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

Mild Traumatic Brain Injury (mTBI) associated with blast exposure has become an increasing issue in military conflicts, with the most common exposure being improvised explosive devices. Exposure to blast accounted for 81% of all casualties reported for Operation Enduring 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 be strongly 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 intracranial pressure occurring at the opposite site of initial blast wave transmission. This observation resulted in the hypothesis of intracranial cavitation of cerebrospinal fluid (CSF), due to the negative pressures generated, as a potential brain injury mechanism. The purpose of this work was to develop an apparatus that generates controlled localized cavitation with similar loading encountered 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 generated loading, and generation of diffuse cavitation. Due to the nuclei from the pressure gauge implementation, a validated numerical model of the apparatus was used to predict the negative fluid pressure in the chamber. The final proposed design for the apparatus incorporated a novel closed cavitation chamber to generate localized cavitation resulting from a reflected compression pulse, which was 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 and without the PMMA chamber using 24 independent tests for strain and end velocity using iv varying striker geometry (cross–correlation: 0.970–0.997). Additionally, the numerical model of the apparatus including the chamber was developed and validated with 27 independent tests for strain and chamber end surface velocity (cross–correlation: 0.921). Cavitation tests on distilled water were performed and a 50% probability of cavitation was measured at a negative pressure of 3.39 MPa ±2%, comparable to values found in the literature. Analysis of the experimental and numerical result trends demonstrated comparable chamber strain (R2: 0.875) and chamber end surface velocity (R2: 0.992). The predicted fluid pressures from the model were verified with a first–order approximation showing good agreement (R2: 0.892). This novel apparatus, incorporating a closed confinement chamber integrated with a polymeric SHPB apparatus, was able to create localized fluid cavitation using a reflected compression wave, with loading comparable to blast exposure. Future studies will investigate the measurement of CSF cavitation pressure and incorporation of the results in computational head-blast models

National Aeronautics and Space Administration (NASA)/American Society for Engineering Education (ASEE) Summer Faculty Fellowship Program, 1994, volume 1

The JSC NASA/ASEE Summer Faculty Fellowship Program was conducted by Texas A&M University and JSC. The objectives of the program, which began nationally in 1964 and at JSC in 1965 are to: (1) further the professional knowledge of qualified engineering and science faculty members, (2) stimulate an exchange of ideas between participants and NASA, (3) enrich and refresh the research and teaching activities of participants' institutions, and (4) contribute to the research objectives of the NASA centers. Each faculty fellow spent at least 10 weeks at JSC engaged in a research project in collaboration with a NASA JSC colleague. This document is a compilation of the final reports on the research projects completed by the faculty fellows during the summer of 1994

Aeronautical engineering: A continuing bibliography with indexes (supplement 271)

This bibliography lists 666 reports, articles, and other documents introduced into the NASA scientific and technical information system in October, 1991. Subject coverage includes design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Proceedings of the NASA Conference on Space Telerobotics, volume 5

Papers presented at the NASA Conference on Space Telerobotics are compiled. The theme of the conference was man-machine collaboration in space. The conference provided a forum for researchers and engineers to exchange ideas on the research and development required for the application of telerobotics technology to the space systems planned for the 1990's and beyond. Volume 5 contains papers related to the following subject areas: robot arm modeling and control, special topics in telerobotics, telerobotic space operations, manipulator control, flight experiment concepts, manipulator coordination, issues in artificial intelligence systems, and research activities at the Johnson Space Center

Large space structures and systems in the space station era: A bibliography with indexes (supplement 04)

Bibliographies and abstracts are listed for 1211 reports, articles, and other documents introduced into the NASA scientific and technical information system between 1 Jul. and 30 Dec. 1991. Its purpose is to provide helpful information to the researcher, manager, and designer in technology development and mission design according to system, interactive analysis and design, structural concepts and control systems, electronics, advanced materials, assembly concepts, propulsion, and solar power satellite systems

Proceedings of the Third International Mobile Satellite Conference (IMSC 1993)

Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial cellular communications services. While the first and second International Mobile Satellite Conferences (IMSC) mostly concentrated on technical advances, this Third IMSC also focuses on the increasing worldwide commercial activities in Mobile Satellite Services. Because of the large service areas provided by such systems, it is important to consider political and regulatory issues in addition to technical and user requirements issues. Topics covered include: the direct broadcast of audio programming from satellites; spacecraft technology; regulatory and policy considerations; advanced system concepts and analysis; propagation; and user requirements and applications