Split-Hopkinson tension bar (SHTB)
The split-Hopkinson tension bar is a device for material testing at strain rates in the range between 200 and 1500 s–1. It consists of two steel bars with diameter 10 mm. They are denoted input and output bars, having lengths 8 m and 7 m, respectively. The sample is mounted between the two bars. Before the test, the input bar is clamped by a locking mechanism located 2 m from the sample. Thereafter, the external 6 m of this bar is prestressed by means of a jack attached at the bar’s end.
By releasing the lock, an elastic stress wave is released, propagating towards the sample with a velocity of 5100 m/s. Applying one-dimensional stress wave theory, the response of the specimen, i.e. stress, strain and strain rate, is determined from records of strain gauges glued to each bar. Highspeed camera instrumentation is also feasible. Moreover, an induction heater fascilitates tests also at elevated temperatures.
The rig has been used for strain-rate characterization of different steel, aluminium and magnesium alloys. High and low temperature tests have been carried out for steel and aluminium. Two designs of the test samples are possible; axisymmetric with diameter 2-3 mm in the gauge part, or sheet with thickness 1-2 mm and width 3 mm.
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