Investigation of Blast–related Fluid Cavitation using a Novel Polymeric Hopkinson Bar–Confinement Chamber Apparatus

Cavitation;Polymer Split Hopkinson Pressure Bar;Mild Traumatic Brain Injury;Negative Pressure;Finite Element Modeling

Bustamante, Michaeladvisor:Cronin, Duane ; affiliation1:Faculty of Engineering ; Cronin, Duane ;

University of Waterloo

关键词: Master Thesis;    Negative Pressure;    Mild Traumatic Brain Injury;    Cavitation;    Finite Element Modeling;    Polymer Split Hopkinson Pressure Bar;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/12194/5/Bustamante_Michael.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

Mild Traumatic Brain Injury (mTBI) associated with blast exposure has become anincreasing issue in military conflicts, with the most common exposure being improvisedexplosive devices. Exposure to blast accounted for 81% of all casualties reported for OperationEnduring Freedom and Operation Iraqi Freedom combined. It has been identified as the'signature injury’ of the military conflicts in Iraq and Afghanistan, and has been reported to bestrongly associated with higher rates of Post–Traumatic Stress Disorder (PTSD), depression,and physical health problems than with other injuries [1].An observation common to most head blast exposure studies is the negative intracranialpressure occurring at the opposite site of initial blast wave transmission. This observationresulted in the hypothesis of intracranial cavitation of cerebrospinal fluid (CSF), due to thenegative pressures generated, as a potential brain injury mechanism. The purpose of this workwas to develop an apparatus that generates controlled localized cavitation with similar loadingencountered in head blast exposure to measure the cavitation pressure thresholds of fluids.Existing dynamic methods of generating cavitation presented limited loading capabilities,boundaries, and were not suitable for testing of biological fluids, such as CSF.Three iterations of the apparatus were developed, and the limitations identified were,potential cavitation nuclei and leakage at the seals and pressure gauge, variability in generatedloading, and generation of diffuse cavitation. Due to the nuclei from the pressure gaugeimplementation, a validated numerical model of the apparatus was used to predict the negativefluid pressure in the chamber.The final proposed design for the apparatus incorporated a novel closed cavitationchamber to generate localized cavitation resulting from a reflected compression pulse, whichwas generated by a spherical steel striker and Polymethyl methacrylate (PMMA) incident bar.Numerical models were developed and validated to model the PMMA incident bar with andwithout the PMMA chamber using 24 independent tests for strain and end velocity usingivvarying striker geometry (cross–correlation: 0.970–0.997). Additionally, the numerical modelof the apparatus including the chamber was developed and validated with 27 independent testsfor strain and chamber end surface velocity (cross–correlation: 0.921).Cavitation tests on distilled water were performed and a 50% probability of cavitationwas measured at a negative pressure of 3.39 MPa ±2%, comparable to values found in theliterature. Analysis of the experimental and numerical result trends demonstrated comparablechamber strain (R2: 0.875) and chamber end surface velocity (R2: 0.992). The predicted fluidpressures from the model were verified with a first–order approximation showing goodagreement (R2: 0.892). This novel apparatus, incorporating a closed confinement chamberintegrated with a polymeric SHPB apparatus, was able to create localized fluid cavitation usinga reflected compression wave, with loading comparable to blast exposure. Future studies willinvestigate the measurement of CSF cavitation pressure and incorporation of the results incomputational head-blast models.