Replacing strain gages by line camera DIC in Hopkinson bar experiments

Overview & Synopsis

Strain gages are widely used to acquire the signals in dynamic experiments with Hopkinson bars. Here, we explore the potential of displacement history measurements with line camera based digital image correlation (DIC) to substitute the role of strain gages and directly obtain particle velocity. After outlining the fundamental equations for deriving stress-strain curves, the technique is applied and validated through split-Hopkinson bar compression and tension tests, as well as direct impact experiments. In direct impact tests, the line camera enables simultaneous measurement of input and output forces, facilitating the verification of quasi-static equilibrium. Moreover, in cases where quasi-static equilibrium is clearly satisfied, a single line camera measurement on the striker bar is sufficient to determine the entire stress-strain curve. Compared to laser interferometry and photon Doppler velocimetry, the line camera DIC system demonstrates superior capability in measuring large displacements of Hopkinson bars. It also offers a reliable non-contact measurement alternative to strain gages, which are prone to delamination under high-impact conditions.