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High-Strain-Rate Gas-Gun Laboratory
The Georgia Tech gas gun is equipped with interferometric, stress-gauge measurement, and high-speed digital data acquisition instrumentation, permitting material testing at strain rates up to 106 s-1, under a range of multiaxial states of stress through normal and pressure-shear (inclined) plate impact experiments.
This single-stage gas gun has an 80 mm diameter, 8 m long gun barrel connected to a 28.5 liter gas chamber separated via a double (rupture) diaphragm on the breech side and connected to a large soft-recovery catcher tank on the muzzle side. Impact velocities between 100 to 1200 ms-1 (reproducible within 5%) can be obtained, and are monitored using four sets of arrival-time velocity pins, connected to a Tektronix Model 640 digitizing oscilloscope as well as digital counters (HP Model No. 5313A, 2 channel, 225 MHz). Time-resolved in-situ stress measurements can be performed using piezoelectric PVDF as well as piezoresistive manganin stress gauges, and particle velocity measurements using the state-of-the-art four-beam VISAR (Velocity Interferometer System for Any Reflector) interferometry. The VISAR uses a doppler effect to measure the free surface velocity in the range of 30-5000 ms-1 with a sensitivity of 2 ms-1 and a depth of field of 12 mm.
The use of four beams permits simultaneous measurements to be performed at any four locations. Two four-channel Tektronix digital oscilloscopes (Model TDS784A) with a sampling rate of 4 Giga points per second are available for high-speed data acquisition. An IMACON 200 high-speed digital camera is also available for real-time imaging. The camera is capable of capturing up to 16 frames at a rate of 200 million frames per second. It is equipped with 4 high speed CCD units and utilizes a backlit flash for optimum image capture. Images are transported via fiber optics to a computer where they are analyzed.