Knowledge Bank

Side impact automobile collisions are a frequent cause of serious injury. In recent years, the amount of attention being paid to these kinds of accidents has increased as evidenced by the implementation of side airbags in most commercial vehicles. Approximately one third of all occurrences of side impact automobile accidents occur in intersections when vehicles travelling at around 30 mph strike vehicles travelling around 15 mph.1 Impacts of this variety create a loading environment with the primary force of impact at an oblique angle to the passengers. Having the capability to reduce the threat to passengers from these types of accidents requires a thorough understanding of the human body response to both oblique and lateral impacts. Currently, anthropomorphic test devices, or crash test dummies, only quantify thoracic deflection, which is the leading indicator for thoracic trauma, in the purely lateral direction. This limits the ability for the ATD to accurately depict the nature of the human thorax under any loading that is not primarily lateral. To improve on NHTSA standards of protection, a better understanding of the human response to oblique, blunt loading is necessary to improve the biofidelity of ATD’s. The motivation behind this study is to clarify differences seen in two related studies done in the Injury Biomechanics Research Lab previously. In 2006, Shaw et al observed the post-mortem human subject (PMHS) response to low energy impacts in both lateral and oblique directions.2 Lateral impacts showed a higher stiffness than oblique impacts according to Shaw. In 2009, a study by Long used a similar protocol but impacted subjects at speeds of 4.5 and 5.5 m/s, a more injurious energy level.3 In contrast to Shaw’s study, the results of their tests indicated similar stiffness responses in both lateral and oblique impacts. To clarify the results of these two studies, their data was reanalyzed using seven different methods for calculating stiffness. The raw data was zeroed, filtered, and inertially compensated before calculating stiffness. The method with the most consistent results across all of the tests between Shaw and Long’s studies, as well as studies completed since 2009, was calculating stiffness, force per unit deflection, from the time of impact to the time of maximum force. From the tests available, lateral and oblique impacts at 4.5 m/s speeds showed a similar response, 33.92 N/mm versus 36.99 N/mm, and a different response at 2.5 m/s speeds, with oblique impacts maintaining relatively the same stiffness (35.08 N/mm) while lateral stiffness increased to 65.69 N/mm. These results support the case that lateral and oblique impacts produce different biomechanical responses.