THIGH INJURY RISK DURING EJECTION: DEVELOPMENT OF AN INJURY CRITERION FOR FEMUR FRACTURE

摘要

The Naval Air Systems Command (NASC) conducted ejection seat testing that suggests that taller pilots may be at a greater risk of midshafi femur fracture during ejection due to their seated geometry in the cockpit. The objective of this study was to evaluate the injury potential posed to a human based on measurements made by an anthropomorphic test device. Biomechanical data from the literature were analyzed to estimate the bending tolerance of the femur for large males at dynamic loading rates characteristic of ejection seat loading. To supplement the data from the literature, four three-point bending tests were conducted to failure on cadaveric femurs from large male donors. Results from the tests were mass-scaled to represent the JPA TS Case 6 large male manikin (i.e. 240 lbs). The mass-scaled failure moment for the specimens tested was-4780 + 1186 in-lbs. This moment tolerance was substantially higher than values reported in the literature. However, when a ratescaling technique was applied to one of the previous studies, the result was very close to the -4780 in-lbs. limit. This suggests that the results of the biomechanical tests are valid and represent the loads characteristic of the catapult phase of an ejection. When the bending tolerance limit was applied to the Ejection Tower data, it indicated a high risk of femur fracture to large aviators with thigh gaps, as measured by a custom-designed tool, greater than 3.5 inches. However, a three-point bend loading was assumed on the ejection seat which was known to overestimate the actual loads. Therefore, further study is required to accurately characterize the distributed loading pattern on the femur to obtain a less conservative prediction.