Investigation of Blast–related Fluid Cavitation using a Novel Polymeric Hopkinson Bar–Confinement Chamber Apparatus
Year: 2017
Type: dissertation
Abstract: Mild Traumatic Brain Injury (mTBI) associated with blast exposure has become an \nincreasing issue in military conflicts, with the most common exposure being improvised \nexplosive devices. Exposure to blast accounted for 81% of all casualties reported for Operation \nEnduring Freedom and Operation Iraqi Freedom combined. It has been identified as the \n‘signature injury’ of the military conflicts in Iraq and Afghanistan, and has been reported to be \nstrongly associated with higher rates of Post–Traumatic Stress Disorder (PTSD), depression, \nand physical health problems than with other injuries [1]. \nAn observation common to most head blast exposure studies is the negative intracranial \npressure occurring at the opposite site of initial blast wave transmission. This observation \nresulted in the hypothesis of intracranial cavitation of cerebrospinal fluid (CSF), due to the \nnegative pressures generated, as a potential brain injury mechanism. The purpose of this work \nwas to develop an apparatus that generates controlled localized cavitation with similar loading \nencountered in head blast exposure to measure the cavitation pressure thresholds of fluids. \nExisting dynamic methods of generating cavitation presented limited loading capabilities, \nboundaries, and were not suitable for testing of biological fluids, such as CSF. \nThree iterations of the apparatus were developed, and the limitations identified were, \npotential cavitation nuclei and leakage at the seals and pressure gauge, variability in generated \nloading, and generation of diffuse cavitation. Due to the nuclei from the pressure gauge \nimplementation, a validated numerical model of the apparatus was used to predict the negative \nfluid pressure in the chamber. \nThe final proposed design for the apparatus incorporated a novel closed cavitation \nchamber to generate localized cavitation resulting from a reflected compression pulse, which \nwas generated by a spherical steel striker and Polymethyl methacrylate (PMMA) incident bar. \nNumerical models were developed and validated to model the PMMA incident bar with and \nwithout the PMMA chamber using 24 independent tests for strain and end velocity using \niv \nvarying striker geometry (cross–correlation: 0.970–0.997). Additionally, the numerical model \nof the apparatus including the chamber was developed and validated with 27 independent tests \nfor strain and chamber end surface velocity (cross–correlation: 0.921). \nCavitation tests on distilled water were performed and a 50% probability of cavitation \nwas measured at a negative pressure of 3.39 MPa ±2%, comparable to values found in the \nliterature. Analysis of the experimental and numerical result trends demonstrated comparable \nchamber strain (R2: 0.875) and chamber end surface velocity (R2: 0.992). The predicted fluid \npressures from the model were verified with a first–order approximation showing good \nagreement (R2: 0.892). This novel apparatus, incorporating a closed confinement chamber \nintegrated with a polymeric SHPB apparatus, was able to create localized fluid cavitation using \na reflected compression wave, with loading comparable to blast exposure. Future studies will \ninvestigate the measurement of CSF cavitation pressure and incorporation of the results in \ncomputational head-blast models.
Source: UWSpace (University of Waterloo)
Author: Michael Bustamante
Language: English
Subfield: Biomedical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2748431520