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).
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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.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/115776 |
| Date | 14 July 2023 |
| Creators | Bianco, Samuel Thomas |
| Contributors | Department of Biomedical Engineering and Mechanics, Kemper, Andrew R., Albert, Devon Lee, Hardy, Warren Nelson, Bolte, John H., Danelson, Kerry Ann, Jermakian, Jessica S. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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