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Air shock pressure-time histories were measured in the HE source region of the Air Force Weapons Laboratory (AFWL) DABS S2 test to determine source characteristics. Steel-ytterbium flatpack gages previously used for the measurement of soil stress were modified, and static, uniaxial strain calibration was performed at pressures to approximately 8 MPa. Results of static calibration at these low pressures and low strain rates agreed well with values extrapolated from high stress (500 MPa) uniaxial strain, shock data, indicating no strain rate effects in the ytterbium piezoresistance sensor and definable response if the tensor state of strain is carefully controlled. The gages survived the environment in the DABS test within 3 m of the HE source and indicated a double shock structure with peak pressures of up to 98 MPa, possible slight prepressurization of the source chamber by the primacord initiation system, less than 5% skewing of the air shock, and slightly higher pressures along the tube axis. Postshot measurement of the gage resistance showed that, for gages in which gross damage did not occur, the pre- and postshot values agreed within a few percent, indicating no gage hysteresis. Flow samplers consisting of steel tubes explosively closed at the ends during shock flow were fielded at two stations, 19 and 26 m on DABS S3 to determine the particulate matter concentration and for comparison of particulate matter arrival time with previously observed pressure variations. |
