The Split-Hopkinson-Bar

The Split-Hopkinson pressure bar is used in material testing. During a test the material characteristics of a specimen are determined under dynamic load conditions. Even though there are various assemblies and techniques to use the Split-Hopkinson pressure bar for tensile, compression, and torsion tests, the basic idea is always the same: A specimen located between two bars (the incident bar and the transmitted bar) is loaded by a shock impulse. The original assembly traces back to Bertram Hopkinson. Since lateron some modifications where performed by Herbert Kolsky, the Split-Hopkinson pressure bar is also known as Kolsky-Bar.

 

The very fast motions during material testing can only be determined and made available for recording by means of high-quality measurement technology. Therefore the Extensometer 200XR of the H.-D. Rudolph GmbH has been used for measurements on the Hopkinson-Spilt pressure bar for many years now.

 

Characteristics of Model 200XR:

  • High bandwidth of 250 kHz (optionally 500 kHz)
  • Sensor resolution in the µm range
  • All measuring signal outputs are live
  • The output signals are calibrated
  • Easy target marking on the specimen or measurement with backlight on edges of specimen
  • Measuring camera, lens units, and illuminators from one supplier
  • Simple and fast set-up of the measuring system
  • Exchangeable lens units for various measuring ranges
  • Follows target motions exceeding 400 m/s
  • l0 adjustable from 1 mm – 500 mm
  • Measurement with special lens units on specimens with a temperature of up to 3000° C

 

Hopkinson Bar

Image 1: Measurement on a Hopkinson Bar with Model 200XR recorded with an oscilloscope. Picture click for zoom!

 

Video 1: Measurement on Hopkinson Bar.

 

 Questions and Answers

Q: How is the specimen marked?

A: The Camera 200XR measures the positions of two black-and-white or white-and-black transitions. Both ends of the bars (incident bar and transmitted bar) are marked either by labels or dull colour. The camera adjusts to the transitions following them also at high velocities of up to at least 400 m/s.

 

Q: What is a calibrated live output?

A: The customer does not have to take care of the calibration. For each lens unit delivered calibration was performed by the producer. Almost instantaneously the measuring signals are available at the outputs of the camera. Therefore Model 200XR is also used for other measuring tasks such as measurements for real-time control.