Short-duration, high-force loading of the lower leg occurs during a variety of events, including indirect (i.e., in-vehicle) contact with landmines. To date, the majority of research on impact loading of the lower extremities has been conducted by the car crash industry. From this, the current standard for designing protective measures for high-impulse scenarios has been selected - a maximum axial load of 5.4 kN measured in an Anthropomorphic Test Device (ATD). This force value, however, gives no indication of the load duration or injury severity. Furthermore, its applicability to high-impulse situations, with higher forces over shorter durations, is not known. The overall objective of this thesis was to investigate the appropriateness of this value for short-duration impulsive loading of the tibia (i.e., lower leg bone) using both cadaveric specimens and test surrogates. Surrogates that were considered for injury prediction were synthetic bones, ATDs, and finite element models.
Experimental testing was accomplished through the development of a pneumatic testing apparatus capable of applying axial loads to test specimens over a large range of magnitudes and velocities. This apparatus was validated to replicate the loading caused by anti-vehicular mine blasts, and was initially used to conduct load-to-failure tests on cadaveric tibias. A new injury criterion was proposed, with a higher force limit (7.9 kN) and inclusion of kinetic energy as a fracture risk factor. Synthetic composite bones were similarly tested, but demonstrated lower impact tolerance and non-biofidelic fracture patterns compared to cadavers. Critical load values from ATDs (12.6 kN) were determined which correspond to injury levels from the cadaveric tests.
To allow computer simulations of survivability analyses, a finite element model of a representative cadaveric specimen was developed using TrueGrid ® and LS-Dyna® softwares. The model was evaluated by comparing to experimental results, with refinements to best represent the experimental axial load, load duration, and strains for both non-fracture and fracture scenarios.
Through experimental testing and development of a finite element model, this thesis investigated the injury criteria for tibias exposed to short-duration, high-force axial loading. Overall, this research will contribute to improved standards for better protection of occupants from lower leg injuries.