The use of improved explosive devices (IEDs) has been increased in recent armed conflicts. When a vehicle is attacked by an IED, the explosion causes deformation of the floor of the vehicle and the transmission of a high-rate axial loading to the lower limb of the occupants. This incident often leads to difficult-to-treat fractures in the ankle and foot. The use of efficient mitigation strategies, such as blast mats and boots, can improve this outcome. Biomechanical tools, such as finite element (FE) models, can facilitate our understanding about injury pathways and inform the design of mitigation strategies by assessing their efficacy in mitigating blast. In this thesis, FE models of the lower extremity of vehicle occupants were developed and validated in relevant loading conditions.

The model validation process was done in two stages. Firstly, model outcomes were compared with experimental data from two sets of experiments. The first of these was the biomechanical behaviour of a human leg when impacted by a rigid floor. Predicted computational model hindfoot forces showed a high level of correlation with data from force sensors. The boundary conditions of the model were then changed to replicate pendulum tests conducted in previous studies. The leg was impacted at speeds between 4 to 6.7 m/s and the computational model was used to predict foot compression and the peak force at the proximal tibia and the impact plate. The computational signals were found to be within the experimental corridors reported in the studies. The model showed good biofidelity for both set-ups which provided the confidence to pursue the incorporation of mitigation systems and the conduction of an injury risk analysis for different vehicle occupant scenarios.

A combat boot and energy-absorbing blast mat were incorporated in the validated computational model. The model was used to predict the injury risk reduction for under-body blast loading cases. The predicted proximal tibia forces and associated injury risk probability indicated that the mitigation systems reduced injury severity for low severity loading cases with increased time to peak. The design of a commonly used combat boot was then improved with the optimization of material parameters and incorporation of frangible structures. The injury risk reduction was evaluated. A study was also pursued to evaluate the effects of anthropometry and posture on calcaneal injury risk. These findings provide a better understanding of the current protection level of vehicle occupants and demonstrated the potential to improve the protection offered by personal mitigation systems for different acceleration profiles relevant to UBB events.

The validated computational model presented in this study can be used further to investigate new ways to protect the foot and ankle with mitigation structures and strategies.