PSI - Issue 37

Pedro J. Sousa et al. / Procedia Structural Integrity 37 (2022) 826–832 Sousa et. al. / Structural Integrity Procedia 00 (2019) 000 – 000

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performed using low-side logic N-channel MOSFETs controllable with 5V TTL inputs, in this case three FQP30N06L from On Semiconductor.

Fig. 8. Electro-pneumatic interfaces: the pressure sensor input on the left and the valve actuation circuit on the right.

The complete system is shown in Fig. 9 independently. The trigger pulse for the high-speed camera is, as previously mentioned, also connected to the DAQ, in this case using a BNC T-shaped connector. For additional accuracy regarding each images’ temporal position, it is also possible to record the exposure output signal for the high -speed camera, which results in recording a pulse train where each one corresponds to one of the acquired images and the trigger pulse identifies image zero.

Fig. 9. Final control setup for the updated split Hopkinson pressure bar

4. Conclusions This article reports the development of a custom control system for split Hopkinson pressure bars that has already been successfully tested in operation, showing good firing pressure accuracy. First, the pneumatic control circuit was redesigned to use a newer set of valves, reducing eventual leaks and including a digital pressure sensor with analogue output. The control system was then developed to use this information and automatically actuate the different valves to ensure a particular user-definable pressure at the triggering moment, and then also provide a set of customizable pulses for image acquisition and synchronization. The developed system as a whole can be seen a specialized tool for UMAI’s typical usage of split Hopkinson pressure bars, which revolve around the use of high-speed cameras and DIC strain measurements in conjunction with typical SHPB measurements.