2011 IR&D Annual Report

Development and Validation of a Shock Tube Apparatus for High-Fidelity Blast Wave Generation, 18-R8132

Principal Investigators
James Mathis
Walt Gray
Thomas Z. Moore
Larry Goland
Trenton Kirchdoerfer

Inclusive Dates:  01/01/10 – Current

Background — SwRI has identified blast and blunt impact trauma as an emerging market opportunity well suited to its impact and blast physics expertise. SwRI's current blast loading method of using high explosives presents limitations in experimental fidelity and repeatability and has been met with skepticism by proposal reviewers in the medical community. Although trauma research using explosives is still being conducted, the shock tube method has become the de facto standard. Large shock tube apparatuses are currently under development at other organizations conducting blast trauma research. Without such a device, a gap will soon appear in SwRI's research capabilities that may severely limit its ability to maintain a viable research program in blast trauma. For that reason, SwRI researchers proposed to design and build a high-fidelity shock tube apparatus.

Approach — The goal is to design and develop a shock tube test apparatus with sufficient flexibility to achieve the range of shock pressure conditions required to study a broad spectrum of blast trauma mechanisms. The apparatus will be unique. It will include an adjustable length high-pressure gas reservoir section allowing for independent tailoring of the shock peak pressure and pulse width (impulse) with a single device. In current shock tubes, the peak pressure and impulse are coupled, and tailoring usually requires changing hardware. This approach has not been attempted before and will require a significant research and design effort. The validity of the apparatus for trauma studies will then be demonstrated experimentally.

Figure 1. SwRI-designed shock tube system.

Accomplishments — A new shock tube system has been designed and fabricated, see Figure 1. The system consists of four primary components: an adjustable length high pressure driver section, a dual burst diaphragm section, a modular expansion section and a test section. The driver section consists of a 4.9-inch internal diameter tube rated at 6,000 psi. The adjustable length is achieved by sliding a movable piston in the tube bore to the desired location along the tube's length. This effectively changes the length of the driver section without having to change hardware. The piston location is infinitely adjustable using a specially designed system. The diaphragm section is a dual diaphragm design allowing for more precise control over shock tube firing and allowing higher driver load pressures to be obtained. The internal diaphragm holder can be quickly accessed by removing a single clamp device and moving the entire driver section away via a roller system. The test section currently consists of a 36-inch diameter, 12-foot long pipe. With the current test section, it is expected that shock pressure up to 20 psi and durations up to 20 milliseconds can be obtained. Much higher shock pressures can be achieved by limiting the diameter of the test section. The modular design of the expansion section will allow for various test sections to be easily installed.

Along with the mechanical design of the system, a complete electronic control system was developed and is currently being installed. The system consists of a control console with various pressure readouts and controls, which actuate the high speed valves used to fill and fire the shock tube.

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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 9 technical divisions.