ASME-Landmark:Split-Hopkinson Pressure Bar Apparatus

The Southwest Research Institute (SwRI) Split-Hopkinson Pressure Bar apparatus is a mechanical test instrument used to characterize the dynamic response of materials at high strain rates (typical of impacts and explosions).

The apparatus, based on devices invented by Bertram Hopkinson and Herbert Kolsky, was developed at SwRI in 1962 by Dr. Ulric Lindholm. Conventional mechanical test systems had been available for years to obtain strength data under long term conditions (hours to days) or static conditions (minutes) using screw or hydraulic loading systems. The maximum deformation or strain rate of these machines is about 0.1 per second (0.1 s-1). Pendulum impact machines can produce strain rates of up to about 100 s-1, yielding only energy absorbed to fracture, but not a complete stress-strain curve. During World War II, strength properties associated with shock waves were developed using light-gas gun or explosively driven flyer-plate impact experiments, producing high hydrostatic pressures and strain rates in excess of 104 s-1. The SwRI Split-Hopkinson Pressure Bar was designed to fill the strain rate range from 102 s-1 to 5.0 x 103 s-1, the time duration of many explosive, ballistic impact, crashes and other accident scenarios of interest for both military and civilian applications.

Notable applications include determining the dynamic strength of steel in North Sea offshore platforms subjected to impact, defining the compressive strength of ceramics used in advanced armors, evaluating pipeline and nuclear pressure vessel steels, and evaluating the strength of materials on the pressurized hulls of the U.S. Space Station under impact from meteorites or other orbital debris impact.

Today, the SwRI Split-Hopkinson Pressure Bar remains the standard test for high strain rate materials characterization. See ASME website for more information