ON THE ABILITY OF PROTECTIVE HEADGEAR TO ALTER SKULL AND BRAIN KINETICS DURING BLAST AND IMPACT: AN EXPERIMENTAL STUDY USING A SURROGATE MODEL OF THE HUMAN HEAD WITH NOVEL INSTRUMENTATION

• Author / Creator

  Azar, Austin

• Blast-induced traumatic brain injury (bTBI) has become increasingly prevalent among military personnel over recent years. Head protection is fielded to mitigate the amount of energy imparted to head, as a result of ballistic and impact exposure. Despite the efficacy of contemporary headgear in protecting the wearer from ballistic and impact threats, rates of bTBI have been continuing to rise. Limited biomechanical literature exists to determine whether or not modern military head protection is able to alter the transmission of blast energy into the head and brain. Using a simulant-based surrogate model of the human head, equipped with a novel array of instrumentation, this thesis aims to investigate the effect of protective headgear on the transmission of energy into the head and brain during blast and impact experiments.The development and validation of an in-fibre Bragg grating (FBG) transducer for measuring kinetics on the inner skull table are first presented. The developed FBG force transducer contains a multi-layered composite superstructure (6 mm nominal diameter) and demonstrates linearity and repeatability under both dynamic impact-response calibrations and blast-loading conditions. Spectral analysis indicates that the presented transducer captures transient kinetics of blast overpressure with an average of 0.12% difference in normalized Fourier amplitudes captured by the FBG and validated reference piezo-electric transducer. Time-domain analysis indicates that the FBG force transducer is repeatable with maximum coefficient of variance for repeated measures at 7.9% whereas the validated reference transducer coefficient of variance is 9.1% (maximum), based on the normalized blast exposure data. The novel force transducer is the first application of FBG technology to measure inner skull kinetics under blast loading and can be used to evaluate the mechanisms of energy transfer into the head during blast exposure.The newly developed transducers were then integrated into a biofidelic simulant-based surrogate model of the head and used to assess whether or not helmets and eye protection can alter mechanical measures during both blast and impact loading scenarios. Free-field blast simulations at an outdoor test range (DRDC Valcartier) were conducted to create realistic blast exposure on the head surrogate using various protection scenarios. Impact loading on the headform was created in a laboratory setting, using a linear monorail drop tower, for the casesiiwith a bare headform and for cases wearing a combat helmet. Specifically, inner skull forces and pressure within the brain parenchyma were investigated for the various blast and impact loading conditions and protection scenarios. Results suggest that adding head protection can attenuate the measured kinetics relative to the case when the surrogate model is unprotected, in both blast and impact. Measurements also demonstrate a propensity towards more spectral content at lower frequencies, relative to an unprotected head, for measurements nearest to the site of loading. Overall, adding head protection was found to attenuate pressure in the brain parenchyma by as much as 49% during blast and 53% during impact, and forces on the inner table of the skull by as much as 80% during blast and 84% during impact, relative to an unprotected head.In summary, this work presents a developed transducer that is a repeatable tool with the capacity to assess inner skull kinetics during blast and impact events and therefore can be applied towards the assessment of relative headgear protection efficacy. A simulant-based surrogate headform, with integrated instrumentation, documents the mitigation of internal kinetics and shift of frequency content with the addition of protective headgear. These results are an important contribution to documenting how the skull and brain react during blast and impact loading when the head is protected relative to when the head is unprotected.

• Subjects / Keywords

  • injury
  • biomechanics
  • blast
  • impact
  • brain
  • surrogate
  • model

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-0h1k-jc48

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.