Split-Hopkinson Pressure-Bar Test using Striker Bar With Variable Cross Section

Split-Hopkinson pressure-bar technique has been widely adopted to evaluate dynamic constitutive relations for various kinds of materials. However, due mainly to a rectangular incident stress pulse with a short rising time, the strain rate becomes considerably higher when a difference in mechanical impedance between a specimen and the pressure bars is large. This tendency may be enhanced when determining strength of specimen because the incident pulse amplitude must be high enough to break a specimen. In this study, stepped and tapered striker bars were proposed to increase the rising time of incident stress pulse. A simple procedure was developed for simulating an incident stress pulse profile generated by a striker bar with variable cross section. Validation was done by comparing predicted incident stress pulse profiles of uniform, 5-stepped and tapered striker bars with those obtained by longitudinal impact experiments. In addition, four kinds of polymer specimens were tested by the three kinds of striker bars. Results showed that the strain rates at failure obtained by the 5-stepped and tapered striker bars were remarkably lower than that obtained by the uniform striker bar regardless of the material properties of specimen