Experimental and Numerical Study on Designing Pulse Shapers for Testing Rocks in Large-Diameter SHPB

Rocks such as Kota sandstone are an excellent construction material. An experimental and numerical study was performed to test Kota sandstone in a large-diameter (76-mm) split Hopkinson pressure bar (SHPB) in a strain rate range of 101–300/s. The primary goal of the current study was to optimize pulse shaper dimensions for dynamic testing of rocks. Pulse shapers of diameters 10, 12, 15, 20, 25, and 30 mm and thicknesses 0.1, 0.5, 1.5, 2.5, 5, and 10 mm were used. It was found that the incident rise time increases and the maximum stress drops as the diameter or thickness increases. For a large-diameter SHPB, it is recommended to use a pulse shaper of diameter 15–20 mm and thickness 2.5 mm. These pulse shaper dimensions produce a ramp-like incident pulse that facilitates dynamic force equilibrium and constant strain rate loading in the rock specimens. Also, the inertia-induced stresses in the rock specimens are negligible. A thicker pulse shaper is suggested if higher strain rates are targeted. The inertia-induced stresses in the pulse shaper increase as its diameter increases and decrease as its thickness increases. Especially when the pulse shaper diameter is increased from 20 mm to 25 or 30 mm, the inertia-induced stresses become large enough to cause oscillations in the incident waves.