New experimental techniques with the split Hopkinson pressure bar

Abstract

The split Hopkinson pressure bar or Kolsky bar has provided for many years a technique for performing compression tests at strain rates approaching 10/sup 4/ s/sup -1/. At these strain rates, the small dimensions possible in a compression test specimen give an advantage over a dynamic tensile test by allowing the stress within the specimen to equilibrate within the shortest possible time. The maximum strain rates possible with this technique are limited by stress wave propagation in the elastic pressure bars as well as in the deforming specimen. This subject is reviewed in this paper, and it is emphasized that a slowly rising excitation is preferred to one that rises steeply. Experimental techniques for pulse shaping and a numerical procedure for correcting the raw data for wave dispersion in the pressure bars are presented. For tests at elevated temperature a bar mover apparatus has been developed which effectively brings the cold pressure bars into contact with the specimen, which is heated with a specially designed furnace, shortly before the pressure wave arrives. This procedure has been used successfully in tests at temperatures as high as 1000/sup 0/C.