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 / 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, e.g., seat belts, and more biofidelic (human-like) anthropomorphic test devices (ATDs), i.e., crash test dummies, 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 (chest) 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 the risk of death.
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, frontal crash tests were simulated in the laboratory using a crash sled. These sled tests were performed on three different human surrogates: the Hybrid III (HIII) ATD, the Test Device for Human Occupant Restraint (THOR-M) ATD, and post-mortem human surrogates (PMHS), i.e., cadavers. 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 (body movements), 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 (forces and moments), 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 how injury risk was predicted.
In order to meet sub-objective 3, the material properties of human rib cortical bone and the structural response of whole ribs were quantified under experimental conditions reminiscent of what the bone would experience during a frontal impact. The rib cortical bone underwent material testing, while the whole ribs underwent bending tests intended to simulate a frontal impact. The rib material properties only partially influenced the structural response of the whole rib. This indicated that other factors, such as rib shape and thickness, were also influencing the structural response. Age was correlated to a decrease in several material properties. However, there was no significant difference between male and female material properties. Some differences in material properties were observed in cortical bone from fractured and intact ribs, indicating that the fracture influenced the rib material properties.
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 finite element (computer) models, which can then be used to evaluate injury prevention strategies for MVCs.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/100947 |
| Date | 04 June 2018 |
| Creators | Albert, Devon Lee |
| Contributors | Department of Biomedical Engineering and Mechanics, Kemper, Andrew R., Stitzel, Joel D., Gabler, Hampton Clay, Agnew, Amanda M, Hardy, Warren N. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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