The Georgia Tech Hopkinson Bar Facility has three Split Hopkinson Bar configurations: Compression Bar, Tension Bar, combined Tension-Torsion or Compression-Torsion Bar.
The compression bar has been used in studies on the dynamic behaviors of a variety of materials including structural steels, laminate composites, PZT ceramics, concrete and ceramics. It is capable of achieving strain rates in the range of 102 – 103 sec-1. Two bar diameters are used, 0.75 inch diameter and 0.5 inch diameters bars with various lengths to control the loading duration. Typical loading durations range between 15 usec – 250 usec. The bars are manufactured from Vascomax C-350 maranging steel heat-treated to a hardness of 59 on the Rockwell C scale. The uni-axial compressive yield strength of the bars is approximately 2.7 GPa.
Strain gauges with a nominal resistance of 1000 ohm are used to record the passing of the stress waves in the Hopkinson bar. The signals form the strain gauges are recorded on high speed digital oscilloscopes. The laboratory uses a Nicolet Pro 42 and a Nicolet Integra 40 high speed digital oscilloscope.The compression bar is also equipped with a recovery system that allows researches to study damage evolution under impact conditions and even allow researchers to apply a 1 cycle load on materials.
The Tension Hopkinson Bar and Combined Tension-Torsion Bar is near completion and will be operational in 1999. The tension bar uses a gas gun and projectile to load specimens in tension. The bars for the tension gun is manufactured from Vascomax C-350 maranging steel with a diameter of 0.75 inches. the ends of the bars are threaded to allow researchers to mount specimens. The tension-torsion bar employs a hydraulic system to load the specimens. The bars are made from Aluminum 7075 – T6 with a diameter of 1 inch. This gun can also be used for a combined compression-torsion load.The gun uses Enerpac hydraulic cylinders to torque and compress or torque and pull a clamped aluminum bar. The specimen is dynamically loaded by releasing the clamped bar and allowing the stored elastic energy to propagate as stress waves towards the specimen.
Recently the lab acquired two Polytec QFV 511 laser vibrometer systems with two fiber optic laser heads and two Polytec QFV 3001 controllers. The systems have a frequency response between 250 – 1500 kHz and can measure vibratory motions with velocities up to 10 m/s in real time. They are being used to characterize the damage evolution in composites.