vehicles. This is likely due to the focus on front seat occupants in both regulatory tests and market-driven crash tests such as the New Car Assessment Program and IIHS frontal overlap tests. This has resulted in many of the advanced occupant protection systems being widely available in the front seat, but sparsely available in the rear seat. Anthropomorphic test devices (ATDs), i.e., crash test dummies, have been developed to investigate occupant safety during frontal MVCs and can be utilized in the investigation of rear seat occupant injuries. However, the biofidelity (similarity of ATD response to a human surrogate) and injury risk criteria used for these ATDs has only been validated when seated in the front seat. To validate the thoracic response and injury risk predictions of the existing frontal ATDs when seated in the rear seat it is necessary to generate new biomechanical data in the rear seat of modern vehicles. The purpose of this work is to quantify the thoracic response of two current 50th percentile male frontal impact ATDs, i.e., the Hybrid III and THOR-50M, and similarly sized male post mortem human surrogates (PMHS) seated in the rear seat during a frontal MVC. Several vehicles were used and chosen to represent various seat geometries and restraint types. There are two restraint types in the rear seat within this body of work, conventional and advanced. A conventional restraint consists of a three point seat belt, while an advanced restraint consists of a three point seat belt with additional safety features installed. Emphasis is placed on the injury risk prediction from the ATD versus actual instances of injuries from the PMHS. A series of frontal sled tests were first performed with the Hybrid III and THOR-50M ATDs. Three different crash pulses derived from vehicle specific US New Car Assessment Program frontal crash data were used: Scaled (32kph), Generic (32kph), and NCAP85 (56kph). v These tests showed that the established injury metrics for the two ATDs were exceeded in some of the high severity tests. A matched comparison analysis between a front and rear seated Hybrid III 50th percentile male ATD is presented and highlights the disparities between front and rear seat occupant safety of modern vehicles during frontal MVCs. The thoracic injury risk was found to be higher in the rear compared to the front for all vehicles. A series of frontal sled tests were then performed with the mid-sized male PMHS using the high severity sled pulse (NCAP85) and four of the vehicles from the ATD tests. The thoracic deflections for the PMHS were normalized by the surrogate chest depth in order to compare them between different sized surrogates, and were found to be higher in vehicles with conventional restraints. All PMHS had severity thoracic injuries. Additionally, there were a larger average number of rib fractures in vehicles with conventional restraints versus advanced restraints. Finally, the thoracic response of each ATD was compared to the PMHS to further the understanding of the effect of different occupant protection systems on thoracic injury risk in a rear seat environment and investigate rear seat biofidelity of each ATD. The THOR-50M had a more biofidelic kinematic response, while the Hybrid III matched the PMHS thoracic deflections and accelerations more accurately when compared with an objective rating metric. The comparison between surrogate responses furthers the understanding of 50th percentile male ATD biofidelity, the ATD injury risk prediction capabilities, and effects of different occupant protection systems on thoracic injuries in the rear seat.

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. / Master of Science / The thorax is one of the most frequently injured body regions in motor vehicle collisions (MVCs), and severe thoracic injuries have been shown to increase mortality risk. Finite element models (FEMs) of the human body are frequently used to evaluate thoracic injury risk. However, the accuracy of these models is dependent on the biomechanical data used to validate them. Although the material properties of bone have been shown to vary with respect to age and loading rate, previous studies that have evaluated the material properties of human rib cortical bone were limited to a small number of subjects, a narrow age range, one loading rate, and one loading mode (tension). Therefore, the purpose of this study was to evaluate the effects of sex, age, and loading rate on the tensile and compressive material properties of 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 (Avg. = 56.4 ± 26.2 years). Compression samples were tested from thirty (n = 30) subjects (M = 19, F = 11) ranging in age from 18 to 95 years (Avg. = 49.0 ± 23.9 years). 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 the other coupon 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. There were no significant differences in 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. In regard to the effect of age, all tensile material properties had significant negative correlations with age at except the modulus at 0.005 strain/s and yield strain at 0.5 strain/s. No significant correlations were observed in material properties with respect to advanced age in compression at either loading rate. Overall, this is the first study to provide the tension and compression data needed to more accurately model and assess differences in the material response of the rib cage for nearly all vehicle occupants of driving age.

