Date of Award
Master of Science
Sarah A. Bentil
Traumatic brain injury (TBI) following blunt force impact to the head yields symptoms that include confusion, headache, dizziness, and speech problems. The injury mechanism resulting in these symptoms is still not well understood, hindering the development of effective countermeasures.To increase our understanding of TBI (without skull fracture), we have designed an apparatus that can reproduce blunt impact forces in a controllable and repeatable manner. The apparatus consists of a simplistic cylindrical head system with tissue and fluid surrogates to represent the brain, cerebrospinal fluid (CSF), and skull. Resultant forces imparted on the outer layer of the skull are recorded using force transducers. A tri-axial accelerometer mounted on the brain and a laser vibrometer are used to measure the acceleration and velocity, respectively. A dedicated shaker is coupled with the head system (i.e. brain-CSF-skull apparatus) to allow for controlled and repeatable testing of blunt loading scenarios of variable complexities.
The selection of the shakers frequency and applied force needed to simulate a TBI, such as a concussion, were guided by the Head Injury Criterion (HIC) scale. The HIC scale is an exponential scale used to rate the severity of skull impact. A HIC of 700 corresponds to a severe concussion sustained by a National Football League (NFL) player during game play. The duration of the blunt impact resulting in concussion is 15 ms, which translates to an acceleration of 74 g-force. Through optimization of the shaker design, a HIC of 700 was not possible without scaling the head system. Due to budget constraints, a 3 hp motor was used to drive the shaker. This system was capable of 12.38 g-force at a duration of 15 ms, which corresponds to a HIC of 8.09. Although the HIC of 8.09 is lower than the desired 700, it was suitable for baseline testing of the prototype head system. A design of experiments (DOE) approach was conducted, to analyze the head system, by considering three different mass settings of a counterweight shaker and six shaker speeds. The system demonstrated repeatability and adjustability through nearly half of the experiments before a substructure fracture halted experiments. The results of the head system before failure are highlighted in this thesis, and reflect the capabilities of the apparatus. Additionally, a discussion for improvements to the design to facilitate future experiments with a biofidelic head geometry is presented. Inclusion of angular impact, in a future design of the system, would also improve the capability of the head system at mimicking TBI; while simultaneously using less power to operate the device.
Timothy J Beavers
Beavers, Timothy J., "A surrogate head system for blunt impact experiments" (2018). Graduate Theses and Dissertations. 16787.