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Interaction of Rifle Discharge Overpressure and Recoil Effects on Brain Response Quantified with Finite Element Head
Javier A Maldonado-Echeverria1, Dilaver Singh1, Simon Ouellet2
1Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, ON N2L 3G1, Canada.
Introduction:
The presence of concussion-like symptoms related to repetitive exposure to overpressure and recoil forces resulting from long-range precision rifle (LPR) training has been reported in the literature. However, the recoil head kinematics, overpressure loadings from LPR discharge, and the interaction of the 2 load paths have not been previously quantified.
Methods:
In the present study, experiments were undertaken using an instrumented head form to measure the overpressure from a single LPR discharge, and to measure head kinematics resulting from recoil using instrumented mouthguards on human volunteers. The measurements were supported with high-speed video to enable estimation of the relative onset timings of overpressure and recoil head kinematics. Planar finite element (FE) head models (in the sagittal and transverse planes) were used to quantify the effect of the measured loadings on the brain response. The models were simulated for a single LPR discharge with 3 boundary conditions: only the overpressure, only the recoil head kinematics, and combining the 2 loadings to investigate the interaction and relative timing of the load paths.
Results:
The onset of recoil head kinematics was measured to vary between operators, occurring between 7.4 and 24.4 ms after the onset of overpressure loading to the head. The FE models showed that the predicted intracranial pressure response was largely governed by the overpressure loading, while strain in the brain was largely governed by recoil head kinematics. No significant interaction between the 2 load paths was observed in the model responses, suggesting that the load paths for overpressure and recoil kinematics are effectively decoupled.
Conclusion:
The results from the study have quantified the magnitudes and relative timings of overpressure and recoil kinematics loadings to the head during a single LPR discharge and can be used to guide prevention and mitigation strategies for operators.