Mitigating injury in side impact has been an important topic of research for decades. In the mid 1980’s the American government began a program intended to improve the crashworthiness of vehicles in side impact. This program ultimately led to the introduction of a dynamic side impact test (Federal Motor Vehicle Safety Standard (FMVSS) 214), which new vehicles must pass, along with a very similar test aimed at consumer awareness (New Car Assessment Program (NCAP) side impact test). The work presented in this thesis involved the study and simulation of these tests to evaluate occupant response in side impact, with a focus on the thoracic response. In the first portion of the work presented here, an in-depth study of the National Highway Traffic Safety Administration (NHTSA) crash test database was performed. In this study the results of the side impact crash tests of 72 vehicles were examined to understand the general trends seen in this type of testing with regards to vehicle velocity, side intrusion, and occupant injury prediction. A series of average velocity profile curves was created from accelerometer data at 18 measurement points on each vehicle crash tested. Additionally the injury criterion measured by the front seat occupant was plotted against several vehicle variables (such as mass and occupant arm to door distance) to study the effect these variable had on the injury predicted by the occupant. No single variable was shown to have a strong correlation to injury, although increasing door intrusion distance, peak lateral velocity, the Head Injury Criterion (HIC), and pelvic acceleration were found to positively correlate to thoracic injury. In addition, increasing vehicle model year, vehicle mass, and arm to door (AD) distance showed negative correlations with thoracic injury. Following the survey of the NHTSA database, a finite element model of the NHTSA side impact test was developed. This model included a full scale Ford Taurus model, a NHTSA barrier model and three side impact anthropometric test device (ATD) occupant models, each representing a different 50th percentile male dummy. Validation of this model was carried out by comparing the simulated vehicle component velocity results to the corridors developed in the NHSTA crash test database study as well as comparing these velocities, the vehicle deformation profile, and the occupant velocity, acceleration and rib deflection to several Ford Taurus crash tests from a similar vintage to the finite element model. As this model was intended as a ‘baseline’ case to study side impact and occupant kinematics in side impact, side airbags were not included in this model. A lack of experimental data and a lack of consensuses within the automotive crash community on the proper method of modeling these devices and their effectiveness in real world impacts also led to their exclusion. Following model validation, a parametric study was carried out to assess the importance of the initial position of the occupant on the vehicle door velocity profile and the predicted occupant injury response. Additionally the effect of the door trim material properties, arm rest properties and the effect of seat belt use were studied. It was found that the lateral position of the occupant had an effect on the door velocity profile, while the vertical and longitudinal position did not. The use of seatbelts was shown to have no significant effect in these simulations, due to minimal interaction between the restraint system and occupant during side impact. Furthermore, there was a general decreasing trend in the injury predicted as the initial position of the occupant was moved further inboard, down and forward in the vehicle. Stiffer interior trim was found to improve the injury prediction of the occupant, while changing the material of the foam door inserts had no effect. It was found that in general the occupant remained in position, due to the inertia of the occupant, while the seat began moving towards the centerline of the vehicle. Future considerations could include more advanced restraint systems to couple the occupant more effectively to the seat, or to develop side interior trim that engages the occupant earlier to reduce the relative velocity between the occupant and intruding door. Overall, the model correlated well with experimental data and provided insight into several areas which could lead to improved occupant protection in side impact. Future work should include integrating side airbags into the model, widening the focus of the areas of injury to include other body regions and integrating more detailed human body models.

Mitigating injury in side impact has been an important topic of research for decades. In the mid 1980’s the American government began a program intended to improve the crashworthiness of vehicles in side impact. This program ultimately led to the introduction of a dynamic side impact test (Federal Motor Vehicle Safety Standard (FMVSS) 214), which new vehicles must pass, along with a very similar test aimed at consumer awareness (New Car Assessment Program (NCAP) side impact test). The work presented in this thesis involved the study and simulation of these tests to evaluate occupant response in side impact, with a focus on the thoracic response. In the first portion of the work presented here, an in-depth study of the National Highway Traffic Safety Administration (NHTSA) crash test database was performed. In this study the results of the side impact crash tests of 72 vehicles were examined to understand the general trends seen in this type of testing with regards to vehicle velocity, side intrusion, and occupant injury prediction. A series of average velocity profile curves was created from accelerometer data at 18 measurement points on each vehicle crash tested. Additionally the injury criterion measured by the front seat occupant was plotted against several vehicle variables (such as mass and occupant arm to door distance) to study the effect these variable had on the injury predicted by the occupant. No single variable was shown to have a strong correlation to injury, although increasing door intrusion distance, peak lateral velocity, the Head Injury Criterion (HIC), and pelvic acceleration were found to positively correlate to thoracic injury. In addition, increasing vehicle model year, vehicle mass, and arm to door (AD) distance showed negative correlations with thoracic injury. Following the survey of the NHTSA database, a finite element model of the NHTSA side impact test was developed. This model included a full scale Ford Taurus model, a NHTSA barrier model and three side impact anthropometric test device (ATD) occupant models, each representing a different 50th percentile male dummy. Validation of this model was carried out by comparing the simulated vehicle component velocity results to the corridors developed in the NHSTA crash test database study as well as comparing these velocities, the vehicle deformation profile, and the occupant velocity, acceleration and rib deflection to several Ford Taurus crash tests from a similar vintage to the finite element model. As this model was intended as a ‘baseline’ case to study side impact and occupant kinematics in side impact, side airbags were not included in this model. A lack of experimental data and a lack of consensuses within the automotive crash community on the proper method of modeling these devices and their effectiveness in real world impacts also led to their exclusion. Following model validation, a parametric study was carried out to assess the importance of the initial position of the occupant on the vehicle door velocity profile and the predicted occupant injury response. Additionally the effect of the door trim material properties, arm rest properties and the effect of seat belt use were studied. It was found that the lateral position of the occupant had an effect on the door velocity profile, while the vertical and longitudinal position did not. The use of seatbelts was shown to have no significant effect in these simulations, due to minimal interaction between the restraint system and occupant during side impact. Furthermore, there was a general decreasing trend in the injury predicted as the initial position of the occupant was moved further inboard, down and forward in the vehicle. Stiffer interior trim was found to improve the injury prediction of the occupant, while changing the material of the foam door inserts had no effect. It was found that in general the occupant remained in position, due to the inertia of the occupant, while the seat began moving towards the centerline of the vehicle. Future considerations could include more advanced restraint systems to couple the occupant more effectively to the seat, or to develop side interior trim that engages the occupant earlier to reduce the relative velocity between the occupant and intruding door. Overall, the model correlated well with experimental data and provided insight into several areas which could lead to improved occupant protection in side impact. Future work should include integrating side airbags into the model, widening the focus of the areas of injury to include other body regions and integrating more detailed human body models.

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. / PHD