Appraisal of Pulse-Shaping Technique in Split Hopkinson Pressure Bar Tests for Brittle Materials: Fid-Bau Portal

Appraisal of Pulse-Shaping Technique in Split Hopkinson Pressure Bar Tests for Brittle Materials

Lu, Y.B. / Li, Q.M.

Split Hopkinson pressure bar (SHPB) technique has been frequently used to measure the uniaxial compressive stress–strain relation of brittle materials at intermediate strain-rates where pulse-shaping technique is employed to improve the stress uniformity and maintain a nearly constant strain-rate in the specimen during the effective loading period. This paper appraises the functions of the pulse-shaping technique in SHPB tests of brittle samples based on numerical simulations of SHPB tests. It is shown that a proper pulse-shaper can attenuate high frequency oscillations of the incident pulse and increase the rise-time of the pulse, resulting in the improvement of stress equilibrium and uniformity along the axial direction of an SHPB specimen. However, it is found that the inertia-induced confinement in the radial direction of a brittle specimen is still significant even though the shaped incident stress pulse can generate a nearly flat plateau in the reflected pulse in the SHPB test. It implies that the achievement of a nearly constant strain-rate represented by a nearly flat plateau in the reflected pulse in an SHPB test may not give a true nearly constant strain-rate in the SHPB specimen. It is concluded that the application of the pulse-shaping technique in SHPB tests on brittle materials may not change the nature of the observed transition strain-rate, which represents the transition of the stress state from a uniaxial-compressive-stress-dominated state to a confined compressive stress state, rather than the start of significant strain-rate effect. Therefore, inertia-induced radial confinement effect needs to be considered in the interpretation of any SHPB results for brittle materials even though a pulse-shaper is used.