Split-Hopkinson Pressure Bars

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Layout of all Hopkinson bars at CAVS in the mechanical testing lab.


Overview of Hopkinson Bars

The Split-Hopkinson Pressure Bars (SHPB) used at CAVS were designed and assembled in house. The attainable strain rates are on the order of 500 /s to 2000 /s. All of the bars use pressurized gas to initiate high strain rate tests. Strain gages are used along the incident bar and the transmitted bar to characterize the stress wave traveling through the bars. The bars are made from many different materials and diameters. The weaker the bar material, the finer the resolution of strain data due to lower forces needed to create identical strains. The limit for this happens if you have a specimen that requires a higher force to fail than the bar does to yield. Because of this, it is generally better that the specimens are matched with a bar that yields the best resolution without causing plastic deformation in the bar. If the diameter of a bar is increased too much to compensate for the difference in strengths of the bar and specimens, the stress wave can be distorted due to a drastic change in impedance.

Hopkinson Bars at CAVS

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